| 1 | /* |
|---|---|
| 2 | * Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved. |
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 4 | * |
| 5 | * This code is free software; you can redistribute it and/or modify it |
| 6 | * under the terms of the GNU General Public License version 2 only, as |
| 7 | * published by the Free Software Foundation. |
| 8 | * |
| 9 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 10 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 11 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 12 | * version 2 for more details (a copy is included in the LICENSE file that |
| 13 | * accompanied this code). |
| 14 | * |
| 15 | * You should have received a copy of the GNU General Public License version |
| 16 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 17 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 18 | * |
| 19 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| 20 | * or visit www.oracle.com if you need additional information or have any |
| 21 | * questions. |
| 22 | * |
| 23 | */ |
| 24 | |
| 25 | #include "precompiled.hpp" |
| 26 | #include "classfile/classLoaderDataGraph.hpp" |
| 27 | #include "classfile/systemDictionary.hpp" |
| 28 | #include "code/codeCache.hpp" |
| 29 | #include "gc/cms/cmsGCStats.hpp" |
| 30 | #include "gc/cms/cmsHeap.hpp" |
| 31 | #include "gc/cms/cmsOopClosures.inline.hpp" |
| 32 | #include "gc/cms/cmsVMOperations.hpp" |
| 33 | #include "gc/cms/compactibleFreeListSpace.hpp" |
| 34 | #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp" |
| 35 | #include "gc/cms/concurrentMarkSweepThread.hpp" |
| 36 | #include "gc/cms/parNewGeneration.hpp" |
| 37 | #include "gc/cms/promotionInfo.inline.hpp" |
| 38 | #include "gc/serial/genMarkSweep.hpp" |
| 39 | #include "gc/serial/tenuredGeneration.hpp" |
| 40 | #include "gc/shared/adaptiveSizePolicy.hpp" |
| 41 | #include "gc/shared/cardGeneration.inline.hpp" |
| 42 | #include "gc/shared/cardTableRS.hpp" |
| 43 | #include "gc/shared/collectedHeap.inline.hpp" |
| 44 | #include "gc/shared/collectorCounters.hpp" |
| 45 | #include "gc/shared/gcLocker.hpp" |
| 46 | #include "gc/shared/gcPolicyCounters.hpp" |
| 47 | #include "gc/shared/gcTimer.hpp" |
| 48 | #include "gc/shared/gcTrace.hpp" |
| 49 | #include "gc/shared/gcTraceTime.inline.hpp" |
| 50 | #include "gc/shared/genCollectedHeap.hpp" |
| 51 | #include "gc/shared/genOopClosures.inline.hpp" |
| 52 | #include "gc/shared/isGCActiveMark.hpp" |
| 53 | #include "gc/shared/owstTaskTerminator.hpp" |
| 54 | #include "gc/shared/referencePolicy.hpp" |
| 55 | #include "gc/shared/referenceProcessorPhaseTimes.hpp" |
| 56 | #include "gc/shared/space.inline.hpp" |
| 57 | #include "gc/shared/strongRootsScope.hpp" |
| 58 | #include "gc/shared/taskqueue.inline.hpp" |
| 59 | #include "gc/shared/weakProcessor.hpp" |
| 60 | #include "gc/shared/workerPolicy.hpp" |
| 61 | #include "logging/log.hpp" |
| 62 | #include "logging/logStream.hpp" |
| 63 | #include "memory/allocation.hpp" |
| 64 | #include "memory/binaryTreeDictionary.inline.hpp" |
| 65 | #include "memory/iterator.inline.hpp" |
| 66 | #include "memory/padded.hpp" |
| 67 | #include "memory/resourceArea.hpp" |
| 68 | #include "memory/universe.hpp" |
| 69 | #include "oops/access.inline.hpp" |
| 70 | #include "oops/oop.inline.hpp" |
| 71 | #include "prims/jvmtiExport.hpp" |
| 72 | #include "runtime/atomic.hpp" |
| 73 | #include "runtime/flags/flagSetting.hpp" |
| 74 | #include "runtime/globals_extension.hpp" |
| 75 | #include "runtime/handles.inline.hpp" |
| 76 | #include "runtime/java.hpp" |
| 77 | #include "runtime/orderAccess.hpp" |
| 78 | #include "runtime/timer.hpp" |
| 79 | #include "runtime/vmThread.hpp" |
| 80 | #include "services/memoryService.hpp" |
| 81 | #include "services/runtimeService.hpp" |
| 82 | #include "utilities/align.hpp" |
| 83 | #include "utilities/stack.inline.hpp" |
| 84 | #if INCLUDE_JVMCI |
| 85 | #include "jvmci/jvmci.hpp" |
| 86 | #endif |
| 87 | |
| 88 | // statics |
| 89 | CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL; |
| 90 | bool CMSCollector::_full_gc_requested = false; |
| 91 | GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc; |
| 92 | |
| 93 | ////////////////////////////////////////////////////////////////// |
| 94 | // In support of CMS/VM thread synchronization |
| 95 | ////////////////////////////////////////////////////////////////// |
| 96 | // We split use of the CGC_lock into 2 "levels". |
| 97 | // The low-level locking is of the usual CGC_lock monitor. We introduce |
| 98 | // a higher level "token" (hereafter "CMS token") built on top of the |
| 99 | // low level monitor (hereafter "CGC lock"). |
| 100 | // The token-passing protocol gives priority to the VM thread. The |
| 101 | // CMS-lock doesn't provide any fairness guarantees, but clients |
| 102 | // should ensure that it is only held for very short, bounded |
| 103 | // durations. |
| 104 | // |
| 105 | // When either of the CMS thread or the VM thread is involved in |
| 106 | // collection operations during which it does not want the other |
| 107 | // thread to interfere, it obtains the CMS token. |
| 108 | // |
| 109 | // If either thread tries to get the token while the other has |
| 110 | // it, that thread waits. However, if the VM thread and CMS thread |
| 111 | // both want the token, then the VM thread gets priority while the |
| 112 | // CMS thread waits. This ensures, for instance, that the "concurrent" |
| 113 | // phases of the CMS thread's work do not block out the VM thread |
| 114 | // for long periods of time as the CMS thread continues to hog |
| 115 | // the token. (See bug 4616232). |
| 116 | // |
| 117 | // The baton-passing functions are, however, controlled by the |
| 118 | // flags _foregroundGCShouldWait and _foregroundGCIsActive, |
| 119 | // and here the low-level CMS lock, not the high level token, |
| 120 | // ensures mutual exclusion. |
| 121 | // |
| 122 | // Two important conditions that we have to satisfy: |
| 123 | // 1. if a thread does a low-level wait on the CMS lock, then it |
| 124 | // relinquishes the CMS token if it were holding that token |
| 125 | // when it acquired the low-level CMS lock. |
| 126 | // 2. any low-level notifications on the low-level lock |
| 127 | // should only be sent when a thread has relinquished the token. |
| 128 | // |
| 129 | // In the absence of either property, we'd have potential deadlock. |
| 130 | // |
| 131 | // We protect each of the CMS (concurrent and sequential) phases |
| 132 | // with the CMS _token_, not the CMS _lock_. |
| 133 | // |
| 134 | // The only code protected by CMS lock is the token acquisition code |
| 135 | // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the |
| 136 | // baton-passing code. |
| 137 | // |
| 138 | // Unfortunately, i couldn't come up with a good abstraction to factor and |
| 139 | // hide the naked CGC_lock manipulation in the baton-passing code |
| 140 | // further below. That's something we should try to do. Also, the proof |
| 141 | // of correctness of this 2-level locking scheme is far from obvious, |
| 142 | // and potentially quite slippery. We have an uneasy suspicion, for instance, |
| 143 | // that there may be a theoretical possibility of delay/starvation in the |
| 144 | // low-level lock/wait/notify scheme used for the baton-passing because of |
| 145 | // potential interference with the priority scheme embodied in the |
| 146 | // CMS-token-passing protocol. See related comments at a CGC_lock->wait() |
| 147 | // invocation further below and marked with "XXX 20011219YSR". |
| 148 | // Indeed, as we note elsewhere, this may become yet more slippery |
| 149 | // in the presence of multiple CMS and/or multiple VM threads. XXX |
| 150 | |
| 151 | class CMSTokenSync: public StackObj { |
| 152 | private: |
| 153 | bool _is_cms_thread; |
| 154 | public: |
| 155 | CMSTokenSync(bool is_cms_thread): |
| 156 | _is_cms_thread(is_cms_thread) { |
| 157 | assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(), |
| 158 | "Incorrect argument to constructor"); |
| 159 | ConcurrentMarkSweepThread::synchronize(_is_cms_thread); |
| 160 | } |
| 161 | |
| 162 | ~CMSTokenSync() { |
| 163 | assert(_is_cms_thread ? |
| 164 | ConcurrentMarkSweepThread::cms_thread_has_cms_token() : |
| 165 | ConcurrentMarkSweepThread::vm_thread_has_cms_token(), |
| 166 | "Incorrect state"); |
| 167 | ConcurrentMarkSweepThread::desynchronize(_is_cms_thread); |
| 168 | } |
| 169 | }; |
| 170 | |
| 171 | // Convenience class that does a CMSTokenSync, and then acquires |
| 172 | // upto three locks. |
| 173 | class CMSTokenSyncWithLocks: public CMSTokenSync { |
| 174 | private: |
| 175 | // Note: locks are acquired in textual declaration order |
| 176 | // and released in the opposite order |
| 177 | MutexLocker _locker1, _locker2, _locker3; |
| 178 | public: |
| 179 | CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1, |
| 180 | Mutex* mutex2 = NULL, Mutex* mutex3 = NULL): |
| 181 | CMSTokenSync(is_cms_thread), |
| 182 | _locker1(mutex1, Mutex::_no_safepoint_check_flag), |
| 183 | _locker2(mutex2, Mutex::_no_safepoint_check_flag), |
| 184 | _locker3(mutex3, Mutex::_no_safepoint_check_flag) |
| 185 | { } |
| 186 | }; |
| 187 | |
| 188 | |
| 189 | ////////////////////////////////////////////////////////////////// |
| 190 | // Concurrent Mark-Sweep Generation ///////////////////////////// |
| 191 | ////////////////////////////////////////////////////////////////// |
| 192 | |
| 193 | NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;) |
| 194 | |
| 195 | // This struct contains per-thread things necessary to support parallel |
| 196 | // young-gen collection. |
| 197 | class CMSParGCThreadState: public CHeapObj<mtGC> { |
| 198 | public: |
| 199 | CompactibleFreeListSpaceLAB lab; |
| 200 | PromotionInfo promo; |
| 201 | |
| 202 | // Constructor. |
| 203 | CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) { |
| 204 | promo.setSpace(cfls); |
| 205 | } |
| 206 | }; |
| 207 | |
| 208 | ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration( |
| 209 | ReservedSpace rs, |
| 210 | size_t initial_byte_size, |
| 211 | size_t min_byte_size, |
| 212 | size_t max_byte_size, |
| 213 | CardTableRS* ct) : |
| 214 | CardGeneration(rs, initial_byte_size, ct), |
| 215 | _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))), |
| 216 | _did_compact(false) |
| 217 | { |
| 218 | HeapWord* bottom = (HeapWord*) _virtual_space.low(); |
| 219 | HeapWord* end = (HeapWord*) _virtual_space.high(); |
| 220 | |
| 221 | _direct_allocated_words = 0; |
| 222 | NOT_PRODUCT( |
| 223 | _numObjectsPromoted = 0; |
| 224 | _numWordsPromoted = 0; |
| 225 | _numObjectsAllocated = 0; |
| 226 | _numWordsAllocated = 0; |
| 227 | ) |
| 228 | |
| 229 | _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end)); |
| 230 | NOT_PRODUCT(debug_cms_space = _cmsSpace;) |
| 231 | _cmsSpace->_old_gen = this; |
| 232 | |
| 233 | _gc_stats = new CMSGCStats(); |
| 234 | |
| 235 | // Verify the assumption that FreeChunk::_prev and OopDesc::_klass |
| 236 | // offsets match. The ability to tell free chunks from objects |
| 237 | // depends on this property. |
| 238 | debug_only( |
| 239 | FreeChunk* junk = NULL; |
| 240 | assert(UseCompressedClassPointers || |
| 241 | junk->prev_addr() == (void*)(oop(junk)->klass_addr()), |
| 242 | "Offset of FreeChunk::_prev within FreeChunk must match" |
| 243 | " that of OopDesc::_klass within OopDesc"); |
| 244 | ) |
| 245 | |
| 246 | _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC); |
| 247 | for (uint i = 0; i < ParallelGCThreads; i++) { |
| 248 | _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace()); |
| 249 | } |
| 250 | |
| 251 | _incremental_collection_failed = false; |
| 252 | // The "dilatation_factor" is the expansion that can occur on |
| 253 | // account of the fact that the minimum object size in the CMS |
| 254 | // generation may be larger than that in, say, a contiguous young |
| 255 | // generation. |
| 256 | // Ideally, in the calculation below, we'd compute the dilatation |
| 257 | // factor as: MinChunkSize/(promoting_gen's min object size) |
| 258 | // Since we do not have such a general query interface for the |
| 259 | // promoting generation, we'll instead just use the minimum |
| 260 | // object size (which today is a header's worth of space); |
| 261 | // note that all arithmetic is in units of HeapWords. |
| 262 | assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking"); |
| 263 | assert(_dilatation_factor >= 1.0, "from previous assert"); |
| 264 | |
| 265 | initialize_performance_counters(min_byte_size, max_byte_size); |
| 266 | } |
| 267 | |
| 268 | |
| 269 | // The field "_initiating_occupancy" represents the occupancy percentage |
| 270 | // at which we trigger a new collection cycle. Unless explicitly specified |
| 271 | // via CMSInitiatingOccupancyFraction (argument "io" below), it |
| 272 | // is calculated by: |
| 273 | // |
| 274 | // Let "f" be MinHeapFreeRatio in |
| 275 | // |
| 276 | // _initiating_occupancy = 100-f + |
| 277 | // f * (CMSTriggerRatio/100) |
| 278 | // where CMSTriggerRatio is the argument "tr" below. |
| 279 | // |
| 280 | // That is, if we assume the heap is at its desired maximum occupancy at the |
| 281 | // end of a collection, we let CMSTriggerRatio of the (purported) free |
| 282 | // space be allocated before initiating a new collection cycle. |
| 283 | // |
| 284 | void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) { |
| 285 | assert(io <= 100 && tr <= 100, "Check the arguments"); |
| 286 | if (io >= 0) { |
| 287 | _initiating_occupancy = (double)io / 100.0; |
| 288 | } else { |
| 289 | _initiating_occupancy = ((100 - MinHeapFreeRatio) + |
| 290 | (double)(tr * MinHeapFreeRatio) / 100.0) |
| 291 | / 100.0; |
| 292 | } |
| 293 | } |
| 294 | |
| 295 | void ConcurrentMarkSweepGeneration::ref_processor_init() { |
| 296 | assert(collector() != NULL, "no collector"); |
| 297 | collector()->ref_processor_init(); |
| 298 | } |
| 299 | |
| 300 | void CMSCollector::ref_processor_init() { |
| 301 | if (_ref_processor == NULL) { |
| 302 | // Allocate and initialize a reference processor |
| 303 | _ref_processor = |
| 304 | new ReferenceProcessor(&_span_based_discoverer, |
| 305 | (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing |
| 306 | ParallelGCThreads, // mt processing degree |
| 307 | _cmsGen->refs_discovery_is_mt(), // mt discovery |
| 308 | MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree |
| 309 | _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic |
| 310 | &_is_alive_closure, // closure for liveness info |
| 311 | false); // disable adjusting number of processing threads |
| 312 | // Initialize the _ref_processor field of CMSGen |
| 313 | _cmsGen->set_ref_processor(_ref_processor); |
| 314 | |
| 315 | } |
| 316 | } |
| 317 | |
| 318 | AdaptiveSizePolicy* CMSCollector::size_policy() { |
| 319 | return CMSHeap::heap()->size_policy(); |
| 320 | } |
| 321 | |
| 322 | void ConcurrentMarkSweepGeneration::initialize_performance_counters(size_t min_old_size, |
| 323 | size_t max_old_size) { |
| 324 | |
| 325 | const char* gen_name = "old"; |
| 326 | // Generation Counters - generation 1, 1 subspace |
| 327 | _gen_counters = new GenerationCounters(gen_name, 1, 1, |
| 328 | min_old_size, max_old_size, &_virtual_space); |
| 329 | |
| 330 | _space_counters = new GSpaceCounters(gen_name, 0, |
| 331 | _virtual_space.reserved_size(), |
| 332 | this, _gen_counters); |
| 333 | } |
| 334 | |
| 335 | CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha): |
| 336 | _cms_gen(cms_gen) |
| 337 | { |
| 338 | assert(alpha <= 100, "bad value"); |
| 339 | _saved_alpha = alpha; |
| 340 | |
| 341 | // Initialize the alphas to the bootstrap value of 100. |
| 342 | _gc0_alpha = _cms_alpha = 100; |
| 343 | |
| 344 | _cms_begin_time.update(); |
| 345 | _cms_end_time.update(); |
| 346 | |
| 347 | _gc0_duration = 0.0; |
| 348 | _gc0_period = 0.0; |
| 349 | _gc0_promoted = 0; |
| 350 | |
| 351 | _cms_duration = 0.0; |
| 352 | _cms_period = 0.0; |
| 353 | _cms_allocated = 0; |
| 354 | |
| 355 | _cms_used_at_gc0_begin = 0; |
| 356 | _cms_used_at_gc0_end = 0; |
| 357 | _allow_duty_cycle_reduction = false; |
| 358 | _valid_bits = 0; |
| 359 | } |
| 360 | |
| 361 | double CMSStats::cms_free_adjustment_factor(size_t free) const { |
| 362 | // TBD: CR 6909490 |
| 363 | return 1.0; |
| 364 | } |
| 365 | |
| 366 | void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) { |
| 367 | } |
| 368 | |
| 369 | // If promotion failure handling is on use |
| 370 | // the padded average size of the promotion for each |
| 371 | // young generation collection. |
| 372 | double CMSStats::time_until_cms_gen_full() const { |
| 373 | size_t cms_free = _cms_gen->cmsSpace()->free(); |
| 374 | CMSHeap* heap = CMSHeap::heap(); |
| 375 | size_t expected_promotion = MIN2(heap->young_gen()->capacity(), |
| 376 | (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average()); |
| 377 | if (cms_free > expected_promotion) { |
| 378 | // Start a cms collection if there isn't enough space to promote |
| 379 | // for the next young collection. Use the padded average as |
| 380 | // a safety factor. |
| 381 | cms_free -= expected_promotion; |
| 382 | |
| 383 | // Adjust by the safety factor. |
| 384 | double cms_free_dbl = (double)cms_free; |
| 385 | double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0; |
| 386 | // Apply a further correction factor which tries to adjust |
| 387 | // for recent occurance of concurrent mode failures. |
| 388 | cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free); |
| 389 | cms_free_dbl = cms_free_dbl * cms_adjustment; |
| 390 | |
| 391 | log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free "SIZE_FORMAT " expected_promotion "SIZE_FORMAT, |
| 392 | cms_free, expected_promotion); |
| 393 | log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0); |
| 394 | // Add 1 in case the consumption rate goes to zero. |
| 395 | return cms_free_dbl / (cms_consumption_rate() + 1.0); |
| 396 | } |
| 397 | return 0.0; |
| 398 | } |
| 399 | |
| 400 | // Compare the duration of the cms collection to the |
| 401 | // time remaining before the cms generation is empty. |
| 402 | // Note that the time from the start of the cms collection |
| 403 | // to the start of the cms sweep (less than the total |
| 404 | // duration of the cms collection) can be used. This |
| 405 | // has been tried and some applications experienced |
| 406 | // promotion failures early in execution. This was |
| 407 | // possibly because the averages were not accurate |
| 408 | // enough at the beginning. |
| 409 | double CMSStats::time_until_cms_start() const { |
| 410 | // We add "gc0_period" to the "work" calculation |
| 411 | // below because this query is done (mostly) at the |
| 412 | // end of a scavenge, so we need to conservatively |
| 413 | // account for that much possible delay |
| 414 | // in the query so as to avoid concurrent mode failures |
| 415 | // due to starting the collection just a wee bit too |
| 416 | // late. |
| 417 | double work = cms_duration() + gc0_period(); |
| 418 | double deadline = time_until_cms_gen_full(); |
| 419 | // If a concurrent mode failure occurred recently, we want to be |
| 420 | // more conservative and halve our expected time_until_cms_gen_full() |
| 421 | if (work > deadline) { |
| 422 | log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ", |
| 423 | cms_duration(), gc0_period(), time_until_cms_gen_full()); |
| 424 | return 0.0; |
| 425 | } |
| 426 | return work - deadline; |
| 427 | } |
| 428 | |
| 429 | #ifndef PRODUCT |
| 430 | void CMSStats::print_on(outputStream *st) const { |
| 431 | st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha); |
| 432 | st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo="SIZE_FORMAT, |
| 433 | gc0_duration(), gc0_period(), gc0_promoted()); |
| 434 | st->print(",cms_dur=%g,cms_per=%g,cms_alloc="SIZE_FORMAT, |
| 435 | cms_duration(), cms_period(), cms_allocated()); |
| 436 | st->print(",cms_since_beg=%g,cms_since_end=%g", |
| 437 | cms_time_since_begin(), cms_time_since_end()); |
| 438 | st->print(",cms_used_beg="SIZE_FORMAT ",cms_used_end="SIZE_FORMAT, |
| 439 | _cms_used_at_gc0_begin, _cms_used_at_gc0_end); |
| 440 | |
| 441 | if (valid()) { |
| 442 | st->print(",promo_rate=%g,cms_alloc_rate=%g", |
| 443 | promotion_rate(), cms_allocation_rate()); |
| 444 | st->print(",cms_consumption_rate=%g,time_until_full=%g", |
| 445 | cms_consumption_rate(), time_until_cms_gen_full()); |
| 446 | } |
| 447 | st->cr(); |
| 448 | } |
| 449 | #endif // #ifndef PRODUCT |
| 450 | |
| 451 | CMSCollector::CollectorState CMSCollector::_collectorState = |
| 452 | CMSCollector::Idling; |
| 453 | bool CMSCollector::_foregroundGCIsActive = false; |
| 454 | bool CMSCollector::_foregroundGCShouldWait = false; |
| 455 | |
| 456 | CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen, |
| 457 | CardTableRS* ct): |
| 458 | _overflow_list(NULL), |
| 459 | _conc_workers(NULL), // may be set later |
| 460 | _completed_initialization(false), |
| 461 | _collection_count_start(0), |
| 462 | _should_unload_classes(CMSClassUnloadingEnabled), |
| 463 | _concurrent_cycles_since_last_unload(0), |
| 464 | _roots_scanning_options(GenCollectedHeap::SO_None), |
| 465 | _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"), |
| 466 | _verifying(false), |
| 467 | _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding), |
| 468 | _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding), |
| 469 | _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()), |
| 470 | _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()), |
| 471 | _cms_start_registered(false), |
| 472 | _cmsGen(cmsGen), |
| 473 | // Adjust span to cover old (cms) gen |
| 474 | _span(cmsGen->reserved()), |
| 475 | _ct(ct), |
| 476 | _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"), |
| 477 | _modUnionTable((CardTable::card_shift - LogHeapWordSize), |
| 478 | -1 /* lock-free */, "No_lock"/* dummy */), |
| 479 | _restart_addr(NULL), |
| 480 | _ser_pmc_preclean_ovflw(0), |
| 481 | _ser_pmc_remark_ovflw(0), |
| 482 | _par_pmc_remark_ovflw(0), |
| 483 | _ser_kac_preclean_ovflw(0), |
| 484 | _ser_kac_ovflw(0), |
| 485 | _par_kac_ovflw(0), |
| 486 | #ifndef PRODUCT |
| 487 | _num_par_pushes(0), |
| 488 | #endif |
| 489 | _span_based_discoverer(_span), |
| 490 | _ref_processor(NULL), // will be set later |
| 491 | // Construct the is_alive_closure with _span & markBitMap |
| 492 | _is_alive_closure(_span, &_markBitMap), |
| 493 | _modUnionClosurePar(&_modUnionTable), |
| 494 | _between_prologue_and_epilogue(false), |
| 495 | _abort_preclean(false), |
| 496 | _start_sampling(false), |
| 497 | _stats(cmsGen), |
| 498 | _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true, |
| 499 | //verify that this lock should be acquired with safepoint check. |
| 500 | Monitor::_safepoint_check_never)), |
| 501 | _eden_chunk_array(NULL), // may be set in ctor body |
| 502 | _eden_chunk_index(0), // -- ditto -- |
| 503 | _eden_chunk_capacity(0), // -- ditto -- |
| 504 | _survivor_chunk_array(NULL), // -- ditto -- |
| 505 | _survivor_chunk_index(0), // -- ditto -- |
| 506 | _survivor_chunk_capacity(0), // -- ditto -- |
| 507 | _survivor_plab_array(NULL) // -- ditto -- |
| 508 | { |
| 509 | // Now expand the span and allocate the collection support structures |
| 510 | // (MUT, marking bit map etc.) to cover both generations subject to |
| 511 | // collection. |
| 512 | |
| 513 | // For use by dirty card to oop closures. |
| 514 | _cmsGen->cmsSpace()->set_collector(this); |
| 515 | |
| 516 | // Allocate MUT and marking bit map |
| 517 | { |
| 518 | MutexLocker x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag); |
| 519 | if (!_markBitMap.allocate(_span)) { |
| 520 | log_warning(gc)("Failed to allocate CMS Bit Map"); |
| 521 | return; |
| 522 | } |
| 523 | assert(_markBitMap.covers(_span), "_markBitMap inconsistency?"); |
| 524 | } |
| 525 | { |
| 526 | _modUnionTable.allocate(_span); |
| 527 | assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?"); |
| 528 | } |
| 529 | |
| 530 | if (!_markStack.allocate(MarkStackSize)) { |
| 531 | log_warning(gc)("Failed to allocate CMS Marking Stack"); |
| 532 | return; |
| 533 | } |
| 534 | |
| 535 | // Support for multi-threaded concurrent phases |
| 536 | if (CMSConcurrentMTEnabled) { |
| 537 | if (FLAG_IS_DEFAULT(ConcGCThreads)) { |
| 538 | // just for now |
| 539 | FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4); |
| 540 | } |
| 541 | if (ConcGCThreads > 1) { |
| 542 | _conc_workers = new YieldingFlexibleWorkGang("CMS Thread", |
| 543 | ConcGCThreads, true); |
| 544 | if (_conc_workers == NULL) { |
| 545 | log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled"); |
| 546 | CMSConcurrentMTEnabled = false; |
| 547 | } else { |
| 548 | _conc_workers->initialize_workers(); |
| 549 | } |
| 550 | } else { |
| 551 | CMSConcurrentMTEnabled = false; |
| 552 | } |
| 553 | } |
| 554 | if (!CMSConcurrentMTEnabled) { |
| 555 | ConcGCThreads = 0; |
| 556 | } else { |
| 557 | // Turn off CMSCleanOnEnter optimization temporarily for |
| 558 | // the MT case where it's not fixed yet; see 6178663. |
| 559 | CMSCleanOnEnter = false; |
| 560 | } |
| 561 | assert((_conc_workers != NULL) == (ConcGCThreads > 1), |
| 562 | "Inconsistency"); |
| 563 | log_debug(gc)("ConcGCThreads: %u", ConcGCThreads); |
| 564 | log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads); |
| 565 | |
| 566 | // Parallel task queues; these are shared for the |
| 567 | // concurrent and stop-world phases of CMS, but |
| 568 | // are not shared with parallel scavenge (ParNew). |
| 569 | { |
| 570 | uint i; |
| 571 | uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads); |
| 572 | |
| 573 | if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled |
| 574 | || ParallelRefProcEnabled) |
| 575 | && num_queues > 0) { |
| 576 | _task_queues = new OopTaskQueueSet(num_queues); |
| 577 | if (_task_queues == NULL) { |
| 578 | log_warning(gc)("task_queues allocation failure."); |
| 579 | return; |
| 580 | } |
| 581 | typedef Padded<OopTaskQueue> PaddedOopTaskQueue; |
| 582 | for (i = 0; i < num_queues; i++) { |
| 583 | PaddedOopTaskQueue *q = new PaddedOopTaskQueue(); |
| 584 | if (q == NULL) { |
| 585 | log_warning(gc)("work_queue allocation failure."); |
| 586 | return; |
| 587 | } |
| 588 | _task_queues->register_queue(i, q); |
| 589 | } |
| 590 | for (i = 0; i < num_queues; i++) { |
| 591 | _task_queues->queue(i)->initialize(); |
| 592 | } |
| 593 | } |
| 594 | } |
| 595 | |
| 596 | _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio); |
| 597 | |
| 598 | // Clip CMSBootstrapOccupancy between 0 and 100. |
| 599 | _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0; |
| 600 | |
| 601 | // Now tell CMS generations the identity of their collector |
| 602 | ConcurrentMarkSweepGeneration::set_collector(this); |
| 603 | |
| 604 | // Create & start a CMS thread for this CMS collector |
| 605 | _cmsThread = ConcurrentMarkSweepThread::start(this); |
| 606 | assert(cmsThread() != NULL, "CMS Thread should have been created"); |
| 607 | assert(cmsThread()->collector() == this, |
| 608 | "CMS Thread should refer to this gen"); |
| 609 | assert(CGC_lock != NULL, "Where's the CGC_lock?"); |
| 610 | |
| 611 | // Support for parallelizing young gen rescan |
| 612 | CMSHeap* heap = CMSHeap::heap(); |
| 613 | _young_gen = heap->young_gen(); |
| 614 | if (heap->supports_inline_contig_alloc()) { |
| 615 | _top_addr = heap->top_addr(); |
| 616 | _end_addr = heap->end_addr(); |
| 617 | assert(_young_gen != NULL, "no _young_gen"); |
| 618 | _eden_chunk_index = 0; |
| 619 | _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain; |
| 620 | _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC); |
| 621 | } |
| 622 | |
| 623 | // Support for parallelizing survivor space rescan |
| 624 | if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) { |
| 625 | const size_t max_plab_samples = |
| 626 | _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize); |
| 627 | |
| 628 | _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC); |
| 629 | _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC); |
| 630 | _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC); |
| 631 | _survivor_chunk_capacity = max_plab_samples; |
| 632 | for (uint i = 0; i < ParallelGCThreads; i++) { |
| 633 | HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC); |
| 634 | ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples); |
| 635 | assert(cur->end() == 0, "Should be 0"); |
| 636 | assert(cur->array() == vec, "Should be vec"); |
| 637 | assert(cur->capacity() == max_plab_samples, "Error"); |
| 638 | } |
| 639 | } |
| 640 | |
| 641 | NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;) |
| 642 | _gc_counters = new CollectorCounters("CMS full collection pauses", 1); |
| 643 | _cgc_counters = new CollectorCounters("CMS concurrent cycle pauses", 2); |
| 644 | _completed_initialization = true; |
| 645 | _inter_sweep_timer.start(); // start of time |
| 646 | } |
| 647 | |
| 648 | const char* ConcurrentMarkSweepGeneration::name() const { |
| 649 | return "concurrent mark-sweep generation"; |
| 650 | } |
| 651 | void ConcurrentMarkSweepGeneration::update_counters() { |
| 652 | if (UsePerfData) { |
| 653 | _space_counters->update_all(); |
| 654 | _gen_counters->update_all(); |
| 655 | } |
| 656 | } |
| 657 | |
| 658 | // this is an optimized version of update_counters(). it takes the |
| 659 | // used value as a parameter rather than computing it. |
| 660 | // |
| 661 | void ConcurrentMarkSweepGeneration::update_counters(size_t used) { |
| 662 | if (UsePerfData) { |
| 663 | _space_counters->update_used(used); |
| 664 | _space_counters->update_capacity(); |
| 665 | _gen_counters->update_all(); |
| 666 | } |
| 667 | } |
| 668 | |
| 669 | void ConcurrentMarkSweepGeneration::print() const { |
| 670 | Generation::print(); |
| 671 | cmsSpace()->print(); |
| 672 | } |
| 673 | |
| 674 | #ifndef PRODUCT |
| 675 | void ConcurrentMarkSweepGeneration::print_statistics() { |
| 676 | cmsSpace()->printFLCensus(0); |
| 677 | } |
| 678 | #endif |
| 679 | |
| 680 | size_t |
| 681 | ConcurrentMarkSweepGeneration::contiguous_available() const { |
| 682 | // dld proposes an improvement in precision here. If the committed |
| 683 | // part of the space ends in a free block we should add that to |
| 684 | // uncommitted size in the calculation below. Will make this |
| 685 | // change later, staying with the approximation below for the |
| 686 | // time being. -- ysr. |
| 687 | return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc()); |
| 688 | } |
| 689 | |
| 690 | size_t |
| 691 | ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const { |
| 692 | return _cmsSpace->max_alloc_in_words() * HeapWordSize; |
| 693 | } |
| 694 | |
| 695 | size_t ConcurrentMarkSweepGeneration::max_available() const { |
| 696 | return free() + _virtual_space.uncommitted_size(); |
| 697 | } |
| 698 | |
| 699 | bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const { |
| 700 | size_t available = max_available(); |
| 701 | size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average(); |
| 702 | bool res = (available >= av_promo) || (available >= max_promotion_in_bytes); |
| 703 | log_trace(gc, promotion)("CMS: promo attempt is%s safe: available("SIZE_FORMAT ") %s av_promo("SIZE_FORMAT "), max_promo("SIZE_FORMAT ")", |
| 704 | res? "": " not", available, res? ">=": "<", av_promo, max_promotion_in_bytes); |
| 705 | return res; |
| 706 | } |
| 707 | |
| 708 | // At a promotion failure dump information on block layout in heap |
| 709 | // (cms old generation). |
| 710 | void ConcurrentMarkSweepGeneration::promotion_failure_occurred() { |
| 711 | Log(gc, promotion) log; |
| 712 | if (log.is_trace()) { |
| 713 | LogStream ls(log.trace()); |
| 714 | cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls); |
| 715 | } |
| 716 | } |
| 717 | |
| 718 | void ConcurrentMarkSweepGeneration::reset_after_compaction() { |
| 719 | // Clear the promotion information. These pointers can be adjusted |
| 720 | // along with all the other pointers into the heap but |
| 721 | // compaction is expected to be a rare event with |
| 722 | // a heap using cms so don't do it without seeing the need. |
| 723 | for (uint i = 0; i < ParallelGCThreads; i++) { |
| 724 | _par_gc_thread_states[i]->promo.reset(); |
| 725 | } |
| 726 | } |
| 727 | |
| 728 | void ConcurrentMarkSweepGeneration::compute_new_size() { |
| 729 | assert_locked_or_safepoint(Heap_lock); |
| 730 | |
| 731 | // If incremental collection failed, we just want to expand |
| 732 | // to the limit. |
| 733 | if (incremental_collection_failed()) { |
| 734 | clear_incremental_collection_failed(); |
| 735 | grow_to_reserved(); |
| 736 | return; |
| 737 | } |
| 738 | |
| 739 | // The heap has been compacted but not reset yet. |
| 740 | // Any metric such as free() or used() will be incorrect. |
| 741 | |
| 742 | CardGeneration::compute_new_size(); |
| 743 | |
| 744 | // Reset again after a possible resizing |
| 745 | if (did_compact()) { |
| 746 | cmsSpace()->reset_after_compaction(); |
| 747 | } |
| 748 | } |
| 749 | |
| 750 | void ConcurrentMarkSweepGeneration::compute_new_size_free_list() { |
| 751 | assert_locked_or_safepoint(Heap_lock); |
| 752 | |
| 753 | // If incremental collection failed, we just want to expand |
| 754 | // to the limit. |
| 755 | if (incremental_collection_failed()) { |
| 756 | clear_incremental_collection_failed(); |
| 757 | grow_to_reserved(); |
| 758 | return; |
| 759 | } |
| 760 | |
| 761 | double free_percentage = ((double) free()) / capacity(); |
| 762 | double desired_free_percentage = (double) MinHeapFreeRatio / 100; |
| 763 | double maximum_free_percentage = (double) MaxHeapFreeRatio / 100; |
| 764 | |
| 765 | // compute expansion delta needed for reaching desired free percentage |
| 766 | if (free_percentage < desired_free_percentage) { |
| 767 | size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); |
| 768 | assert(desired_capacity >= capacity(), "invalid expansion size"); |
| 769 | size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes); |
| 770 | Log(gc) log; |
| 771 | if (log.is_trace()) { |
| 772 | size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); |
| 773 | log.trace("From compute_new_size: "); |
| 774 | log.trace(" Free fraction %f", free_percentage); |
| 775 | log.trace(" Desired free fraction %f", desired_free_percentage); |
| 776 | log.trace(" Maximum free fraction %f", maximum_free_percentage); |
| 777 | log.trace(" Capacity "SIZE_FORMAT, capacity() / 1000); |
| 778 | log.trace(" Desired capacity "SIZE_FORMAT, desired_capacity / 1000); |
| 779 | CMSHeap* heap = CMSHeap::heap(); |
| 780 | size_t young_size = heap->young_gen()->capacity(); |
| 781 | log.trace(" Young gen size "SIZE_FORMAT, young_size / 1000); |
| 782 | log.trace(" unsafe_max_alloc_nogc "SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000); |
| 783 | log.trace(" contiguous available "SIZE_FORMAT, contiguous_available() / 1000); |
| 784 | log.trace(" Expand by "SIZE_FORMAT " (bytes)", expand_bytes); |
| 785 | } |
| 786 | // safe if expansion fails |
| 787 | expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio); |
| 788 | log.trace(" Expanded free fraction %f", ((double) free()) / capacity()); |
| 789 | } else { |
| 790 | size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); |
| 791 | assert(desired_capacity <= capacity(), "invalid expansion size"); |
| 792 | size_t shrink_bytes = capacity() - desired_capacity; |
| 793 | // Don't shrink unless the delta is greater than the minimum shrink we want |
| 794 | if (shrink_bytes >= MinHeapDeltaBytes) { |
| 795 | shrink_free_list_by(shrink_bytes); |
| 796 | } |
| 797 | } |
| 798 | } |
| 799 | |
| 800 | Mutex* ConcurrentMarkSweepGeneration::freelistLock() const { |
| 801 | return cmsSpace()->freelistLock(); |
| 802 | } |
| 803 | |
| 804 | HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) { |
| 805 | CMSSynchronousYieldRequest yr; |
| 806 | MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag); |
| 807 | return have_lock_and_allocate(size, tlab); |
| 808 | } |
| 809 | |
| 810 | HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size, |
| 811 | bool tlab /* ignored */) { |
| 812 | assert_lock_strong(freelistLock()); |
| 813 | size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size); |
| 814 | HeapWord* res = cmsSpace()->allocate(adjustedSize); |
| 815 | // Allocate the object live (grey) if the background collector has |
| 816 | // started marking. This is necessary because the marker may |
| 817 | // have passed this address and consequently this object will |
| 818 | // not otherwise be greyed and would be incorrectly swept up. |
| 819 | // Note that if this object contains references, the writing |
| 820 | // of those references will dirty the card containing this object |
| 821 | // allowing the object to be blackened (and its references scanned) |
| 822 | // either during a preclean phase or at the final checkpoint. |
| 823 | if (res != NULL) { |
| 824 | // We may block here with an uninitialized object with |
| 825 | // its mark-bit or P-bits not yet set. Such objects need |
| 826 | // to be safely navigable by block_start(). |
| 827 | assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here."); |
| 828 | assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size"); |
| 829 | collector()->direct_allocated(res, adjustedSize); |
| 830 | _direct_allocated_words += adjustedSize; |
| 831 | // allocation counters |
| 832 | NOT_PRODUCT( |
| 833 | _numObjectsAllocated++; |
| 834 | _numWordsAllocated += (int)adjustedSize; |
| 835 | ) |
| 836 | } |
| 837 | return res; |
| 838 | } |
| 839 | |
| 840 | // In the case of direct allocation by mutators in a generation that |
| 841 | // is being concurrently collected, the object must be allocated |
| 842 | // live (grey) if the background collector has started marking. |
| 843 | // This is necessary because the marker may |
| 844 | // have passed this address and consequently this object will |
| 845 | // not otherwise be greyed and would be incorrectly swept up. |
| 846 | // Note that if this object contains references, the writing |
| 847 | // of those references will dirty the card containing this object |
| 848 | // allowing the object to be blackened (and its references scanned) |
| 849 | // either during a preclean phase or at the final checkpoint. |
| 850 | void CMSCollector::direct_allocated(HeapWord* start, size_t size) { |
| 851 | assert(_markBitMap.covers(start, size), "Out of bounds"); |
| 852 | if (_collectorState >= Marking) { |
| 853 | MutexLocker y(_markBitMap.lock(), |
| 854 | Mutex::_no_safepoint_check_flag); |
| 855 | // [see comments preceding SweepClosure::do_blk() below for details] |
| 856 | // |
| 857 | // Can the P-bits be deleted now? JJJ |
| 858 | // |
| 859 | // 1. need to mark the object as live so it isn't collected |
| 860 | // 2. need to mark the 2nd bit to indicate the object may be uninitialized |
| 861 | // 3. need to mark the end of the object so marking, precleaning or sweeping |
| 862 | // can skip over uninitialized or unparsable objects. An allocated |
| 863 | // object is considered uninitialized for our purposes as long as |
| 864 | // its klass word is NULL. All old gen objects are parsable |
| 865 | // as soon as they are initialized.) |
| 866 | _markBitMap.mark(start); // object is live |
| 867 | _markBitMap.mark(start + 1); // object is potentially uninitialized? |
| 868 | _markBitMap.mark(start + size - 1); |
| 869 | // mark end of object |
| 870 | } |
| 871 | // check that oop looks uninitialized |
| 872 | assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL"); |
| 873 | } |
| 874 | |
| 875 | void CMSCollector::promoted(bool par, HeapWord* start, |
| 876 | bool is_obj_array, size_t obj_size) { |
| 877 | assert(_markBitMap.covers(start), "Out of bounds"); |
| 878 | // See comment in direct_allocated() about when objects should |
| 879 | // be allocated live. |
| 880 | if (_collectorState >= Marking) { |
| 881 | // we already hold the marking bit map lock, taken in |
| 882 | // the prologue |
| 883 | if (par) { |
| 884 | _markBitMap.par_mark(start); |
| 885 | } else { |
| 886 | _markBitMap.mark(start); |
| 887 | } |
| 888 | // We don't need to mark the object as uninitialized (as |
| 889 | // in direct_allocated above) because this is being done with the |
| 890 | // world stopped and the object will be initialized by the |
| 891 | // time the marking, precleaning or sweeping get to look at it. |
| 892 | // But see the code for copying objects into the CMS generation, |
| 893 | // where we need to ensure that concurrent readers of the |
| 894 | // block offset table are able to safely navigate a block that |
| 895 | // is in flux from being free to being allocated (and in |
| 896 | // transition while being copied into) and subsequently |
| 897 | // becoming a bona-fide object when the copy/promotion is complete. |
| 898 | assert(SafepointSynchronize::is_at_safepoint(), |
| 899 | "expect promotion only at safepoints"); |
| 900 | |
| 901 | if (_collectorState < Sweeping) { |
| 902 | // Mark the appropriate cards in the modUnionTable, so that |
| 903 | // this object gets scanned before the sweep. If this is |
| 904 | // not done, CMS generation references in the object might |
| 905 | // not get marked. |
| 906 | // For the case of arrays, which are otherwise precisely |
| 907 | // marked, we need to dirty the entire array, not just its head. |
| 908 | if (is_obj_array) { |
| 909 | // The [par_]mark_range() method expects mr.end() below to |
| 910 | // be aligned to the granularity of a bit's representation |
| 911 | // in the heap. In the case of the MUT below, that's a |
| 912 | // card size. |
| 913 | MemRegion mr(start, |
| 914 | align_up(start + obj_size, |
| 915 | CardTable::card_size /* bytes */)); |
| 916 | if (par) { |
| 917 | _modUnionTable.par_mark_range(mr); |
| 918 | } else { |
| 919 | _modUnionTable.mark_range(mr); |
| 920 | } |
| 921 | } else { // not an obj array; we can just mark the head |
| 922 | if (par) { |
| 923 | _modUnionTable.par_mark(start); |
| 924 | } else { |
| 925 | _modUnionTable.mark(start); |
| 926 | } |
| 927 | } |
| 928 | } |
| 929 | } |
| 930 | } |
| 931 | |
| 932 | oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) { |
| 933 | assert(obj_size == (size_t)obj->size(), "bad obj_size passed in"); |
| 934 | // allocate, copy and if necessary update promoinfo -- |
| 935 | // delegate to underlying space. |
| 936 | assert_lock_strong(freelistLock()); |
| 937 | |
| 938 | #ifndef PRODUCT |
| 939 | if (CMSHeap::heap()->promotion_should_fail()) { |
| 940 | return NULL; |
| 941 | } |
| 942 | #endif // #ifndef PRODUCT |
| 943 | |
| 944 | oop res = _cmsSpace->promote(obj, obj_size); |
| 945 | if (res == NULL) { |
| 946 | // expand and retry |
| 947 | size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords |
| 948 | expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion); |
| 949 | // Since this is the old generation, we don't try to promote |
| 950 | // into a more senior generation. |
| 951 | res = _cmsSpace->promote(obj, obj_size); |
| 952 | } |
| 953 | if (res != NULL) { |
| 954 | // See comment in allocate() about when objects should |
| 955 | // be allocated live. |
| 956 | assert(oopDesc::is_oop(obj), "Will dereference klass pointer below"); |
| 957 | collector()->promoted(false, // Not parallel |
| 958 | (HeapWord*)res, obj->is_objArray(), obj_size); |
| 959 | // promotion counters |
| 960 | NOT_PRODUCT( |
| 961 | _numObjectsPromoted++; |
| 962 | _numWordsPromoted += |
| 963 | (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size())); |
| 964 | ) |
| 965 | } |
| 966 | return res; |
| 967 | } |
| 968 | |
| 969 | |
| 970 | // IMPORTANT: Notes on object size recognition in CMS. |
| 971 | // --------------------------------------------------- |
| 972 | // A block of storage in the CMS generation is always in |
| 973 | // one of three states. A free block (FREE), an allocated |
| 974 | // object (OBJECT) whose size() method reports the correct size, |
| 975 | // and an intermediate state (TRANSIENT) in which its size cannot |
| 976 | // be accurately determined. |
| 977 | // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS) |
| 978 | // ----------------------------------------------------- |
| 979 | // FREE: klass_word & 1 == 1; mark_word holds block size |
| 980 | // |
| 981 | // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0; |
| 982 | // obj->size() computes correct size |
| 983 | // |
| 984 | // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT |
| 985 | // |
| 986 | // STATE IDENTIFICATION: (64 bit+COOPS) |
| 987 | // ------------------------------------ |
| 988 | // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size |
| 989 | // |
| 990 | // OBJECT: klass_word installed; klass_word != 0; |
| 991 | // obj->size() computes correct size |
| 992 | // |
| 993 | // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT |
| 994 | // |
| 995 | // |
| 996 | // STATE TRANSITION DIAGRAM |
| 997 | // |
| 998 | // mut / parnew mut / parnew |
| 999 | // FREE --------------------> TRANSIENT ---------------------> OBJECT --| |
| 1000 | // ^ | |
| 1001 | // |------------------------ DEAD <------------------------------------| |
| 1002 | // sweep mut |
| 1003 | // |
| 1004 | // While a block is in TRANSIENT state its size cannot be determined |
| 1005 | // so readers will either need to come back later or stall until |
| 1006 | // the size can be determined. Note that for the case of direct |
| 1007 | // allocation, P-bits, when available, may be used to determine the |
| 1008 | // size of an object that may not yet have been initialized. |
| 1009 | |
| 1010 | // Things to support parallel young-gen collection. |
| 1011 | oop |
| 1012 | ConcurrentMarkSweepGeneration::par_promote(int thread_num, |
| 1013 | oop old, markOop m, |
| 1014 | size_t word_sz) { |
| 1015 | #ifndef PRODUCT |
| 1016 | if (CMSHeap::heap()->promotion_should_fail()) { |
| 1017 | return NULL; |
| 1018 | } |
| 1019 | #endif // #ifndef PRODUCT |
| 1020 | |
| 1021 | CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; |
| 1022 | PromotionInfo* promoInfo = &ps->promo; |
| 1023 | // if we are tracking promotions, then first ensure space for |
| 1024 | // promotion (including spooling space for saving header if necessary). |
| 1025 | // then allocate and copy, then track promoted info if needed. |
| 1026 | // When tracking (see PromotionInfo::track()), the mark word may |
| 1027 | // be displaced and in this case restoration of the mark word |
| 1028 | // occurs in the (oop_since_save_marks_)iterate phase. |
| 1029 | if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) { |
| 1030 | // Out of space for allocating spooling buffers; |
| 1031 | // try expanding and allocating spooling buffers. |
| 1032 | if (!expand_and_ensure_spooling_space(promoInfo)) { |
| 1033 | return NULL; |
| 1034 | } |
| 1035 | } |
| 1036 | assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant"); |
| 1037 | const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz); |
| 1038 | HeapWord* obj_ptr = ps->lab.alloc(alloc_sz); |
| 1039 | if (obj_ptr == NULL) { |
| 1040 | obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz); |
| 1041 | if (obj_ptr == NULL) { |
| 1042 | return NULL; |
| 1043 | } |
| 1044 | } |
| 1045 | oop obj = oop(obj_ptr); |
| 1046 | OrderAccess::storestore(); |
| 1047 | assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); |
| 1048 | assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); |
| 1049 | // IMPORTANT: See note on object initialization for CMS above. |
| 1050 | // Otherwise, copy the object. Here we must be careful to insert the |
| 1051 | // klass pointer last, since this marks the block as an allocated object. |
| 1052 | // Except with compressed oops it's the mark word. |
| 1053 | HeapWord* old_ptr = (HeapWord*)old; |
| 1054 | // Restore the mark word copied above. |
| 1055 | obj->set_mark_raw(m); |
| 1056 | assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); |
| 1057 | assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); |
| 1058 | OrderAccess::storestore(); |
| 1059 | |
| 1060 | if (UseCompressedClassPointers) { |
| 1061 | // Copy gap missed by (aligned) header size calculation below |
| 1062 | obj->set_klass_gap(old->klass_gap()); |
| 1063 | } |
| 1064 | if (word_sz > (size_t)oopDesc::header_size()) { |
| 1065 | Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(), |
| 1066 | obj_ptr + oopDesc::header_size(), |
| 1067 | word_sz - oopDesc::header_size()); |
| 1068 | } |
| 1069 | |
| 1070 | // Now we can track the promoted object, if necessary. We take care |
| 1071 | // to delay the transition from uninitialized to full object |
| 1072 | // (i.e., insertion of klass pointer) until after, so that it |
| 1073 | // atomically becomes a promoted object. |
| 1074 | if (promoInfo->tracking()) { |
| 1075 | promoInfo->track((PromotedObject*)obj, old->klass()); |
| 1076 | } |
| 1077 | assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); |
| 1078 | assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); |
| 1079 | assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below"); |
| 1080 | |
| 1081 | // Finally, install the klass pointer (this should be volatile). |
| 1082 | OrderAccess::storestore(); |
| 1083 | obj->set_klass(old->klass()); |
| 1084 | // We should now be able to calculate the right size for this object |
| 1085 | assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object"); |
| 1086 | |
| 1087 | collector()->promoted(true, // parallel |
| 1088 | obj_ptr, old->is_objArray(), word_sz); |
| 1089 | |
| 1090 | NOT_PRODUCT( |
| 1091 | Atomic::inc(&_numObjectsPromoted); |
| 1092 | Atomic::add(alloc_sz, &_numWordsPromoted); |
| 1093 | ) |
| 1094 | |
| 1095 | return obj; |
| 1096 | } |
| 1097 | |
| 1098 | void |
| 1099 | ConcurrentMarkSweepGeneration:: |
| 1100 | par_promote_alloc_done(int thread_num) { |
| 1101 | CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; |
| 1102 | ps->lab.retire(thread_num); |
| 1103 | } |
| 1104 | |
| 1105 | void |
| 1106 | ConcurrentMarkSweepGeneration:: |
| 1107 | par_oop_since_save_marks_iterate_done(int thread_num) { |
| 1108 | CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; |
| 1109 | ParScanWithoutBarrierClosure* dummy_cl = NULL; |
| 1110 | ps->promo.promoted_oops_iterate(dummy_cl); |
| 1111 | |
| 1112 | // Because card-scanning has been completed, subsequent phases |
| 1113 | // (e.g., reference processing) will not need to recognize which |
| 1114 | // objects have been promoted during this GC. So, we can now disable |
| 1115 | // promotion tracking. |
| 1116 | ps->promo.stopTrackingPromotions(); |
| 1117 | } |
| 1118 | |
| 1119 | bool ConcurrentMarkSweepGeneration::should_collect(bool full, |
| 1120 | size_t size, |
| 1121 | bool tlab) |
| 1122 | { |
| 1123 | // We allow a STW collection only if a full |
| 1124 | // collection was requested. |
| 1125 | return full || should_allocate(size, tlab); // FIX ME !!! |
| 1126 | // This and promotion failure handling are connected at the |
| 1127 | // hip and should be fixed by untying them. |
| 1128 | } |
| 1129 | |
| 1130 | bool CMSCollector::shouldConcurrentCollect() { |
| 1131 | LogTarget(Trace, gc) log; |
| 1132 | |
| 1133 | if (_full_gc_requested) { |
| 1134 | log.print("CMSCollector: collect because of explicit gc request (or GCLocker)"); |
| 1135 | return true; |
| 1136 | } |
| 1137 | |
| 1138 | FreelistLocker x(this); |
| 1139 | // ------------------------------------------------------------------ |
| 1140 | // Print out lots of information which affects the initiation of |
| 1141 | // a collection. |
| 1142 | if (log.is_enabled() && stats().valid()) { |
| 1143 | log.print("CMSCollector shouldConcurrentCollect: "); |
| 1144 | |
| 1145 | LogStream out(log); |
| 1146 | stats().print_on(&out); |
| 1147 | |
| 1148 | log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full()); |
| 1149 | log.print("free="SIZE_FORMAT, _cmsGen->free()); |
| 1150 | log.print("contiguous_available="SIZE_FORMAT, _cmsGen->contiguous_available()); |
| 1151 | log.print("promotion_rate=%g", stats().promotion_rate()); |
| 1152 | log.print("cms_allocation_rate=%g", stats().cms_allocation_rate()); |
| 1153 | log.print("occupancy=%3.7f", _cmsGen->occupancy()); |
| 1154 | log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy()); |
| 1155 | log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin()); |
| 1156 | log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end()); |
| 1157 | log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect()); |
| 1158 | } |
| 1159 | // ------------------------------------------------------------------ |
| 1160 | |
| 1161 | // If the estimated time to complete a cms collection (cms_duration()) |
| 1162 | // is less than the estimated time remaining until the cms generation |
| 1163 | // is full, start a collection. |
| 1164 | if (!UseCMSInitiatingOccupancyOnly) { |
| 1165 | if (stats().valid()) { |
| 1166 | if (stats().time_until_cms_start() == 0.0) { |
| 1167 | return true; |
| 1168 | } |
| 1169 | } else { |
| 1170 | // We want to conservatively collect somewhat early in order |
| 1171 | // to try and "bootstrap" our CMS/promotion statistics; |
| 1172 | // this branch will not fire after the first successful CMS |
| 1173 | // collection because the stats should then be valid. |
| 1174 | if (_cmsGen->occupancy() >= _bootstrap_occupancy) { |
| 1175 | log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f", |
| 1176 | _cmsGen->occupancy(), _bootstrap_occupancy); |
| 1177 | return true; |
| 1178 | } |
| 1179 | } |
| 1180 | } |
| 1181 | |
| 1182 | // Otherwise, we start a collection cycle if |
| 1183 | // old gen want a collection cycle started. Each may use |
| 1184 | // an appropriate criterion for making this decision. |
| 1185 | // XXX We need to make sure that the gen expansion |
| 1186 | // criterion dovetails well with this. XXX NEED TO FIX THIS |
| 1187 | if (_cmsGen->should_concurrent_collect()) { |
| 1188 | log.print("CMS old gen initiated"); |
| 1189 | return true; |
| 1190 | } |
| 1191 | |
| 1192 | // We start a collection if we believe an incremental collection may fail; |
| 1193 | // this is not likely to be productive in practice because it's probably too |
| 1194 | // late anyway. |
| 1195 | CMSHeap* heap = CMSHeap::heap(); |
| 1196 | if (heap->incremental_collection_will_fail(true /* consult_young */)) { |
| 1197 | log.print("CMSCollector: collect because incremental collection will fail "); |
| 1198 | return true; |
| 1199 | } |
| 1200 | |
| 1201 | if (MetaspaceGC::should_concurrent_collect()) { |
| 1202 | log.print("CMSCollector: collect for metadata allocation "); |
| 1203 | return true; |
| 1204 | } |
| 1205 | |
| 1206 | // CMSTriggerInterval starts a CMS cycle if enough time has passed. |
| 1207 | if (CMSTriggerInterval >= 0) { |
| 1208 | if (CMSTriggerInterval == 0) { |
| 1209 | // Trigger always |
| 1210 | return true; |
| 1211 | } |
| 1212 | |
| 1213 | // Check the CMS time since begin (we do not check the stats validity |
| 1214 | // as we want to be able to trigger the first CMS cycle as well) |
| 1215 | if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) { |
| 1216 | if (stats().valid()) { |
| 1217 | log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)", |
| 1218 | stats().cms_time_since_begin()); |
| 1219 | } else { |
| 1220 | log.print("CMSCollector: collect because of trigger interval (first collection)"); |
| 1221 | } |
| 1222 | return true; |
| 1223 | } |
| 1224 | } |
| 1225 | |
| 1226 | return false; |
| 1227 | } |
| 1228 | |
| 1229 | void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); } |
| 1230 | |
| 1231 | // Clear _expansion_cause fields of constituent generations |
| 1232 | void CMSCollector::clear_expansion_cause() { |
| 1233 | _cmsGen->clear_expansion_cause(); |
| 1234 | } |
| 1235 | |
| 1236 | // We should be conservative in starting a collection cycle. To |
| 1237 | // start too eagerly runs the risk of collecting too often in the |
| 1238 | // extreme. To collect too rarely falls back on full collections, |
| 1239 | // which works, even if not optimum in terms of concurrent work. |
| 1240 | // As a work around for too eagerly collecting, use the flag |
| 1241 | // UseCMSInitiatingOccupancyOnly. This also has the advantage of |
| 1242 | // giving the user an easily understandable way of controlling the |
| 1243 | // collections. |
| 1244 | // We want to start a new collection cycle if any of the following |
| 1245 | // conditions hold: |
| 1246 | // . our current occupancy exceeds the configured initiating occupancy |
| 1247 | // for this generation, or |
| 1248 | // . we recently needed to expand this space and have not, since that |
| 1249 | // expansion, done a collection of this generation, or |
| 1250 | // . the underlying space believes that it may be a good idea to initiate |
| 1251 | // a concurrent collection (this may be based on criteria such as the |
| 1252 | // following: the space uses linear allocation and linear allocation is |
| 1253 | // going to fail, or there is believed to be excessive fragmentation in |
| 1254 | // the generation, etc... or ... |
| 1255 | // [.(currently done by CMSCollector::shouldConcurrentCollect() only for |
| 1256 | // the case of the old generation; see CR 6543076): |
| 1257 | // we may be approaching a point at which allocation requests may fail because |
| 1258 | // we will be out of sufficient free space given allocation rate estimates.] |
| 1259 | bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const { |
| 1260 | |
| 1261 | assert_lock_strong(freelistLock()); |
| 1262 | if (occupancy() > initiating_occupancy()) { |
| 1263 | log_trace(gc)(" %s: collect because of occupancy %f / %f ", |
| 1264 | short_name(), occupancy(), initiating_occupancy()); |
| 1265 | return true; |
| 1266 | } |
| 1267 | if (UseCMSInitiatingOccupancyOnly) { |
| 1268 | return false; |
| 1269 | } |
| 1270 | if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) { |
| 1271 | log_trace(gc)(" %s: collect because expanded for allocation ", short_name()); |
| 1272 | return true; |
| 1273 | } |
| 1274 | return false; |
| 1275 | } |
| 1276 | |
| 1277 | void ConcurrentMarkSweepGeneration::collect(bool full, |
| 1278 | bool clear_all_soft_refs, |
| 1279 | size_t size, |
| 1280 | bool tlab) |
| 1281 | { |
| 1282 | collector()->collect(full, clear_all_soft_refs, size, tlab); |
| 1283 | } |
| 1284 | |
| 1285 | void CMSCollector::collect(bool full, |
| 1286 | bool clear_all_soft_refs, |
| 1287 | size_t size, |
| 1288 | bool tlab) |
| 1289 | { |
| 1290 | // The following "if" branch is present for defensive reasons. |
| 1291 | // In the current uses of this interface, it can be replaced with: |
| 1292 | // assert(!GCLocker.is_active(), "Can't be called otherwise"); |
| 1293 | // But I am not placing that assert here to allow future |
| 1294 | // generality in invoking this interface. |
| 1295 | if (GCLocker::is_active()) { |
| 1296 | // A consistency test for GCLocker |
| 1297 | assert(GCLocker::needs_gc(), "Should have been set already"); |
| 1298 | // Skip this foreground collection, instead |
| 1299 | // expanding the heap if necessary. |
| 1300 | // Need the free list locks for the call to free() in compute_new_size() |
| 1301 | compute_new_size(); |
| 1302 | return; |
| 1303 | } |
| 1304 | acquire_control_and_collect(full, clear_all_soft_refs); |
| 1305 | } |
| 1306 | |
| 1307 | void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) { |
| 1308 | CMSHeap* heap = CMSHeap::heap(); |
| 1309 | unsigned int gc_count = heap->total_full_collections(); |
| 1310 | if (gc_count == full_gc_count) { |
| 1311 | MutexLocker y(CGC_lock, Mutex::_no_safepoint_check_flag); |
| 1312 | _full_gc_requested = true; |
| 1313 | _full_gc_cause = cause; |
| 1314 | CGC_lock->notify(); // nudge CMS thread |
| 1315 | } else { |
| 1316 | assert(gc_count > full_gc_count, "Error: causal loop"); |
| 1317 | } |
| 1318 | } |
| 1319 | |
| 1320 | bool CMSCollector::is_external_interruption() { |
| 1321 | GCCause::Cause cause = CMSHeap::heap()->gc_cause(); |
| 1322 | return GCCause::is_user_requested_gc(cause) || |
| 1323 | GCCause::is_serviceability_requested_gc(cause); |
| 1324 | } |
| 1325 | |
| 1326 | void CMSCollector::report_concurrent_mode_interruption() { |
| 1327 | if (is_external_interruption()) { |
| 1328 | log_debug(gc)("Concurrent mode interrupted"); |
| 1329 | } else { |
| 1330 | log_debug(gc)("Concurrent mode failure"); |
| 1331 | _gc_tracer_cm->report_concurrent_mode_failure(); |
| 1332 | } |
| 1333 | } |
| 1334 | |
| 1335 | |
| 1336 | // The foreground and background collectors need to coordinate in order |
| 1337 | // to make sure that they do not mutually interfere with CMS collections. |
| 1338 | // When a background collection is active, |
| 1339 | // the foreground collector may need to take over (preempt) and |
| 1340 | // synchronously complete an ongoing collection. Depending on the |
| 1341 | // frequency of the background collections and the heap usage |
| 1342 | // of the application, this preemption can be seldom or frequent. |
| 1343 | // There are only certain |
| 1344 | // points in the background collection that the "collection-baton" |
| 1345 | // can be passed to the foreground collector. |
| 1346 | // |
| 1347 | // The foreground collector will wait for the baton before |
| 1348 | // starting any part of the collection. The foreground collector |
| 1349 | // will only wait at one location. |
| 1350 | // |
| 1351 | // The background collector will yield the baton before starting a new |
| 1352 | // phase of the collection (e.g., before initial marking, marking from roots, |
| 1353 | // precleaning, final re-mark, sweep etc.) This is normally done at the head |
| 1354 | // of the loop which switches the phases. The background collector does some |
| 1355 | // of the phases (initial mark, final re-mark) with the world stopped. |
| 1356 | // Because of locking involved in stopping the world, |
| 1357 | // the foreground collector should not block waiting for the background |
| 1358 | // collector when it is doing a stop-the-world phase. The background |
| 1359 | // collector will yield the baton at an additional point just before |
| 1360 | // it enters a stop-the-world phase. Once the world is stopped, the |
| 1361 | // background collector checks the phase of the collection. If the |
| 1362 | // phase has not changed, it proceeds with the collection. If the |
| 1363 | // phase has changed, it skips that phase of the collection. See |
| 1364 | // the comments on the use of the Heap_lock in collect_in_background(). |
| 1365 | // |
| 1366 | // Variable used in baton passing. |
| 1367 | // _foregroundGCIsActive - Set to true by the foreground collector when |
| 1368 | // it wants the baton. The foreground clears it when it has finished |
| 1369 | // the collection. |
| 1370 | // _foregroundGCShouldWait - Set to true by the background collector |
| 1371 | // when it is running. The foreground collector waits while |
| 1372 | // _foregroundGCShouldWait is true. |
| 1373 | // CGC_lock - monitor used to protect access to the above variables |
| 1374 | // and to notify the foreground and background collectors. |
| 1375 | // _collectorState - current state of the CMS collection. |
| 1376 | // |
| 1377 | // The foreground collector |
| 1378 | // acquires the CGC_lock |
| 1379 | // sets _foregroundGCIsActive |
| 1380 | // waits on the CGC_lock for _foregroundGCShouldWait to be false |
| 1381 | // various locks acquired in preparation for the collection |
| 1382 | // are released so as not to block the background collector |
| 1383 | // that is in the midst of a collection |
| 1384 | // proceeds with the collection |
| 1385 | // clears _foregroundGCIsActive |
| 1386 | // returns |
| 1387 | // |
| 1388 | // The background collector in a loop iterating on the phases of the |
| 1389 | // collection |
| 1390 | // acquires the CGC_lock |
| 1391 | // sets _foregroundGCShouldWait |
| 1392 | // if _foregroundGCIsActive is set |
| 1393 | // clears _foregroundGCShouldWait, notifies _CGC_lock |
| 1394 | // waits on _CGC_lock for _foregroundGCIsActive to become false |
| 1395 | // and exits the loop. |
| 1396 | // otherwise |
| 1397 | // proceed with that phase of the collection |
| 1398 | // if the phase is a stop-the-world phase, |
| 1399 | // yield the baton once more just before enqueueing |
| 1400 | // the stop-world CMS operation (executed by the VM thread). |
| 1401 | // returns after all phases of the collection are done |
| 1402 | // |
| 1403 | |
| 1404 | void CMSCollector::acquire_control_and_collect(bool full, |
| 1405 | bool clear_all_soft_refs) { |
| 1406 | assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint"); |
| 1407 | assert(!Thread::current()->is_ConcurrentGC_thread(), |
| 1408 | "shouldn't try to acquire control from self!"); |
| 1409 | |
| 1410 | // Start the protocol for acquiring control of the |
| 1411 | // collection from the background collector (aka CMS thread). |
| 1412 | assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), |
| 1413 | "VM thread should have CMS token"); |
| 1414 | // Remember the possibly interrupted state of an ongoing |
| 1415 | // concurrent collection |
| 1416 | CollectorState first_state = _collectorState; |
| 1417 | |
| 1418 | // Signal to a possibly ongoing concurrent collection that |
| 1419 | // we want to do a foreground collection. |
| 1420 | _foregroundGCIsActive = true; |
| 1421 | |
| 1422 | // release locks and wait for a notify from the background collector |
| 1423 | // releasing the locks in only necessary for phases which |
| 1424 | // do yields to improve the granularity of the collection. |
| 1425 | assert_lock_strong(bitMapLock()); |
| 1426 | // We need to lock the Free list lock for the space that we are |
| 1427 | // currently collecting. |
| 1428 | assert(haveFreelistLocks(), "Must be holding free list locks"); |
| 1429 | bitMapLock()->unlock(); |
| 1430 | releaseFreelistLocks(); |
| 1431 | { |
| 1432 | MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag); |
| 1433 | if (_foregroundGCShouldWait) { |
| 1434 | // We are going to be waiting for action for the CMS thread; |
| 1435 | // it had better not be gone (for instance at shutdown)! |
| 1436 | assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(), |
| 1437 | "CMS thread must be running"); |
| 1438 | // Wait here until the background collector gives us the go-ahead |
| 1439 | ConcurrentMarkSweepThread::clear_CMS_flag( |
| 1440 | ConcurrentMarkSweepThread::CMS_vm_has_token); // release token |
| 1441 | // Get a possibly blocked CMS thread going: |
| 1442 | // Note that we set _foregroundGCIsActive true above, |
| 1443 | // without protection of the CGC_lock. |
| 1444 | CGC_lock->notify(); |
| 1445 | assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(), |
| 1446 | "Possible deadlock"); |
| 1447 | while (_foregroundGCShouldWait) { |
| 1448 | // wait for notification |
| 1449 | CGC_lock->wait_without_safepoint_check(); |
| 1450 | // Possibility of delay/starvation here, since CMS token does |
| 1451 | // not know to give priority to VM thread? Actually, i think |
| 1452 | // there wouldn't be any delay/starvation, but the proof of |
| 1453 | // that "fact" (?) appears non-trivial. XXX 20011219YSR |
| 1454 | } |
| 1455 | ConcurrentMarkSweepThread::set_CMS_flag( |
| 1456 | ConcurrentMarkSweepThread::CMS_vm_has_token); |
| 1457 | } |
| 1458 | } |
| 1459 | // The CMS_token is already held. Get back the other locks. |
| 1460 | assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), |
| 1461 | "VM thread should have CMS token"); |
| 1462 | getFreelistLocks(); |
| 1463 | bitMapLock()->lock_without_safepoint_check(); |
| 1464 | log_debug(gc, state)("CMS foreground collector has asked for control "INTPTR_FORMAT " with first state %d", |
| 1465 | p2i(Thread::current()), first_state); |
| 1466 | log_debug(gc, state)(" gets control with state %d", _collectorState); |
| 1467 | |
| 1468 | // Inform cms gen if this was due to partial collection failing. |
| 1469 | // The CMS gen may use this fact to determine its expansion policy. |
| 1470 | CMSHeap* heap = CMSHeap::heap(); |
| 1471 | if (heap->incremental_collection_will_fail(false /* don't consult_young */)) { |
| 1472 | assert(!_cmsGen->incremental_collection_failed(), |
| 1473 | "Should have been noticed, reacted to and cleared"); |
| 1474 | _cmsGen->set_incremental_collection_failed(); |
| 1475 | } |
| 1476 | |
| 1477 | if (first_state > Idling) { |
| 1478 | report_concurrent_mode_interruption(); |
| 1479 | } |
| 1480 | |
| 1481 | set_did_compact(true); |
| 1482 | |
| 1483 | // If the collection is being acquired from the background |
| 1484 | // collector, there may be references on the discovered |
| 1485 | // references lists. Abandon those references, since some |
| 1486 | // of them may have become unreachable after concurrent |
| 1487 | // discovery; the STW compacting collector will redo discovery |
| 1488 | // more precisely, without being subject to floating garbage. |
| 1489 | // Leaving otherwise unreachable references in the discovered |
| 1490 | // lists would require special handling. |
| 1491 | ref_processor()->disable_discovery(); |
| 1492 | ref_processor()->abandon_partial_discovery(); |
| 1493 | ref_processor()->verify_no_references_recorded(); |
| 1494 | |
| 1495 | if (first_state > Idling) { |
| 1496 | save_heap_summary(); |
| 1497 | } |
| 1498 | |
| 1499 | do_compaction_work(clear_all_soft_refs); |
| 1500 | |
| 1501 | // Has the GC time limit been exceeded? |
| 1502 | size_t max_eden_size = _young_gen->max_eden_size(); |
| 1503 | GCCause::Cause gc_cause = heap->gc_cause(); |
| 1504 | size_policy()->check_gc_overhead_limit(_young_gen->eden()->used(), |
| 1505 | _cmsGen->max_capacity(), |
| 1506 | max_eden_size, |
| 1507 | full, |
| 1508 | gc_cause, |
| 1509 | heap->soft_ref_policy()); |
| 1510 | |
| 1511 | // Reset the expansion cause, now that we just completed |
| 1512 | // a collection cycle. |
| 1513 | clear_expansion_cause(); |
| 1514 | _foregroundGCIsActive = false; |
| 1515 | return; |
| 1516 | } |
| 1517 | |
| 1518 | // Resize the tenured generation |
| 1519 | // after obtaining the free list locks for the |
| 1520 | // two generations. |
| 1521 | void CMSCollector::compute_new_size() { |
| 1522 | assert_locked_or_safepoint(Heap_lock); |
| 1523 | FreelistLocker z(this); |
| 1524 | MetaspaceGC::compute_new_size(); |
| 1525 | _cmsGen->compute_new_size_free_list(); |
| 1526 | } |
| 1527 | |
| 1528 | // A work method used by the foreground collector to do |
| 1529 | // a mark-sweep-compact. |
| 1530 | void CMSCollector::do_compaction_work(bool clear_all_soft_refs) { |
| 1531 | CMSHeap* heap = CMSHeap::heap(); |
| 1532 | |
| 1533 | STWGCTimer* gc_timer = GenMarkSweep::gc_timer(); |
| 1534 | gc_timer->register_gc_start(); |
| 1535 | |
| 1536 | SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer(); |
| 1537 | gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start()); |
| 1538 | |
| 1539 | heap->pre_full_gc_dump(gc_timer); |
| 1540 | |
| 1541 | GCTraceTime(Trace, gc, phases) t("CMS:MSC"); |
| 1542 | |
| 1543 | // Temporarily widen the span of the weak reference processing to |
| 1544 | // the entire heap. |
| 1545 | MemRegion new_span(CMSHeap::heap()->reserved_region()); |
| 1546 | ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span); |
| 1547 | // Temporarily, clear the "is_alive_non_header" field of the |
| 1548 | // reference processor. |
| 1549 | ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL); |
| 1550 | // Temporarily make reference _processing_ single threaded (non-MT). |
| 1551 | ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false); |
| 1552 | // Temporarily make refs discovery atomic |
| 1553 | ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true); |
| 1554 | // Temporarily make reference _discovery_ single threaded (non-MT) |
| 1555 | ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false); |
| 1556 | |
| 1557 | ref_processor()->set_enqueuing_is_done(false); |
| 1558 | ref_processor()->enable_discovery(); |
| 1559 | ref_processor()->setup_policy(clear_all_soft_refs); |
| 1560 | // If an asynchronous collection finishes, the _modUnionTable is |
| 1561 | // all clear. If we are assuming the collection from an asynchronous |
| 1562 | // collection, clear the _modUnionTable. |
| 1563 | assert(_collectorState != Idling || _modUnionTable.isAllClear(), |
| 1564 | "_modUnionTable should be clear if the baton was not passed"); |
| 1565 | _modUnionTable.clear_all(); |
| 1566 | assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(), |
| 1567 | "mod union for klasses should be clear if the baton was passed"); |
| 1568 | _ct->cld_rem_set()->clear_mod_union(); |
| 1569 | |
| 1570 | |
| 1571 | // We must adjust the allocation statistics being maintained |
| 1572 | // in the free list space. We do so by reading and clearing |
| 1573 | // the sweep timer and updating the block flux rate estimates below. |
| 1574 | assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive"); |
| 1575 | if (_inter_sweep_timer.is_active()) { |
| 1576 | _inter_sweep_timer.stop(); |
| 1577 | // Note that we do not use this sample to update the _inter_sweep_estimate. |
| 1578 | _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()), |
| 1579 | _inter_sweep_estimate.padded_average(), |
| 1580 | _intra_sweep_estimate.padded_average()); |
| 1581 | } |
| 1582 | |
| 1583 | GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs); |
| 1584 | #ifdef ASSERT |
| 1585 | CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); |
| 1586 | size_t free_size = cms_space->free(); |
| 1587 | assert(free_size == |
| 1588 | pointer_delta(cms_space->end(), cms_space->compaction_top()) |
| 1589 | * HeapWordSize, |
| 1590 | "All the free space should be compacted into one chunk at top"); |
| 1591 | assert(cms_space->dictionary()->total_chunk_size( |
| 1592 | debug_only(cms_space->freelistLock())) == 0 || |
| 1593 | cms_space->totalSizeInIndexedFreeLists() == 0, |
| 1594 | "All the free space should be in a single chunk"); |
| 1595 | size_t num = cms_space->totalCount(); |
| 1596 | assert((free_size == 0 && num == 0) || |
| 1597 | (free_size > 0 && (num == 1 || num == 2)), |
| 1598 | "There should be at most 2 free chunks after compaction"); |
| 1599 | #endif // ASSERT |
| 1600 | _collectorState = Resetting; |
| 1601 | assert(_restart_addr == NULL, |
| 1602 | "Should have been NULL'd before baton was passed"); |
| 1603 | reset_stw(); |
| 1604 | _cmsGen->reset_after_compaction(); |
| 1605 | _concurrent_cycles_since_last_unload = 0; |
| 1606 | |
| 1607 | // Clear any data recorded in the PLAB chunk arrays. |
| 1608 | if (_survivor_plab_array != NULL) { |
| 1609 | reset_survivor_plab_arrays(); |
| 1610 | } |
| 1611 | |
| 1612 | // Adjust the per-size allocation stats for the next epoch. |
| 1613 | _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */); |
| 1614 | // Restart the "inter sweep timer" for the next epoch. |
| 1615 | _inter_sweep_timer.reset(); |
| 1616 | _inter_sweep_timer.start(); |
| 1617 | |
| 1618 | // No longer a need to do a concurrent collection for Metaspace. |
| 1619 | MetaspaceGC::set_should_concurrent_collect(false); |
| 1620 | |
| 1621 | heap->post_full_gc_dump(gc_timer); |
| 1622 | |
| 1623 | gc_timer->register_gc_end(); |
| 1624 | |
| 1625 | gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions()); |
| 1626 | |
| 1627 | // For a mark-sweep-compact, compute_new_size() will be called |
| 1628 | // in the heap's do_collection() method. |
| 1629 | } |
| 1630 | |
| 1631 | void CMSCollector::print_eden_and_survivor_chunk_arrays() { |
| 1632 | Log(gc, heap) log; |
| 1633 | if (!log.is_trace()) { |
| 1634 | return; |
| 1635 | } |
| 1636 | |
| 1637 | ContiguousSpace* eden_space = _young_gen->eden(); |
| 1638 | ContiguousSpace* from_space = _young_gen->from(); |
| 1639 | ContiguousSpace* to_space = _young_gen->to(); |
| 1640 | // Eden |
| 1641 | if (_eden_chunk_array != NULL) { |
| 1642 | log.trace("eden "PTR_FORMAT "-"PTR_FORMAT "-"PTR_FORMAT "("SIZE_FORMAT ")", |
| 1643 | p2i(eden_space->bottom()), p2i(eden_space->top()), |
| 1644 | p2i(eden_space->end()), eden_space->capacity()); |
| 1645 | log.trace("_eden_chunk_index="SIZE_FORMAT ", _eden_chunk_capacity="SIZE_FORMAT, |
| 1646 | _eden_chunk_index, _eden_chunk_capacity); |
| 1647 | for (size_t i = 0; i < _eden_chunk_index; i++) { |
| 1648 | log.trace("_eden_chunk_array["SIZE_FORMAT "]="PTR_FORMAT, i, p2i(_eden_chunk_array[i])); |
| 1649 | } |
| 1650 | } |
| 1651 | // Survivor |
| 1652 | if (_survivor_chunk_array != NULL) { |
| 1653 | log.trace("survivor "PTR_FORMAT "-"PTR_FORMAT "-"PTR_FORMAT "("SIZE_FORMAT ")", |
| 1654 | p2i(from_space->bottom()), p2i(from_space->top()), |
| 1655 | p2i(from_space->end()), from_space->capacity()); |
| 1656 | log.trace("_survivor_chunk_index="SIZE_FORMAT ", _survivor_chunk_capacity="SIZE_FORMAT, |
| 1657 | _survivor_chunk_index, _survivor_chunk_capacity); |
| 1658 | for (size_t i = 0; i < _survivor_chunk_index; i++) { |
| 1659 | log.trace("_survivor_chunk_array["SIZE_FORMAT "]="PTR_FORMAT, i, p2i(_survivor_chunk_array[i])); |
| 1660 | } |
| 1661 | } |
| 1662 | } |
| 1663 | |
| 1664 | void CMSCollector::getFreelistLocks() const { |
| 1665 | // Get locks for all free lists in all generations that this |
| 1666 | // collector is responsible for |
| 1667 | _cmsGen->freelistLock()->lock_without_safepoint_check(); |
| 1668 | } |
| 1669 | |
| 1670 | void CMSCollector::releaseFreelistLocks() const { |
| 1671 | // Release locks for all free lists in all generations that this |
| 1672 | // collector is responsible for |
| 1673 | _cmsGen->freelistLock()->unlock(); |
| 1674 | } |
| 1675 | |
| 1676 | bool CMSCollector::haveFreelistLocks() const { |
| 1677 | // Check locks for all free lists in all generations that this |
| 1678 | // collector is responsible for |
| 1679 | assert_lock_strong(_cmsGen->freelistLock()); |
| 1680 | PRODUCT_ONLY(ShouldNotReachHere()); |
| 1681 | return true; |
| 1682 | } |
| 1683 | |
| 1684 | // A utility class that is used by the CMS collector to |
| 1685 | // temporarily "release" the foreground collector from its |
| 1686 | // usual obligation to wait for the background collector to |
| 1687 | // complete an ongoing phase before proceeding. |
| 1688 | class ReleaseForegroundGC: public StackObj { |
| 1689 | private: |
| 1690 | CMSCollector* _c; |
| 1691 | public: |
| 1692 | ReleaseForegroundGC(CMSCollector* c) : _c(c) { |
| 1693 | assert(_c->_foregroundGCShouldWait, "Else should not need to call"); |
| 1694 | MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag); |
| 1695 | // allow a potentially blocked foreground collector to proceed |
| 1696 | _c->_foregroundGCShouldWait = false; |
| 1697 | if (_c->_foregroundGCIsActive) { |
| 1698 | CGC_lock->notify(); |
| 1699 | } |
| 1700 | assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| 1701 | "Possible deadlock"); |
| 1702 | } |
| 1703 | |
| 1704 | ~ReleaseForegroundGC() { |
| 1705 | assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?"); |
| 1706 | MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag); |
| 1707 | _c->_foregroundGCShouldWait = true; |
| 1708 | } |
| 1709 | }; |
| 1710 | |
| 1711 | void CMSCollector::collect_in_background(GCCause::Cause cause) { |
| 1712 | assert(Thread::current()->is_ConcurrentGC_thread(), |
| 1713 | "A CMS asynchronous collection is only allowed on a CMS thread."); |
| 1714 | |
| 1715 | CMSHeap* heap = CMSHeap::heap(); |
| 1716 | { |
| 1717 | MutexLocker hl(Heap_lock, Mutex::_no_safepoint_check_flag); |
| 1718 | FreelistLocker fll(this); |
| 1719 | MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag); |
| 1720 | if (_foregroundGCIsActive) { |
| 1721 | // The foreground collector is. Skip this |
| 1722 | // background collection. |
| 1723 | assert(!_foregroundGCShouldWait, "Should be clear"); |
| 1724 | return; |
| 1725 | } else { |
| 1726 | assert(_collectorState == Idling, "Should be idling before start."); |
| 1727 | _collectorState = InitialMarking; |
| 1728 | register_gc_start(cause); |
| 1729 | // Reset the expansion cause, now that we are about to begin |
| 1730 | // a new cycle. |
| 1731 | clear_expansion_cause(); |
| 1732 | |
| 1733 | // Clear the MetaspaceGC flag since a concurrent collection |
| 1734 | // is starting but also clear it after the collection. |
| 1735 | MetaspaceGC::set_should_concurrent_collect(false); |
| 1736 | } |
| 1737 | // Decide if we want to enable class unloading as part of the |
| 1738 | // ensuing concurrent GC cycle. |
| 1739 | update_should_unload_classes(); |
| 1740 | _full_gc_requested = false; // acks all outstanding full gc requests |
| 1741 | _full_gc_cause = GCCause::_no_gc; |
| 1742 | // Signal that we are about to start a collection |
| 1743 | heap->increment_total_full_collections(); // ... starting a collection cycle |
| 1744 | _collection_count_start = heap->total_full_collections(); |
| 1745 | } |
| 1746 | |
| 1747 | size_t prev_used = _cmsGen->used(); |
| 1748 | |
| 1749 | // The change of the collection state is normally done at this level; |
| 1750 | // the exceptions are phases that are executed while the world is |
| 1751 | // stopped. For those phases the change of state is done while the |
| 1752 | // world is stopped. For baton passing purposes this allows the |
| 1753 | // background collector to finish the phase and change state atomically. |
| 1754 | // The foreground collector cannot wait on a phase that is done |
| 1755 | // while the world is stopped because the foreground collector already |
| 1756 | // has the world stopped and would deadlock. |
| 1757 | while (_collectorState != Idling) { |
| 1758 | log_debug(gc, state)("Thread "INTPTR_FORMAT " in CMS state %d", |
| 1759 | p2i(Thread::current()), _collectorState); |
| 1760 | // The foreground collector |
| 1761 | // holds the Heap_lock throughout its collection. |
| 1762 | // holds the CMS token (but not the lock) |
| 1763 | // except while it is waiting for the background collector to yield. |
| 1764 | // |
| 1765 | // The foreground collector should be blocked (not for long) |
| 1766 | // if the background collector is about to start a phase |
| 1767 | // executed with world stopped. If the background |
| 1768 | // collector has already started such a phase, the |
| 1769 | // foreground collector is blocked waiting for the |
| 1770 | // Heap_lock. The stop-world phases (InitialMarking and FinalMarking) |
| 1771 | // are executed in the VM thread. |
| 1772 | // |
| 1773 | // The locking order is |
| 1774 | // PendingListLock (PLL) -- if applicable (FinalMarking) |
| 1775 | // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue()) |
| 1776 | // CMS token (claimed in |
| 1777 | // stop_world_and_do() --> |
| 1778 | // safepoint_synchronize() --> |
| 1779 | // CMSThread::synchronize()) |
| 1780 | |
| 1781 | { |
| 1782 | // Check if the FG collector wants us to yield. |
| 1783 | CMSTokenSync x(true); // is cms thread |
| 1784 | if (waitForForegroundGC()) { |
| 1785 | // We yielded to a foreground GC, nothing more to be |
| 1786 | // done this round. |
| 1787 | assert(_foregroundGCShouldWait == false, "We set it to false in " |
| 1788 | "waitForForegroundGC()"); |
| 1789 | log_debug(gc, state)("CMS Thread "INTPTR_FORMAT " exiting collection CMS state %d", |
| 1790 | p2i(Thread::current()), _collectorState); |
| 1791 | return; |
| 1792 | } else { |
| 1793 | // The background collector can run but check to see if the |
| 1794 | // foreground collector has done a collection while the |
| 1795 | // background collector was waiting to get the CGC_lock |
| 1796 | // above. If yes, break so that _foregroundGCShouldWait |
| 1797 | // is cleared before returning. |
| 1798 | if (_collectorState == Idling) { |
| 1799 | break; |
| 1800 | } |
| 1801 | } |
| 1802 | } |
| 1803 | |
| 1804 | assert(_foregroundGCShouldWait, "Foreground collector, if active, " |
| 1805 | "should be waiting"); |
| 1806 | |
| 1807 | switch (_collectorState) { |
| 1808 | case InitialMarking: |
| 1809 | { |
| 1810 | ReleaseForegroundGC x(this); |
| 1811 | stats().record_cms_begin(); |
| 1812 | VM_CMS_Initial_Mark initial_mark_op(this); |
| 1813 | VMThread::execute(&initial_mark_op); |
| 1814 | } |
| 1815 | // The collector state may be any legal state at this point |
| 1816 | // since the background collector may have yielded to the |
| 1817 | // foreground collector. |
| 1818 | break; |
| 1819 | case Marking: |
| 1820 | // initial marking in checkpointRootsInitialWork has been completed |
| 1821 | if (markFromRoots()) { // we were successful |
| 1822 | assert(_collectorState == Precleaning, "Collector state should " |
| 1823 | "have changed"); |
| 1824 | } else { |
| 1825 | assert(_foregroundGCIsActive, "Internal state inconsistency"); |
| 1826 | } |
| 1827 | break; |
| 1828 | case Precleaning: |
| 1829 | // marking from roots in markFromRoots has been completed |
| 1830 | preclean(); |
| 1831 | assert(_collectorState == AbortablePreclean || |
| 1832 | _collectorState == FinalMarking, |
| 1833 | "Collector state should have changed"); |
| 1834 | break; |
| 1835 | case AbortablePreclean: |
| 1836 | abortable_preclean(); |
| 1837 | assert(_collectorState == FinalMarking, "Collector state should " |
| 1838 | "have changed"); |
| 1839 | break; |
| 1840 | case FinalMarking: |
| 1841 | { |
| 1842 | ReleaseForegroundGC x(this); |
| 1843 | |
| 1844 | VM_CMS_Final_Remark final_remark_op(this); |
| 1845 | VMThread::execute(&final_remark_op); |
| 1846 | } |
| 1847 | assert(_foregroundGCShouldWait, "block post-condition"); |
| 1848 | break; |
| 1849 | case Sweeping: |
| 1850 | // final marking in checkpointRootsFinal has been completed |
| 1851 | sweep(); |
| 1852 | assert(_collectorState == Resizing, "Collector state change " |
| 1853 | "to Resizing must be done under the free_list_lock"); |
| 1854 | |
| 1855 | case Resizing: { |
| 1856 | // Sweeping has been completed... |
| 1857 | // At this point the background collection has completed. |
| 1858 | // Don't move the call to compute_new_size() down |
| 1859 | // into code that might be executed if the background |
| 1860 | // collection was preempted. |
| 1861 | { |
| 1862 | ReleaseForegroundGC x(this); // unblock FG collection |
| 1863 | MutexLocker y(Heap_lock, Mutex::_no_safepoint_check_flag); |
| 1864 | CMSTokenSync z(true); // not strictly needed. |
| 1865 | if (_collectorState == Resizing) { |
| 1866 | compute_new_size(); |
| 1867 | save_heap_summary(); |
| 1868 | _collectorState = Resetting; |
| 1869 | } else { |
| 1870 | assert(_collectorState == Idling, "The state should only change" |
| 1871 | " because the foreground collector has finished the collection"); |
| 1872 | } |
| 1873 | } |
| 1874 | break; |
| 1875 | } |
| 1876 | case Resetting: |
| 1877 | // CMS heap resizing has been completed |
| 1878 | reset_concurrent(); |
| 1879 | assert(_collectorState == Idling, "Collector state should " |
| 1880 | "have changed"); |
| 1881 | |
| 1882 | MetaspaceGC::set_should_concurrent_collect(false); |
| 1883 | |
| 1884 | stats().record_cms_end(); |
| 1885 | // Don't move the concurrent_phases_end() and compute_new_size() |
| 1886 | // calls to here because a preempted background collection |
| 1887 | // has it's state set to "Resetting". |
| 1888 | break; |
| 1889 | case Idling: |
| 1890 | default: |
| 1891 | ShouldNotReachHere(); |
| 1892 | break; |
| 1893 | } |
| 1894 | log_debug(gc, state)(" Thread "INTPTR_FORMAT " done - next CMS state %d", |
| 1895 | p2i(Thread::current()), _collectorState); |
| 1896 | assert(_foregroundGCShouldWait, "block post-condition"); |
| 1897 | } |
| 1898 | |
| 1899 | // Should this be in gc_epilogue? |
| 1900 | heap->counters()->update_counters(); |
| 1901 | |
| 1902 | { |
| 1903 | // Clear _foregroundGCShouldWait and, in the event that the |
| 1904 | // foreground collector is waiting, notify it, before |
| 1905 | // returning. |
| 1906 | MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag); |
| 1907 | _foregroundGCShouldWait = false; |
| 1908 | if (_foregroundGCIsActive) { |
| 1909 | CGC_lock->notify(); |
| 1910 | } |
| 1911 | assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| 1912 | "Possible deadlock"); |
| 1913 | } |
| 1914 | log_debug(gc, state)("CMS Thread "INTPTR_FORMAT " exiting collection CMS state %d", |
| 1915 | p2i(Thread::current()), _collectorState); |
| 1916 | log_info(gc, heap)("Old: "SIZE_FORMAT "K->"SIZE_FORMAT "K("SIZE_FORMAT "K)", |
| 1917 | prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K); |
| 1918 | } |
| 1919 | |
| 1920 | void CMSCollector::register_gc_start(GCCause::Cause cause) { |
| 1921 | _cms_start_registered = true; |
| 1922 | _gc_timer_cm->register_gc_start(); |
| 1923 | _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start()); |
| 1924 | } |
| 1925 | |
| 1926 | void CMSCollector::register_gc_end() { |
| 1927 | if (_cms_start_registered) { |
| 1928 | report_heap_summary(GCWhen::AfterGC); |
| 1929 | |
| 1930 | _gc_timer_cm->register_gc_end(); |
| 1931 | _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions()); |
| 1932 | _cms_start_registered = false; |
| 1933 | } |
| 1934 | } |
| 1935 | |
| 1936 | void CMSCollector::save_heap_summary() { |
| 1937 | CMSHeap* heap = CMSHeap::heap(); |
| 1938 | _last_heap_summary = heap->create_heap_summary(); |
| 1939 | _last_metaspace_summary = heap->create_metaspace_summary(); |
| 1940 | } |
| 1941 | |
| 1942 | void CMSCollector::report_heap_summary(GCWhen::Type when) { |
| 1943 | _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary); |
| 1944 | _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary); |
| 1945 | } |
| 1946 | |
| 1947 | bool CMSCollector::waitForForegroundGC() { |
| 1948 | bool res = false; |
| 1949 | assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| 1950 | "CMS thread should have CMS token"); |
| 1951 | // Block the foreground collector until the |
| 1952 | // background collectors decides whether to |
| 1953 | // yield. |
| 1954 | MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag); |
| 1955 | _foregroundGCShouldWait = true; |
| 1956 | if (_foregroundGCIsActive) { |
| 1957 | // The background collector yields to the |
| 1958 | // foreground collector and returns a value |
| 1959 | // indicating that it has yielded. The foreground |
| 1960 | // collector can proceed. |
| 1961 | res = true; |
| 1962 | _foregroundGCShouldWait = false; |
| 1963 | ConcurrentMarkSweepThread::clear_CMS_flag( |
| 1964 | ConcurrentMarkSweepThread::CMS_cms_has_token); |
| 1965 | ConcurrentMarkSweepThread::set_CMS_flag( |
| 1966 | ConcurrentMarkSweepThread::CMS_cms_wants_token); |
| 1967 | // Get a possibly blocked foreground thread going |
| 1968 | CGC_lock->notify(); |
| 1969 | log_debug(gc, state)("CMS Thread "INTPTR_FORMAT " waiting at CMS state %d", |
| 1970 | p2i(Thread::current()), _collectorState); |
| 1971 | while (_foregroundGCIsActive) { |
| 1972 | CGC_lock->wait_without_safepoint_check(); |
| 1973 | } |
| 1974 | ConcurrentMarkSweepThread::set_CMS_flag( |
| 1975 | ConcurrentMarkSweepThread::CMS_cms_has_token); |
| 1976 | ConcurrentMarkSweepThread::clear_CMS_flag( |
| 1977 | ConcurrentMarkSweepThread::CMS_cms_wants_token); |
| 1978 | } |
| 1979 | log_debug(gc, state)("CMS Thread "INTPTR_FORMAT " continuing at CMS state %d", |
| 1980 | p2i(Thread::current()), _collectorState); |
| 1981 | return res; |
| 1982 | } |
| 1983 | |
| 1984 | // Because of the need to lock the free lists and other structures in |
| 1985 | // the collector, common to all the generations that the collector is |
| 1986 | // collecting, we need the gc_prologues of individual CMS generations |
| 1987 | // delegate to their collector. It may have been simpler had the |
| 1988 | // current infrastructure allowed one to call a prologue on a |
| 1989 | // collector. In the absence of that we have the generation's |
| 1990 | // prologue delegate to the collector, which delegates back |
| 1991 | // some "local" work to a worker method in the individual generations |
| 1992 | // that it's responsible for collecting, while itself doing any |
| 1993 | // work common to all generations it's responsible for. A similar |
| 1994 | // comment applies to the gc_epilogue()'s. |
| 1995 | // The role of the variable _between_prologue_and_epilogue is to |
| 1996 | // enforce the invocation protocol. |
| 1997 | void CMSCollector::gc_prologue(bool full) { |
| 1998 | // Call gc_prologue_work() for the CMSGen |
| 1999 | // we are responsible for. |
| 2000 | |
| 2001 | // The following locking discipline assumes that we are only called |
| 2002 | // when the world is stopped. |
| 2003 | assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption"); |
| 2004 | |
| 2005 | // The CMSCollector prologue must call the gc_prologues for the |
| 2006 | // "generations" that it's responsible |
| 2007 | // for. |
| 2008 | |
| 2009 | assert( Thread::current()->is_VM_thread() |
| 2010 | || ( CMSScavengeBeforeRemark |
| 2011 | && Thread::current()->is_ConcurrentGC_thread()), |
| 2012 | "Incorrect thread type for prologue execution"); |
| 2013 | |
| 2014 | if (_between_prologue_and_epilogue) { |
| 2015 | // We have already been invoked; this is a gc_prologue delegation |
| 2016 | // from yet another CMS generation that we are responsible for, just |
| 2017 | // ignore it since all relevant work has already been done. |
| 2018 | return; |
| 2019 | } |
| 2020 | |
| 2021 | // set a bit saying prologue has been called; cleared in epilogue |
| 2022 | _between_prologue_and_epilogue = true; |
| 2023 | // Claim locks for common data structures, then call gc_prologue_work() |
| 2024 | // for each CMSGen. |
| 2025 | |
| 2026 | getFreelistLocks(); // gets free list locks on constituent spaces |
| 2027 | bitMapLock()->lock_without_safepoint_check(); |
| 2028 | |
| 2029 | // Should call gc_prologue_work() for all cms gens we are responsible for |
| 2030 | bool duringMarking = _collectorState >= Marking |
| 2031 | && _collectorState < Sweeping; |
| 2032 | |
| 2033 | // The young collections clear the modified oops state, which tells if |
| 2034 | // there are any modified oops in the class. The remark phase also needs |
| 2035 | // that information. Tell the young collection to save the union of all |
| 2036 | // modified klasses. |
| 2037 | if (duringMarking) { |
| 2038 | _ct->cld_rem_set()->set_accumulate_modified_oops(true); |
| 2039 | } |
| 2040 | |
| 2041 | bool registerClosure = duringMarking; |
| 2042 | |
| 2043 | _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar); |
| 2044 | |
| 2045 | if (!full) { |
| 2046 | stats().record_gc0_begin(); |
| 2047 | } |
| 2048 | } |
| 2049 | |
| 2050 | void ConcurrentMarkSweepGeneration::gc_prologue(bool full) { |
| 2051 | |
| 2052 | _capacity_at_prologue = capacity(); |
| 2053 | _used_at_prologue = used(); |
| 2054 | |
| 2055 | // We enable promotion tracking so that card-scanning can recognize |
| 2056 | // which objects have been promoted during this GC and skip them. |
| 2057 | for (uint i = 0; i < ParallelGCThreads; i++) { |
| 2058 | _par_gc_thread_states[i]->promo.startTrackingPromotions(); |
| 2059 | } |
| 2060 | |
| 2061 | // Delegate to CMScollector which knows how to coordinate between |
| 2062 | // this and any other CMS generations that it is responsible for |
| 2063 | // collecting. |
| 2064 | collector()->gc_prologue(full); |
| 2065 | } |
| 2066 | |
| 2067 | // This is a "private" interface for use by this generation's CMSCollector. |
| 2068 | // Not to be called directly by any other entity (for instance, |
| 2069 | // GenCollectedHeap, which calls the "public" gc_prologue method above). |
| 2070 | void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full, |
| 2071 | bool registerClosure, ModUnionClosure* modUnionClosure) { |
| 2072 | assert(!incremental_collection_failed(), "Shouldn't be set yet"); |
| 2073 | assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL, |
| 2074 | "Should be NULL"); |
| 2075 | if (registerClosure) { |
| 2076 | cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure); |
| 2077 | } |
| 2078 | cmsSpace()->gc_prologue(); |
| 2079 | // Clear stat counters |
| 2080 | NOT_PRODUCT( |
| 2081 | assert(_numObjectsPromoted == 0, "check"); |
| 2082 | assert(_numWordsPromoted == 0, "check"); |
| 2083 | log_develop_trace(gc, alloc)("Allocated "SIZE_FORMAT " objects, "SIZE_FORMAT " bytes concurrently", |
| 2084 | _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord)); |
| 2085 | _numObjectsAllocated = 0; |
| 2086 | _numWordsAllocated = 0; |
| 2087 | ) |
| 2088 | } |
| 2089 | |
| 2090 | void CMSCollector::gc_epilogue(bool full) { |
| 2091 | // The following locking discipline assumes that we are only called |
| 2092 | // when the world is stopped. |
| 2093 | assert(SafepointSynchronize::is_at_safepoint(), |
| 2094 | "world is stopped assumption"); |
| 2095 | |
| 2096 | // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks |
| 2097 | // if linear allocation blocks need to be appropriately marked to allow the |
| 2098 | // the blocks to be parsable. We also check here whether we need to nudge the |
| 2099 | // CMS collector thread to start a new cycle (if it's not already active). |
| 2100 | assert( Thread::current()->is_VM_thread() |
| 2101 | || ( CMSScavengeBeforeRemark |
| 2102 | && Thread::current()->is_ConcurrentGC_thread()), |
| 2103 | "Incorrect thread type for epilogue execution"); |
| 2104 | |
| 2105 | if (!_between_prologue_and_epilogue) { |
| 2106 | // We have already been invoked; this is a gc_epilogue delegation |
| 2107 | // from yet another CMS generation that we are responsible for, just |
| 2108 | // ignore it since all relevant work has already been done. |
| 2109 | return; |
| 2110 | } |
| 2111 | assert(haveFreelistLocks(), "must have freelist locks"); |
| 2112 | assert_lock_strong(bitMapLock()); |
| 2113 | |
| 2114 | _ct->cld_rem_set()->set_accumulate_modified_oops(false); |
| 2115 | |
| 2116 | _cmsGen->gc_epilogue_work(full); |
| 2117 | |
| 2118 | if (_collectorState == AbortablePreclean || _collectorState == Precleaning) { |
| 2119 | // in case sampling was not already enabled, enable it |
| 2120 | _start_sampling = true; |
| 2121 | } |
| 2122 | // reset _eden_chunk_array so sampling starts afresh |
| 2123 | _eden_chunk_index = 0; |
| 2124 | |
| 2125 | size_t cms_used = _cmsGen->cmsSpace()->used(); |
| 2126 | |
| 2127 | // update performance counters - this uses a special version of |
| 2128 | // update_counters() that allows the utilization to be passed as a |
| 2129 | // parameter, avoiding multiple calls to used(). |
| 2130 | // |
| 2131 | _cmsGen->update_counters(cms_used); |
| 2132 | |
| 2133 | bitMapLock()->unlock(); |
| 2134 | releaseFreelistLocks(); |
| 2135 | |
| 2136 | if (!CleanChunkPoolAsync) { |
| 2137 | Chunk::clean_chunk_pool(); |
| 2138 | } |
| 2139 | |
| 2140 | set_did_compact(false); |
| 2141 | _between_prologue_and_epilogue = false; // ready for next cycle |
| 2142 | } |
| 2143 | |
| 2144 | void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) { |
| 2145 | collector()->gc_epilogue(full); |
| 2146 | |
| 2147 | // When using ParNew, promotion tracking should have already been |
| 2148 | // disabled. However, the prologue (which enables promotion |
| 2149 | // tracking) and epilogue are called irrespective of the type of |
| 2150 | // GC. So they will also be called before and after Full GCs, during |
| 2151 | // which promotion tracking will not be explicitly disabled. So, |
| 2152 | // it's safer to also disable it here too (to be symmetric with |
| 2153 | // enabling it in the prologue). |
| 2154 | for (uint i = 0; i < ParallelGCThreads; i++) { |
| 2155 | _par_gc_thread_states[i]->promo.stopTrackingPromotions(); |
| 2156 | } |
| 2157 | } |
| 2158 | |
| 2159 | void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) { |
| 2160 | assert(!incremental_collection_failed(), "Should have been cleared"); |
| 2161 | cmsSpace()->setPreconsumptionDirtyCardClosure(NULL); |
| 2162 | cmsSpace()->gc_epilogue(); |
| 2163 | // Print stat counters |
| 2164 | NOT_PRODUCT( |
| 2165 | assert(_numObjectsAllocated == 0, "check"); |
| 2166 | assert(_numWordsAllocated == 0, "check"); |
| 2167 | log_develop_trace(gc, promotion)("Promoted "SIZE_FORMAT " objects, "SIZE_FORMAT " bytes", |
| 2168 | _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord)); |
| 2169 | _numObjectsPromoted = 0; |
| 2170 | _numWordsPromoted = 0; |
| 2171 | ) |
| 2172 | |
| 2173 | // Call down the chain in contiguous_available needs the freelistLock |
| 2174 | // so print this out before releasing the freeListLock. |
| 2175 | log_develop_trace(gc)(" Contiguous available "SIZE_FORMAT " bytes ", contiguous_available()); |
| 2176 | } |
| 2177 | |
| 2178 | #ifndef PRODUCT |
| 2179 | bool CMSCollector::have_cms_token() { |
| 2180 | Thread* thr = Thread::current(); |
| 2181 | if (thr->is_VM_thread()) { |
| 2182 | return ConcurrentMarkSweepThread::vm_thread_has_cms_token(); |
| 2183 | } else if (thr->is_ConcurrentGC_thread()) { |
| 2184 | return ConcurrentMarkSweepThread::cms_thread_has_cms_token(); |
| 2185 | } else if (thr->is_GC_task_thread()) { |
| 2186 | return ConcurrentMarkSweepThread::vm_thread_has_cms_token() && |
| 2187 | ParGCRareEvent_lock->owned_by_self(); |
| 2188 | } |
| 2189 | return false; |
| 2190 | } |
| 2191 | |
| 2192 | // Check reachability of the given heap address in CMS generation, |
| 2193 | // treating all other generations as roots. |
| 2194 | bool CMSCollector::is_cms_reachable(HeapWord* addr) { |
| 2195 | // We could "guarantee" below, rather than assert, but I'll |
| 2196 | // leave these as "asserts" so that an adventurous debugger |
| 2197 | // could try this in the product build provided some subset of |
| 2198 | // the conditions were met, provided they were interested in the |
| 2199 | // results and knew that the computation below wouldn't interfere |
| 2200 | // with other concurrent computations mutating the structures |
| 2201 | // being read or written. |
| 2202 | assert(SafepointSynchronize::is_at_safepoint(), |
| 2203 | "Else mutations in object graph will make answer suspect"); |
| 2204 | assert(have_cms_token(), "Should hold cms token"); |
| 2205 | assert(haveFreelistLocks(), "must hold free list locks"); |
| 2206 | assert_lock_strong(bitMapLock()); |
| 2207 | |
| 2208 | // Clear the marking bit map array before starting, but, just |
| 2209 | // for kicks, first report if the given address is already marked |
| 2210 | tty->print_cr("Start: Address "PTR_FORMAT " is%s marked", p2i(addr), |
| 2211 | _markBitMap.isMarked(addr) ? "": " not"); |
| 2212 | |
| 2213 | if (verify_after_remark()) { |
| 2214 | MutexLocker x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); |
| 2215 | bool result = verification_mark_bm()->isMarked(addr); |
| 2216 | tty->print_cr("TransitiveMark: Address "PTR_FORMAT " %s marked", p2i(addr), |
| 2217 | result ? "IS": "is NOT"); |
| 2218 | return result; |
| 2219 | } else { |
| 2220 | tty->print_cr("Could not compute result"); |
| 2221 | return false; |
| 2222 | } |
| 2223 | } |
| 2224 | #endif |
| 2225 | |
| 2226 | void |
| 2227 | CMSCollector::print_on_error(outputStream* st) { |
| 2228 | CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector; |
| 2229 | if (collector != NULL) { |
| 2230 | CMSBitMap* bitmap = &collector->_markBitMap; |
| 2231 | st->print_cr("Marking Bits: (CMSBitMap*) "PTR_FORMAT, p2i(bitmap)); |
| 2232 | bitmap->print_on_error(st, " Bits: "); |
| 2233 | |
| 2234 | st->cr(); |
| 2235 | |
| 2236 | CMSBitMap* mut_bitmap = &collector->_modUnionTable; |
| 2237 | st->print_cr("Mod Union Table: (CMSBitMap*) "PTR_FORMAT, p2i(mut_bitmap)); |
| 2238 | mut_bitmap->print_on_error(st, " Bits: "); |
| 2239 | } |
| 2240 | } |
| 2241 | |
| 2242 | //////////////////////////////////////////////////////// |
| 2243 | // CMS Verification Support |
| 2244 | //////////////////////////////////////////////////////// |
| 2245 | // Following the remark phase, the following invariant |
| 2246 | // should hold -- each object in the CMS heap which is |
| 2247 | // marked in markBitMap() should be marked in the verification_mark_bm(). |
| 2248 | |
| 2249 | class VerifyMarkedClosure: public BitMapClosure { |
| 2250 | CMSBitMap* _marks; |
| 2251 | bool _failed; |
| 2252 | |
| 2253 | public: |
| 2254 | VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {} |
| 2255 | |
| 2256 | bool do_bit(size_t offset) { |
| 2257 | HeapWord* addr = _marks->offsetToHeapWord(offset); |
| 2258 | if (!_marks->isMarked(addr)) { |
| 2259 | Log(gc, verify) log; |
| 2260 | ResourceMark rm; |
| 2261 | LogStream ls(log.error()); |
| 2262 | oop(addr)->print_on(&ls); |
| 2263 | log.error(" ("INTPTR_FORMAT " should have been marked)", p2i(addr)); |
| 2264 | _failed = true; |
| 2265 | } |
| 2266 | return true; |
| 2267 | } |
| 2268 | |
| 2269 | bool failed() { return _failed; } |
| 2270 | }; |
| 2271 | |
| 2272 | bool CMSCollector::verify_after_remark() { |
| 2273 | GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking."); |
| 2274 | MutexLocker ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); |
| 2275 | static bool init = false; |
| 2276 | |
| 2277 | assert(SafepointSynchronize::is_at_safepoint(), |
| 2278 | "Else mutations in object graph will make answer suspect"); |
| 2279 | assert(have_cms_token(), |
| 2280 | "Else there may be mutual interference in use of " |
| 2281 | " verification data structures"); |
| 2282 | assert(_collectorState > Marking && _collectorState <= Sweeping, |
| 2283 | "Else marking info checked here may be obsolete"); |
| 2284 | assert(haveFreelistLocks(), "must hold free list locks"); |
| 2285 | assert_lock_strong(bitMapLock()); |
| 2286 | |
| 2287 | |
| 2288 | // Allocate marking bit map if not already allocated |
| 2289 | if (!init) { // first time |
| 2290 | if (!verification_mark_bm()->allocate(_span)) { |
| 2291 | return false; |
| 2292 | } |
| 2293 | init = true; |
| 2294 | } |
| 2295 | |
| 2296 | assert(verification_mark_stack()->isEmpty(), "Should be empty"); |
| 2297 | |
| 2298 | // Turn off refs discovery -- so we will be tracing through refs. |
| 2299 | // This is as intended, because by this time |
| 2300 | // GC must already have cleared any refs that need to be cleared, |
| 2301 | // and traced those that need to be marked; moreover, |
| 2302 | // the marking done here is not going to interfere in any |
| 2303 | // way with the marking information used by GC. |
| 2304 | NoRefDiscovery no_discovery(ref_processor()); |
| 2305 | |
| 2306 | #if COMPILER2_OR_JVMCI |
| 2307 | DerivedPointerTableDeactivate dpt_deact; |
| 2308 | #endif |
| 2309 | |
| 2310 | // Clear any marks from a previous round |
| 2311 | verification_mark_bm()->clear_all(); |
| 2312 | assert(verification_mark_stack()->isEmpty(), "markStack should be empty"); |
| 2313 | verify_work_stacks_empty(); |
| 2314 | |
| 2315 | CMSHeap* heap = CMSHeap::heap(); |
| 2316 | heap->ensure_parsability(false); // fill TLABs, but no need to retire them |
| 2317 | // Update the saved marks which may affect the root scans. |
| 2318 | heap->save_marks(); |
| 2319 | |
| 2320 | if (CMSRemarkVerifyVariant == 1) { |
| 2321 | // In this first variant of verification, we complete |
| 2322 | // all marking, then check if the new marks-vector is |
| 2323 | // a subset of the CMS marks-vector. |
| 2324 | verify_after_remark_work_1(); |
| 2325 | } else { |
| 2326 | guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2"); |
| 2327 | // In this second variant of verification, we flag an error |
| 2328 | // (i.e. an object reachable in the new marks-vector not reachable |
| 2329 | // in the CMS marks-vector) immediately, also indicating the |
| 2330 | // identify of an object (A) that references the unmarked object (B) -- |
| 2331 | // presumably, a mutation to A failed to be picked up by preclean/remark? |
| 2332 | verify_after_remark_work_2(); |
| 2333 | } |
| 2334 | |
| 2335 | return true; |
| 2336 | } |
| 2337 | |
| 2338 | void CMSCollector::verify_after_remark_work_1() { |
| 2339 | ResourceMark rm; |
| 2340 | HandleMark hm; |
| 2341 | CMSHeap* heap = CMSHeap::heap(); |
| 2342 | |
| 2343 | // Get a clear set of claim bits for the roots processing to work with. |
| 2344 | ClassLoaderDataGraph::clear_claimed_marks(); |
| 2345 | |
| 2346 | // Mark from roots one level into CMS |
| 2347 | MarkRefsIntoClosure notOlder(_span, verification_mark_bm()); |
| 2348 | heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. |
| 2349 | |
| 2350 | { |
| 2351 | StrongRootsScope srs(1); |
| 2352 | |
| 2353 | heap->cms_process_roots(&srs, |
| 2354 | true, // young gen as roots |
| 2355 | GenCollectedHeap::ScanningOption(roots_scanning_options()), |
| 2356 | should_unload_classes(), |
| 2357 | ¬Older, |
| 2358 | NULL); |
| 2359 | } |
| 2360 | |
| 2361 | // Now mark from the roots |
| 2362 | MarkFromRootsClosure markFromRootsClosure(this, _span, |
| 2363 | verification_mark_bm(), verification_mark_stack(), |
| 2364 | false /* don't yield */, true /* verifying */); |
| 2365 | assert(_restart_addr == NULL, "Expected pre-condition"); |
| 2366 | verification_mark_bm()->iterate(&markFromRootsClosure); |
| 2367 | while (_restart_addr != NULL) { |
| 2368 | // Deal with stack overflow: by restarting at the indicated |
| 2369 | // address. |
| 2370 | HeapWord* ra = _restart_addr; |
| 2371 | markFromRootsClosure.reset(ra); |
| 2372 | _restart_addr = NULL; |
| 2373 | verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); |
| 2374 | } |
| 2375 | assert(verification_mark_stack()->isEmpty(), "Should have been drained"); |
| 2376 | verify_work_stacks_empty(); |
| 2377 | |
| 2378 | // Marking completed -- now verify that each bit marked in |
| 2379 | // verification_mark_bm() is also marked in markBitMap(); flag all |
| 2380 | // errors by printing corresponding objects. |
| 2381 | VerifyMarkedClosure vcl(markBitMap()); |
| 2382 | verification_mark_bm()->iterate(&vcl); |
| 2383 | if (vcl.failed()) { |
| 2384 | Log(gc, verify) log; |
| 2385 | log.error("Failed marking verification after remark"); |
| 2386 | ResourceMark rm; |
| 2387 | LogStream ls(log.error()); |
| 2388 | heap->print_on(&ls); |
| 2389 | fatal("CMS: failed marking verification after remark"); |
| 2390 | } |
| 2391 | } |
| 2392 | |
| 2393 | class VerifyCLDOopsCLDClosure : public CLDClosure { |
| 2394 | class VerifyCLDOopsClosure : public OopClosure { |
| 2395 | CMSBitMap* _bitmap; |
| 2396 | public: |
| 2397 | VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { } |
| 2398 | void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); } |
| 2399 | void do_oop(narrowOop* p) { ShouldNotReachHere(); } |
| 2400 | } _oop_closure; |
| 2401 | public: |
| 2402 | VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {} |
| 2403 | void do_cld(ClassLoaderData* cld) { |
| 2404 | cld->oops_do(&_oop_closure, ClassLoaderData::_claim_none, false); |
| 2405 | } |
| 2406 | }; |
| 2407 | |
| 2408 | void CMSCollector::verify_after_remark_work_2() { |
| 2409 | ResourceMark rm; |
| 2410 | HandleMark hm; |
| 2411 | CMSHeap* heap = CMSHeap::heap(); |
| 2412 | |
| 2413 | // Get a clear set of claim bits for the roots processing to work with. |
| 2414 | ClassLoaderDataGraph::clear_claimed_marks(); |
| 2415 | |
| 2416 | // Mark from roots one level into CMS |
| 2417 | MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(), |
| 2418 | markBitMap()); |
| 2419 | CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong); |
| 2420 | |
| 2421 | heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. |
| 2422 | |
| 2423 | { |
| 2424 | StrongRootsScope srs(1); |
| 2425 | |
| 2426 | heap->cms_process_roots(&srs, |
| 2427 | true, // young gen as roots |
| 2428 | GenCollectedHeap::ScanningOption(roots_scanning_options()), |
| 2429 | should_unload_classes(), |
| 2430 | ¬Older, |
| 2431 | &cld_closure); |
| 2432 | } |
| 2433 | |
| 2434 | // Now mark from the roots |
| 2435 | MarkFromRootsVerifyClosure markFromRootsClosure(this, _span, |
| 2436 | verification_mark_bm(), markBitMap(), verification_mark_stack()); |
| 2437 | assert(_restart_addr == NULL, "Expected pre-condition"); |
| 2438 | verification_mark_bm()->iterate(&markFromRootsClosure); |
| 2439 | while (_restart_addr != NULL) { |
| 2440 | // Deal with stack overflow: by restarting at the indicated |
| 2441 | // address. |
| 2442 | HeapWord* ra = _restart_addr; |
| 2443 | markFromRootsClosure.reset(ra); |
| 2444 | _restart_addr = NULL; |
| 2445 | verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); |
| 2446 | } |
| 2447 | assert(verification_mark_stack()->isEmpty(), "Should have been drained"); |
| 2448 | verify_work_stacks_empty(); |
| 2449 | |
| 2450 | VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm()); |
| 2451 | ClassLoaderDataGraph::cld_do(&verify_cld_oops); |
| 2452 | |
| 2453 | // Marking completed -- now verify that each bit marked in |
| 2454 | // verification_mark_bm() is also marked in markBitMap(); flag all |
| 2455 | // errors by printing corresponding objects. |
| 2456 | VerifyMarkedClosure vcl(markBitMap()); |
| 2457 | verification_mark_bm()->iterate(&vcl); |
| 2458 | assert(!vcl.failed(), "Else verification above should not have succeeded"); |
| 2459 | } |
| 2460 | |
| 2461 | void ConcurrentMarkSweepGeneration::save_marks() { |
| 2462 | // delegate to CMS space |
| 2463 | cmsSpace()->save_marks(); |
| 2464 | } |
| 2465 | |
| 2466 | bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() { |
| 2467 | return cmsSpace()->no_allocs_since_save_marks(); |
| 2468 | } |
| 2469 | |
| 2470 | void |
| 2471 | ConcurrentMarkSweepGeneration::oop_iterate(OopIterateClosure* cl) { |
| 2472 | if (freelistLock()->owned_by_self()) { |
| 2473 | Generation::oop_iterate(cl); |
| 2474 | } else { |
| 2475 | MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag); |
| 2476 | Generation::oop_iterate(cl); |
| 2477 | } |
| 2478 | } |
| 2479 | |
| 2480 | void |
| 2481 | ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) { |
| 2482 | if (freelistLock()->owned_by_self()) { |
| 2483 | Generation::object_iterate(cl); |
| 2484 | } else { |
| 2485 | MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag); |
| 2486 | Generation::object_iterate(cl); |
| 2487 | } |
| 2488 | } |
| 2489 | |
| 2490 | void |
| 2491 | ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) { |
| 2492 | if (freelistLock()->owned_by_self()) { |
| 2493 | Generation::safe_object_iterate(cl); |
| 2494 | } else { |
| 2495 | MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag); |
| 2496 | Generation::safe_object_iterate(cl); |
| 2497 | } |
| 2498 | } |
| 2499 | |
| 2500 | void |
| 2501 | ConcurrentMarkSweepGeneration::post_compact() { |
| 2502 | } |
| 2503 | |
| 2504 | void |
| 2505 | ConcurrentMarkSweepGeneration::prepare_for_verify() { |
| 2506 | // Fix the linear allocation blocks to look like free blocks. |
| 2507 | |
| 2508 | // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those |
| 2509 | // are not called when the heap is verified during universe initialization and |
| 2510 | // at vm shutdown. |
| 2511 | if (freelistLock()->owned_by_self()) { |
| 2512 | cmsSpace()->prepare_for_verify(); |
| 2513 | } else { |
| 2514 | MutexLocker fll(freelistLock(), Mutex::_no_safepoint_check_flag); |
| 2515 | cmsSpace()->prepare_for_verify(); |
| 2516 | } |
| 2517 | } |
| 2518 | |
| 2519 | void |
| 2520 | ConcurrentMarkSweepGeneration::verify() { |
| 2521 | // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those |
| 2522 | // are not called when the heap is verified during universe initialization and |
| 2523 | // at vm shutdown. |
| 2524 | if (freelistLock()->owned_by_self()) { |
| 2525 | cmsSpace()->verify(); |
| 2526 | } else { |
| 2527 | MutexLocker fll(freelistLock(), Mutex::_no_safepoint_check_flag); |
| 2528 | cmsSpace()->verify(); |
| 2529 | } |
| 2530 | } |
| 2531 | |
| 2532 | void CMSCollector::verify() { |
| 2533 | _cmsGen->verify(); |
| 2534 | } |
| 2535 | |
| 2536 | #ifndef PRODUCT |
| 2537 | bool CMSCollector::overflow_list_is_empty() const { |
| 2538 | assert(_num_par_pushes >= 0, "Inconsistency"); |
| 2539 | if (_overflow_list == NULL) { |
| 2540 | assert(_num_par_pushes == 0, "Inconsistency"); |
| 2541 | } |
| 2542 | return _overflow_list == NULL; |
| 2543 | } |
| 2544 | |
| 2545 | // The methods verify_work_stacks_empty() and verify_overflow_empty() |
| 2546 | // merely consolidate assertion checks that appear to occur together frequently. |
| 2547 | void CMSCollector::verify_work_stacks_empty() const { |
| 2548 | assert(_markStack.isEmpty(), "Marking stack should be empty"); |
| 2549 | assert(overflow_list_is_empty(), "Overflow list should be empty"); |
| 2550 | } |
| 2551 | |
| 2552 | void CMSCollector::verify_overflow_empty() const { |
| 2553 | assert(overflow_list_is_empty(), "Overflow list should be empty"); |
| 2554 | assert(no_preserved_marks(), "No preserved marks"); |
| 2555 | } |
| 2556 | #endif // PRODUCT |
| 2557 | |
| 2558 | // Decide if we want to enable class unloading as part of the |
| 2559 | // ensuing concurrent GC cycle. We will collect and |
| 2560 | // unload classes if it's the case that: |
| 2561 | // (a) class unloading is enabled at the command line, and |
| 2562 | // (b) old gen is getting really full |
| 2563 | // NOTE: Provided there is no change in the state of the heap between |
| 2564 | // calls to this method, it should have idempotent results. Moreover, |
| 2565 | // its results should be monotonically increasing (i.e. going from 0 to 1, |
| 2566 | // but not 1 to 0) between successive calls between which the heap was |
| 2567 | // not collected. For the implementation below, it must thus rely on |
| 2568 | // the property that concurrent_cycles_since_last_unload() |
| 2569 | // will not decrease unless a collection cycle happened and that |
| 2570 | // _cmsGen->is_too_full() are |
| 2571 | // themselves also monotonic in that sense. See check_monotonicity() |
| 2572 | // below. |
| 2573 | void CMSCollector::update_should_unload_classes() { |
| 2574 | _should_unload_classes = false; |
| 2575 | if (CMSClassUnloadingEnabled) { |
| 2576 | _should_unload_classes = (concurrent_cycles_since_last_unload() >= |
| 2577 | CMSClassUnloadingMaxInterval) |
| 2578 | || _cmsGen->is_too_full(); |
| 2579 | } |
| 2580 | } |
| 2581 | |
| 2582 | bool ConcurrentMarkSweepGeneration::is_too_full() const { |
| 2583 | bool res = should_concurrent_collect(); |
| 2584 | res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0); |
| 2585 | return res; |
| 2586 | } |
| 2587 | |
| 2588 | void CMSCollector::setup_cms_unloading_and_verification_state() { |
| 2589 | const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC |
| 2590 | || VerifyBeforeExit; |
| 2591 | const int rso = GenCollectedHeap::SO_AllCodeCache; |
| 2592 | |
| 2593 | // We set the proper root for this CMS cycle here. |
| 2594 | if (should_unload_classes()) { // Should unload classes this cycle |
| 2595 | remove_root_scanning_option(rso); // Shrink the root set appropriately |
| 2596 | set_verifying(should_verify); // Set verification state for this cycle |
| 2597 | return; // Nothing else needs to be done at this time |
| 2598 | } |
| 2599 | |
| 2600 | // Not unloading classes this cycle |
| 2601 | assert(!should_unload_classes(), "Inconsistency!"); |
| 2602 | |
| 2603 | // If we are not unloading classes then add SO_AllCodeCache to root |
| 2604 | // scanning options. |
| 2605 | add_root_scanning_option(rso); |
| 2606 | |
| 2607 | if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) { |
| 2608 | set_verifying(true); |
| 2609 | } else if (verifying() && !should_verify) { |
| 2610 | // We were verifying, but some verification flags got disabled. |
| 2611 | set_verifying(false); |
| 2612 | // Exclude symbols, strings and code cache elements from root scanning to |
| 2613 | // reduce IM and RM pauses. |
| 2614 | remove_root_scanning_option(rso); |
| 2615 | } |
| 2616 | } |
| 2617 | |
| 2618 | |
| 2619 | #ifndef PRODUCT |
| 2620 | HeapWord* CMSCollector::block_start(const void* p) const { |
| 2621 | const HeapWord* addr = (HeapWord*)p; |
| 2622 | if (_span.contains(p)) { |
| 2623 | if (_cmsGen->cmsSpace()->is_in_reserved(addr)) { |
| 2624 | return _cmsGen->cmsSpace()->block_start(p); |
| 2625 | } |
| 2626 | } |
| 2627 | return NULL; |
| 2628 | } |
| 2629 | #endif |
| 2630 | |
| 2631 | HeapWord* |
| 2632 | ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size, |
| 2633 | bool tlab, |
| 2634 | bool parallel) { |
| 2635 | CMSSynchronousYieldRequest yr; |
| 2636 | assert(!tlab, "Can't deal with TLAB allocation"); |
| 2637 | MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag); |
| 2638 | expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation); |
| 2639 | if (GCExpandToAllocateDelayMillis > 0) { |
| 2640 | os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); |
| 2641 | } |
| 2642 | return have_lock_and_allocate(word_size, tlab); |
| 2643 | } |
| 2644 | |
| 2645 | void ConcurrentMarkSweepGeneration::expand_for_gc_cause( |
| 2646 | size_t bytes, |
| 2647 | size_t expand_bytes, |
| 2648 | CMSExpansionCause::Cause cause) |
| 2649 | { |
| 2650 | |
| 2651 | bool success = expand(bytes, expand_bytes); |
| 2652 | |
| 2653 | // remember why we expanded; this information is used |
| 2654 | // by shouldConcurrentCollect() when making decisions on whether to start |
| 2655 | // a new CMS cycle. |
| 2656 | if (success) { |
| 2657 | set_expansion_cause(cause); |
| 2658 | log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause)); |
| 2659 | } |
| 2660 | } |
| 2661 | |
| 2662 | HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) { |
| 2663 | HeapWord* res = NULL; |
| 2664 | MutexLocker x(ParGCRareEvent_lock); |
| 2665 | while (true) { |
| 2666 | // Expansion by some other thread might make alloc OK now: |
| 2667 | res = ps->lab.alloc(word_sz); |
| 2668 | if (res != NULL) return res; |
| 2669 | // If there's not enough expansion space available, give up. |
| 2670 | if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) { |
| 2671 | return NULL; |
| 2672 | } |
| 2673 | // Otherwise, we try expansion. |
| 2674 | expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab); |
| 2675 | // Now go around the loop and try alloc again; |
| 2676 | // A competing par_promote might beat us to the expansion space, |
| 2677 | // so we may go around the loop again if promotion fails again. |
| 2678 | if (GCExpandToAllocateDelayMillis > 0) { |
| 2679 | os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); |
| 2680 | } |
| 2681 | } |
| 2682 | } |
| 2683 | |
| 2684 | |
| 2685 | bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space( |
| 2686 | PromotionInfo* promo) { |
| 2687 | MutexLocker x(ParGCRareEvent_lock); |
| 2688 | size_t refill_size_bytes = promo->refillSize() * HeapWordSize; |
| 2689 | while (true) { |
| 2690 | // Expansion by some other thread might make alloc OK now: |
| 2691 | if (promo->ensure_spooling_space()) { |
| 2692 | assert(promo->has_spooling_space(), |
| 2693 | "Post-condition of successful ensure_spooling_space()"); |
| 2694 | return true; |
| 2695 | } |
| 2696 | // If there's not enough expansion space available, give up. |
| 2697 | if (_virtual_space.uncommitted_size() < refill_size_bytes) { |
| 2698 | return false; |
| 2699 | } |
| 2700 | // Otherwise, we try expansion. |
| 2701 | expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space); |
| 2702 | // Now go around the loop and try alloc again; |
| 2703 | // A competing allocation might beat us to the expansion space, |
| 2704 | // so we may go around the loop again if allocation fails again. |
| 2705 | if (GCExpandToAllocateDelayMillis > 0) { |
| 2706 | os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); |
| 2707 | } |
| 2708 | } |
| 2709 | } |
| 2710 | |
| 2711 | void ConcurrentMarkSweepGeneration::shrink(size_t bytes) { |
| 2712 | // Only shrink if a compaction was done so that all the free space |
| 2713 | // in the generation is in a contiguous block at the end. |
| 2714 | if (did_compact()) { |
| 2715 | CardGeneration::shrink(bytes); |
| 2716 | } |
| 2717 | } |
| 2718 | |
| 2719 | void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() { |
| 2720 | assert_locked_or_safepoint(Heap_lock); |
| 2721 | } |
| 2722 | |
| 2723 | void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) { |
| 2724 | assert_locked_or_safepoint(Heap_lock); |
| 2725 | assert_lock_strong(freelistLock()); |
| 2726 | log_trace(gc)("Shrinking of CMS not yet implemented"); |
| 2727 | return; |
| 2728 | } |
| 2729 | |
| 2730 | |
| 2731 | // Simple ctor/dtor wrapper for accounting & timer chores around concurrent |
| 2732 | // phases. |
| 2733 | class CMSPhaseAccounting: public StackObj { |
| 2734 | public: |
| 2735 | CMSPhaseAccounting(CMSCollector *collector, |
| 2736 | const char *title); |
| 2737 | ~CMSPhaseAccounting(); |
| 2738 | |
| 2739 | private: |
| 2740 | CMSCollector *_collector; |
| 2741 | const char *_title; |
| 2742 | GCTraceConcTime(Info, gc) _trace_time; |
| 2743 | |
| 2744 | public: |
| 2745 | // Not MT-safe; so do not pass around these StackObj's |
| 2746 | // where they may be accessed by other threads. |
| 2747 | double wallclock_millis() { |
| 2748 | return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time()); |
| 2749 | } |
| 2750 | }; |
| 2751 | |
| 2752 | CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector, |
| 2753 | const char *title) : |
| 2754 | _collector(collector), _title(title), _trace_time(title) { |
| 2755 | |
| 2756 | _collector->resetYields(); |
| 2757 | _collector->resetTimer(); |
| 2758 | _collector->startTimer(); |
| 2759 | _collector->gc_timer_cm()->register_gc_concurrent_start(title); |
| 2760 | } |
| 2761 | |
| 2762 | CMSPhaseAccounting::~CMSPhaseAccounting() { |
| 2763 | _collector->gc_timer_cm()->register_gc_concurrent_end(); |
| 2764 | _collector->stopTimer(); |
| 2765 | log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_millis(_collector->timerTicks())); |
| 2766 | log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields()); |
| 2767 | } |
| 2768 | |
| 2769 | // CMS work |
| 2770 | |
| 2771 | // The common parts of CMSParInitialMarkTask and CMSParRemarkTask. |
| 2772 | class CMSParMarkTask : public AbstractGangTask { |
| 2773 | protected: |
| 2774 | CMSCollector* _collector; |
| 2775 | uint _n_workers; |
| 2776 | CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) : |
| 2777 | AbstractGangTask(name), |
| 2778 | _collector(collector), |
| 2779 | _n_workers(n_workers) {} |
| 2780 | // Work method in support of parallel rescan ... of young gen spaces |
| 2781 | void do_young_space_rescan(OopsInGenClosure* cl, |
| 2782 | ContiguousSpace* space, |
| 2783 | HeapWord** chunk_array, size_t chunk_top); |
| 2784 | void work_on_young_gen_roots(OopsInGenClosure* cl); |
| 2785 | }; |
| 2786 | |
| 2787 | // Parallel initial mark task |
| 2788 | class CMSParInitialMarkTask: public CMSParMarkTask { |
| 2789 | StrongRootsScope* _strong_roots_scope; |
| 2790 | public: |
| 2791 | CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) : |
| 2792 | CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers), |
| 2793 | _strong_roots_scope(strong_roots_scope) {} |
| 2794 | void work(uint worker_id); |
| 2795 | }; |
| 2796 | |
| 2797 | // Checkpoint the roots into this generation from outside |
| 2798 | // this generation. [Note this initial checkpoint need only |
| 2799 | // be approximate -- we'll do a catch up phase subsequently.] |
| 2800 | void CMSCollector::checkpointRootsInitial() { |
| 2801 | assert(_collectorState == InitialMarking, "Wrong collector state"); |
| 2802 | check_correct_thread_executing(); |
| 2803 | TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause()); |
| 2804 | |
| 2805 | save_heap_summary(); |
| 2806 | report_heap_summary(GCWhen::BeforeGC); |
| 2807 | |
| 2808 | ReferenceProcessor* rp = ref_processor(); |
| 2809 | assert(_restart_addr == NULL, "Control point invariant"); |
| 2810 | { |
| 2811 | // acquire locks for subsequent manipulations |
| 2812 | MutexLocker x(bitMapLock(), |
| 2813 | Mutex::_no_safepoint_check_flag); |
| 2814 | checkpointRootsInitialWork(); |
| 2815 | // enable ("weak") refs discovery |
| 2816 | rp->enable_discovery(); |
| 2817 | _collectorState = Marking; |
| 2818 | } |
| 2819 | } |
| 2820 | |
| 2821 | void CMSCollector::checkpointRootsInitialWork() { |
| 2822 | assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped"); |
| 2823 | assert(_collectorState == InitialMarking, "just checking"); |
| 2824 | |
| 2825 | // Already have locks. |
| 2826 | assert_lock_strong(bitMapLock()); |
| 2827 | assert(_markBitMap.isAllClear(), "was reset at end of previous cycle"); |
| 2828 | |
| 2829 | // Setup the verification and class unloading state for this |
| 2830 | // CMS collection cycle. |
| 2831 | setup_cms_unloading_and_verification_state(); |
| 2832 | |
| 2833 | GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm); |
| 2834 | |
| 2835 | // Reset all the PLAB chunk arrays if necessary. |
| 2836 | if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) { |
| 2837 | reset_survivor_plab_arrays(); |
| 2838 | } |
| 2839 | |
| 2840 | ResourceMark rm; |
| 2841 | HandleMark hm; |
| 2842 | |
| 2843 | MarkRefsIntoClosure notOlder(_span, &_markBitMap); |
| 2844 | CMSHeap* heap = CMSHeap::heap(); |
| 2845 | |
| 2846 | verify_work_stacks_empty(); |
| 2847 | verify_overflow_empty(); |
| 2848 | |
| 2849 | heap->ensure_parsability(false); // fill TLABs, but no need to retire them |
| 2850 | // Update the saved marks which may affect the root scans. |
| 2851 | heap->save_marks(); |
| 2852 | |
| 2853 | // weak reference processing has not started yet. |
| 2854 | ref_processor()->set_enqueuing_is_done(false); |
| 2855 | |
| 2856 | // Need to remember all newly created CLDs, |
| 2857 | // so that we can guarantee that the remark finds them. |
| 2858 | ClassLoaderDataGraph::remember_new_clds(true); |
| 2859 | |
| 2860 | // Whenever a CLD is found, it will be claimed before proceeding to mark |
| 2861 | // the klasses. The claimed marks need to be cleared before marking starts. |
| 2862 | ClassLoaderDataGraph::clear_claimed_marks(); |
| 2863 | |
| 2864 | print_eden_and_survivor_chunk_arrays(); |
| 2865 | |
| 2866 | { |
| 2867 | #if COMPILER2_OR_JVMCI |
| 2868 | DerivedPointerTableDeactivate dpt_deact; |
| 2869 | #endif |
| 2870 | if (CMSParallelInitialMarkEnabled) { |
| 2871 | // The parallel version. |
| 2872 | WorkGang* workers = heap->workers(); |
| 2873 | assert(workers != NULL, "Need parallel worker threads."); |
| 2874 | uint n_workers = workers->active_workers(); |
| 2875 | |
| 2876 | StrongRootsScope srs(n_workers); |
| 2877 | |
| 2878 | CMSParInitialMarkTask tsk(this, &srs, n_workers); |
| 2879 | initialize_sequential_subtasks_for_young_gen_rescan(n_workers); |
| 2880 | // If the total workers is greater than 1, then multiple workers |
| 2881 | // may be used at some time and the initialization has been set |
| 2882 | // such that the single threaded path cannot be used. |
| 2883 | if (workers->total_workers() > 1) { |
| 2884 | workers->run_task(&tsk); |
| 2885 | } else { |
| 2886 | tsk.work(0); |
| 2887 | } |
| 2888 | } else { |
| 2889 | // The serial version. |
| 2890 | CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong); |
| 2891 | heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. |
| 2892 | |
| 2893 | StrongRootsScope srs(1); |
| 2894 | |
| 2895 | heap->cms_process_roots(&srs, |
| 2896 | true, // young gen as roots |
| 2897 | GenCollectedHeap::ScanningOption(roots_scanning_options()), |
| 2898 | should_unload_classes(), |
| 2899 | ¬Older, |
| 2900 | &cld_closure); |
| 2901 | } |
| 2902 | } |
| 2903 | |
| 2904 | // Clear mod-union table; it will be dirtied in the prologue of |
| 2905 | // CMS generation per each young generation collection. |
| 2906 | |
| 2907 | assert(_modUnionTable.isAllClear(), |
| 2908 | "Was cleared in most recent final checkpoint phase" |
| 2909 | " or no bits are set in the gc_prologue before the start of the next " |
| 2910 | "subsequent marking phase."); |
| 2911 | |
| 2912 | assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be"); |
| 2913 | |
| 2914 | // Save the end of the used_region of the constituent generations |
| 2915 | // to be used to limit the extent of sweep in each generation. |
| 2916 | save_sweep_limits(); |
| 2917 | verify_overflow_empty(); |
| 2918 | } |
| 2919 | |
| 2920 | bool CMSCollector::markFromRoots() { |
| 2921 | // we might be tempted to assert that: |
| 2922 | // assert(!SafepointSynchronize::is_at_safepoint(), |
| 2923 | // "inconsistent argument?"); |
| 2924 | // However that wouldn't be right, because it's possible that |
| 2925 | // a safepoint is indeed in progress as a young generation |
| 2926 | // stop-the-world GC happens even as we mark in this generation. |
| 2927 | assert(_collectorState == Marking, "inconsistent state?"); |
| 2928 | check_correct_thread_executing(); |
| 2929 | verify_overflow_empty(); |
| 2930 | |
| 2931 | // Weak ref discovery note: We may be discovering weak |
| 2932 | // refs in this generation concurrent (but interleaved) with |
| 2933 | // weak ref discovery by the young generation collector. |
| 2934 | |
| 2935 | CMSTokenSyncWithLocks ts(true, bitMapLock()); |
| 2936 | GCTraceCPUTime tcpu; |
| 2937 | CMSPhaseAccounting pa(this, "Concurrent Mark"); |
| 2938 | bool res = markFromRootsWork(); |
| 2939 | if (res) { |
| 2940 | _collectorState = Precleaning; |
| 2941 | } else { // We failed and a foreground collection wants to take over |
| 2942 | assert(_foregroundGCIsActive, "internal state inconsistency"); |
| 2943 | assert(_restart_addr == NULL, "foreground will restart from scratch"); |
| 2944 | log_debug(gc)("bailing out to foreground collection"); |
| 2945 | } |
| 2946 | verify_overflow_empty(); |
| 2947 | return res; |
| 2948 | } |
| 2949 | |
| 2950 | bool CMSCollector::markFromRootsWork() { |
| 2951 | // iterate over marked bits in bit map, doing a full scan and mark |
| 2952 | // from these roots using the following algorithm: |
| 2953 | // . if oop is to the right of the current scan pointer, |
| 2954 | // mark corresponding bit (we'll process it later) |
| 2955 | // . else (oop is to left of current scan pointer) |
| 2956 | // push oop on marking stack |
| 2957 | // . drain the marking stack |
| 2958 | |
| 2959 | // Note that when we do a marking step we need to hold the |
| 2960 | // bit map lock -- recall that direct allocation (by mutators) |
| 2961 | // and promotion (by the young generation collector) is also |
| 2962 | // marking the bit map. [the so-called allocate live policy.] |
| 2963 | // Because the implementation of bit map marking is not |
| 2964 | // robust wrt simultaneous marking of bits in the same word, |
| 2965 | // we need to make sure that there is no such interference |
| 2966 | // between concurrent such updates. |
| 2967 | |
| 2968 | // already have locks |
| 2969 | assert_lock_strong(bitMapLock()); |
| 2970 | |
| 2971 | verify_work_stacks_empty(); |
| 2972 | verify_overflow_empty(); |
| 2973 | bool result = false; |
| 2974 | if (CMSConcurrentMTEnabled && ConcGCThreads > 0) { |
| 2975 | result = do_marking_mt(); |
| 2976 | } else { |
| 2977 | result = do_marking_st(); |
| 2978 | } |
| 2979 | return result; |
| 2980 | } |
| 2981 | |
| 2982 | // Forward decl |
| 2983 | class CMSConcMarkingTask; |
| 2984 | |
| 2985 | class CMSConcMarkingParallelTerminator: public ParallelTaskTerminator { |
| 2986 | CMSCollector* _collector; |
| 2987 | CMSConcMarkingTask* _task; |
| 2988 | public: |
| 2989 | virtual void yield(); |
| 2990 | |
| 2991 | // "n_threads" is the number of threads to be terminated. |
| 2992 | // "queue_set" is a set of work queues of other threads. |
| 2993 | // "collector" is the CMS collector associated with this task terminator. |
| 2994 | // "yield" indicates whether we need the gang as a whole to yield. |
| 2995 | CMSConcMarkingParallelTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) : |
| 2996 | ParallelTaskTerminator(n_threads, queue_set), |
| 2997 | _collector(collector) { } |
| 2998 | |
| 2999 | void set_task(CMSConcMarkingTask* task) { |
| 3000 | _task = task; |
| 3001 | } |
| 3002 | }; |
| 3003 | |
| 3004 | class CMSConcMarkingOWSTTerminator: public OWSTTaskTerminator { |
| 3005 | CMSCollector* _collector; |
| 3006 | CMSConcMarkingTask* _task; |
| 3007 | public: |
| 3008 | virtual void yield(); |
| 3009 | |
| 3010 | // "n_threads" is the number of threads to be terminated. |
| 3011 | // "queue_set" is a set of work queues of other threads. |
| 3012 | // "collector" is the CMS collector associated with this task terminator. |
| 3013 | // "yield" indicates whether we need the gang as a whole to yield. |
| 3014 | CMSConcMarkingOWSTTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) : |
| 3015 | OWSTTaskTerminator(n_threads, queue_set), |
| 3016 | _collector(collector) { } |
| 3017 | |
| 3018 | void set_task(CMSConcMarkingTask* task) { |
| 3019 | _task = task; |
| 3020 | } |
| 3021 | }; |
| 3022 | |
| 3023 | class CMSConcMarkingTaskTerminator { |
| 3024 | private: |
| 3025 | ParallelTaskTerminator* _term; |
| 3026 | public: |
| 3027 | CMSConcMarkingTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) { |
| 3028 | if (UseOWSTTaskTerminator) { |
| 3029 | _term = new CMSConcMarkingOWSTTerminator(n_threads, queue_set, collector); |
| 3030 | } else { |
| 3031 | _term = new CMSConcMarkingParallelTerminator(n_threads, queue_set, collector); |
| 3032 | } |
| 3033 | } |
| 3034 | ~CMSConcMarkingTaskTerminator() { |
| 3035 | assert(_term != NULL, "Must not be NULL"); |
| 3036 | delete _term; |
| 3037 | } |
| 3038 | |
| 3039 | void set_task(CMSConcMarkingTask* task); |
| 3040 | ParallelTaskTerminator* terminator() const { return _term; } |
| 3041 | }; |
| 3042 | |
| 3043 | class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator { |
| 3044 | CMSConcMarkingTask* _task; |
| 3045 | public: |
| 3046 | bool should_exit_termination(); |
| 3047 | void set_task(CMSConcMarkingTask* task) { |
| 3048 | _task = task; |
| 3049 | } |
| 3050 | }; |
| 3051 | |
| 3052 | // MT Concurrent Marking Task |
| 3053 | class CMSConcMarkingTask: public YieldingFlexibleGangTask { |
| 3054 | CMSCollector* _collector; |
| 3055 | uint _n_workers; // requested/desired # workers |
| 3056 | bool _result; |
| 3057 | CompactibleFreeListSpace* _cms_space; |
| 3058 | char _pad_front[64]; // padding to ... |
| 3059 | HeapWord* volatile _global_finger; // ... avoid sharing cache line |
| 3060 | char _pad_back[64]; |
| 3061 | HeapWord* _restart_addr; |
| 3062 | |
| 3063 | // Exposed here for yielding support |
| 3064 | Mutex* const _bit_map_lock; |
| 3065 | |
| 3066 | // The per thread work queues, available here for stealing |
| 3067 | OopTaskQueueSet* _task_queues; |
| 3068 | |
| 3069 | // Termination (and yielding) support |
| 3070 | CMSConcMarkingTaskTerminator _term; |
| 3071 | CMSConcMarkingTerminatorTerminator _term_term; |
| 3072 | |
| 3073 | public: |
| 3074 | CMSConcMarkingTask(CMSCollector* collector, |
| 3075 | CompactibleFreeListSpace* cms_space, |
| 3076 | YieldingFlexibleWorkGang* workers, |
| 3077 | OopTaskQueueSet* task_queues): |
| 3078 | YieldingFlexibleGangTask("Concurrent marking done multi-threaded"), |
| 3079 | _collector(collector), |
| 3080 | _n_workers(0), |
| 3081 | _result(true), |
| 3082 | _cms_space(cms_space), |
| 3083 | _bit_map_lock(collector->bitMapLock()), |
| 3084 | _task_queues(task_queues), |
| 3085 | _term(_n_workers, task_queues, _collector) |
| 3086 | { |
| 3087 | _requested_size = _n_workers; |
| 3088 | _term.set_task(this); |
| 3089 | _term_term.set_task(this); |
| 3090 | _restart_addr = _global_finger = _cms_space->bottom(); |
| 3091 | } |
| 3092 | |
| 3093 | |
| 3094 | OopTaskQueueSet* task_queues() { return _task_queues; } |
| 3095 | |
| 3096 | OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } |
| 3097 | |
| 3098 | HeapWord* volatile* global_finger_addr() { return &_global_finger; } |
| 3099 | |
| 3100 | ParallelTaskTerminator* terminator() { return _term.terminator(); } |
| 3101 | |
| 3102 | virtual void set_for_termination(uint active_workers) { |
| 3103 | terminator()->reset_for_reuse(active_workers); |
| 3104 | } |
| 3105 | |
| 3106 | void work(uint worker_id); |
| 3107 | bool should_yield() { |
| 3108 | return ConcurrentMarkSweepThread::should_yield() |
| 3109 | && !_collector->foregroundGCIsActive(); |
| 3110 | } |
| 3111 | |
| 3112 | virtual void coordinator_yield(); // stuff done by coordinator |
| 3113 | bool result() { return _result; } |
| 3114 | |
| 3115 | void reset(HeapWord* ra) { |
| 3116 | assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)"); |
| 3117 | _restart_addr = _global_finger = ra; |
| 3118 | _term.terminator()->reset_for_reuse(); |
| 3119 | } |
| 3120 | |
| 3121 | static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, |
| 3122 | OopTaskQueue* work_q); |
| 3123 | |
| 3124 | private: |
| 3125 | void do_scan_and_mark(int i, CompactibleFreeListSpace* sp); |
| 3126 | void do_work_steal(int i); |
| 3127 | void bump_global_finger(HeapWord* f); |
| 3128 | }; |
| 3129 | |
| 3130 | bool CMSConcMarkingTerminatorTerminator::should_exit_termination() { |
| 3131 | assert(_task != NULL, "Error"); |
| 3132 | return _task->yielding(); |
| 3133 | // Note that we do not need the disjunct || _task->should_yield() above |
| 3134 | // because we want terminating threads to yield only if the task |
| 3135 | // is already in the midst of yielding, which happens only after at least one |
| 3136 | // thread has yielded. |
| 3137 | } |
| 3138 | |
| 3139 | void CMSConcMarkingParallelTerminator::yield() { |
| 3140 | if (_task->should_yield()) { |
| 3141 | _task->yield(); |
| 3142 | } else { |
| 3143 | ParallelTaskTerminator::yield(); |
| 3144 | } |
| 3145 | } |
| 3146 | |
| 3147 | void CMSConcMarkingOWSTTerminator::yield() { |
| 3148 | if (_task->should_yield()) { |
| 3149 | _task->yield(); |
| 3150 | } else { |
| 3151 | OWSTTaskTerminator::yield(); |
| 3152 | } |
| 3153 | } |
| 3154 | |
| 3155 | void CMSConcMarkingTaskTerminator::set_task(CMSConcMarkingTask* task) { |
| 3156 | if (UseOWSTTaskTerminator) { |
| 3157 | ((CMSConcMarkingOWSTTerminator*)_term)->set_task(task); |
| 3158 | } else { |
| 3159 | ((CMSConcMarkingParallelTerminator*)_term)->set_task(task); |
| 3160 | } |
| 3161 | } |
| 3162 | |
| 3163 | //////////////////////////////////////////////////////////////// |
| 3164 | // Concurrent Marking Algorithm Sketch |
| 3165 | //////////////////////////////////////////////////////////////// |
| 3166 | // Until all tasks exhausted (both spaces): |
| 3167 | // -- claim next available chunk |
| 3168 | // -- bump global finger via CAS |
| 3169 | // -- find first object that starts in this chunk |
| 3170 | // and start scanning bitmap from that position |
| 3171 | // -- scan marked objects for oops |
| 3172 | // -- CAS-mark target, and if successful: |
| 3173 | // . if target oop is above global finger (volatile read) |
| 3174 | // nothing to do |
| 3175 | // . if target oop is in chunk and above local finger |
| 3176 | // then nothing to do |
| 3177 | // . else push on work-queue |
| 3178 | // -- Deal with possible overflow issues: |
| 3179 | // . local work-queue overflow causes stuff to be pushed on |
| 3180 | // global (common) overflow queue |
| 3181 | // . always first empty local work queue |
| 3182 | // . then get a batch of oops from global work queue if any |
| 3183 | // . then do work stealing |
| 3184 | // -- When all tasks claimed (both spaces) |
| 3185 | // and local work queue empty, |
| 3186 | // then in a loop do: |
| 3187 | // . check global overflow stack; steal a batch of oops and trace |
| 3188 | // . try to steal from other threads oif GOS is empty |
| 3189 | // . if neither is available, offer termination |
| 3190 | // -- Terminate and return result |
| 3191 | // |
| 3192 | void CMSConcMarkingTask::work(uint worker_id) { |
| 3193 | elapsedTimer _timer; |
| 3194 | ResourceMark rm; |
| 3195 | HandleMark hm; |
| 3196 | |
| 3197 | DEBUG_ONLY(_collector->verify_overflow_empty();) |
| 3198 | |
| 3199 | // Before we begin work, our work queue should be empty |
| 3200 | assert(work_queue(worker_id)->size() == 0, "Expected to be empty"); |
| 3201 | // Scan the bitmap covering _cms_space, tracing through grey objects. |
| 3202 | _timer.start(); |
| 3203 | do_scan_and_mark(worker_id, _cms_space); |
| 3204 | _timer.stop(); |
| 3205 | log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds()); |
| 3206 | |
| 3207 | // ... do work stealing |
| 3208 | _timer.reset(); |
| 3209 | _timer.start(); |
| 3210 | do_work_steal(worker_id); |
| 3211 | _timer.stop(); |
| 3212 | log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds()); |
| 3213 | assert(_collector->_markStack.isEmpty(), "Should have been emptied"); |
| 3214 | assert(work_queue(worker_id)->size() == 0, "Should have been emptied"); |
| 3215 | // Note that under the current task protocol, the |
| 3216 | // following assertion is true even of the spaces |
| 3217 | // expanded since the completion of the concurrent |
| 3218 | // marking. XXX This will likely change under a strict |
| 3219 | // ABORT semantics. |
| 3220 | // After perm removal the comparison was changed to |
| 3221 | // greater than or equal to from strictly greater than. |
| 3222 | // Before perm removal the highest address sweep would |
| 3223 | // have been at the end of perm gen but now is at the |
| 3224 | // end of the tenured gen. |
| 3225 | assert(_global_finger >= _cms_space->end(), |
| 3226 | "All tasks have been completed"); |
| 3227 | DEBUG_ONLY(_collector->verify_overflow_empty();) |
| 3228 | } |
| 3229 | |
| 3230 | void CMSConcMarkingTask::bump_global_finger(HeapWord* f) { |
| 3231 | HeapWord* read = _global_finger; |
| 3232 | HeapWord* cur = read; |
| 3233 | while (f > read) { |
| 3234 | cur = read; |
| 3235 | read = Atomic::cmpxchg(f, &_global_finger, cur); |
| 3236 | if (cur == read) { |
| 3237 | // our cas succeeded |
| 3238 | assert(_global_finger >= f, "protocol consistency"); |
| 3239 | break; |
| 3240 | } |
| 3241 | } |
| 3242 | } |
| 3243 | |
| 3244 | // This is really inefficient, and should be redone by |
| 3245 | // using (not yet available) block-read and -write interfaces to the |
| 3246 | // stack and the work_queue. XXX FIX ME !!! |
| 3247 | bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, |
| 3248 | OopTaskQueue* work_q) { |
| 3249 | // Fast lock-free check |
| 3250 | if (ovflw_stk->length() == 0) { |
| 3251 | return false; |
| 3252 | } |
| 3253 | assert(work_q->size() == 0, "Shouldn't steal"); |
| 3254 | MutexLocker ml(ovflw_stk->par_lock(), |
| 3255 | Mutex::_no_safepoint_check_flag); |
| 3256 | // Grab up to 1/4 the size of the work queue |
| 3257 | size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, |
| 3258 | (size_t)ParGCDesiredObjsFromOverflowList); |
| 3259 | num = MIN2(num, ovflw_stk->length()); |
| 3260 | for (int i = (int) num; i > 0; i--) { |
| 3261 | oop cur = ovflw_stk->pop(); |
| 3262 | assert(cur != NULL, "Counted wrong?"); |
| 3263 | work_q->push(cur); |
| 3264 | } |
| 3265 | return num > 0; |
| 3266 | } |
| 3267 | |
| 3268 | void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) { |
| 3269 | SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); |
| 3270 | int n_tasks = pst->n_tasks(); |
| 3271 | // We allow that there may be no tasks to do here because |
| 3272 | // we are restarting after a stack overflow. |
| 3273 | assert(pst->valid() || n_tasks == 0, "Uninitialized use?"); |
| 3274 | uint nth_task = 0; |
| 3275 | |
| 3276 | HeapWord* aligned_start = sp->bottom(); |
| 3277 | if (sp->used_region().contains(_restart_addr)) { |
| 3278 | // Align down to a card boundary for the start of 0th task |
| 3279 | // for this space. |
| 3280 | aligned_start = align_down(_restart_addr, CardTable::card_size); |
| 3281 | } |
| 3282 | |
| 3283 | size_t chunk_size = sp->marking_task_size(); |
| 3284 | while (pst->try_claim_task(/* reference */ nth_task)) { |
| 3285 | // Having claimed the nth task in this space, |
| 3286 | // compute the chunk that it corresponds to: |
| 3287 | MemRegion span = MemRegion(aligned_start + nth_task*chunk_size, |
| 3288 | aligned_start + (nth_task+1)*chunk_size); |
| 3289 | // Try and bump the global finger via a CAS; |
| 3290 | // note that we need to do the global finger bump |
| 3291 | // _before_ taking the intersection below, because |
| 3292 | // the task corresponding to that region will be |
| 3293 | // deemed done even if the used_region() expands |
| 3294 | // because of allocation -- as it almost certainly will |
| 3295 | // during start-up while the threads yield in the |
| 3296 | // closure below. |
| 3297 | HeapWord* finger = span.end(); |
| 3298 | bump_global_finger(finger); // atomically |
| 3299 | // There are null tasks here corresponding to chunks |
| 3300 | // beyond the "top" address of the space. |
| 3301 | span = span.intersection(sp->used_region()); |
| 3302 | if (!span.is_empty()) { // Non-null task |
| 3303 | HeapWord* prev_obj; |
| 3304 | assert(!span.contains(_restart_addr) || nth_task == 0, |
| 3305 | "Inconsistency"); |
| 3306 | if (nth_task == 0) { |
| 3307 | // For the 0th task, we'll not need to compute a block_start. |
| 3308 | if (span.contains(_restart_addr)) { |
| 3309 | // In the case of a restart because of stack overflow, |
| 3310 | // we might additionally skip a chunk prefix. |
| 3311 | prev_obj = _restart_addr; |
| 3312 | } else { |
| 3313 | prev_obj = span.start(); |
| 3314 | } |
| 3315 | } else { |
| 3316 | // We want to skip the first object because |
| 3317 | // the protocol is to scan any object in its entirety |
| 3318 | // that _starts_ in this span; a fortiori, any |
| 3319 | // object starting in an earlier span is scanned |
| 3320 | // as part of an earlier claimed task. |
| 3321 | // Below we use the "careful" version of block_start |
| 3322 | // so we do not try to navigate uninitialized objects. |
| 3323 | prev_obj = sp->block_start_careful(span.start()); |
| 3324 | // Below we use a variant of block_size that uses the |
| 3325 | // Printezis bits to avoid waiting for allocated |
| 3326 | // objects to become initialized/parsable. |
| 3327 | while (prev_obj < span.start()) { |
| 3328 | size_t sz = sp->block_size_no_stall(prev_obj, _collector); |
| 3329 | if (sz > 0) { |
| 3330 | prev_obj += sz; |
| 3331 | } else { |
| 3332 | // In this case we may end up doing a bit of redundant |
| 3333 | // scanning, but that appears unavoidable, short of |
| 3334 | // locking the free list locks; see bug 6324141. |
| 3335 | break; |
| 3336 | } |
| 3337 | } |
| 3338 | } |
| 3339 | if (prev_obj < span.end()) { |
| 3340 | MemRegion my_span = MemRegion(prev_obj, span.end()); |
| 3341 | // Do the marking work within a non-empty span -- |
| 3342 | // the last argument to the constructor indicates whether the |
| 3343 | // iteration should be incremental with periodic yields. |
| 3344 | ParMarkFromRootsClosure cl(this, _collector, my_span, |
| 3345 | &_collector->_markBitMap, |
| 3346 | work_queue(i), |
| 3347 | &_collector->_markStack); |
| 3348 | _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end()); |
| 3349 | } // else nothing to do for this task |
| 3350 | } // else nothing to do for this task |
| 3351 | } |
| 3352 | // We'd be tempted to assert here that since there are no |
| 3353 | // more tasks left to claim in this space, the global_finger |
| 3354 | // must exceed space->top() and a fortiori space->end(). However, |
| 3355 | // that would not quite be correct because the bumping of |
| 3356 | // global_finger occurs strictly after the claiming of a task, |
| 3357 | // so by the time we reach here the global finger may not yet |
| 3358 | // have been bumped up by the thread that claimed the last |
| 3359 | // task. |
| 3360 | pst->all_tasks_completed(); |
| 3361 | } |
| 3362 | |
| 3363 | class ParConcMarkingClosure: public MetadataVisitingOopIterateClosure { |
| 3364 | private: |
| 3365 | CMSCollector* _collector; |
| 3366 | CMSConcMarkingTask* _task; |
| 3367 | MemRegion _span; |
| 3368 | CMSBitMap* _bit_map; |
| 3369 | CMSMarkStack* _overflow_stack; |
| 3370 | OopTaskQueue* _work_queue; |
| 3371 | protected: |
| 3372 | DO_OOP_WORK_DEFN |
| 3373 | public: |
| 3374 | ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue, |
| 3375 | CMSBitMap* bit_map, CMSMarkStack* overflow_stack): |
| 3376 | MetadataVisitingOopIterateClosure(collector->ref_processor()), |
| 3377 | _collector(collector), |
| 3378 | _task(task), |
| 3379 | _span(collector->_span), |
| 3380 | _bit_map(bit_map), |
| 3381 | _overflow_stack(overflow_stack), |
| 3382 | _work_queue(work_queue) |
| 3383 | { } |
| 3384 | virtual void do_oop(oop* p); |
| 3385 | virtual void do_oop(narrowOop* p); |
| 3386 | |
| 3387 | void trim_queue(size_t max); |
| 3388 | void handle_stack_overflow(HeapWord* lost); |
| 3389 | void do_yield_check() { |
| 3390 | if (_task->should_yield()) { |
| 3391 | _task->yield(); |
| 3392 | } |
| 3393 | } |
| 3394 | }; |
| 3395 | |
| 3396 | DO_OOP_WORK_IMPL(ParConcMarkingClosure) |
| 3397 | |
| 3398 | // Grey object scanning during work stealing phase -- |
| 3399 | // the salient assumption here is that any references |
| 3400 | // that are in these stolen objects being scanned must |
| 3401 | // already have been initialized (else they would not have |
| 3402 | // been published), so we do not need to check for |
| 3403 | // uninitialized objects before pushing here. |
| 3404 | void ParConcMarkingClosure::do_oop(oop obj) { |
| 3405 | assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at "PTR_FORMAT, p2i(obj)); |
| 3406 | HeapWord* addr = (HeapWord*)obj; |
| 3407 | // Check if oop points into the CMS generation |
| 3408 | // and is not marked |
| 3409 | if (_span.contains(addr) && !_bit_map->isMarked(addr)) { |
| 3410 | // a white object ... |
| 3411 | // If we manage to "claim" the object, by being the |
| 3412 | // first thread to mark it, then we push it on our |
| 3413 | // marking stack |
| 3414 | if (_bit_map->par_mark(addr)) { // ... now grey |
| 3415 | // push on work queue (grey set) |
| 3416 | bool simulate_overflow = false; |
| 3417 | NOT_PRODUCT( |
| 3418 | if (CMSMarkStackOverflowALot && |
| 3419 | _collector->simulate_overflow()) { |
| 3420 | // simulate a stack overflow |
| 3421 | simulate_overflow = true; |
| 3422 | } |
| 3423 | ) |
| 3424 | if (simulate_overflow || |
| 3425 | !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) { |
| 3426 | // stack overflow |
| 3427 | log_trace(gc)("CMS marking stack overflow (benign) at "SIZE_FORMAT, _overflow_stack->capacity()); |
| 3428 | // We cannot assert that the overflow stack is full because |
| 3429 | // it may have been emptied since. |
| 3430 | assert(simulate_overflow || |
| 3431 | _work_queue->size() == _work_queue->max_elems(), |
| 3432 | "Else push should have succeeded"); |
| 3433 | handle_stack_overflow(addr); |
| 3434 | } |
| 3435 | } // Else, some other thread got there first |
| 3436 | do_yield_check(); |
| 3437 | } |
| 3438 | } |
| 3439 | |
| 3440 | void ParConcMarkingClosure::trim_queue(size_t max) { |
| 3441 | while (_work_queue->size() > max) { |
| 3442 | oop new_oop; |
| 3443 | if (_work_queue->pop_local(new_oop)) { |
| 3444 | assert(oopDesc::is_oop(new_oop), "Should be an oop"); |
| 3445 | assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object"); |
| 3446 | assert(_span.contains((HeapWord*)new_oop), "Not in span"); |
| 3447 | new_oop->oop_iterate(this); // do_oop() above |
| 3448 | do_yield_check(); |
| 3449 | } |
| 3450 | } |
| 3451 | } |
| 3452 | |
| 3453 | // Upon stack overflow, we discard (part of) the stack, |
| 3454 | // remembering the least address amongst those discarded |
| 3455 | // in CMSCollector's _restart_address. |
| 3456 | void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) { |
| 3457 | // We need to do this under a mutex to prevent other |
| 3458 | // workers from interfering with the work done below. |
| 3459 | MutexLocker ml(_overflow_stack->par_lock(), |
| 3460 | Mutex::_no_safepoint_check_flag); |
| 3461 | // Remember the least grey address discarded |
| 3462 | HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); |
| 3463 | _collector->lower_restart_addr(ra); |
| 3464 | _overflow_stack->reset(); // discard stack contents |
| 3465 | _overflow_stack->expand(); // expand the stack if possible |
| 3466 | } |
| 3467 | |
| 3468 | |
| 3469 | void CMSConcMarkingTask::do_work_steal(int i) { |
| 3470 | OopTaskQueue* work_q = work_queue(i); |
| 3471 | oop obj_to_scan; |
| 3472 | CMSBitMap* bm = &(_collector->_markBitMap); |
| 3473 | CMSMarkStack* ovflw = &(_collector->_markStack); |
| 3474 | ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw); |
| 3475 | while (true) { |
| 3476 | cl.trim_queue(0); |
| 3477 | assert(work_q->size() == 0, "Should have been emptied above"); |
| 3478 | if (get_work_from_overflow_stack(ovflw, work_q)) { |
| 3479 | // Can't assert below because the work obtained from the |
| 3480 | // overflow stack may already have been stolen from us. |
| 3481 | // assert(work_q->size() > 0, "Work from overflow stack"); |
| 3482 | continue; |
| 3483 | } else if (task_queues()->steal(i, /* reference */ obj_to_scan)) { |
| 3484 | assert(oopDesc::is_oop(obj_to_scan), "Should be an oop"); |
| 3485 | assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object"); |
| 3486 | obj_to_scan->oop_iterate(&cl); |
| 3487 | } else if (terminator()->offer_termination(&_term_term)) { |
| 3488 | assert(work_q->size() == 0, "Impossible!"); |
| 3489 | break; |
| 3490 | } else if (yielding() || should_yield()) { |
| 3491 | yield(); |
| 3492 | } |
| 3493 | } |
| 3494 | } |
| 3495 | |
| 3496 | // This is run by the CMS (coordinator) thread. |
| 3497 | void CMSConcMarkingTask::coordinator_yield() { |
| 3498 | assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| 3499 | "CMS thread should hold CMS token"); |
| 3500 | // First give up the locks, then yield, then re-lock |
| 3501 | // We should probably use a constructor/destructor idiom to |
| 3502 | // do this unlock/lock or modify the MutexUnlocker class to |
| 3503 | // serve our purpose. XXX |
| 3504 | assert_lock_strong(_bit_map_lock); |
| 3505 | _bit_map_lock->unlock(); |
| 3506 | ConcurrentMarkSweepThread::desynchronize(true); |
| 3507 | _collector->stopTimer(); |
| 3508 | _collector->incrementYields(); |
| 3509 | |
| 3510 | // It is possible for whichever thread initiated the yield request |
| 3511 | // not to get a chance to wake up and take the bitmap lock between |
| 3512 | // this thread releasing it and reacquiring it. So, while the |
| 3513 | // should_yield() flag is on, let's sleep for a bit to give the |
| 3514 | // other thread a chance to wake up. The limit imposed on the number |
| 3515 | // of iterations is defensive, to avoid any unforseen circumstances |
| 3516 | // putting us into an infinite loop. Since it's always been this |
| 3517 | // (coordinator_yield()) method that was observed to cause the |
| 3518 | // problem, we are using a parameter (CMSCoordinatorYieldSleepCount) |
| 3519 | // which is by default non-zero. For the other seven methods that |
| 3520 | // also perform the yield operation, as are using a different |
| 3521 | // parameter (CMSYieldSleepCount) which is by default zero. This way we |
| 3522 | // can enable the sleeping for those methods too, if necessary. |
| 3523 | // See 6442774. |
| 3524 | // |
| 3525 | // We really need to reconsider the synchronization between the GC |
| 3526 | // thread and the yield-requesting threads in the future and we |
| 3527 | // should really use wait/notify, which is the recommended |
| 3528 | // way of doing this type of interaction. Additionally, we should |
| 3529 | // consolidate the eight methods that do the yield operation and they |
| 3530 | // are almost identical into one for better maintainability and |
| 3531 | // readability. See 6445193. |
| 3532 | // |
| 3533 | // Tony 2006.06.29 |
| 3534 | for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount && |
| 3535 | ConcurrentMarkSweepThread::should_yield() && |
| 3536 | !CMSCollector::foregroundGCIsActive(); ++i) { |
| 3537 | os::sleep(Thread::current(), 1, false); |
| 3538 | } |
| 3539 | |
| 3540 | ConcurrentMarkSweepThread::synchronize(true); |
| 3541 | _bit_map_lock->lock_without_safepoint_check(); |
| 3542 | _collector->startTimer(); |
| 3543 | } |
| 3544 | |
| 3545 | bool CMSCollector::do_marking_mt() { |
| 3546 | assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition"); |
| 3547 | uint num_workers = WorkerPolicy::calc_active_conc_workers(conc_workers()->total_workers(), |
| 3548 | conc_workers()->active_workers(), |
| 3549 | Threads::number_of_non_daemon_threads()); |
| 3550 | num_workers = conc_workers()->update_active_workers(num_workers); |
| 3551 | log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers()); |
| 3552 | |
| 3553 | CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); |
| 3554 | |
| 3555 | CMSConcMarkingTask tsk(this, |
| 3556 | cms_space, |
| 3557 | conc_workers(), |
| 3558 | task_queues()); |
| 3559 | |
| 3560 | // Since the actual number of workers we get may be different |
| 3561 | // from the number we requested above, do we need to do anything different |
| 3562 | // below? In particular, may be we need to subclass the SequantialSubTasksDone |
| 3563 | // class?? XXX |
| 3564 | cms_space ->initialize_sequential_subtasks_for_marking(num_workers); |
| 3565 | |
| 3566 | // Refs discovery is already non-atomic. |
| 3567 | assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic"); |
| 3568 | assert(ref_processor()->discovery_is_mt(), "Discovery should be MT"); |
| 3569 | conc_workers()->start_task(&tsk); |
| 3570 | while (tsk.yielded()) { |
| 3571 | tsk.coordinator_yield(); |
| 3572 | conc_workers()->continue_task(&tsk); |
| 3573 | } |
| 3574 | // If the task was aborted, _restart_addr will be non-NULL |
| 3575 | assert(tsk.completed() || _restart_addr != NULL, "Inconsistency"); |
| 3576 | while (_restart_addr != NULL) { |
| 3577 | // XXX For now we do not make use of ABORTED state and have not |
| 3578 | // yet implemented the right abort semantics (even in the original |
| 3579 | // single-threaded CMS case). That needs some more investigation |
| 3580 | // and is deferred for now; see CR# TBF. 07252005YSR. XXX |
| 3581 | assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency"); |
| 3582 | // If _restart_addr is non-NULL, a marking stack overflow |
| 3583 | // occurred; we need to do a fresh marking iteration from the |
| 3584 | // indicated restart address. |
| 3585 | if (_foregroundGCIsActive) { |
| 3586 | // We may be running into repeated stack overflows, having |
| 3587 | // reached the limit of the stack size, while making very |
| 3588 | // slow forward progress. It may be best to bail out and |
| 3589 | // let the foreground collector do its job. |
| 3590 | // Clear _restart_addr, so that foreground GC |
| 3591 | // works from scratch. This avoids the headache of |
| 3592 | // a "rescan" which would otherwise be needed because |
| 3593 | // of the dirty mod union table & card table. |
| 3594 | _restart_addr = NULL; |
| 3595 | return false; |
| 3596 | } |
| 3597 | // Adjust the task to restart from _restart_addr |
| 3598 | tsk.reset(_restart_addr); |
| 3599 | cms_space ->initialize_sequential_subtasks_for_marking(num_workers, |
| 3600 | _restart_addr); |
| 3601 | _restart_addr = NULL; |
| 3602 | // Get the workers going again |
| 3603 | conc_workers()->start_task(&tsk); |
| 3604 | while (tsk.yielded()) { |
| 3605 | tsk.coordinator_yield(); |
| 3606 | conc_workers()->continue_task(&tsk); |
| 3607 | } |
| 3608 | } |
| 3609 | assert(tsk.completed(), "Inconsistency"); |
| 3610 | assert(tsk.result() == true, "Inconsistency"); |
| 3611 | return true; |
| 3612 | } |
| 3613 | |
| 3614 | bool CMSCollector::do_marking_st() { |
| 3615 | ResourceMark rm; |
| 3616 | HandleMark hm; |
| 3617 | |
| 3618 | // Temporarily make refs discovery single threaded (non-MT) |
| 3619 | ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false); |
| 3620 | MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap, |
| 3621 | &_markStack, CMSYield); |
| 3622 | // the last argument to iterate indicates whether the iteration |
| 3623 | // should be incremental with periodic yields. |
| 3624 | _markBitMap.iterate(&markFromRootsClosure); |
| 3625 | // If _restart_addr is non-NULL, a marking stack overflow |
| 3626 | // occurred; we need to do a fresh iteration from the |
| 3627 | // indicated restart address. |
| 3628 | while (_restart_addr != NULL) { |
| 3629 | if (_foregroundGCIsActive) { |
| 3630 | // We may be running into repeated stack overflows, having |
| 3631 | // reached the limit of the stack size, while making very |
| 3632 | // slow forward progress. It may be best to bail out and |
| 3633 | // let the foreground collector do its job. |
| 3634 | // Clear _restart_addr, so that foreground GC |
| 3635 | // works from scratch. This avoids the headache of |
| 3636 | // a "rescan" which would otherwise be needed because |
| 3637 | // of the dirty mod union table & card table. |
| 3638 | _restart_addr = NULL; |
| 3639 | return false; // indicating failure to complete marking |
| 3640 | } |
| 3641 | // Deal with stack overflow: |
| 3642 | // we restart marking from _restart_addr |
| 3643 | HeapWord* ra = _restart_addr; |
| 3644 | markFromRootsClosure.reset(ra); |
| 3645 | _restart_addr = NULL; |
| 3646 | _markBitMap.iterate(&markFromRootsClosure, ra, _span.end()); |
| 3647 | } |
| 3648 | return true; |
| 3649 | } |
| 3650 | |
| 3651 | void CMSCollector::preclean() { |
| 3652 | check_correct_thread_executing(); |
| 3653 | assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread"); |
| 3654 | verify_work_stacks_empty(); |
| 3655 | verify_overflow_empty(); |
| 3656 | _abort_preclean = false; |
| 3657 | if (CMSPrecleaningEnabled) { |
| 3658 | if (!CMSEdenChunksRecordAlways) { |
| 3659 | _eden_chunk_index = 0; |
| 3660 | } |
| 3661 | size_t used = get_eden_used(); |
| 3662 | size_t capacity = get_eden_capacity(); |
| 3663 | // Don't start sampling unless we will get sufficiently |
| 3664 | // many samples. |
| 3665 | if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100) |
| 3666 | * CMSScheduleRemarkEdenPenetration)) { |
| 3667 | _start_sampling = true; |
| 3668 | } else { |
| 3669 | _start_sampling = false; |
| 3670 | } |
| 3671 | GCTraceCPUTime tcpu; |
| 3672 | CMSPhaseAccounting pa(this, "Concurrent Preclean"); |
| 3673 | preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1); |
| 3674 | } |
| 3675 | CMSTokenSync x(true); // is cms thread |
| 3676 | if (CMSPrecleaningEnabled) { |
| 3677 | sample_eden(); |
| 3678 | _collectorState = AbortablePreclean; |
| 3679 | } else { |
| 3680 | _collectorState = FinalMarking; |
| 3681 | } |
| 3682 | verify_work_stacks_empty(); |
| 3683 | verify_overflow_empty(); |
| 3684 | } |
| 3685 | |
| 3686 | // Try and schedule the remark such that young gen |
| 3687 | // occupancy is CMSScheduleRemarkEdenPenetration %. |
| 3688 | void CMSCollector::abortable_preclean() { |
| 3689 | check_correct_thread_executing(); |
| 3690 | assert(CMSPrecleaningEnabled, "Inconsistent control state"); |
| 3691 | assert(_collectorState == AbortablePreclean, "Inconsistent control state"); |
| 3692 | |
| 3693 | // If Eden's current occupancy is below this threshold, |
| 3694 | // immediately schedule the remark; else preclean |
| 3695 | // past the next scavenge in an effort to |
| 3696 | // schedule the pause as described above. By choosing |
| 3697 | // CMSScheduleRemarkEdenSizeThreshold >= max eden size |
| 3698 | // we will never do an actual abortable preclean cycle. |
| 3699 | if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) { |
| 3700 | GCTraceCPUTime tcpu; |
| 3701 | CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean"); |
| 3702 | // We need more smarts in the abortable preclean |
| 3703 | // loop below to deal with cases where allocation |
| 3704 | // in young gen is very very slow, and our precleaning |
| 3705 | // is running a losing race against a horde of |
| 3706 | // mutators intent on flooding us with CMS updates |
| 3707 | // (dirty cards). |
| 3708 | // One, admittedly dumb, strategy is to give up |
| 3709 | // after a certain number of abortable precleaning loops |
| 3710 | // or after a certain maximum time. We want to make |
| 3711 | // this smarter in the next iteration. |
| 3712 | // XXX FIX ME!!! YSR |
| 3713 | size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0; |
| 3714 | while (!(should_abort_preclean() || |
| 3715 | ConcurrentMarkSweepThread::cmst()->should_terminate())) { |
| 3716 | workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2); |
| 3717 | cumworkdone += workdone; |
| 3718 | loops++; |
| 3719 | // Voluntarily terminate abortable preclean phase if we have |
| 3720 | // been at it for too long. |
| 3721 | if ((CMSMaxAbortablePrecleanLoops != 0) && |
| 3722 | loops >= CMSMaxAbortablePrecleanLoops) { |
| 3723 | log_debug(gc)(" CMS: abort preclean due to loops "); |
| 3724 | break; |
| 3725 | } |
| 3726 | if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) { |
| 3727 | log_debug(gc)(" CMS: abort preclean due to time "); |
| 3728 | break; |
| 3729 | } |
| 3730 | // If we are doing little work each iteration, we should |
| 3731 | // take a short break. |
| 3732 | if (workdone < CMSAbortablePrecleanMinWorkPerIteration) { |
| 3733 | // Sleep for some time, waiting for work to accumulate |
| 3734 | stopTimer(); |
| 3735 | cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis); |
| 3736 | startTimer(); |
| 3737 | waited++; |
| 3738 | } |
| 3739 | } |
| 3740 | log_trace(gc)(" ["SIZE_FORMAT " iterations, "SIZE_FORMAT " waits, "SIZE_FORMAT " cards)] ", |
| 3741 | loops, waited, cumworkdone); |
| 3742 | } |
| 3743 | CMSTokenSync x(true); // is cms thread |
| 3744 | if (_collectorState != Idling) { |
| 3745 | assert(_collectorState == AbortablePreclean, |
| 3746 | "Spontaneous state transition?"); |
| 3747 | _collectorState = FinalMarking; |
| 3748 | } // Else, a foreground collection completed this CMS cycle. |
| 3749 | return; |
| 3750 | } |
| 3751 | |
| 3752 | // Respond to an Eden sampling opportunity |
| 3753 | void CMSCollector::sample_eden() { |
| 3754 | // Make sure a young gc cannot sneak in between our |
| 3755 | // reading and recording of a sample. |
| 3756 | assert(Thread::current()->is_ConcurrentGC_thread(), |
| 3757 | "Only the cms thread may collect Eden samples"); |
| 3758 | assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| 3759 | "Should collect samples while holding CMS token"); |
| 3760 | if (!_start_sampling) { |
| 3761 | return; |
| 3762 | } |
| 3763 | // When CMSEdenChunksRecordAlways is true, the eden chunk array |
| 3764 | // is populated by the young generation. |
| 3765 | if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) { |
| 3766 | if (_eden_chunk_index < _eden_chunk_capacity) { |
| 3767 | _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample |
| 3768 | assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr, |
| 3769 | "Unexpected state of Eden"); |
| 3770 | // We'd like to check that what we just sampled is an oop-start address; |
| 3771 | // however, we cannot do that here since the object may not yet have been |
| 3772 | // initialized. So we'll instead do the check when we _use_ this sample |
| 3773 | // later. |
| 3774 | if (_eden_chunk_index == 0 || |
| 3775 | (pointer_delta(_eden_chunk_array[_eden_chunk_index], |
| 3776 | _eden_chunk_array[_eden_chunk_index-1]) |
| 3777 | >= CMSSamplingGrain)) { |
| 3778 | _eden_chunk_index++; // commit sample |
| 3779 | } |
| 3780 | } |
| 3781 | } |
| 3782 | if ((_collectorState == AbortablePreclean) && !_abort_preclean) { |
| 3783 | size_t used = get_eden_used(); |
| 3784 | size_t capacity = get_eden_capacity(); |
| 3785 | assert(used <= capacity, "Unexpected state of Eden"); |
| 3786 | if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) { |
| 3787 | _abort_preclean = true; |
| 3788 | } |
| 3789 | } |
| 3790 | } |
| 3791 | |
| 3792 | size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) { |
| 3793 | assert(_collectorState == Precleaning || |
| 3794 | _collectorState == AbortablePreclean, "incorrect state"); |
| 3795 | ResourceMark rm; |
| 3796 | HandleMark hm; |
| 3797 | |
| 3798 | // Precleaning is currently not MT but the reference processor |
| 3799 | // may be set for MT. Disable it temporarily here. |
| 3800 | ReferenceProcessor* rp = ref_processor(); |
| 3801 | ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false); |
| 3802 | |
| 3803 | // Do one pass of scrubbing the discovered reference lists |
| 3804 | // to remove any reference objects with strongly-reachable |
| 3805 | // referents. |
| 3806 | if (clean_refs) { |
| 3807 | CMSPrecleanRefsYieldClosure yield_cl(this); |
| 3808 | assert(_span_based_discoverer.span().equals(_span), "Spans should be equal"); |
| 3809 | CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap, |
| 3810 | &_markStack, true /* preclean */); |
| 3811 | CMSDrainMarkingStackClosure complete_trace(this, |
| 3812 | _span, &_markBitMap, &_markStack, |
| 3813 | &keep_alive, true /* preclean */); |
| 3814 | |
| 3815 | // We don't want this step to interfere with a young |
| 3816 | // collection because we don't want to take CPU |
| 3817 | // or memory bandwidth away from the young GC threads |
| 3818 | // (which may be as many as there are CPUs). |
| 3819 | // Note that we don't need to protect ourselves from |
| 3820 | // interference with mutators because they can't |
| 3821 | // manipulate the discovered reference lists nor affect |
| 3822 | // the computed reachability of the referents, the |
| 3823 | // only properties manipulated by the precleaning |
| 3824 | // of these reference lists. |
| 3825 | stopTimer(); |
| 3826 | CMSTokenSyncWithLocks x(true /* is cms thread */, |
| 3827 | bitMapLock()); |
| 3828 | startTimer(); |
| 3829 | sample_eden(); |
| 3830 | |
| 3831 | // The following will yield to allow foreground |
| 3832 | // collection to proceed promptly. XXX YSR: |
| 3833 | // The code in this method may need further |
| 3834 | // tweaking for better performance and some restructuring |
| 3835 | // for cleaner interfaces. |
| 3836 | GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases |
| 3837 | rp->preclean_discovered_references( |
| 3838 | rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl, |
| 3839 | gc_timer); |
| 3840 | } |
| 3841 | |
| 3842 | if (clean_survivor) { // preclean the active survivor space(s) |
| 3843 | PushAndMarkClosure pam_cl(this, _span, ref_processor(), |
| 3844 | &_markBitMap, &_modUnionTable, |
| 3845 | &_markStack, true /* precleaning phase */); |
| 3846 | stopTimer(); |
| 3847 | CMSTokenSyncWithLocks ts(true /* is cms thread */, |
| 3848 | bitMapLock()); |
| 3849 | startTimer(); |
| 3850 | unsigned int before_count = |
| 3851 | CMSHeap::heap()->total_collections(); |
| 3852 | SurvivorSpacePrecleanClosure |
| 3853 | sss_cl(this, _span, &_markBitMap, &_markStack, |
| 3854 | &pam_cl, before_count, CMSYield); |
| 3855 | _young_gen->from()->object_iterate_careful(&sss_cl); |
| 3856 | _young_gen->to()->object_iterate_careful(&sss_cl); |
| 3857 | } |
| 3858 | MarkRefsIntoAndScanClosure |
| 3859 | mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable, |
| 3860 | &_markStack, this, CMSYield, |
| 3861 | true /* precleaning phase */); |
| 3862 | // CAUTION: The following closure has persistent state that may need to |
| 3863 | // be reset upon a decrease in the sequence of addresses it |
| 3864 | // processes. |
| 3865 | ScanMarkedObjectsAgainCarefullyClosure |
| 3866 | smoac_cl(this, _span, |
| 3867 | &_markBitMap, &_markStack, &mrias_cl, CMSYield); |
| 3868 | |
| 3869 | // Preclean dirty cards in ModUnionTable and CardTable using |
| 3870 | // appropriate convergence criterion; |
| 3871 | // repeat CMSPrecleanIter times unless we find that |
| 3872 | // we are losing. |
| 3873 | assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large"); |
| 3874 | assert(CMSPrecleanNumerator < CMSPrecleanDenominator, |
| 3875 | "Bad convergence multiplier"); |
| 3876 | assert(CMSPrecleanThreshold >= 100, |
| 3877 | "Unreasonably low CMSPrecleanThreshold"); |
| 3878 | |
| 3879 | size_t numIter, cumNumCards, lastNumCards, curNumCards; |
| 3880 | for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0; |
| 3881 | numIter < CMSPrecleanIter; |
| 3882 | numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) { |
| 3883 | curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl); |
| 3884 | log_trace(gc)(" (modUnionTable: "SIZE_FORMAT " cards)", curNumCards); |
| 3885 | // Either there are very few dirty cards, so re-mark |
| 3886 | // pause will be small anyway, or our pre-cleaning isn't |
| 3887 | // that much faster than the rate at which cards are being |
| 3888 | // dirtied, so we might as well stop and re-mark since |
| 3889 | // precleaning won't improve our re-mark time by much. |
| 3890 | if (curNumCards <= CMSPrecleanThreshold || |
| 3891 | (numIter > 0 && |
| 3892 | (curNumCards * CMSPrecleanDenominator > |
| 3893 | lastNumCards * CMSPrecleanNumerator))) { |
| 3894 | numIter++; |
| 3895 | cumNumCards += curNumCards; |
| 3896 | break; |
| 3897 | } |
| 3898 | } |
| 3899 | |
| 3900 | preclean_cld(&mrias_cl, _cmsGen->freelistLock()); |
| 3901 | |
| 3902 | curNumCards = preclean_card_table(_cmsGen, &smoac_cl); |
| 3903 | cumNumCards += curNumCards; |
| 3904 | log_trace(gc)(" (cardTable: "SIZE_FORMAT " cards, re-scanned "SIZE_FORMAT " cards, "SIZE_FORMAT " iterations)", |
| 3905 | curNumCards, cumNumCards, numIter); |
| 3906 | return cumNumCards; // as a measure of useful work done |
| 3907 | } |
| 3908 | |
| 3909 | // PRECLEANING NOTES: |
| 3910 | // Precleaning involves: |
| 3911 | // . reading the bits of the modUnionTable and clearing the set bits. |
| 3912 | // . For the cards corresponding to the set bits, we scan the |
| 3913 | // objects on those cards. This means we need the free_list_lock |
| 3914 | // so that we can safely iterate over the CMS space when scanning |
| 3915 | // for oops. |
| 3916 | // . When we scan the objects, we'll be both reading and setting |
| 3917 | // marks in the marking bit map, so we'll need the marking bit map. |
| 3918 | // . For protecting _collector_state transitions, we take the CGC_lock. |
| 3919 | // Note that any races in the reading of of card table entries by the |
| 3920 | // CMS thread on the one hand and the clearing of those entries by the |
| 3921 | // VM thread or the setting of those entries by the mutator threads on the |
| 3922 | // other are quite benign. However, for efficiency it makes sense to keep |
| 3923 | // the VM thread from racing with the CMS thread while the latter is |
| 3924 | // dirty card info to the modUnionTable. We therefore also use the |
| 3925 | // CGC_lock to protect the reading of the card table and the mod union |
| 3926 | // table by the CM thread. |
| 3927 | // . We run concurrently with mutator updates, so scanning |
| 3928 | // needs to be done carefully -- we should not try to scan |
| 3929 | // potentially uninitialized objects. |
| 3930 | // |
| 3931 | // Locking strategy: While holding the CGC_lock, we scan over and |
| 3932 | // reset a maximal dirty range of the mod union / card tables, then lock |
| 3933 | // the free_list_lock and bitmap lock to do a full marking, then |
| 3934 | // release these locks; and repeat the cycle. This allows for a |
| 3935 | // certain amount of fairness in the sharing of these locks between |
| 3936 | // the CMS collector on the one hand, and the VM thread and the |
| 3937 | // mutators on the other. |
| 3938 | |
| 3939 | // NOTE: preclean_mod_union_table() and preclean_card_table() |
| 3940 | // further below are largely identical; if you need to modify |
| 3941 | // one of these methods, please check the other method too. |
| 3942 | |
| 3943 | size_t CMSCollector::preclean_mod_union_table( |
| 3944 | ConcurrentMarkSweepGeneration* old_gen, |
| 3945 | ScanMarkedObjectsAgainCarefullyClosure* cl) { |
| 3946 | verify_work_stacks_empty(); |
| 3947 | verify_overflow_empty(); |
| 3948 | |
| 3949 | // strategy: starting with the first card, accumulate contiguous |
| 3950 | // ranges of dirty cards; clear these cards, then scan the region |
| 3951 | // covered by these cards. |
| 3952 | |
| 3953 | // Since all of the MUT is committed ahead, we can just use |
| 3954 | // that, in case the generations expand while we are precleaning. |
| 3955 | // It might also be fine to just use the committed part of the |
| 3956 | // generation, but we might potentially miss cards when the |
| 3957 | // generation is rapidly expanding while we are in the midst |
| 3958 | // of precleaning. |
| 3959 | HeapWord* startAddr = old_gen->reserved().start(); |
| 3960 | HeapWord* endAddr = old_gen->reserved().end(); |
| 3961 | |
| 3962 | cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding |
| 3963 | |
| 3964 | size_t numDirtyCards, cumNumDirtyCards; |
| 3965 | HeapWord *nextAddr, *lastAddr; |
| 3966 | for (cumNumDirtyCards = numDirtyCards = 0, |
| 3967 | nextAddr = lastAddr = startAddr; |
| 3968 | nextAddr < endAddr; |
| 3969 | nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { |
| 3970 | |
| 3971 | ResourceMark rm; |
| 3972 | HandleMark hm; |
| 3973 | |
| 3974 | MemRegion dirtyRegion; |
| 3975 | { |
| 3976 | stopTimer(); |
| 3977 | // Potential yield point |
| 3978 | CMSTokenSync ts(true); |
| 3979 | startTimer(); |
| 3980 | sample_eden(); |
| 3981 | // Get dirty region starting at nextOffset (inclusive), |
| 3982 | // simultaneously clearing it. |
| 3983 | dirtyRegion = |
| 3984 | _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr); |
| 3985 | assert(dirtyRegion.start() >= nextAddr, |
| 3986 | "returned region inconsistent?"); |
| 3987 | } |
| 3988 | // Remember where the next search should begin. |
| 3989 | // The returned region (if non-empty) is a right open interval, |
| 3990 | // so lastOffset is obtained from the right end of that |
| 3991 | // interval. |
| 3992 | lastAddr = dirtyRegion.end(); |
| 3993 | // Should do something more transparent and less hacky XXX |
| 3994 | numDirtyCards = |
| 3995 | _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size()); |
| 3996 | |
| 3997 | // We'll scan the cards in the dirty region (with periodic |
| 3998 | // yields for foreground GC as needed). |
| 3999 | if (!dirtyRegion.is_empty()) { |
| 4000 | assert(numDirtyCards > 0, "consistency check"); |
| 4001 | HeapWord* stop_point = NULL; |
| 4002 | stopTimer(); |
| 4003 | // Potential yield point |
| 4004 | CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), |
| 4005 | bitMapLock()); |
| 4006 | startTimer(); |
| 4007 | { |
| 4008 | verify_work_stacks_empty(); |
| 4009 | verify_overflow_empty(); |
| 4010 | sample_eden(); |
| 4011 | stop_point = |
| 4012 | old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); |
| 4013 | } |
| 4014 | if (stop_point != NULL) { |
| 4015 | // The careful iteration stopped early either because it found an |
| 4016 | // uninitialized object, or because we were in the midst of an |
| 4017 | // "abortable preclean", which should now be aborted. Redirty |
| 4018 | // the bits corresponding to the partially-scanned or unscanned |
| 4019 | // cards. We'll either restart at the next block boundary or |
| 4020 | // abort the preclean. |
| 4021 | assert((_collectorState == AbortablePreclean && should_abort_preclean()), |
| 4022 | "Should only be AbortablePreclean."); |
| 4023 | _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end())); |
| 4024 | if (should_abort_preclean()) { |
| 4025 | break; // out of preclean loop |
| 4026 | } else { |
| 4027 | // Compute the next address at which preclean should pick up; |
| 4028 | // might need bitMapLock in order to read P-bits. |
| 4029 | lastAddr = next_card_start_after_block(stop_point); |
| 4030 | } |
| 4031 | } |
| 4032 | } else { |
| 4033 | assert(lastAddr == endAddr, "consistency check"); |
| 4034 | assert(numDirtyCards == 0, "consistency check"); |
| 4035 | break; |
| 4036 | } |
| 4037 | } |
| 4038 | verify_work_stacks_empty(); |
| 4039 | verify_overflow_empty(); |
| 4040 | return cumNumDirtyCards; |
| 4041 | } |
| 4042 | |
| 4043 | // NOTE: preclean_mod_union_table() above and preclean_card_table() |
| 4044 | // below are largely identical; if you need to modify |
| 4045 | // one of these methods, please check the other method too. |
| 4046 | |
| 4047 | size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen, |
| 4048 | ScanMarkedObjectsAgainCarefullyClosure* cl) { |
| 4049 | // strategy: it's similar to precleamModUnionTable above, in that |
| 4050 | // we accumulate contiguous ranges of dirty cards, mark these cards |
| 4051 | // precleaned, then scan the region covered by these cards. |
| 4052 | HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high()); |
| 4053 | HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low()); |
| 4054 | |
| 4055 | cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding |
| 4056 | |
| 4057 | size_t numDirtyCards, cumNumDirtyCards; |
| 4058 | HeapWord *lastAddr, *nextAddr; |
| 4059 | |
| 4060 | for (cumNumDirtyCards = numDirtyCards = 0, |
| 4061 | nextAddr = lastAddr = startAddr; |
| 4062 | nextAddr < endAddr; |
| 4063 | nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { |
| 4064 | |
| 4065 | ResourceMark rm; |
| 4066 | HandleMark hm; |
| 4067 | |
| 4068 | MemRegion dirtyRegion; |
| 4069 | { |
| 4070 | // See comments in "Precleaning notes" above on why we |
| 4071 | // do this locking. XXX Could the locking overheads be |
| 4072 | // too high when dirty cards are sparse? [I don't think so.] |
| 4073 | stopTimer(); |
| 4074 | CMSTokenSync x(true); // is cms thread |
| 4075 | startTimer(); |
| 4076 | sample_eden(); |
| 4077 | // Get and clear dirty region from card table |
| 4078 | dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr), |
| 4079 | true, |
| 4080 | CardTable::precleaned_card_val()); |
| 4081 | |
| 4082 | assert(dirtyRegion.start() >= nextAddr, |
| 4083 | "returned region inconsistent?"); |
| 4084 | } |
| 4085 | lastAddr = dirtyRegion.end(); |
| 4086 | numDirtyCards = |
| 4087 | dirtyRegion.word_size()/CardTable::card_size_in_words; |
| 4088 | |
| 4089 | if (!dirtyRegion.is_empty()) { |
| 4090 | stopTimer(); |
| 4091 | CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock()); |
| 4092 | startTimer(); |
| 4093 | sample_eden(); |
| 4094 | verify_work_stacks_empty(); |
| 4095 | verify_overflow_empty(); |
| 4096 | HeapWord* stop_point = |
| 4097 | old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); |
| 4098 | if (stop_point != NULL) { |
| 4099 | assert((_collectorState == AbortablePreclean && should_abort_preclean()), |
| 4100 | "Should only be AbortablePreclean."); |
| 4101 | _ct->invalidate(MemRegion(stop_point, dirtyRegion.end())); |
| 4102 | if (should_abort_preclean()) { |
| 4103 | break; // out of preclean loop |
| 4104 | } else { |
| 4105 | // Compute the next address at which preclean should pick up. |
| 4106 | lastAddr = next_card_start_after_block(stop_point); |
| 4107 | } |
| 4108 | } |
| 4109 | } else { |
| 4110 | break; |
| 4111 | } |
| 4112 | } |
| 4113 | verify_work_stacks_empty(); |
| 4114 | verify_overflow_empty(); |
| 4115 | return cumNumDirtyCards; |
| 4116 | } |
| 4117 | |
| 4118 | class PrecleanCLDClosure : public CLDClosure { |
| 4119 | MetadataVisitingOopsInGenClosure* _cm_closure; |
| 4120 | public: |
| 4121 | PrecleanCLDClosure(MetadataVisitingOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {} |
| 4122 | void do_cld(ClassLoaderData* cld) { |
| 4123 | if (cld->has_accumulated_modified_oops()) { |
| 4124 | cld->clear_accumulated_modified_oops(); |
| 4125 | |
| 4126 | _cm_closure->do_cld(cld); |
| 4127 | } |
| 4128 | } |
| 4129 | }; |
| 4130 | |
| 4131 | // The freelist lock is needed to prevent asserts, is it really needed? |
| 4132 | void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) { |
| 4133 | // Needed to walk CLDG |
| 4134 | MutexLocker ml(ClassLoaderDataGraph_lock); |
| 4135 | |
| 4136 | cl->set_freelistLock(freelistLock); |
| 4137 | |
| 4138 | CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock()); |
| 4139 | |
| 4140 | // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean? |
| 4141 | // SSS: We should probably check if precleaning should be aborted, at suitable intervals? |
| 4142 | PrecleanCLDClosure preclean_closure(cl); |
| 4143 | ClassLoaderDataGraph::cld_do(&preclean_closure); |
| 4144 | |
| 4145 | verify_work_stacks_empty(); |
| 4146 | verify_overflow_empty(); |
| 4147 | } |
| 4148 | |
| 4149 | void CMSCollector::checkpointRootsFinal() { |
| 4150 | assert(_collectorState == FinalMarking, "incorrect state transition?"); |
| 4151 | check_correct_thread_executing(); |
| 4152 | // world is stopped at this checkpoint |
| 4153 | assert(SafepointSynchronize::is_at_safepoint(), |
| 4154 | "world should be stopped"); |
| 4155 | TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause()); |
| 4156 | |
| 4157 | verify_work_stacks_empty(); |
| 4158 | verify_overflow_empty(); |
| 4159 | |
| 4160 | log_debug(gc)("YG occupancy: "SIZE_FORMAT " K ("SIZE_FORMAT " K)", |
| 4161 | _young_gen->used() / K, _young_gen->capacity() / K); |
| 4162 | { |
| 4163 | if (CMSScavengeBeforeRemark) { |
| 4164 | CMSHeap* heap = CMSHeap::heap(); |
| 4165 | // Temporarily set flag to false, GCH->do_collection will |
| 4166 | // expect it to be false and set to true |
| 4167 | FlagSetting fl(heap->_is_gc_active, false); |
| 4168 | |
| 4169 | heap->do_collection(true, // full (i.e. force, see below) |
| 4170 | false, // !clear_all_soft_refs |
| 4171 | 0, // size |
| 4172 | false, // is_tlab |
| 4173 | GenCollectedHeap::YoungGen // type |
| 4174 | ); |
| 4175 | } |
| 4176 | FreelistLocker x(this); |
| 4177 | MutexLocker y(bitMapLock(), |
| 4178 | Mutex::_no_safepoint_check_flag); |
| 4179 | checkpointRootsFinalWork(); |
| 4180 | } |
| 4181 | verify_work_stacks_empty(); |
| 4182 | verify_overflow_empty(); |
| 4183 | } |
| 4184 | |
| 4185 | void CMSCollector::checkpointRootsFinalWork() { |
| 4186 | GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm); |
| 4187 | |
| 4188 | assert(haveFreelistLocks(), "must have free list locks"); |
| 4189 | assert_lock_strong(bitMapLock()); |
| 4190 | |
| 4191 | ResourceMark rm; |
| 4192 | HandleMark hm; |
| 4193 | |
| 4194 | CMSHeap* heap = CMSHeap::heap(); |
| 4195 | |
| 4196 | assert(haveFreelistLocks(), "must have free list locks"); |
| 4197 | assert_lock_strong(bitMapLock()); |
| 4198 | |
| 4199 | // We might assume that we need not fill TLAB's when |
| 4200 | // CMSScavengeBeforeRemark is set, because we may have just done |
| 4201 | // a scavenge which would have filled all TLAB's -- and besides |
| 4202 | // Eden would be empty. This however may not always be the case -- |
| 4203 | // for instance although we asked for a scavenge, it may not have |
| 4204 | // happened because of a JNI critical section. We probably need |
| 4205 | // a policy for deciding whether we can in that case wait until |
| 4206 | // the critical section releases and then do the remark following |
| 4207 | // the scavenge, and skip it here. In the absence of that policy, |
| 4208 | // or of an indication of whether the scavenge did indeed occur, |
| 4209 | // we cannot rely on TLAB's having been filled and must do |
| 4210 | // so here just in case a scavenge did not happen. |
| 4211 | heap->ensure_parsability(false); // fill TLAB's, but no need to retire them |
| 4212 | // Update the saved marks which may affect the root scans. |
| 4213 | heap->save_marks(); |
| 4214 | |
| 4215 | print_eden_and_survivor_chunk_arrays(); |
| 4216 | |
| 4217 | { |
| 4218 | #if COMPILER2_OR_JVMCI |
| 4219 | DerivedPointerTableDeactivate dpt_deact; |
| 4220 | #endif |
| 4221 | |
| 4222 | // Note on the role of the mod union table: |
| 4223 | // Since the marker in "markFromRoots" marks concurrently with |
| 4224 | // mutators, it is possible for some reachable objects not to have been |
| 4225 | // scanned. For instance, an only reference to an object A was |
| 4226 | // placed in object B after the marker scanned B. Unless B is rescanned, |
| 4227 | // A would be collected. Such updates to references in marked objects |
| 4228 | // are detected via the mod union table which is the set of all cards |
| 4229 | // dirtied since the first checkpoint in this GC cycle and prior to |
| 4230 | // the most recent young generation GC, minus those cleaned up by the |
| 4231 | // concurrent precleaning. |
| 4232 | if (CMSParallelRemarkEnabled) { |
| 4233 | GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm); |
| 4234 | do_remark_parallel(); |
| 4235 | } else { |
| 4236 | GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm); |
| 4237 | do_remark_non_parallel(); |
| 4238 | } |
| 4239 | } |
| 4240 | verify_work_stacks_empty(); |
| 4241 | verify_overflow_empty(); |
| 4242 | |
| 4243 | { |
| 4244 | GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm); |
| 4245 | refProcessingWork(); |
| 4246 | } |
| 4247 | verify_work_stacks_empty(); |
| 4248 | verify_overflow_empty(); |
| 4249 | |
| 4250 | if (should_unload_classes()) { |
| 4251 | heap->prune_scavengable_nmethods(); |
| 4252 | } |
| 4253 | JvmtiExport::gc_epilogue(); |
| 4254 | |
| 4255 | // If we encountered any (marking stack / work queue) overflow |
| 4256 | // events during the current CMS cycle, take appropriate |
| 4257 | // remedial measures, where possible, so as to try and avoid |
| 4258 | // recurrence of that condition. |
| 4259 | assert(_markStack.isEmpty(), "No grey objects"); |
| 4260 | size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw + |
| 4261 | _ser_kac_ovflw + _ser_kac_preclean_ovflw; |
| 4262 | if (ser_ovflw > 0) { |
| 4263 | log_trace(gc)("Marking stack overflow (benign) (pmc_pc="SIZE_FORMAT ", pmc_rm="SIZE_FORMAT ", kac="SIZE_FORMAT ", kac_preclean="SIZE_FORMAT ")", |
| 4264 | _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw); |
| 4265 | _markStack.expand(); |
| 4266 | _ser_pmc_remark_ovflw = 0; |
| 4267 | _ser_pmc_preclean_ovflw = 0; |
| 4268 | _ser_kac_preclean_ovflw = 0; |
| 4269 | _ser_kac_ovflw = 0; |
| 4270 | } |
| 4271 | if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) { |
| 4272 | log_trace(gc)("Work queue overflow (benign) (pmc_rm="SIZE_FORMAT ", kac="SIZE_FORMAT ")", |
| 4273 | _par_pmc_remark_ovflw, _par_kac_ovflw); |
| 4274 | _par_pmc_remark_ovflw = 0; |
| 4275 | _par_kac_ovflw = 0; |
| 4276 | } |
| 4277 | if (_markStack._hit_limit > 0) { |
| 4278 | log_trace(gc)(" (benign) Hit max stack size limit ("SIZE_FORMAT ")", |
| 4279 | _markStack._hit_limit); |
| 4280 | } |
| 4281 | if (_markStack._failed_double > 0) { |
| 4282 | log_trace(gc)(" (benign) Failed stack doubling ("SIZE_FORMAT "), current capacity "SIZE_FORMAT, |
| 4283 | _markStack._failed_double, _markStack.capacity()); |
| 4284 | } |
| 4285 | _markStack._hit_limit = 0; |
| 4286 | _markStack._failed_double = 0; |
| 4287 | |
| 4288 | if ((VerifyAfterGC || VerifyDuringGC) && |
| 4289 | CMSHeap::heap()->total_collections() >= VerifyGCStartAt) { |
| 4290 | verify_after_remark(); |
| 4291 | } |
| 4292 | |
| 4293 | _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure); |
| 4294 | |
| 4295 | // Change under the freelistLocks. |
| 4296 | _collectorState = Sweeping; |
| 4297 | // Call isAllClear() under bitMapLock |
| 4298 | assert(_modUnionTable.isAllClear(), |
| 4299 | "Should be clear by end of the final marking"); |
| 4300 | assert(_ct->cld_rem_set()->mod_union_is_clear(), |
| 4301 | "Should be clear by end of the final marking"); |
| 4302 | } |
| 4303 | |
| 4304 | void CMSParInitialMarkTask::work(uint worker_id) { |
| 4305 | elapsedTimer _timer; |
| 4306 | ResourceMark rm; |
| 4307 | HandleMark hm; |
| 4308 | |
| 4309 | // ---------- scan from roots -------------- |
| 4310 | _timer.start(); |
| 4311 | CMSHeap* heap = CMSHeap::heap(); |
| 4312 | ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap)); |
| 4313 | |
| 4314 | // ---------- young gen roots -------------- |
| 4315 | { |
| 4316 | work_on_young_gen_roots(&par_mri_cl); |
| 4317 | _timer.stop(); |
| 4318 | log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); |
| 4319 | } |
| 4320 | |
| 4321 | // ---------- remaining roots -------------- |
| 4322 | _timer.reset(); |
| 4323 | _timer.start(); |
| 4324 | |
| 4325 | CLDToOopClosure cld_closure(&par_mri_cl, ClassLoaderData::_claim_strong); |
| 4326 | |
| 4327 | heap->cms_process_roots(_strong_roots_scope, |
| 4328 | false, // yg was scanned above |
| 4329 | GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), |
| 4330 | _collector->should_unload_classes(), |
| 4331 | &par_mri_cl, |
| 4332 | &cld_closure); |
| 4333 | |
| 4334 | assert(_collector->should_unload_classes() |
| 4335 | || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache), |
| 4336 | "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); |
| 4337 | _timer.stop(); |
| 4338 | log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); |
| 4339 | } |
| 4340 | |
| 4341 | // Parallel remark task |
| 4342 | class CMSParRemarkTask: public CMSParMarkTask { |
| 4343 | CompactibleFreeListSpace* _cms_space; |
| 4344 | |
| 4345 | // The per-thread work queues, available here for stealing. |
| 4346 | OopTaskQueueSet* _task_queues; |
| 4347 | TaskTerminator _term; |
| 4348 | StrongRootsScope* _strong_roots_scope; |
| 4349 | |
| 4350 | public: |
| 4351 | // A value of 0 passed to n_workers will cause the number of |
| 4352 | // workers to be taken from the active workers in the work gang. |
| 4353 | CMSParRemarkTask(CMSCollector* collector, |
| 4354 | CompactibleFreeListSpace* cms_space, |
| 4355 | uint n_workers, WorkGang* workers, |
| 4356 | OopTaskQueueSet* task_queues, |
| 4357 | StrongRootsScope* strong_roots_scope): |
| 4358 | CMSParMarkTask("Rescan roots and grey objects in parallel", |
| 4359 | collector, n_workers), |
| 4360 | _cms_space(cms_space), |
| 4361 | _task_queues(task_queues), |
| 4362 | _term(n_workers, task_queues), |
| 4363 | _strong_roots_scope(strong_roots_scope) { } |
| 4364 | |
| 4365 | OopTaskQueueSet* task_queues() { return _task_queues; } |
| 4366 | |
| 4367 | OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } |
| 4368 | |
| 4369 | ParallelTaskTerminator* terminator() { return _term.terminator(); } |
| 4370 | uint n_workers() { return _n_workers; } |
| 4371 | |
| 4372 | void work(uint worker_id); |
| 4373 | |
| 4374 | private: |
| 4375 | // ... of dirty cards in old space |
| 4376 | void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i, |
| 4377 | ParMarkRefsIntoAndScanClosure* cl); |
| 4378 | |
| 4379 | // ... work stealing for the above |
| 4380 | void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl); |
| 4381 | }; |
| 4382 | |
| 4383 | class RemarkCLDClosure : public CLDClosure { |
| 4384 | CLDToOopClosure _cm_closure; |
| 4385 | public: |
| 4386 | RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure, ClassLoaderData::_claim_strong) {} |
| 4387 | void do_cld(ClassLoaderData* cld) { |
| 4388 | // Check if we have modified any oops in the CLD during the concurrent marking. |
| 4389 | if (cld->has_accumulated_modified_oops()) { |
| 4390 | cld->clear_accumulated_modified_oops(); |
| 4391 | |
| 4392 | // We could have transfered the current modified marks to the accumulated marks, |
| 4393 | // like we do with the Card Table to Mod Union Table. But it's not really necessary. |
| 4394 | } else if (cld->has_modified_oops()) { |
| 4395 | // Don't clear anything, this info is needed by the next young collection. |
| 4396 | } else { |
| 4397 | // No modified oops in the ClassLoaderData. |
| 4398 | return; |
| 4399 | } |
| 4400 | |
| 4401 | // The klass has modified fields, need to scan the klass. |
| 4402 | _cm_closure.do_cld(cld); |
| 4403 | } |
| 4404 | }; |
| 4405 | |
| 4406 | void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) { |
| 4407 | ParNewGeneration* young_gen = _collector->_young_gen; |
| 4408 | ContiguousSpace* eden_space = young_gen->eden(); |
| 4409 | ContiguousSpace* from_space = young_gen->from(); |
| 4410 | ContiguousSpace* to_space = young_gen->to(); |
| 4411 | |
| 4412 | HeapWord** eca = _collector->_eden_chunk_array; |
| 4413 | size_t ect = _collector->_eden_chunk_index; |
| 4414 | HeapWord** sca = _collector->_survivor_chunk_array; |
| 4415 | size_t sct = _collector->_survivor_chunk_index; |
| 4416 | |
| 4417 | assert(ect <= _collector->_eden_chunk_capacity, "out of bounds"); |
| 4418 | assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds"); |
| 4419 | |
| 4420 | do_young_space_rescan(cl, to_space, NULL, 0); |
| 4421 | do_young_space_rescan(cl, from_space, sca, sct); |
| 4422 | do_young_space_rescan(cl, eden_space, eca, ect); |
| 4423 | } |
| 4424 | |
| 4425 | // work_queue(i) is passed to the closure |
| 4426 | // ParMarkRefsIntoAndScanClosure. The "i" parameter |
| 4427 | // also is passed to do_dirty_card_rescan_tasks() and to |
| 4428 | // do_work_steal() to select the i-th task_queue. |
| 4429 | |
| 4430 | void CMSParRemarkTask::work(uint worker_id) { |
| 4431 | elapsedTimer _timer; |
| 4432 | ResourceMark rm; |
| 4433 | HandleMark hm; |
| 4434 | |
| 4435 | // ---------- rescan from roots -------------- |
| 4436 | _timer.start(); |
| 4437 | CMSHeap* heap = CMSHeap::heap(); |
| 4438 | ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector, |
| 4439 | _collector->_span, _collector->ref_processor(), |
| 4440 | &(_collector->_markBitMap), |
| 4441 | work_queue(worker_id)); |
| 4442 | |
| 4443 | // Rescan young gen roots first since these are likely |
| 4444 | // coarsely partitioned and may, on that account, constitute |
| 4445 | // the critical path; thus, it's best to start off that |
| 4446 | // work first. |
| 4447 | // ---------- young gen roots -------------- |
| 4448 | { |
| 4449 | work_on_young_gen_roots(&par_mrias_cl); |
| 4450 | _timer.stop(); |
| 4451 | log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); |
| 4452 | } |
| 4453 | |
| 4454 | // ---------- remaining roots -------------- |
| 4455 | _timer.reset(); |
| 4456 | _timer.start(); |
| 4457 | heap->cms_process_roots(_strong_roots_scope, |
| 4458 | false, // yg was scanned above |
| 4459 | GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), |
| 4460 | _collector->should_unload_classes(), |
| 4461 | &par_mrias_cl, |
| 4462 | NULL); // The dirty klasses will be handled below |
| 4463 | |
| 4464 | assert(_collector->should_unload_classes() |
| 4465 | || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache), |
| 4466 | "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); |
| 4467 | _timer.stop(); |
| 4468 | log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); |
| 4469 | |
| 4470 | // ---------- unhandled CLD scanning ---------- |
| 4471 | if (worker_id == 0) { // Single threaded at the moment. |
| 4472 | _timer.reset(); |
| 4473 | _timer.start(); |
| 4474 | |
| 4475 | // Scan all new class loader data objects and new dependencies that were |
| 4476 | // introduced during concurrent marking. |
| 4477 | ResourceMark rm; |
| 4478 | GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds(); |
| 4479 | for (int i = 0; i < array->length(); i++) { |
| 4480 | Devirtualizer::do_cld(&par_mrias_cl, array->at(i)); |
| 4481 | } |
| 4482 | |
| 4483 | // We don't need to keep track of new CLDs anymore. |
| 4484 | ClassLoaderDataGraph::remember_new_clds(false); |
| 4485 | |
| 4486 | _timer.stop(); |
| 4487 | log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); |
| 4488 | } |
| 4489 | |
| 4490 | // We might have added oops to ClassLoaderData::_handles during the |
| 4491 | // concurrent marking phase. These oops do not always point to newly allocated objects |
| 4492 | // that are guaranteed to be kept alive. Hence, |
| 4493 | // we do have to revisit the _handles block during the remark phase. |
| 4494 | |
| 4495 | // ---------- dirty CLD scanning ---------- |
| 4496 | if (worker_id == 0) { // Single threaded at the moment. |
| 4497 | _timer.reset(); |
| 4498 | _timer.start(); |
| 4499 | |
| 4500 | // Scan all classes that was dirtied during the concurrent marking phase. |
| 4501 | RemarkCLDClosure remark_closure(&par_mrias_cl); |
| 4502 | ClassLoaderDataGraph::cld_do(&remark_closure); |
| 4503 | |
| 4504 | _timer.stop(); |
| 4505 | log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); |
| 4506 | } |
| 4507 | |
| 4508 | |
| 4509 | // ---------- rescan dirty cards ------------ |
| 4510 | _timer.reset(); |
| 4511 | _timer.start(); |
| 4512 | |
| 4513 | // Do the rescan tasks for each of the two spaces |
| 4514 | // (cms_space) in turn. |
| 4515 | // "worker_id" is passed to select the task_queue for "worker_id" |
| 4516 | do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl); |
| 4517 | _timer.stop(); |
| 4518 | log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds()); |
| 4519 | |
| 4520 | // ---------- steal work from other threads ... |
| 4521 | // ---------- ... and drain overflow list. |
| 4522 | _timer.reset(); |
| 4523 | _timer.start(); |
| 4524 | do_work_steal(worker_id, &par_mrias_cl); |
| 4525 | _timer.stop(); |
| 4526 | log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds()); |
| 4527 | } |
| 4528 | |
| 4529 | void |
| 4530 | CMSParMarkTask::do_young_space_rescan( |
| 4531 | OopsInGenClosure* cl, ContiguousSpace* space, |
| 4532 | HeapWord** chunk_array, size_t chunk_top) { |
| 4533 | // Until all tasks completed: |
| 4534 | // . claim an unclaimed task |
| 4535 | // . compute region boundaries corresponding to task claimed |
| 4536 | // using chunk_array |
| 4537 | // . par_oop_iterate(cl) over that region |
| 4538 | |
| 4539 | ResourceMark rm; |
| 4540 | HandleMark hm; |
| 4541 | |
| 4542 | SequentialSubTasksDone* pst = space->par_seq_tasks(); |
| 4543 | |
| 4544 | uint nth_task = 0; |
| 4545 | uint n_tasks = pst->n_tasks(); |
| 4546 | |
| 4547 | if (n_tasks > 0) { |
| 4548 | assert(pst->valid(), "Uninitialized use?"); |
| 4549 | HeapWord *start, *end; |
| 4550 | while (pst->try_claim_task(/* reference */ nth_task)) { |
| 4551 | // We claimed task # nth_task; compute its boundaries. |
| 4552 | if (chunk_top == 0) { // no samples were taken |
| 4553 | assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task"); |
| 4554 | start = space->bottom(); |
| 4555 | end = space->top(); |
| 4556 | } else if (nth_task == 0) { |
| 4557 | start = space->bottom(); |
| 4558 | end = chunk_array[nth_task]; |
| 4559 | } else if (nth_task < (uint)chunk_top) { |
| 4560 | assert(nth_task >= 1, "Control point invariant"); |
| 4561 | start = chunk_array[nth_task - 1]; |
| 4562 | end = chunk_array[nth_task]; |
| 4563 | } else { |
| 4564 | assert(nth_task == (uint)chunk_top, "Control point invariant"); |
| 4565 | start = chunk_array[chunk_top - 1]; |
| 4566 | end = space->top(); |
| 4567 | } |
| 4568 | MemRegion mr(start, end); |
| 4569 | // Verify that mr is in space |
| 4570 | assert(mr.is_empty() || space->used_region().contains(mr), |
| 4571 | "Should be in space"); |
| 4572 | // Verify that "start" is an object boundary |
| 4573 | assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())), |
| 4574 | "Should be an oop"); |
| 4575 | space->par_oop_iterate(mr, cl); |
| 4576 | } |
| 4577 | pst->all_tasks_completed(); |
| 4578 | } |
| 4579 | } |
| 4580 | |
| 4581 | void |
| 4582 | CMSParRemarkTask::do_dirty_card_rescan_tasks( |
| 4583 | CompactibleFreeListSpace* sp, int i, |
| 4584 | ParMarkRefsIntoAndScanClosure* cl) { |
| 4585 | // Until all tasks completed: |
| 4586 | // . claim an unclaimed task |
| 4587 | // . compute region boundaries corresponding to task claimed |
| 4588 | // . transfer dirty bits ct->mut for that region |
| 4589 | // . apply rescanclosure to dirty mut bits for that region |
| 4590 | |
| 4591 | ResourceMark rm; |
| 4592 | HandleMark hm; |
| 4593 | |
| 4594 | OopTaskQueue* work_q = work_queue(i); |
| 4595 | ModUnionClosure modUnionClosure(&(_collector->_modUnionTable)); |
| 4596 | // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! |
| 4597 | // CAUTION: This closure has state that persists across calls to |
| 4598 | // the work method dirty_range_iterate_clear() in that it has |
| 4599 | // embedded in it a (subtype of) UpwardsObjectClosure. The |
| 4600 | // use of that state in the embedded UpwardsObjectClosure instance |
| 4601 | // assumes that the cards are always iterated (even if in parallel |
| 4602 | // by several threads) in monotonically increasing order per each |
| 4603 | // thread. This is true of the implementation below which picks |
| 4604 | // card ranges (chunks) in monotonically increasing order globally |
| 4605 | // and, a-fortiori, in monotonically increasing order per thread |
| 4606 | // (the latter order being a subsequence of the former). |
| 4607 | // If the work code below is ever reorganized into a more chaotic |
| 4608 | // work-partitioning form than the current "sequential tasks" |
| 4609 | // paradigm, the use of that persistent state will have to be |
| 4610 | // revisited and modified appropriately. See also related |
| 4611 | // bug 4756801 work on which should examine this code to make |
| 4612 | // sure that the changes there do not run counter to the |
| 4613 | // assumptions made here and necessary for correctness and |
| 4614 | // efficiency. Note also that this code might yield inefficient |
| 4615 | // behavior in the case of very large objects that span one or |
| 4616 | // more work chunks. Such objects would potentially be scanned |
| 4617 | // several times redundantly. Work on 4756801 should try and |
| 4618 | // address that performance anomaly if at all possible. XXX |
| 4619 | MemRegion full_span = _collector->_span; |
| 4620 | CMSBitMap* bm = &(_collector->_markBitMap); // shared |
| 4621 | MarkFromDirtyCardsClosure |
| 4622 | greyRescanClosure(_collector, full_span, // entire span of interest |
| 4623 | sp, bm, work_q, cl); |
| 4624 | |
| 4625 | SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); |
| 4626 | assert(pst->valid(), "Uninitialized use?"); |
| 4627 | uint nth_task = 0; |
| 4628 | const int alignment = CardTable::card_size * BitsPerWord; |
| 4629 | MemRegion span = sp->used_region(); |
| 4630 | HeapWord* start_addr = span.start(); |
| 4631 | HeapWord* end_addr = align_up(span.end(), alignment); |
| 4632 | const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units |
| 4633 | assert(is_aligned(start_addr, alignment), "Check alignment"); |
| 4634 | assert(is_aligned(chunk_size, alignment), "Check alignment"); |
| 4635 | |
| 4636 | while (pst->try_claim_task(/* reference */ nth_task)) { |
| 4637 | // Having claimed the nth_task, compute corresponding mem-region, |
| 4638 | // which is a-fortiori aligned correctly (i.e. at a MUT boundary). |
| 4639 | // The alignment restriction ensures that we do not need any |
| 4640 | // synchronization with other gang-workers while setting or |
| 4641 | // clearing bits in thus chunk of the MUT. |
| 4642 | MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size, |
| 4643 | start_addr + (nth_task+1)*chunk_size); |
| 4644 | // The last chunk's end might be way beyond end of the |
| 4645 | // used region. In that case pull back appropriately. |
| 4646 | if (this_span.end() > end_addr) { |
| 4647 | this_span.set_end(end_addr); |
| 4648 | assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)"); |
| 4649 | } |
| 4650 | // Iterate over the dirty cards covering this chunk, marking them |
| 4651 | // precleaned, and setting the corresponding bits in the mod union |
| 4652 | // table. Since we have been careful to partition at Card and MUT-word |
| 4653 | // boundaries no synchronization is needed between parallel threads. |
| 4654 | _collector->_ct->dirty_card_iterate(this_span, |
| 4655 | &modUnionClosure); |
| 4656 | |
| 4657 | // Having transferred these marks into the modUnionTable, |
| 4658 | // rescan the marked objects on the dirty cards in the modUnionTable. |
| 4659 | // Even if this is at a synchronous collection, the initial marking |
| 4660 | // may have been done during an asynchronous collection so there |
| 4661 | // may be dirty bits in the mod-union table. |
| 4662 | _collector->_modUnionTable.dirty_range_iterate_clear( |
| 4663 | this_span, &greyRescanClosure); |
| 4664 | _collector->_modUnionTable.verifyNoOneBitsInRange( |
| 4665 | this_span.start(), |
| 4666 | this_span.end()); |
| 4667 | } |
| 4668 | pst->all_tasks_completed(); // declare that i am done |
| 4669 | } |
| 4670 | |
| 4671 | // . see if we can share work_queues with ParNew? XXX |
| 4672 | void |
| 4673 | CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl) { |
| 4674 | OopTaskQueue* work_q = work_queue(i); |
| 4675 | NOT_PRODUCT(int num_steals = 0;) |
| 4676 | oop obj_to_scan; |
| 4677 | CMSBitMap* bm = &(_collector->_markBitMap); |
| 4678 | |
| 4679 | while (true) { |
| 4680 | // Completely finish any left over work from (an) earlier round(s) |
| 4681 | cl->trim_queue(0); |
| 4682 | size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, |
| 4683 | (size_t)ParGCDesiredObjsFromOverflowList); |
| 4684 | // Now check if there's any work in the overflow list |
| 4685 | // Passing ParallelGCThreads as the third parameter, no_of_gc_threads, |
| 4686 | // only affects the number of attempts made to get work from the |
| 4687 | // overflow list and does not affect the number of workers. Just |
| 4688 | // pass ParallelGCThreads so this behavior is unchanged. |
| 4689 | if (_collector->par_take_from_overflow_list(num_from_overflow_list, |
| 4690 | work_q, |
| 4691 | ParallelGCThreads)) { |
| 4692 | // found something in global overflow list; |
| 4693 | // not yet ready to go stealing work from others. |
| 4694 | // We'd like to assert(work_q->size() != 0, ...) |
| 4695 | // because we just took work from the overflow list, |
| 4696 | // but of course we can't since all of that could have |
| 4697 | // been already stolen from us. |
| 4698 | // "He giveth and He taketh away." |
| 4699 | continue; |
| 4700 | } |
| 4701 | // Verify that we have no work before we resort to stealing |
| 4702 | assert(work_q->size() == 0, "Have work, shouldn't steal"); |
| 4703 | // Try to steal from other queues that have work |
| 4704 | if (task_queues()->steal(i, /* reference */ obj_to_scan)) { |
| 4705 | NOT_PRODUCT(num_steals++;) |
| 4706 | assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!"); |
| 4707 | assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); |
| 4708 | // Do scanning work |
| 4709 | obj_to_scan->oop_iterate(cl); |
| 4710 | // Loop around, finish this work, and try to steal some more |
| 4711 | } else if (terminator()->offer_termination()) { |
| 4712 | break; // nirvana from the infinite cycle |
| 4713 | } |
| 4714 | } |
| 4715 | log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals); |
| 4716 | assert(work_q->size() == 0 && _collector->overflow_list_is_empty(), |
| 4717 | "Else our work is not yet done"); |
| 4718 | } |
| 4719 | |
| 4720 | // Record object boundaries in _eden_chunk_array by sampling the eden |
| 4721 | // top in the slow-path eden object allocation code path and record |
| 4722 | // the boundaries, if CMSEdenChunksRecordAlways is true. If |
| 4723 | // CMSEdenChunksRecordAlways is false, we use the other asynchronous |
| 4724 | // sampling in sample_eden() that activates during the part of the |
| 4725 | // preclean phase. |
| 4726 | void CMSCollector::sample_eden_chunk() { |
| 4727 | if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) { |
| 4728 | if (_eden_chunk_lock->try_lock()) { |
| 4729 | // Record a sample. This is the critical section. The contents |
| 4730 | // of the _eden_chunk_array have to be non-decreasing in the |
| 4731 | // address order. |
| 4732 | _eden_chunk_array[_eden_chunk_index] = *_top_addr; |
| 4733 | assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr, |
| 4734 | "Unexpected state of Eden"); |
| 4735 | if (_eden_chunk_index == 0 || |
| 4736 | ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) && |
| 4737 | (pointer_delta(_eden_chunk_array[_eden_chunk_index], |
| 4738 | _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) { |
| 4739 | _eden_chunk_index++; // commit sample |
| 4740 | } |
| 4741 | _eden_chunk_lock->unlock(); |
| 4742 | } |
| 4743 | } |
| 4744 | } |
| 4745 | |
| 4746 | // Return a thread-local PLAB recording array, as appropriate. |
| 4747 | void* CMSCollector::get_data_recorder(int thr_num) { |
| 4748 | if (_survivor_plab_array != NULL && |
| 4749 | (CMSPLABRecordAlways || |
| 4750 | (_collectorState > Marking && _collectorState < FinalMarking))) { |
| 4751 | assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds"); |
| 4752 | ChunkArray* ca = &_survivor_plab_array[thr_num]; |
| 4753 | ca->reset(); // clear it so that fresh data is recorded |
| 4754 | return (void*) ca; |
| 4755 | } else { |
| 4756 | return NULL; |
| 4757 | } |
| 4758 | } |
| 4759 | |
| 4760 | // Reset all the thread-local PLAB recording arrays |
| 4761 | void CMSCollector::reset_survivor_plab_arrays() { |
| 4762 | for (uint i = 0; i < ParallelGCThreads; i++) { |
| 4763 | _survivor_plab_array[i].reset(); |
| 4764 | } |
| 4765 | } |
| 4766 | |
| 4767 | // Merge the per-thread plab arrays into the global survivor chunk |
| 4768 | // array which will provide the partitioning of the survivor space |
| 4769 | // for CMS initial scan and rescan. |
| 4770 | void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv, |
| 4771 | int no_of_gc_threads) { |
| 4772 | assert(_survivor_plab_array != NULL, "Error"); |
| 4773 | assert(_survivor_chunk_array != NULL, "Error"); |
| 4774 | assert(_collectorState == FinalMarking || |
| 4775 | (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error"); |
| 4776 | for (int j = 0; j < no_of_gc_threads; j++) { |
| 4777 | _cursor[j] = 0; |
| 4778 | } |
| 4779 | HeapWord* top = surv->top(); |
| 4780 | size_t i; |
| 4781 | for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries |
| 4782 | HeapWord* min_val = top; // Higher than any PLAB address |
| 4783 | uint min_tid = 0; // position of min_val this round |
| 4784 | for (int j = 0; j < no_of_gc_threads; j++) { |
| 4785 | ChunkArray* cur_sca = &_survivor_plab_array[j]; |
| 4786 | if (_cursor[j] == cur_sca->end()) { |
| 4787 | continue; |
| 4788 | } |
| 4789 | assert(_cursor[j] < cur_sca->end(), "ctl pt invariant"); |
| 4790 | HeapWord* cur_val = cur_sca->nth(_cursor[j]); |
| 4791 | assert(surv->used_region().contains(cur_val), "Out of bounds value"); |
| 4792 | if (cur_val < min_val) { |
| 4793 | min_tid = j; |
| 4794 | min_val = cur_val; |
| 4795 | } else { |
| 4796 | assert(cur_val < top, "All recorded addresses should be less"); |
| 4797 | } |
| 4798 | } |
| 4799 | // At this point min_val and min_tid are respectively |
| 4800 | // the least address in _survivor_plab_array[j]->nth(_cursor[j]) |
| 4801 | // and the thread (j) that witnesses that address. |
| 4802 | // We record this address in the _survivor_chunk_array[i] |
| 4803 | // and increment _cursor[min_tid] prior to the next round i. |
| 4804 | if (min_val == top) { |
| 4805 | break; |
| 4806 | } |
| 4807 | _survivor_chunk_array[i] = min_val; |
| 4808 | _cursor[min_tid]++; |
| 4809 | } |
| 4810 | // We are all done; record the size of the _survivor_chunk_array |
| 4811 | _survivor_chunk_index = i; // exclusive: [0, i) |
| 4812 | log_trace(gc, survivor)(" (Survivor:"SIZE_FORMAT "chunks) ", i); |
| 4813 | // Verify that we used up all the recorded entries |
| 4814 | #ifdef ASSERT |
| 4815 | size_t total = 0; |
| 4816 | for (int j = 0; j < no_of_gc_threads; j++) { |
| 4817 | assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant"); |
| 4818 | total += _cursor[j]; |
| 4819 | } |
| 4820 | assert(total == _survivor_chunk_index, "Ctl Pt Invariant"); |
| 4821 | // Check that the merged array is in sorted order |
| 4822 | if (total > 0) { |
| 4823 | for (size_t i = 0; i < total - 1; i++) { |
| 4824 | log_develop_trace(gc, survivor)(" (chunk"SIZE_FORMAT ":"INTPTR_FORMAT ") ", |
| 4825 | i, p2i(_survivor_chunk_array[i])); |
| 4826 | assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1], |
| 4827 | "Not sorted"); |
| 4828 | } |
| 4829 | } |
| 4830 | #endif // ASSERT |
| 4831 | } |
| 4832 | |
| 4833 | // Set up the space's par_seq_tasks structure for work claiming |
| 4834 | // for parallel initial scan and rescan of young gen. |
| 4835 | // See ParRescanTask where this is currently used. |
| 4836 | void |
| 4837 | CMSCollector:: |
| 4838 | initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) { |
| 4839 | assert(n_threads > 0, "Unexpected n_threads argument"); |
| 4840 | |
| 4841 | // Eden space |
| 4842 | if (!_young_gen->eden()->is_empty()) { |
| 4843 | SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks(); |
| 4844 | assert(!pst->valid(), "Clobbering existing data?"); |
| 4845 | // Each valid entry in [0, _eden_chunk_index) represents a task. |
| 4846 | size_t n_tasks = _eden_chunk_index + 1; |
| 4847 | assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error"); |
| 4848 | // Sets the condition for completion of the subtask (how many threads |
| 4849 | // need to finish in order to be done). |
| 4850 | pst->set_n_threads(n_threads); |
| 4851 | pst->set_n_tasks((int)n_tasks); |
| 4852 | } |
| 4853 | |
| 4854 | // Merge the survivor plab arrays into _survivor_chunk_array |
| 4855 | if (_survivor_plab_array != NULL) { |
| 4856 | merge_survivor_plab_arrays(_young_gen->from(), n_threads); |
| 4857 | } else { |
| 4858 | assert(_survivor_chunk_index == 0, "Error"); |
| 4859 | } |
| 4860 | |
| 4861 | // To space |
| 4862 | { |
| 4863 | SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks(); |
| 4864 | assert(!pst->valid(), "Clobbering existing data?"); |
| 4865 | // Sets the condition for completion of the subtask (how many threads |
| 4866 | // need to finish in order to be done). |
| 4867 | pst->set_n_threads(n_threads); |
| 4868 | pst->set_n_tasks(1); |
| 4869 | assert(pst->valid(), "Error"); |
| 4870 | } |
| 4871 | |
| 4872 | // From space |
| 4873 | { |
| 4874 | SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks(); |
| 4875 | assert(!pst->valid(), "Clobbering existing data?"); |
| 4876 | size_t n_tasks = _survivor_chunk_index + 1; |
| 4877 | assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error"); |
| 4878 | // Sets the condition for completion of the subtask (how many threads |
| 4879 | // need to finish in order to be done). |
| 4880 | pst->set_n_threads(n_threads); |
| 4881 | pst->set_n_tasks((int)n_tasks); |
| 4882 | assert(pst->valid(), "Error"); |
| 4883 | } |
| 4884 | } |
| 4885 | |
| 4886 | // Parallel version of remark |
| 4887 | void CMSCollector::do_remark_parallel() { |
| 4888 | CMSHeap* heap = CMSHeap::heap(); |
| 4889 | WorkGang* workers = heap->workers(); |
| 4890 | assert(workers != NULL, "Need parallel worker threads."); |
| 4891 | // Choose to use the number of GC workers most recently set |
| 4892 | // into "active_workers". |
| 4893 | uint n_workers = workers->active_workers(); |
| 4894 | |
| 4895 | CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); |
| 4896 | |
| 4897 | StrongRootsScope srs(n_workers); |
| 4898 | |
| 4899 | CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs); |
| 4900 | |
| 4901 | // We won't be iterating over the cards in the card table updating |
| 4902 | // the younger_gen cards, so we shouldn't call the following else |
| 4903 | // the verification code as well as subsequent younger_refs_iterate |
| 4904 | // code would get confused. XXX |
| 4905 | // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel |
| 4906 | |
| 4907 | // The young gen rescan work will not be done as part of |
| 4908 | // process_roots (which currently doesn't know how to |
| 4909 | // parallelize such a scan), but rather will be broken up into |
| 4910 | // a set of parallel tasks (via the sampling that the [abortable] |
| 4911 | // preclean phase did of eden, plus the [two] tasks of |
| 4912 | // scanning the [two] survivor spaces. Further fine-grain |
| 4913 | // parallelization of the scanning of the survivor spaces |
| 4914 | // themselves, and of precleaning of the young gen itself |
| 4915 | // is deferred to the future. |
| 4916 | initialize_sequential_subtasks_for_young_gen_rescan(n_workers); |
| 4917 | |
| 4918 | // The dirty card rescan work is broken up into a "sequence" |
| 4919 | // of parallel tasks (per constituent space) that are dynamically |
| 4920 | // claimed by the parallel threads. |
| 4921 | cms_space->initialize_sequential_subtasks_for_rescan(n_workers); |
| 4922 | |
| 4923 | // It turns out that even when we're using 1 thread, doing the work in a |
| 4924 | // separate thread causes wide variance in run times. We can't help this |
| 4925 | // in the multi-threaded case, but we special-case n=1 here to get |
| 4926 | // repeatable measurements of the 1-thread overhead of the parallel code. |
| 4927 | if (n_workers > 1) { |
| 4928 | // Make refs discovery MT-safe, if it isn't already: it may not |
| 4929 | // necessarily be so, since it's possible that we are doing |
| 4930 | // ST marking. |
| 4931 | ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true); |
| 4932 | workers->run_task(&tsk); |
| 4933 | } else { |
| 4934 | ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false); |
| 4935 | tsk.work(0); |
| 4936 | } |
| 4937 | |
| 4938 | // restore, single-threaded for now, any preserved marks |
| 4939 | // as a result of work_q overflow |
| 4940 | restore_preserved_marks_if_any(); |
| 4941 | } |
| 4942 | |
| 4943 | // Non-parallel version of remark |
| 4944 | void CMSCollector::do_remark_non_parallel() { |
| 4945 | ResourceMark rm; |
| 4946 | HandleMark hm; |
| 4947 | CMSHeap* heap = CMSHeap::heap(); |
| 4948 | ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false); |
| 4949 | |
| 4950 | MarkRefsIntoAndScanClosure |
| 4951 | mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */, |
| 4952 | &_markStack, this, |
| 4953 | false /* should_yield */, false /* not precleaning */); |
| 4954 | MarkFromDirtyCardsClosure |
| 4955 | markFromDirtyCardsClosure(this, _span, |
| 4956 | NULL, // space is set further below |
| 4957 | &_markBitMap, &_markStack, &mrias_cl); |
| 4958 | { |
| 4959 | GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm); |
| 4960 | // Iterate over the dirty cards, setting the corresponding bits in the |
| 4961 | // mod union table. |
| 4962 | { |
| 4963 | ModUnionClosure modUnionClosure(&_modUnionTable); |
| 4964 | _ct->dirty_card_iterate(_cmsGen->used_region(), |
| 4965 | &modUnionClosure); |
| 4966 | } |
| 4967 | // Having transferred these marks into the modUnionTable, we just need |
| 4968 | // to rescan the marked objects on the dirty cards in the modUnionTable. |
| 4969 | // The initial marking may have been done during an asynchronous |
| 4970 | // collection so there may be dirty bits in the mod-union table. |
| 4971 | const int alignment = CardTable::card_size * BitsPerWord; |
| 4972 | { |
| 4973 | // ... First handle dirty cards in CMS gen |
| 4974 | markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace()); |
| 4975 | MemRegion ur = _cmsGen->used_region(); |
| 4976 | HeapWord* lb = ur.start(); |
| 4977 | HeapWord* ub = align_up(ur.end(), alignment); |
| 4978 | MemRegion cms_span(lb, ub); |
| 4979 | _modUnionTable.dirty_range_iterate_clear(cms_span, |
| 4980 | &markFromDirtyCardsClosure); |
| 4981 | verify_work_stacks_empty(); |
| 4982 | log_trace(gc)(" (re-scanned "SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards()); |
| 4983 | } |
| 4984 | } |
| 4985 | if (VerifyDuringGC && |
| 4986 | CMSHeap::heap()->total_collections() >= VerifyGCStartAt) { |
| 4987 | HandleMark hm; // Discard invalid handles created during verification |
| 4988 | Universe::verify(); |
| 4989 | } |
| 4990 | { |
| 4991 | GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm); |
| 4992 | |
| 4993 | verify_work_stacks_empty(); |
| 4994 | |
| 4995 | heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. |
| 4996 | StrongRootsScope srs(1); |
| 4997 | |
| 4998 | heap->cms_process_roots(&srs, |
| 4999 | true, // young gen as roots |
| 5000 | GenCollectedHeap::ScanningOption(roots_scanning_options()), |
| 5001 | should_unload_classes(), |
| 5002 | &mrias_cl, |
| 5003 | NULL); // The dirty klasses will be handled below |
| 5004 | |
| 5005 | assert(should_unload_classes() |
| 5006 | || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache), |
| 5007 | "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); |
| 5008 | } |
| 5009 | |
| 5010 | { |
| 5011 | GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm); |
| 5012 | |
| 5013 | verify_work_stacks_empty(); |
| 5014 | |
| 5015 | // Scan all class loader data objects that might have been introduced |
| 5016 | // during concurrent marking. |
| 5017 | ResourceMark rm; |
| 5018 | GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds(); |
| 5019 | for (int i = 0; i < array->length(); i++) { |
| 5020 | Devirtualizer::do_cld(&mrias_cl, array->at(i)); |
| 5021 | } |
| 5022 | |
| 5023 | // We don't need to keep track of new CLDs anymore. |
| 5024 | ClassLoaderDataGraph::remember_new_clds(false); |
| 5025 | |
| 5026 | verify_work_stacks_empty(); |
| 5027 | } |
| 5028 | |
| 5029 | // We might have added oops to ClassLoaderData::_handles during the |
| 5030 | // concurrent marking phase. These oops do not point to newly allocated objects |
| 5031 | // that are guaranteed to be kept alive. Hence, |
| 5032 | // we do have to revisit the _handles block during the remark phase. |
| 5033 | { |
| 5034 | GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm); |
| 5035 | |
| 5036 | verify_work_stacks_empty(); |
| 5037 | |
| 5038 | RemarkCLDClosure remark_closure(&mrias_cl); |
| 5039 | ClassLoaderDataGraph::cld_do(&remark_closure); |
| 5040 | |
| 5041 | verify_work_stacks_empty(); |
| 5042 | } |
| 5043 | |
| 5044 | verify_work_stacks_empty(); |
| 5045 | // Restore evacuated mark words, if any, used for overflow list links |
| 5046 | restore_preserved_marks_if_any(); |
| 5047 | |
| 5048 | verify_overflow_empty(); |
| 5049 | } |
| 5050 | |
| 5051 | //////////////////////////////////////////////////////// |
| 5052 | // Parallel Reference Processing Task Proxy Class |
| 5053 | //////////////////////////////////////////////////////// |
| 5054 | class AbstractGangTaskWOopQueues : public AbstractGangTask { |
| 5055 | OopTaskQueueSet* _queues; |
| 5056 | TaskTerminator _terminator; |
| 5057 | public: |
| 5058 | AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) : |
| 5059 | AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {} |
| 5060 | ParallelTaskTerminator* terminator() { return _terminator.terminator(); } |
| 5061 | OopTaskQueueSet* queues() { return _queues; } |
| 5062 | }; |
| 5063 | |
| 5064 | class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues { |
| 5065 | typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; |
| 5066 | CMSCollector* _collector; |
| 5067 | CMSBitMap* _mark_bit_map; |
| 5068 | const MemRegion _span; |
| 5069 | ProcessTask& _task; |
| 5070 | |
| 5071 | public: |
| 5072 | CMSRefProcTaskProxy(ProcessTask& task, |
| 5073 | CMSCollector* collector, |
| 5074 | const MemRegion& span, |
| 5075 | CMSBitMap* mark_bit_map, |
| 5076 | AbstractWorkGang* workers, |
| 5077 | OopTaskQueueSet* task_queues): |
| 5078 | AbstractGangTaskWOopQueues("Process referents by policy in parallel", |
| 5079 | task_queues, |
| 5080 | workers->active_workers()), |
| 5081 | _collector(collector), |
| 5082 | _mark_bit_map(mark_bit_map), |
| 5083 | _span(span), |
| 5084 | _task(task) |
| 5085 | { |
| 5086 | assert(_collector->_span.equals(_span) && !_span.is_empty(), |
| 5087 | "Inconsistency in _span"); |
| 5088 | } |
| 5089 | |
| 5090 | OopTaskQueueSet* task_queues() { return queues(); } |
| 5091 | |
| 5092 | OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } |
| 5093 | |
| 5094 | void do_work_steal(int i, |
| 5095 | CMSParDrainMarkingStackClosure* drain, |
| 5096 | CMSParKeepAliveClosure* keep_alive); |
| 5097 | |
| 5098 | virtual void work(uint worker_id); |
| 5099 | }; |
| 5100 | |
| 5101 | void CMSRefProcTaskProxy::work(uint worker_id) { |
| 5102 | ResourceMark rm; |
| 5103 | HandleMark hm; |
| 5104 | assert(_collector->_span.equals(_span), "Inconsistency in _span"); |
| 5105 | CMSParKeepAliveClosure par_keep_alive(_collector, _span, |
| 5106 | _mark_bit_map, |
| 5107 | work_queue(worker_id)); |
| 5108 | CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span, |
| 5109 | _mark_bit_map, |
| 5110 | work_queue(worker_id)); |
| 5111 | CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map); |
| 5112 | _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack); |
| 5113 | if (_task.marks_oops_alive()) { |
| 5114 | do_work_steal(worker_id, &par_drain_stack, &par_keep_alive); |
| 5115 | } |
| 5116 | assert(work_queue(worker_id)->size() == 0, "work_queue should be empty"); |
| 5117 | assert(_collector->_overflow_list == NULL, "non-empty _overflow_list"); |
| 5118 | } |
| 5119 | |
| 5120 | CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector, |
| 5121 | MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue): |
| 5122 | _span(span), |
| 5123 | _work_queue(work_queue), |
| 5124 | _bit_map(bit_map), |
| 5125 | _mark_and_push(collector, span, bit_map, work_queue), |
| 5126 | _low_water_mark(MIN2((work_queue->max_elems()/4), |
| 5127 | ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))) |
| 5128 | { } |
| 5129 | |
| 5130 | // . see if we can share work_queues with ParNew? XXX |
| 5131 | void CMSRefProcTaskProxy::do_work_steal(int i, |
| 5132 | CMSParDrainMarkingStackClosure* drain, |
| 5133 | CMSParKeepAliveClosure* keep_alive) { |
| 5134 | OopTaskQueue* work_q = work_queue(i); |
| 5135 | NOT_PRODUCT(int num_steals = 0;) |
| 5136 | oop obj_to_scan; |
| 5137 | |
| 5138 | while (true) { |
| 5139 | // Completely finish any left over work from (an) earlier round(s) |
| 5140 | drain->trim_queue(0); |
| 5141 | size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, |
| 5142 | (size_t)ParGCDesiredObjsFromOverflowList); |
| 5143 | // Now check if there's any work in the overflow list |
| 5144 | // Passing ParallelGCThreads as the third parameter, no_of_gc_threads, |
| 5145 | // only affects the number of attempts made to get work from the |
| 5146 | // overflow list and does not affect the number of workers. Just |
| 5147 | // pass ParallelGCThreads so this behavior is unchanged. |
| 5148 | if (_collector->par_take_from_overflow_list(num_from_overflow_list, |
| 5149 | work_q, |
| 5150 | ParallelGCThreads)) { |
| 5151 | // Found something in global overflow list; |
| 5152 | // not yet ready to go stealing work from others. |
| 5153 | // We'd like to assert(work_q->size() != 0, ...) |
| 5154 | // because we just took work from the overflow list, |
| 5155 | // but of course we can't, since all of that might have |
| 5156 | // been already stolen from us. |
| 5157 | continue; |
| 5158 | } |
| 5159 | // Verify that we have no work before we resort to stealing |
| 5160 | assert(work_q->size() == 0, "Have work, shouldn't steal"); |
| 5161 | // Try to steal from other queues that have work |
| 5162 | if (task_queues()->steal(i, /* reference */ obj_to_scan)) { |
| 5163 | NOT_PRODUCT(num_steals++;) |
| 5164 | assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!"); |
| 5165 | assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); |
| 5166 | // Do scanning work |
| 5167 | obj_to_scan->oop_iterate(keep_alive); |
| 5168 | // Loop around, finish this work, and try to steal some more |
| 5169 | } else if (terminator()->offer_termination()) { |
| 5170 | break; // nirvana from the infinite cycle |
| 5171 | } |
| 5172 | } |
| 5173 | log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals); |
| 5174 | } |
| 5175 | |
| 5176 | void CMSRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers) { |
| 5177 | CMSHeap* heap = CMSHeap::heap(); |
| 5178 | WorkGang* workers = heap->workers(); |
| 5179 | assert(workers != NULL, "Need parallel worker threads."); |
| 5180 | assert(workers->active_workers() == ergo_workers, |
| 5181 | "Ergonomically chosen workers (%u) must be equal to active workers (%u)", |
| 5182 | ergo_workers, workers->active_workers()); |
| 5183 | CMSRefProcTaskProxy rp_task(task, &_collector, |
| 5184 | _collector.ref_processor_span(), |
| 5185 | _collector.markBitMap(), |
| 5186 | workers, _collector.task_queues()); |
| 5187 | workers->run_task(&rp_task, workers->active_workers()); |
| 5188 | } |
| 5189 | |
| 5190 | void CMSCollector::refProcessingWork() { |
| 5191 | ResourceMark rm; |
| 5192 | HandleMark hm; |
| 5193 | |
| 5194 | ReferenceProcessor* rp = ref_processor(); |
| 5195 | assert(_span_based_discoverer.span().equals(_span), "Spans should be equal"); |
| 5196 | assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete"); |
| 5197 | // Process weak references. |
| 5198 | rp->setup_policy(false); |
| 5199 | verify_work_stacks_empty(); |
| 5200 | |
| 5201 | ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->max_num_queues()); |
| 5202 | { |
| 5203 | GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm); |
| 5204 | |
| 5205 | // Setup keep_alive and complete closures. |
| 5206 | CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap, |
| 5207 | &_markStack, false /* !preclean */); |
| 5208 | CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this, |
| 5209 | _span, &_markBitMap, &_markStack, |
| 5210 | &cmsKeepAliveClosure, false /* !preclean */); |
| 5211 | |
| 5212 | ReferenceProcessorStats stats; |
| 5213 | if (rp->processing_is_mt()) { |
| 5214 | // Set the degree of MT here. If the discovery is done MT, there |
| 5215 | // may have been a different number of threads doing the discovery |
| 5216 | // and a different number of discovered lists may have Ref objects. |
| 5217 | // That is OK as long as the Reference lists are balanced (see |
| 5218 | // balance_all_queues() and balance_queues()). |
| 5219 | CMSHeap* heap = CMSHeap::heap(); |
| 5220 | uint active_workers = ParallelGCThreads; |
| 5221 | WorkGang* workers = heap->workers(); |
| 5222 | if (workers != NULL) { |
| 5223 | active_workers = workers->active_workers(); |
| 5224 | // The expectation is that active_workers will have already |
| 5225 | // been set to a reasonable value. If it has not been set, |
| 5226 | // investigate. |
| 5227 | assert(active_workers > 0, "Should have been set during scavenge"); |
| 5228 | } |
| 5229 | rp->set_active_mt_degree(active_workers); |
| 5230 | CMSRefProcTaskExecutor task_executor(*this); |
| 5231 | stats = rp->process_discovered_references(&_is_alive_closure, |
| 5232 | &cmsKeepAliveClosure, |
| 5233 | &cmsDrainMarkingStackClosure, |
| 5234 | &task_executor, |
| 5235 | &pt); |
| 5236 | } else { |
| 5237 | stats = rp->process_discovered_references(&_is_alive_closure, |
| 5238 | &cmsKeepAliveClosure, |
| 5239 | &cmsDrainMarkingStackClosure, |
| 5240 | NULL, |
| 5241 | &pt); |
| 5242 | } |
| 5243 | _gc_tracer_cm->report_gc_reference_stats(stats); |
| 5244 | pt.print_all_references(); |
| 5245 | } |
| 5246 | |
| 5247 | // This is the point where the entire marking should have completed. |
| 5248 | verify_work_stacks_empty(); |
| 5249 | |
| 5250 | { |
| 5251 | GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm); |
| 5252 | WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl); |
| 5253 | } |
| 5254 | |
| 5255 | if (should_unload_classes()) { |
| 5256 | { |
| 5257 | GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm); |
| 5258 | |
| 5259 | // Unload classes and purge the SystemDictionary. |
| 5260 | bool purged_class = SystemDictionary::do_unloading(_gc_timer_cm); |
| 5261 | |
| 5262 | // Unload nmethods. |
| 5263 | CodeCache::do_unloading(&_is_alive_closure, purged_class); |
| 5264 | |
| 5265 | // Prune dead klasses from subklass/sibling/implementor lists. |
| 5266 | Klass::clean_weak_klass_links(purged_class); |
| 5267 | |
| 5268 | // Clean JVMCI metadata handles. |
| 5269 | JVMCI_ONLY(JVMCI::do_unloading(purged_class)); |
| 5270 | } |
| 5271 | } |
| 5272 | |
| 5273 | // Restore any preserved marks as a result of mark stack or |
| 5274 | // work queue overflow |
| 5275 | restore_preserved_marks_if_any(); // done single-threaded for now |
| 5276 | |
| 5277 | rp->set_enqueuing_is_done(true); |
| 5278 | rp->verify_no_references_recorded(); |
| 5279 | } |
| 5280 | |
| 5281 | #ifndef PRODUCT |
| 5282 | void CMSCollector::check_correct_thread_executing() { |
| 5283 | Thread* t = Thread::current(); |
| 5284 | // Only the VM thread or the CMS thread should be here. |
| 5285 | assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(), |
| 5286 | "Unexpected thread type"); |
| 5287 | // If this is the vm thread, the foreground process |
| 5288 | // should not be waiting. Note that _foregroundGCIsActive is |
| 5289 | // true while the foreground collector is waiting. |
| 5290 | if (_foregroundGCShouldWait) { |
| 5291 | // We cannot be the VM thread |
| 5292 | assert(t->is_ConcurrentGC_thread(), |
| 5293 | "Should be CMS thread"); |
| 5294 | } else { |
| 5295 | // We can be the CMS thread only if we are in a stop-world |
| 5296 | // phase of CMS collection. |
| 5297 | if (t->is_ConcurrentGC_thread()) { |
| 5298 | assert(_collectorState == InitialMarking || |
| 5299 | _collectorState == FinalMarking, |
| 5300 | "Should be a stop-world phase"); |
| 5301 | // The CMS thread should be holding the CMS_token. |
| 5302 | assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| 5303 | "Potential interference with concurrently " |
| 5304 | "executing VM thread"); |
| 5305 | } |
| 5306 | } |
| 5307 | } |
| 5308 | #endif |
| 5309 | |
| 5310 | void CMSCollector::sweep() { |
| 5311 | assert(_collectorState == Sweeping, "just checking"); |
| 5312 | check_correct_thread_executing(); |
| 5313 | verify_work_stacks_empty(); |
| 5314 | verify_overflow_empty(); |
| 5315 | increment_sweep_count(); |
| 5316 | TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause()); |
| 5317 | |
| 5318 | _inter_sweep_timer.stop(); |
| 5319 | _inter_sweep_estimate.sample(_inter_sweep_timer.seconds()); |
| 5320 | |
| 5321 | assert(!_intra_sweep_timer.is_active(), "Should not be active"); |
| 5322 | _intra_sweep_timer.reset(); |
| 5323 | _intra_sweep_timer.start(); |
| 5324 | { |
| 5325 | GCTraceCPUTime tcpu; |
| 5326 | CMSPhaseAccounting pa(this, "Concurrent Sweep"); |
| 5327 | // First sweep the old gen |
| 5328 | { |
| 5329 | CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(), |
| 5330 | bitMapLock()); |
| 5331 | sweepWork(_cmsGen); |
| 5332 | } |
| 5333 | |
| 5334 | // Update Universe::_heap_*_at_gc figures. |
| 5335 | // We need all the free list locks to make the abstract state |
| 5336 | // transition from Sweeping to Resetting. See detailed note |
| 5337 | // further below. |
| 5338 | { |
| 5339 | CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock()); |
| 5340 | // Update heap occupancy information which is used as |
| 5341 | // input to soft ref clearing policy at the next gc. |
| 5342 | Universe::update_heap_info_at_gc(); |
| 5343 | _collectorState = Resizing; |
| 5344 | } |
| 5345 | } |
| 5346 | verify_work_stacks_empty(); |
| 5347 | verify_overflow_empty(); |
| 5348 | |
| 5349 | if (should_unload_classes()) { |
| 5350 | // Delay purge to the beginning of the next safepoint. Metaspace::contains |
| 5351 | // requires that the virtual spaces are stable and not deleted. |
| 5352 | ClassLoaderDataGraph::set_should_purge(true); |
| 5353 | } |
| 5354 | |
| 5355 | _intra_sweep_timer.stop(); |
| 5356 | _intra_sweep_estimate.sample(_intra_sweep_timer.seconds()); |
| 5357 | |
| 5358 | _inter_sweep_timer.reset(); |
| 5359 | _inter_sweep_timer.start(); |
| 5360 | |
| 5361 | // We need to use a monotonically non-decreasing time in ms |
| 5362 | // or we will see time-warp warnings and os::javaTimeMillis() |
| 5363 | // does not guarantee monotonicity. |
| 5364 | jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; |
| 5365 | update_time_of_last_gc(now); |
| 5366 | |
| 5367 | // NOTE on abstract state transitions: |
| 5368 | // Mutators allocate-live and/or mark the mod-union table dirty |
| 5369 | // based on the state of the collection. The former is done in |
| 5370 | // the interval [Marking, Sweeping] and the latter in the interval |
| 5371 | // [Marking, Sweeping). Thus the transitions into the Marking state |
| 5372 | // and out of the Sweeping state must be synchronously visible |
| 5373 | // globally to the mutators. |
| 5374 | // The transition into the Marking state happens with the world |
| 5375 | // stopped so the mutators will globally see it. Sweeping is |
| 5376 | // done asynchronously by the background collector so the transition |
| 5377 | // from the Sweeping state to the Resizing state must be done |
| 5378 | // under the freelistLock (as is the check for whether to |
| 5379 | // allocate-live and whether to dirty the mod-union table). |
| 5380 | assert(_collectorState == Resizing, "Change of collector state to" |
| 5381 | " Resizing must be done under the freelistLocks (plural)"); |
| 5382 | |
| 5383 | // Now that sweeping has been completed, we clear |
| 5384 | // the incremental_collection_failed flag, |
| 5385 | // thus inviting a younger gen collection to promote into |
| 5386 | // this generation. If such a promotion may still fail, |
| 5387 | // the flag will be set again when a young collection is |
| 5388 | // attempted. |
| 5389 | CMSHeap* heap = CMSHeap::heap(); |
| 5390 | heap->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up |
| 5391 | heap->update_full_collections_completed(_collection_count_start); |
| 5392 | } |
| 5393 | |
| 5394 | // FIX ME!!! Looks like this belongs in CFLSpace, with |
| 5395 | // CMSGen merely delegating to it. |
| 5396 | void ConcurrentMarkSweepGeneration::setNearLargestChunk() { |
| 5397 | double nearLargestPercent = FLSLargestBlockCoalesceProximity; |
| 5398 | HeapWord* minAddr = _cmsSpace->bottom(); |
| 5399 | HeapWord* largestAddr = |
| 5400 | (HeapWord*) _cmsSpace->dictionary()->find_largest_dict(); |
| 5401 | if (largestAddr == NULL) { |
| 5402 | // The dictionary appears to be empty. In this case |
| 5403 | // try to coalesce at the end of the heap. |
| 5404 | largestAddr = _cmsSpace->end(); |
| 5405 | } |
| 5406 | size_t largestOffset = pointer_delta(largestAddr, minAddr); |
| 5407 | size_t nearLargestOffset = |
| 5408 | (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize; |
| 5409 | log_debug(gc, freelist)("CMS: Large Block: "PTR_FORMAT "; Proximity: "PTR_FORMAT " -> "PTR_FORMAT, |
| 5410 | p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset)); |
| 5411 | _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset); |
| 5412 | } |
| 5413 | |
| 5414 | bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) { |
| 5415 | return addr >= _cmsSpace->nearLargestChunk(); |
| 5416 | } |
| 5417 | |
| 5418 | FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() { |
| 5419 | return _cmsSpace->find_chunk_at_end(); |
| 5420 | } |
| 5421 | |
| 5422 | void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation, |
| 5423 | bool full) { |
| 5424 | // If the young generation has been collected, gather any statistics |
| 5425 | // that are of interest at this point. |
| 5426 | bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation); |
| 5427 | if (!full && current_is_young) { |
| 5428 | // Gather statistics on the young generation collection. |
| 5429 | collector()->stats().record_gc0_end(used()); |
| 5430 | } |
| 5431 | } |
| 5432 | |
| 5433 | void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) { |
| 5434 | // We iterate over the space(s) underlying this generation, |
| 5435 | // checking the mark bit map to see if the bits corresponding |
| 5436 | // to specific blocks are marked or not. Blocks that are |
| 5437 | // marked are live and are not swept up. All remaining blocks |
| 5438 | // are swept up, with coalescing on-the-fly as we sweep up |
| 5439 | // contiguous free and/or garbage blocks: |
| 5440 | // We need to ensure that the sweeper synchronizes with allocators |
| 5441 | // and stop-the-world collectors. In particular, the following |
| 5442 | // locks are used: |
| 5443 | // . CMS token: if this is held, a stop the world collection cannot occur |
| 5444 | // . freelistLock: if this is held no allocation can occur from this |
| 5445 | // generation by another thread |
| 5446 | // . bitMapLock: if this is held, no other thread can access or update |
| 5447 | // |
| 5448 | |
| 5449 | // Note that we need to hold the freelistLock if we use |
| 5450 | // block iterate below; else the iterator might go awry if |
| 5451 | // a mutator (or promotion) causes block contents to change |
| 5452 | // (for instance if the allocator divvies up a block). |
| 5453 | // If we hold the free list lock, for all practical purposes |
| 5454 | // young generation GC's can't occur (they'll usually need to |
| 5455 | // promote), so we might as well prevent all young generation |
| 5456 | // GC's while we do a sweeping step. For the same reason, we might |
| 5457 | // as well take the bit map lock for the entire duration |
| 5458 | |
| 5459 | // check that we hold the requisite locks |
| 5460 | assert(have_cms_token(), "Should hold cms token"); |
| 5461 | assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep"); |
| 5462 | assert_lock_strong(old_gen->freelistLock()); |
| 5463 | assert_lock_strong(bitMapLock()); |
| 5464 | |
| 5465 | assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context"); |
| 5466 | assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context"); |
| 5467 | old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()), |
| 5468 | _inter_sweep_estimate.padded_average(), |
| 5469 | _intra_sweep_estimate.padded_average()); |
| 5470 | old_gen->setNearLargestChunk(); |
| 5471 | |
| 5472 | { |
| 5473 | SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield); |
| 5474 | old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure); |
| 5475 | // We need to free-up/coalesce garbage/blocks from a |
| 5476 | // co-terminal free run. This is done in the SweepClosure |
| 5477 | // destructor; so, do not remove this scope, else the |
| 5478 | // end-of-sweep-census below will be off by a little bit. |
| 5479 | } |
| 5480 | old_gen->cmsSpace()->sweep_completed(); |
| 5481 | old_gen->cmsSpace()->endSweepFLCensus(sweep_count()); |
| 5482 | if (should_unload_classes()) { // unloaded classes this cycle, |
| 5483 | _concurrent_cycles_since_last_unload = 0; // ... reset count |
| 5484 | } else { // did not unload classes, |
| 5485 | _concurrent_cycles_since_last_unload++; // ... increment count |
| 5486 | } |
| 5487 | } |
| 5488 | |
| 5489 | // Reset CMS data structures (for now just the marking bit map) |
| 5490 | // preparatory for the next cycle. |
| 5491 | void CMSCollector::reset_concurrent() { |
| 5492 | CMSTokenSyncWithLocks ts(true, bitMapLock()); |
| 5493 | |
| 5494 | // If the state is not "Resetting", the foreground thread |
| 5495 | // has done a collection and the resetting. |
| 5496 | if (_collectorState != Resetting) { |
| 5497 | assert(_collectorState == Idling, "The state should only change" |
| 5498 | " because the foreground collector has finished the collection"); |
| 5499 | return; |
| 5500 | } |
| 5501 | |
| 5502 | { |
| 5503 | // Clear the mark bitmap (no grey objects to start with) |
| 5504 | // for the next cycle. |
| 5505 | GCTraceCPUTime tcpu; |
| 5506 | CMSPhaseAccounting cmspa(this, "Concurrent Reset"); |
| 5507 | |
| 5508 | HeapWord* curAddr = _markBitMap.startWord(); |
| 5509 | while (curAddr < _markBitMap.endWord()) { |
| 5510 | size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr); |
| 5511 | MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining)); |
| 5512 | _markBitMap.clear_large_range(chunk); |
| 5513 | if (ConcurrentMarkSweepThread::should_yield() && |
| 5514 | !foregroundGCIsActive() && |
| 5515 | CMSYield) { |
| 5516 | assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| 5517 | "CMS thread should hold CMS token"); |
| 5518 | assert_lock_strong(bitMapLock()); |
| 5519 | bitMapLock()->unlock(); |
| 5520 | ConcurrentMarkSweepThread::desynchronize(true); |
| 5521 | stopTimer(); |
| 5522 | incrementYields(); |
| 5523 | |
| 5524 | // See the comment in coordinator_yield() |
| 5525 | for (unsigned i = 0; i < CMSYieldSleepCount && |
| 5526 | ConcurrentMarkSweepThread::should_yield() && |
| 5527 | !CMSCollector::foregroundGCIsActive(); ++i) { |
| 5528 | os::sleep(Thread::current(), 1, false); |
| 5529 | } |
| 5530 | |
| 5531 | ConcurrentMarkSweepThread::synchronize(true); |
| 5532 | bitMapLock()->lock_without_safepoint_check(); |
| 5533 | startTimer(); |
| 5534 | } |
| 5535 | curAddr = chunk.end(); |
| 5536 | } |
| 5537 | // A successful mostly concurrent collection has been done. |
| 5538 | // Because only the full (i.e., concurrent mode failure) collections |
| 5539 | // are being measured for gc overhead limits, clean the "near" flag |
| 5540 | // and count. |
| 5541 | size_policy()->reset_gc_overhead_limit_count(); |
| 5542 | _collectorState = Idling; |
| 5543 | } |
| 5544 | |
| 5545 | register_gc_end(); |
| 5546 | } |
| 5547 | |
| 5548 | // Same as above but for STW paths |
| 5549 | void CMSCollector::reset_stw() { |
| 5550 | // already have the lock |
| 5551 | assert(_collectorState == Resetting, "just checking"); |
| 5552 | assert_lock_strong(bitMapLock()); |
| 5553 | GCIdMark gc_id_mark(_cmsThread->gc_id()); |
| 5554 | _markBitMap.clear_all(); |
| 5555 | _collectorState = Idling; |
| 5556 | register_gc_end(); |
| 5557 | } |
| 5558 | |
| 5559 | void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) { |
| 5560 | GCTraceCPUTime tcpu; |
| 5561 | TraceCollectorStats tcs_cgc(cgc_counters()); |
| 5562 | |
| 5563 | switch (op) { |
| 5564 | case CMS_op_checkpointRootsInitial: { |
| 5565 | GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true); |
| 5566 | SvcGCMarker sgcm(SvcGCMarker::CONCURRENT); |
| 5567 | checkpointRootsInitial(); |
| 5568 | break; |
| 5569 | } |
| 5570 | case CMS_op_checkpointRootsFinal: { |
| 5571 | GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true); |
| 5572 | SvcGCMarker sgcm(SvcGCMarker::CONCURRENT); |
| 5573 | checkpointRootsFinal(); |
| 5574 | break; |
| 5575 | } |
| 5576 | default: |
| 5577 | fatal("No such CMS_op"); |
| 5578 | } |
| 5579 | } |
| 5580 | |
| 5581 | #ifndef PRODUCT |
| 5582 | size_t const CMSCollector::skip_header_HeapWords() { |
| 5583 | return FreeChunk::header_size(); |
| 5584 | } |
| 5585 | |
| 5586 | // Try and collect here conditions that should hold when |
| 5587 | // CMS thread is exiting. The idea is that the foreground GC |
| 5588 | // thread should not be blocked if it wants to terminate |
| 5589 | // the CMS thread and yet continue to run the VM for a while |
| 5590 | // after that. |
| 5591 | void CMSCollector::verify_ok_to_terminate() const { |
| 5592 | assert(Thread::current()->is_ConcurrentGC_thread(), |
| 5593 | "should be called by CMS thread"); |
| 5594 | assert(!_foregroundGCShouldWait, "should be false"); |
| 5595 | // We could check here that all the various low-level locks |
| 5596 | // are not held by the CMS thread, but that is overkill; see |
| 5597 | // also CMSThread::verify_ok_to_terminate() where the CGC_lock |
| 5598 | // is checked. |
| 5599 | } |
| 5600 | #endif |
| 5601 | |
| 5602 | size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const { |
| 5603 | assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1), |
| 5604 | "missing Printezis mark?"); |
| 5605 | HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); |
| 5606 | size_t size = pointer_delta(nextOneAddr + 1, addr); |
| 5607 | assert(size == CompactibleFreeListSpace::adjustObjectSize(size), |
| 5608 | "alignment problem"); |
| 5609 | assert(size >= 3, "Necessary for Printezis marks to work"); |
| 5610 | return size; |
| 5611 | } |
| 5612 | |
| 5613 | // A variant of the above (block_size_using_printezis_bits()) except |
| 5614 | // that we return 0 if the P-bits are not yet set. |
| 5615 | size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const { |
| 5616 | if (_markBitMap.isMarked(addr + 1)) { |
| 5617 | assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects"); |
| 5618 | HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); |
| 5619 | size_t size = pointer_delta(nextOneAddr + 1, addr); |
| 5620 | assert(size == CompactibleFreeListSpace::adjustObjectSize(size), |
| 5621 | "alignment problem"); |
| 5622 | assert(size >= 3, "Necessary for Printezis marks to work"); |
| 5623 | return size; |
| 5624 | } |
| 5625 | return 0; |
| 5626 | } |
| 5627 | |
| 5628 | HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const { |
| 5629 | size_t sz = 0; |
| 5630 | oop p = (oop)addr; |
| 5631 | if (p->klass_or_null_acquire() != NULL) { |
| 5632 | sz = CompactibleFreeListSpace::adjustObjectSize(p->size()); |
| 5633 | } else { |
| 5634 | sz = block_size_using_printezis_bits(addr); |
| 5635 | } |
| 5636 | assert(sz > 0, "size must be nonzero"); |
| 5637 | HeapWord* next_block = addr + sz; |
| 5638 | HeapWord* next_card = align_up(next_block, CardTable::card_size); |
| 5639 | assert(align_down((uintptr_t)addr, CardTable::card_size) < |
| 5640 | align_down((uintptr_t)next_card, CardTable::card_size), |
| 5641 | "must be different cards"); |
| 5642 | return next_card; |
| 5643 | } |
| 5644 | |
| 5645 | |
| 5646 | // CMS Bit Map Wrapper ///////////////////////////////////////// |
| 5647 | |
| 5648 | // Construct a CMS bit map infrastructure, but don't create the |
| 5649 | // bit vector itself. That is done by a separate call CMSBitMap::allocate() |
| 5650 | // further below. |
| 5651 | CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name): |
| 5652 | _shifter(shifter), |
| 5653 | _bm(), |
| 5654 | _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true, |
| 5655 | Monitor::_safepoint_check_never) : NULL) |
| 5656 | { |
| 5657 | _bmStartWord = 0; |
| 5658 | _bmWordSize = 0; |
| 5659 | } |
| 5660 | |
| 5661 | bool CMSBitMap::allocate(MemRegion mr) { |
| 5662 | _bmStartWord = mr.start(); |
| 5663 | _bmWordSize = mr.word_size(); |
| 5664 | ReservedSpace brs(ReservedSpace::allocation_align_size_up( |
| 5665 | (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1)); |
| 5666 | if (!brs.is_reserved()) { |
| 5667 | log_warning(gc)("CMS bit map allocation failure"); |
| 5668 | return false; |
| 5669 | } |
| 5670 | // For now we'll just commit all of the bit map up front. |
| 5671 | // Later on we'll try to be more parsimonious with swap. |
| 5672 | if (!_virtual_space.initialize(brs, brs.size())) { |
| 5673 | log_warning(gc)("CMS bit map backing store failure"); |
| 5674 | return false; |
| 5675 | } |
| 5676 | assert(_virtual_space.committed_size() == brs.size(), |
| 5677 | "didn't reserve backing store for all of CMS bit map?"); |
| 5678 | assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >= |
| 5679 | _bmWordSize, "inconsistency in bit map sizing"); |
| 5680 | _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter); |
| 5681 | |
| 5682 | // bm.clear(); // can we rely on getting zero'd memory? verify below |
| 5683 | assert(isAllClear(), |
| 5684 | "Expected zero'd memory from ReservedSpace constructor"); |
| 5685 | assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()), |
| 5686 | "consistency check"); |
| 5687 | return true; |
| 5688 | } |
| 5689 | |
| 5690 | void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) { |
| 5691 | HeapWord *next_addr, *end_addr, *last_addr; |
| 5692 | assert_locked(); |
| 5693 | assert(covers(mr), "out-of-range error"); |
| 5694 | // XXX assert that start and end are appropriately aligned |
| 5695 | for (next_addr = mr.start(), end_addr = mr.end(); |
| 5696 | next_addr < end_addr; next_addr = last_addr) { |
| 5697 | MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr); |
| 5698 | last_addr = dirty_region.end(); |
| 5699 | if (!dirty_region.is_empty()) { |
| 5700 | cl->do_MemRegion(dirty_region); |
| 5701 | } else { |
| 5702 | assert(last_addr == end_addr, "program logic"); |
| 5703 | return; |
| 5704 | } |
| 5705 | } |
| 5706 | } |
| 5707 | |
| 5708 | void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const { |
| 5709 | _bm.print_on_error(st, prefix); |
| 5710 | } |
| 5711 | |
| 5712 | #ifndef PRODUCT |
| 5713 | void CMSBitMap::assert_locked() const { |
| 5714 | CMSLockVerifier::assert_locked(lock()); |
| 5715 | } |
| 5716 | |
| 5717 | bool CMSBitMap::covers(MemRegion mr) const { |
| 5718 | // assert(_bm.map() == _virtual_space.low(), "map inconsistency"); |
| 5719 | assert((size_t)_bm.size() == (_bmWordSize >> _shifter), |
| 5720 | "size inconsistency"); |
| 5721 | return (mr.start() >= _bmStartWord) && |
| 5722 | (mr.end() <= endWord()); |
| 5723 | } |
| 5724 | |
| 5725 | bool CMSBitMap::covers(HeapWord* start, size_t size) const { |
| 5726 | return (start >= _bmStartWord && (start + size) <= endWord()); |
| 5727 | } |
| 5728 | |
| 5729 | void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) { |
| 5730 | // verify that there are no 1 bits in the interval [left, right) |
| 5731 | FalseBitMapClosure falseBitMapClosure; |
| 5732 | iterate(&falseBitMapClosure, left, right); |
| 5733 | } |
| 5734 | |
| 5735 | void CMSBitMap::region_invariant(MemRegion mr) |
| 5736 | { |
| 5737 | assert_locked(); |
| 5738 | // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize)); |
| 5739 | assert(!mr.is_empty(), "unexpected empty region"); |
| 5740 | assert(covers(mr), "mr should be covered by bit map"); |
| 5741 | // convert address range into offset range |
| 5742 | size_t start_ofs = heapWordToOffset(mr.start()); |
| 5743 | // Make sure that end() is appropriately aligned |
| 5744 | assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))), |
| 5745 | "Misaligned mr.end()"); |
| 5746 | size_t end_ofs = heapWordToOffset(mr.end()); |
| 5747 | assert(end_ofs > start_ofs, "Should mark at least one bit"); |
| 5748 | } |
| 5749 | |
| 5750 | #endif |
| 5751 | |
| 5752 | bool CMSMarkStack::allocate(size_t size) { |
| 5753 | // allocate a stack of the requisite depth |
| 5754 | ReservedSpace rs(ReservedSpace::allocation_align_size_up( |
| 5755 | size * sizeof(oop))); |
| 5756 | if (!rs.is_reserved()) { |
| 5757 | log_warning(gc)("CMSMarkStack allocation failure"); |
| 5758 | return false; |
| 5759 | } |
| 5760 | if (!_virtual_space.initialize(rs, rs.size())) { |
| 5761 | log_warning(gc)("CMSMarkStack backing store failure"); |
| 5762 | return false; |
| 5763 | } |
| 5764 | assert(_virtual_space.committed_size() == rs.size(), |
| 5765 | "didn't reserve backing store for all of CMS stack?"); |
| 5766 | _base = (oop*)(_virtual_space.low()); |
| 5767 | _index = 0; |
| 5768 | _capacity = size; |
| 5769 | NOT_PRODUCT(_max_depth = 0); |
| 5770 | return true; |
| 5771 | } |
| 5772 | |
| 5773 | // XXX FIX ME !!! In the MT case we come in here holding a |
| 5774 | // leaf lock. For printing we need to take a further lock |
| 5775 | // which has lower rank. We need to recalibrate the two |
| 5776 | // lock-ranks involved in order to be able to print the |
| 5777 | // messages below. (Or defer the printing to the caller. |
| 5778 | // For now we take the expedient path of just disabling the |
| 5779 | // messages for the problematic case.) |
| 5780 | void CMSMarkStack::expand() { |
| 5781 | assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted"); |
| 5782 | if (_capacity == MarkStackSizeMax) { |
| 5783 | if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) { |
| 5784 | // We print a warning message only once per CMS cycle. |
| 5785 | log_debug(gc)(" (benign) Hit CMSMarkStack max size limit"); |
| 5786 | } |
| 5787 | return; |
| 5788 | } |
| 5789 | // Double capacity if possible |
| 5790 | size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax); |
| 5791 | // Do not give up existing stack until we have managed to |
| 5792 | // get the double capacity that we desired. |
| 5793 | ReservedSpace rs(ReservedSpace::allocation_align_size_up( |
| 5794 | new_capacity * sizeof(oop))); |
| 5795 | if (rs.is_reserved()) { |
| 5796 | // Release the backing store associated with old stack |
| 5797 | _virtual_space.release(); |
| 5798 | // Reinitialize virtual space for new stack |
| 5799 | if (!_virtual_space.initialize(rs, rs.size())) { |
| 5800 | fatal("Not enough swap for expanded marking stack"); |
| 5801 | } |
| 5802 | _base = (oop*)(_virtual_space.low()); |
| 5803 | _index = 0; |
| 5804 | _capacity = new_capacity; |
| 5805 | } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) { |
| 5806 | // Failed to double capacity, continue; |
| 5807 | // we print a detail message only once per CMS cycle. |
| 5808 | log_debug(gc)(" (benign) Failed to expand marking stack from "SIZE_FORMAT "K to "SIZE_FORMAT "K", |
| 5809 | _capacity / K, new_capacity / K); |
| 5810 | } |
| 5811 | } |
| 5812 | |
| 5813 | |
| 5814 | // Closures |
| 5815 | // XXX: there seems to be a lot of code duplication here; |
| 5816 | // should refactor and consolidate common code. |
| 5817 | |
| 5818 | // This closure is used to mark refs into the CMS generation in |
| 5819 | // the CMS bit map. Called at the first checkpoint. This closure |
| 5820 | // assumes that we do not need to re-mark dirty cards; if the CMS |
| 5821 | // generation on which this is used is not an oldest |
| 5822 | // generation then this will lose younger_gen cards! |
| 5823 | |
| 5824 | MarkRefsIntoClosure::MarkRefsIntoClosure( |
| 5825 | MemRegion span, CMSBitMap* bitMap): |
| 5826 | _span(span), |
| 5827 | _bitMap(bitMap) |
| 5828 | { |
| 5829 | assert(ref_discoverer() == NULL, "deliberately left NULL"); |
| 5830 | assert(_bitMap->covers(_span), "_bitMap/_span mismatch"); |
| 5831 | } |
| 5832 | |
| 5833 | void MarkRefsIntoClosure::do_oop(oop obj) { |
| 5834 | // if p points into _span, then mark corresponding bit in _markBitMap |
| 5835 | assert(oopDesc::is_oop(obj), "expected an oop"); |
| 5836 | HeapWord* addr = (HeapWord*)obj; |
| 5837 | if (_span.contains(addr)) { |
| 5838 | // this should be made more efficient |
| 5839 | _bitMap->mark(addr); |
| 5840 | } |
| 5841 | } |
| 5842 | |
| 5843 | ParMarkRefsIntoClosure::ParMarkRefsIntoClosure( |
| 5844 | MemRegion span, CMSBitMap* bitMap): |
| 5845 | _span(span), |
| 5846 | _bitMap(bitMap) |
| 5847 | { |
| 5848 | assert(ref_discoverer() == NULL, "deliberately left NULL"); |
| 5849 | assert(_bitMap->covers(_span), "_bitMap/_span mismatch"); |
| 5850 | } |
| 5851 | |
| 5852 | void ParMarkRefsIntoClosure::do_oop(oop obj) { |
| 5853 | // if p points into _span, then mark corresponding bit in _markBitMap |
| 5854 | assert(oopDesc::is_oop(obj), "expected an oop"); |
| 5855 | HeapWord* addr = (HeapWord*)obj; |
| 5856 | if (_span.contains(addr)) { |
| 5857 | // this should be made more efficient |
| 5858 | _bitMap->par_mark(addr); |
| 5859 | } |
| 5860 | } |
| 5861 | |
| 5862 | // A variant of the above, used for CMS marking verification. |
| 5863 | MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure( |
| 5864 | MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm): |
| 5865 | _span(span), |
| 5866 | _verification_bm(verification_bm), |
| 5867 | _cms_bm(cms_bm) |
| 5868 | { |
| 5869 | assert(ref_discoverer() == NULL, "deliberately left NULL"); |
| 5870 | assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch"); |
| 5871 | } |
| 5872 | |
| 5873 | void MarkRefsIntoVerifyClosure::do_oop(oop obj) { |
| 5874 | // if p points into _span, then mark corresponding bit in _markBitMap |
| 5875 | assert(oopDesc::is_oop(obj), "expected an oop"); |
| 5876 | HeapWord* addr = (HeapWord*)obj; |
| 5877 | if (_span.contains(addr)) { |
| 5878 | _verification_bm->mark(addr); |
| 5879 | if (!_cms_bm->isMarked(addr)) { |
| 5880 | Log(gc, verify) log; |
| 5881 | ResourceMark rm; |
| 5882 | LogStream ls(log.error()); |
| 5883 | oop(addr)->print_on(&ls); |
| 5884 | log.error(" ("INTPTR_FORMAT " should have been marked)", p2i(addr)); |
| 5885 | fatal("... aborting"); |
| 5886 | } |
| 5887 | } |
| 5888 | } |
| 5889 | |
| 5890 | ////////////////////////////////////////////////// |
| 5891 | // MarkRefsIntoAndScanClosure |
| 5892 | ////////////////////////////////////////////////// |
| 5893 | |
| 5894 | MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span, |
| 5895 | ReferenceDiscoverer* rd, |
| 5896 | CMSBitMap* bit_map, |
| 5897 | CMSBitMap* mod_union_table, |
| 5898 | CMSMarkStack* mark_stack, |
| 5899 | CMSCollector* collector, |
| 5900 | bool should_yield, |
| 5901 | bool concurrent_precleaning): |
| 5902 | _span(span), |
| 5903 | _bit_map(bit_map), |
| 5904 | _mark_stack(mark_stack), |
| 5905 | _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table, |
| 5906 | mark_stack, concurrent_precleaning), |
| 5907 | _collector(collector), |
| 5908 | _freelistLock(NULL), |
| 5909 | _yield(should_yield), |
| 5910 | _concurrent_precleaning(concurrent_precleaning) |
| 5911 | { |
| 5912 | // FIXME: Should initialize in base class constructor. |
| 5913 | assert(rd != NULL, "ref_discoverer shouldn't be NULL"); |
| 5914 | set_ref_discoverer_internal(rd); |
| 5915 | } |
| 5916 | |
| 5917 | // This closure is used to mark refs into the CMS generation at the |
| 5918 | // second (final) checkpoint, and to scan and transitively follow |
| 5919 | // the unmarked oops. It is also used during the concurrent precleaning |
| 5920 | // phase while scanning objects on dirty cards in the CMS generation. |
| 5921 | // The marks are made in the marking bit map and the marking stack is |
| 5922 | // used for keeping the (newly) grey objects during the scan. |
| 5923 | // The parallel version (Par_...) appears further below. |
| 5924 | void MarkRefsIntoAndScanClosure::do_oop(oop obj) { |
| 5925 | if (obj != NULL) { |
| 5926 | assert(oopDesc::is_oop(obj), "expected an oop"); |
| 5927 | HeapWord* addr = (HeapWord*)obj; |
| 5928 | assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); |
| 5929 | assert(_collector->overflow_list_is_empty(), |
| 5930 | "overflow list should be empty"); |
| 5931 | if (_span.contains(addr) && |
| 5932 | !_bit_map->isMarked(addr)) { |
| 5933 | // mark bit map (object is now grey) |
| 5934 | _bit_map->mark(addr); |
| 5935 | // push on marking stack (stack should be empty), and drain the |
| 5936 | // stack by applying this closure to the oops in the oops popped |
| 5937 | // from the stack (i.e. blacken the grey objects) |
| 5938 | bool res = _mark_stack->push(obj); |
| 5939 | assert(res, "Should have space to push on empty stack"); |
| 5940 | do { |
| 5941 | oop new_oop = _mark_stack->pop(); |
| 5942 | assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop"); |
| 5943 | assert(_bit_map->isMarked((HeapWord*)new_oop), |
| 5944 | "only grey objects on this stack"); |
| 5945 | // iterate over the oops in this oop, marking and pushing |
| 5946 | // the ones in CMS heap (i.e. in _span). |
| 5947 | new_oop->oop_iterate(&_pushAndMarkClosure); |
| 5948 | // check if it's time to yield |
| 5949 | do_yield_check(); |
| 5950 | } while (!_mark_stack->isEmpty() || |
| 5951 | (!_concurrent_precleaning && take_from_overflow_list())); |
| 5952 | // if marking stack is empty, and we are not doing this |
| 5953 | // during precleaning, then check the overflow list |
| 5954 | } |
| 5955 | assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); |
| 5956 | assert(_collector->overflow_list_is_empty(), |
| 5957 | "overflow list was drained above"); |
| 5958 | |
| 5959 | assert(_collector->no_preserved_marks(), |
| 5960 | "All preserved marks should have been restored above"); |
| 5961 | } |
| 5962 | } |
| 5963 | |
| 5964 | void MarkRefsIntoAndScanClosure::do_yield_work() { |
| 5965 | assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| 5966 | "CMS thread should hold CMS token"); |
| 5967 | assert_lock_strong(_freelistLock); |
| 5968 | assert_lock_strong(_bit_map->lock()); |
| 5969 | // relinquish the free_list_lock and bitMaplock() |
| 5970 | _bit_map->lock()->unlock(); |
| 5971 | _freelistLock->unlock(); |
| 5972 | ConcurrentMarkSweepThread::desynchronize(true); |
| 5973 | _collector->stopTimer(); |
| 5974 | _collector->incrementYields(); |
| 5975 | |
| 5976 | // See the comment in coordinator_yield() |
| 5977 | for (unsigned i = 0; |
| 5978 | i < CMSYieldSleepCount && |
| 5979 | ConcurrentMarkSweepThread::should_yield() && |
| 5980 | !CMSCollector::foregroundGCIsActive(); |
| 5981 | ++i) { |
| 5982 | os::sleep(Thread::current(), 1, false); |
| 5983 | } |
| 5984 | |
| 5985 | ConcurrentMarkSweepThread::synchronize(true); |
| 5986 | _freelistLock->lock_without_safepoint_check(); |
| 5987 | _bit_map->lock()->lock_without_safepoint_check(); |
| 5988 | _collector->startTimer(); |
| 5989 | } |
| 5990 | |
| 5991 | /////////////////////////////////////////////////////////// |
| 5992 | // ParMarkRefsIntoAndScanClosure: a parallel version of |
| 5993 | // MarkRefsIntoAndScanClosure |
| 5994 | /////////////////////////////////////////////////////////// |
| 5995 | ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure( |
| 5996 | CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd, |
| 5997 | CMSBitMap* bit_map, OopTaskQueue* work_queue): |
| 5998 | _span(span), |
| 5999 | _bit_map(bit_map), |
| 6000 | _work_queue(work_queue), |
| 6001 | _low_water_mark(MIN2((work_queue->max_elems()/4), |
| 6002 | ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))), |
| 6003 | _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue) |
| 6004 | { |
| 6005 | // FIXME: Should initialize in base class constructor. |
| 6006 | assert(rd != NULL, "ref_discoverer shouldn't be NULL"); |
| 6007 | set_ref_discoverer_internal(rd); |
| 6008 | } |
| 6009 | |
| 6010 | // This closure is used to mark refs into the CMS generation at the |
| 6011 | // second (final) checkpoint, and to scan and transitively follow |
| 6012 | // the unmarked oops. The marks are made in the marking bit map and |
| 6013 | // the work_queue is used for keeping the (newly) grey objects during |
| 6014 | // the scan phase whence they are also available for stealing by parallel |
| 6015 | // threads. Since the marking bit map is shared, updates are |
| 6016 | // synchronized (via CAS). |
| 6017 | void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) { |
| 6018 | if (obj != NULL) { |
| 6019 | // Ignore mark word because this could be an already marked oop |
| 6020 | // that may be chained at the end of the overflow list. |
| 6021 | assert(oopDesc::is_oop(obj, true), "expected an oop"); |
| 6022 | HeapWord* addr = (HeapWord*)obj; |
| 6023 | if (_span.contains(addr) && |
| 6024 | !_bit_map->isMarked(addr)) { |
| 6025 | // mark bit map (object will become grey): |
| 6026 | // It is possible for several threads to be |
| 6027 | // trying to "claim" this object concurrently; |
| 6028 | // the unique thread that succeeds in marking the |
| 6029 | // object first will do the subsequent push on |
| 6030 | // to the work queue (or overflow list). |
| 6031 | if (_bit_map->par_mark(addr)) { |
| 6032 | // push on work_queue (which may not be empty), and trim the |
| 6033 | // queue to an appropriate length by applying this closure to |
| 6034 | // the oops in the oops popped from the stack (i.e. blacken the |
| 6035 | // grey objects) |
| 6036 | bool res = _work_queue->push(obj); |
| 6037 | assert(res, "Low water mark should be less than capacity?"); |
| 6038 | trim_queue(_low_water_mark); |
| 6039 | } // Else, another thread claimed the object |
| 6040 | } |
| 6041 | } |
| 6042 | } |
| 6043 | |
| 6044 | // This closure is used to rescan the marked objects on the dirty cards |
| 6045 | // in the mod union table and the card table proper. |
| 6046 | size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m( |
| 6047 | oop p, MemRegion mr) { |
| 6048 | |
| 6049 | size_t size = 0; |
| 6050 | HeapWord* addr = (HeapWord*)p; |
| 6051 | DEBUG_ONLY(_collector->verify_work_stacks_empty();) |
| 6052 | assert(_span.contains(addr), "we are scanning the CMS generation"); |
| 6053 | // check if it's time to yield |
| 6054 | if (do_yield_check()) { |
| 6055 | // We yielded for some foreground stop-world work, |
| 6056 | // and we have been asked to abort this ongoing preclean cycle. |
| 6057 | return 0; |
| 6058 | } |
| 6059 | if (_bitMap->isMarked(addr)) { |
| 6060 | // it's marked; is it potentially uninitialized? |
| 6061 | if (p->klass_or_null_acquire() != NULL) { |
| 6062 | // an initialized object; ignore mark word in verification below |
| 6063 | // since we are running concurrent with mutators |
| 6064 | assert(oopDesc::is_oop(p, true), "should be an oop"); |
| 6065 | if (p->is_objArray()) { |
| 6066 | // objArrays are precisely marked; restrict scanning |
| 6067 | // to dirty cards only. |
| 6068 | size = CompactibleFreeListSpace::adjustObjectSize( |
| 6069 | p->oop_iterate_size(_scanningClosure, mr)); |
| 6070 | } else { |
| 6071 | // A non-array may have been imprecisely marked; we need |
| 6072 | // to scan object in its entirety. |
| 6073 | size = CompactibleFreeListSpace::adjustObjectSize( |
| 6074 | p->oop_iterate_size(_scanningClosure)); |
| 6075 | } |
| 6076 | #ifdef ASSERT |
| 6077 | size_t direct_size = |
| 6078 | CompactibleFreeListSpace::adjustObjectSize(p->size()); |
| 6079 | assert(size == direct_size, "Inconsistency in size"); |
| 6080 | assert(size >= 3, "Necessary for Printezis marks to work"); |
| 6081 | HeapWord* start_pbit = addr + 1; |
| 6082 | HeapWord* end_pbit = addr + size - 1; |
| 6083 | assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit), |
| 6084 | "inconsistent Printezis mark"); |
| 6085 | // Verify inner mark bits (between Printezis bits) are clear, |
| 6086 | // but don't repeat if there are multiple dirty regions for |
| 6087 | // the same object, to avoid potential O(N^2) performance. |
| 6088 | if (addr != _last_scanned_object) { |
| 6089 | _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit); |
| 6090 | _last_scanned_object = addr; |
| 6091 | } |
| 6092 | #endif // ASSERT |
| 6093 | } else { |
| 6094 | // An uninitialized object. |
| 6095 | assert(_bitMap->isMarked(addr+1), "missing Printezis mark?"); |
| 6096 | HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); |
| 6097 | size = pointer_delta(nextOneAddr + 1, addr); |
| 6098 | assert(size == CompactibleFreeListSpace::adjustObjectSize(size), |
| 6099 | "alignment problem"); |
| 6100 | // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass() |
| 6101 | // will dirty the card when the klass pointer is installed in the |
| 6102 | // object (signaling the completion of initialization). |
| 6103 | } |
| 6104 | } else { |
| 6105 | // Either a not yet marked object or an uninitialized object |
| 6106 | if (p->klass_or_null_acquire() == NULL) { |
| 6107 | // An uninitialized object, skip to the next card, since |
| 6108 | // we may not be able to read its P-bits yet. |
| 6109 | assert(size == 0, "Initial value"); |
| 6110 | } else { |
| 6111 | // An object not (yet) reached by marking: we merely need to |
| 6112 | // compute its size so as to go look at the next block. |
| 6113 | assert(oopDesc::is_oop(p, true), "should be an oop"); |
| 6114 | size = CompactibleFreeListSpace::adjustObjectSize(p->size()); |
| 6115 | } |
| 6116 | } |
| 6117 | DEBUG_ONLY(_collector->verify_work_stacks_empty();) |
| 6118 | return size; |
| 6119 | } |
| 6120 | |
| 6121 | void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() { |
| 6122 | assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| 6123 | "CMS thread should hold CMS token"); |
| 6124 | assert_lock_strong(_freelistLock); |
| 6125 | assert_lock_strong(_bitMap->lock()); |
| 6126 | // relinquish the free_list_lock and bitMaplock() |
| 6127 | _bitMap->lock()->unlock(); |
| 6128 | _freelistLock->unlock(); |
| 6129 | ConcurrentMarkSweepThread::desynchronize(true); |
| 6130 | _collector->stopTimer(); |
| 6131 | _collector->incrementYields(); |
| 6132 | |
| 6133 | // See the comment in coordinator_yield() |
| 6134 | for (unsigned i = 0; i < CMSYieldSleepCount && |
| 6135 | ConcurrentMarkSweepThread::should_yield() && |
| 6136 | !CMSCollector::foregroundGCIsActive(); ++i) { |
| 6137 | os::sleep(Thread::current(), 1, false); |
| 6138 | } |
| 6139 | |
| 6140 | ConcurrentMarkSweepThread::synchronize(true); |
| 6141 | _freelistLock->lock_without_safepoint_check(); |
| 6142 | _bitMap->lock()->lock_without_safepoint_check(); |
| 6143 | _collector->startTimer(); |
| 6144 | } |
| 6145 | |
| 6146 | |
| 6147 | ////////////////////////////////////////////////////////////////// |
| 6148 | // SurvivorSpacePrecleanClosure |
| 6149 | ////////////////////////////////////////////////////////////////// |
| 6150 | // This (single-threaded) closure is used to preclean the oops in |
| 6151 | // the survivor spaces. |
| 6152 | size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) { |
| 6153 | |
| 6154 | HeapWord* addr = (HeapWord*)p; |
| 6155 | DEBUG_ONLY(_collector->verify_work_stacks_empty();) |
| 6156 | assert(!_span.contains(addr), "we are scanning the survivor spaces"); |
| 6157 | assert(p->klass_or_null() != NULL, "object should be initialized"); |
| 6158 | // an initialized object; ignore mark word in verification below |
| 6159 | // since we are running concurrent with mutators |
| 6160 | assert(oopDesc::is_oop(p, true), "should be an oop"); |
| 6161 | // Note that we do not yield while we iterate over |
| 6162 | // the interior oops of p, pushing the relevant ones |
| 6163 | // on our marking stack. |
| 6164 | size_t size = p->oop_iterate_size(_scanning_closure); |
| 6165 | do_yield_check(); |
| 6166 | // Observe that below, we do not abandon the preclean |
| 6167 | // phase as soon as we should; rather we empty the |
| 6168 | // marking stack before returning. This is to satisfy |
| 6169 | // some existing assertions. In general, it may be a |
| 6170 | // good idea to abort immediately and complete the marking |
| 6171 | // from the grey objects at a later time. |
| 6172 | while (!_mark_stack->isEmpty()) { |
| 6173 | oop new_oop = _mark_stack->pop(); |
| 6174 | assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop"); |
| 6175 | assert(_bit_map->isMarked((HeapWord*)new_oop), |
| 6176 | "only grey objects on this stack"); |
| 6177 | // iterate over the oops in this oop, marking and pushing |
| 6178 | // the ones in CMS heap (i.e. in _span). |
| 6179 | new_oop->oop_iterate(_scanning_closure); |
| 6180 | // check if it's time to yield |
| 6181 | do_yield_check(); |
| 6182 | } |
| 6183 | unsigned int after_count = |
| 6184 | CMSHeap::heap()->total_collections(); |
| 6185 | bool abort = (_before_count != after_count) || |
| 6186 | _collector->should_abort_preclean(); |
| 6187 | return abort ? 0 : size; |
| 6188 | } |
| 6189 | |
| 6190 | void SurvivorSpacePrecleanClosure::do_yield_work() { |
| 6191 | assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| 6192 | "CMS thread should hold CMS token"); |
| 6193 | assert_lock_strong(_bit_map->lock()); |
| 6194 | // Relinquish the bit map lock |
| 6195 | _bit_map->lock()->unlock(); |
| 6196 | ConcurrentMarkSweepThread::desynchronize(true); |
| 6197 | _collector->stopTimer(); |
| 6198 | _collector->incrementYields(); |
| 6199 | |
| 6200 | // See the comment in coordinator_yield() |
| 6201 | for (unsigned i = 0; i < CMSYieldSleepCount && |
| 6202 | ConcurrentMarkSweepThread::should_yield() && |
| 6203 | !CMSCollector::foregroundGCIsActive(); ++i) { |
| 6204 | os::sleep(Thread::current(), 1, false); |
| 6205 | } |
| 6206 | |
| 6207 | ConcurrentMarkSweepThread::synchronize(true); |
| 6208 | _bit_map->lock()->lock_without_safepoint_check(); |
| 6209 | _collector->startTimer(); |
| 6210 | } |
| 6211 | |
| 6212 | // This closure is used to rescan the marked objects on the dirty cards |
| 6213 | // in the mod union table and the card table proper. In the parallel |
| 6214 | // case, although the bitMap is shared, we do a single read so the |
| 6215 | // isMarked() query is "safe". |
| 6216 | bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) { |
| 6217 | // Ignore mark word because we are running concurrent with mutators |
| 6218 | assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at "PTR_FORMAT, p2i(p)); |
| 6219 | HeapWord* addr = (HeapWord*)p; |
| 6220 | assert(_span.contains(addr), "we are scanning the CMS generation"); |
| 6221 | bool is_obj_array = false; |
| 6222 | #ifdef ASSERT |
| 6223 | if (!_parallel) { |
| 6224 | assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); |
| 6225 | assert(_collector->overflow_list_is_empty(), |
| 6226 | "overflow list should be empty"); |
| 6227 | |
| 6228 | } |
| 6229 | #endif // ASSERT |
| 6230 | if (_bit_map->isMarked(addr)) { |
| 6231 | // Obj arrays are precisely marked, non-arrays are not; |
| 6232 | // so we scan objArrays precisely and non-arrays in their |
| 6233 | // entirety. |
| 6234 | if (p->is_objArray()) { |
| 6235 | is_obj_array = true; |
| 6236 | if (_parallel) { |
| 6237 | p->oop_iterate(_par_scan_closure, mr); |
| 6238 | } else { |
| 6239 | p->oop_iterate(_scan_closure, mr); |
| 6240 | } |
| 6241 | } else { |
| 6242 | if (_parallel) { |
| 6243 | p->oop_iterate(_par_scan_closure); |
| 6244 | } else { |
| 6245 | p->oop_iterate(_scan_closure); |
| 6246 | } |
| 6247 | } |
| 6248 | } |
| 6249 | #ifdef ASSERT |
| 6250 | if (!_parallel) { |
| 6251 | assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); |
| 6252 | assert(_collector->overflow_list_is_empty(), |
| 6253 | "overflow list should be empty"); |
| 6254 | |
| 6255 | } |
| 6256 | #endif // ASSERT |
| 6257 | return is_obj_array; |
| 6258 | } |
| 6259 | |
| 6260 | MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector, |
| 6261 | MemRegion span, |
| 6262 | CMSBitMap* bitMap, CMSMarkStack* markStack, |
| 6263 | bool should_yield, bool verifying): |
| 6264 | _collector(collector), |
| 6265 | _span(span), |
| 6266 | _bitMap(bitMap), |
| 6267 | _mut(&collector->_modUnionTable), |
| 6268 | _markStack(markStack), |
| 6269 | _yield(should_yield), |
| 6270 | _skipBits(0) |
| 6271 | { |
| 6272 | assert(_markStack->isEmpty(), "stack should be empty"); |
| 6273 | _finger = _bitMap->startWord(); |
| 6274 | _threshold = _finger; |
| 6275 | assert(_collector->_restart_addr == NULL, "Sanity check"); |
| 6276 | assert(_span.contains(_finger), "Out of bounds _finger?"); |
| 6277 | DEBUG_ONLY(_verifying = verifying;) |
| 6278 | } |
| 6279 | |
| 6280 | void MarkFromRootsClosure::reset(HeapWord* addr) { |
| 6281 | assert(_markStack->isEmpty(), "would cause duplicates on stack"); |
| 6282 | assert(_span.contains(addr), "Out of bounds _finger?"); |
| 6283 | _finger = addr; |
| 6284 | _threshold = align_up(_finger, CardTable::card_size); |
| 6285 | } |
| 6286 | |
| 6287 | // Should revisit to see if this should be restructured for |
| 6288 | // greater efficiency. |
| 6289 | bool MarkFromRootsClosure::do_bit(size_t offset) { |
| 6290 | if (_skipBits > 0) { |
| 6291 | _skipBits--; |
| 6292 | return true; |
| 6293 | } |
| 6294 | // convert offset into a HeapWord* |
| 6295 | HeapWord* addr = _bitMap->startWord() + offset; |
| 6296 | assert(_bitMap->endWord() && addr < _bitMap->endWord(), |
| 6297 | "address out of range"); |
| 6298 | assert(_bitMap->isMarked(addr), "tautology"); |
| 6299 | if (_bitMap->isMarked(addr+1)) { |
| 6300 | // this is an allocated but not yet initialized object |
| 6301 | assert(_skipBits == 0, "tautology"); |
| 6302 | _skipBits = 2; // skip next two marked bits ("Printezis-marks") |
| 6303 | oop p = oop(addr); |
| 6304 | if (p->klass_or_null_acquire() == NULL) { |
| 6305 | DEBUG_ONLY(if (!_verifying) {) |
| 6306 | // We re-dirty the cards on which this object lies and increase |
| 6307 | // the _threshold so that we'll come back to scan this object |
| 6308 | // during the preclean or remark phase. (CMSCleanOnEnter) |
| 6309 | if (CMSCleanOnEnter) { |
| 6310 | size_t sz = _collector->block_size_using_printezis_bits(addr); |
| 6311 | HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size); |
| 6312 | MemRegion redirty_range = MemRegion(addr, end_card_addr); |
| 6313 | assert(!redirty_range.is_empty(), "Arithmetical tautology"); |
| 6314 | // Bump _threshold to end_card_addr; note that |
| 6315 | // _threshold cannot possibly exceed end_card_addr, anyhow. |
| 6316 | // This prevents future clearing of the card as the scan proceeds |
| 6317 | // to the right. |
| 6318 | assert(_threshold <= end_card_addr, |
| 6319 | "Because we are just scanning into this object"); |
| 6320 | if (_threshold < end_card_addr) { |
| 6321 | _threshold = end_card_addr; |
| 6322 | } |
| 6323 | if (p->klass_or_null_acquire() != NULL) { |
| 6324 | // Redirty the range of cards... |
| 6325 | _mut->mark_range(redirty_range); |
| 6326 | } // ...else the setting of klass will dirty the card anyway. |
| 6327 | } |
| 6328 | DEBUG_ONLY(}) |
| 6329 | return true; |
| 6330 | } |
| 6331 | } |
| 6332 | scanOopsInOop(addr); |
| 6333 | return true; |
| 6334 | } |
| 6335 | |
| 6336 | // We take a break if we've been at this for a while, |
| 6337 | // so as to avoid monopolizing the locks involved. |
| 6338 | void MarkFromRootsClosure::do_yield_work() { |
| 6339 | // First give up the locks, then yield, then re-lock |
| 6340 | // We should probably use a constructor/destructor idiom to |
| 6341 | // do this unlock/lock or modify the MutexUnlocker class to |
| 6342 | // serve our purpose. XXX |
| 6343 | assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| 6344 | "CMS thread should hold CMS token"); |
| 6345 | assert_lock_strong(_bitMap->lock()); |
| 6346 | _bitMap->lock()->unlock(); |
| 6347 | ConcurrentMarkSweepThread::desynchronize(true); |
| 6348 | _collector->stopTimer(); |
| 6349 | _collector->incrementYields(); |
| 6350 | |
| 6351 | // See the comment in coordinator_yield() |
| 6352 | for (unsigned i = 0; i < CMSYieldSleepCount && |
| 6353 | ConcurrentMarkSweepThread::should_yield() && |
| 6354 | !CMSCollector::foregroundGCIsActive(); ++i) { |
| 6355 | os::sleep(Thread::current(), 1, false); |
| 6356 | } |
| 6357 | |
| 6358 | ConcurrentMarkSweepThread::synchronize(true); |
| 6359 | _bitMap->lock()->lock_without_safepoint_check(); |
| 6360 | _collector->startTimer(); |
| 6361 | } |
| 6362 | |
| 6363 | void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) { |
| 6364 | assert(_bitMap->isMarked(ptr), "expected bit to be set"); |
| 6365 | assert(_markStack->isEmpty(), |
| 6366 | "should drain stack to limit stack usage"); |
| 6367 | // convert ptr to an oop preparatory to scanning |
| 6368 | oop obj = oop(ptr); |
| 6369 | // Ignore mark word in verification below, since we |
| 6370 | // may be running concurrent with mutators. |
| 6371 | assert(oopDesc::is_oop(obj, true), "should be an oop"); |
| 6372 | assert(_finger <= ptr, "_finger runneth ahead"); |
| 6373 | // advance the finger to right end of this object |
| 6374 | _finger = ptr + obj->size(); |
| 6375 | assert(_finger > ptr, "we just incremented it above"); |
| 6376 | // On large heaps, it may take us some time to get through |
| 6377 | // the marking phase. During |
| 6378 | // this time it's possible that a lot of mutations have |
| 6379 | // accumulated in the card table and the mod union table -- |
| 6380 | // these mutation records are redundant until we have |
| 6381 | // actually traced into the corresponding card. |
| 6382 | // Here, we check whether advancing the finger would make |
| 6383 | // us cross into a new card, and if so clear corresponding |
| 6384 | // cards in the MUT (preclean them in the card-table in the |
| 6385 | // future). |
| 6386 | |
| 6387 | DEBUG_ONLY(if (!_verifying) {) |
| 6388 | // The clean-on-enter optimization is disabled by default, |
| 6389 | // until we fix 6178663. |
| 6390 | if (CMSCleanOnEnter && (_finger > _threshold)) { |
| 6391 | // [_threshold, _finger) represents the interval |
| 6392 | // of cards to be cleared in MUT (or precleaned in card table). |
| 6393 | // The set of cards to be cleared is all those that overlap |
| 6394 | // with the interval [_threshold, _finger); note that |
| 6395 | // _threshold is always kept card-aligned but _finger isn't |
| 6396 | // always card-aligned. |
| 6397 | HeapWord* old_threshold = _threshold; |
| 6398 | assert(is_aligned(old_threshold, CardTable::card_size), |
| 6399 | "_threshold should always be card-aligned"); |
| 6400 | _threshold = align_up(_finger, CardTable::card_size); |
| 6401 | MemRegion mr(old_threshold, _threshold); |
| 6402 | assert(!mr.is_empty(), "Control point invariant"); |
| 6403 | assert(_span.contains(mr), "Should clear within span"); |
| 6404 | _mut->clear_range(mr); |
| 6405 | } |
| 6406 | DEBUG_ONLY(}) |
| 6407 | // Note: the finger doesn't advance while we drain |
| 6408 | // the stack below. |
| 6409 | PushOrMarkClosure pushOrMarkClosure(_collector, |
| 6410 | _span, _bitMap, _markStack, |
| 6411 | _finger, this); |
| 6412 | bool res = _markStack->push(obj); |
| 6413 | assert(res, "Empty non-zero size stack should have space for single push"); |
| 6414 | while (!_markStack->isEmpty()) { |
| 6415 | oop new_oop = _markStack->pop(); |
| 6416 | // Skip verifying header mark word below because we are |
| 6417 | // running concurrent with mutators. |
| 6418 | assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop"); |
| 6419 | // now scan this oop's oops |
| 6420 | new_oop->oop_iterate(&pushOrMarkClosure); |
| 6421 | do_yield_check(); |
| 6422 | } |
| 6423 | assert(_markStack->isEmpty(), "tautology, emphasizing post-condition"); |
| 6424 | } |
| 6425 | |
| 6426 | ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task, |
| 6427 | CMSCollector* collector, MemRegion span, |
| 6428 | CMSBitMap* bit_map, |
| 6429 | OopTaskQueue* work_queue, |
| 6430 | CMSMarkStack* overflow_stack): |
| 6431 | _collector(collector), |
| 6432 | _whole_span(collector->_span), |
| 6433 | _span(span), |
| 6434 | _bit_map(bit_map), |
| 6435 | _mut(&collector->_modUnionTable), |
| 6436 | _work_queue(work_queue), |
| 6437 | _overflow_stack(overflow_stack), |
| 6438 | _skip_bits(0), |
| 6439 | _task(task) |
| 6440 | { |
| 6441 | assert(_work_queue->size() == 0, "work_queue should be empty"); |
| 6442 | _finger = span.start(); |
| 6443 | _threshold = _finger; // XXX Defer clear-on-enter optimization for now |
| 6444 | assert(_span.contains(_finger), "Out of bounds _finger?"); |
| 6445 | } |
| 6446 | |
| 6447 | // Should revisit to see if this should be restructured for |
| 6448 | // greater efficiency. |
| 6449 | bool ParMarkFromRootsClosure::do_bit(size_t offset) { |
| 6450 | if (_skip_bits > 0) { |
| 6451 | _skip_bits--; |
| 6452 | return true; |
| 6453 | } |
| 6454 | // convert offset into a HeapWord* |
| 6455 | HeapWord* addr = _bit_map->startWord() + offset; |
| 6456 | assert(_bit_map->endWord() && addr < _bit_map->endWord(), |
| 6457 | "address out of range"); |
| 6458 | assert(_bit_map->isMarked(addr), "tautology"); |
| 6459 | if (_bit_map->isMarked(addr+1)) { |
| 6460 | // this is an allocated object that might not yet be initialized |
| 6461 | assert(_skip_bits == 0, "tautology"); |
| 6462 | _skip_bits = 2; // skip next two marked bits ("Printezis-marks") |
| 6463 | oop p = oop(addr); |
| 6464 | if (p->klass_or_null_acquire() == NULL) { |
| 6465 | // in the case of Clean-on-Enter optimization, redirty card |
| 6466 | // and avoid clearing card by increasing the threshold. |
| 6467 | return true; |
| 6468 | } |
| 6469 | } |
| 6470 | scan_oops_in_oop(addr); |
| 6471 | return true; |
| 6472 | } |
| 6473 | |
| 6474 | void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) { |
| 6475 | assert(_bit_map->isMarked(ptr), "expected bit to be set"); |
| 6476 | // Should we assert that our work queue is empty or |
| 6477 | // below some drain limit? |
| 6478 | assert(_work_queue->size() == 0, |
| 6479 | "should drain stack to limit stack usage"); |
| 6480 | // convert ptr to an oop preparatory to scanning |
| 6481 | oop obj = oop(ptr); |
| 6482 | // Ignore mark word in verification below, since we |
| 6483 | // may be running concurrent with mutators. |
| 6484 | assert(oopDesc::is_oop(obj, true), "should be an oop"); |
| 6485 | assert(_finger <= ptr, "_finger runneth ahead"); |
| 6486 | // advance the finger to right end of this object |
| 6487 | _finger = ptr + obj->size(); |
| 6488 | assert(_finger > ptr, "we just incremented it above"); |
| 6489 | // On large heaps, it may take us some time to get through |
| 6490 | // the marking phase. During |
| 6491 | // this time it's possible that a lot of mutations have |
| 6492 | // accumulated in the card table and the mod union table -- |
| 6493 | // these mutation records are redundant until we have |
| 6494 | // actually traced into the corresponding card. |
| 6495 | // Here, we check whether advancing the finger would make |
| 6496 | // us cross into a new card, and if so clear corresponding |
| 6497 | // cards in the MUT (preclean them in the card-table in the |
| 6498 | // future). |
| 6499 | |
| 6500 | // The clean-on-enter optimization is disabled by default, |
| 6501 | // until we fix 6178663. |
| 6502 | if (CMSCleanOnEnter && (_finger > _threshold)) { |
| 6503 | // [_threshold, _finger) represents the interval |
| 6504 | // of cards to be cleared in MUT (or precleaned in card table). |
| 6505 | // The set of cards to be cleared is all those that overlap |
| 6506 | // with the interval [_threshold, _finger); note that |
| 6507 | // _threshold is always kept card-aligned but _finger isn't |
| 6508 | // always card-aligned. |
| 6509 | HeapWord* old_threshold = _threshold; |
| 6510 | assert(is_aligned(old_threshold, CardTable::card_size), |
| 6511 | "_threshold should always be card-aligned"); |
| 6512 | _threshold = align_up(_finger, CardTable::card_size); |
| 6513 | MemRegion mr(old_threshold, _threshold); |
| 6514 | assert(!mr.is_empty(), "Control point invariant"); |
| 6515 | assert(_span.contains(mr), "Should clear within span"); // _whole_span ?? |
| 6516 | _mut->clear_range(mr); |
| 6517 | } |
| 6518 | |
| 6519 | // Note: the local finger doesn't advance while we drain |
| 6520 | // the stack below, but the global finger sure can and will. |
| 6521 | HeapWord* volatile* gfa = _task->global_finger_addr(); |
| 6522 | ParPushOrMarkClosure pushOrMarkClosure(_collector, |
| 6523 | _span, _bit_map, |
| 6524 | _work_queue, |
| 6525 | _overflow_stack, |
| 6526 | _finger, |
| 6527 | gfa, this); |
| 6528 | bool res = _work_queue->push(obj); // overflow could occur here |
| 6529 | assert(res, "Will hold once we use workqueues"); |
| 6530 | while (true) { |
| 6531 | oop new_oop; |
| 6532 | if (!_work_queue->pop_local(new_oop)) { |
| 6533 | // We emptied our work_queue; check if there's stuff that can |
| 6534 | // be gotten from the overflow stack. |
| 6535 | if (CMSConcMarkingTask::get_work_from_overflow_stack( |
| 6536 | _overflow_stack, _work_queue)) { |
| 6537 | do_yield_check(); |
| 6538 | continue; |
| 6539 | } else { // done |
| 6540 | break; |
| 6541 | } |
| 6542 | } |
| 6543 | // Skip verifying header mark word below because we are |
| 6544 | // running concurrent with mutators. |
| 6545 | assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop"); |
| 6546 | // now scan this oop's oops |
| 6547 | new_oop->oop_iterate(&pushOrMarkClosure); |
| 6548 | do_yield_check(); |
| 6549 | } |
| 6550 | assert(_work_queue->size() == 0, "tautology, emphasizing post-condition"); |
| 6551 | } |
| 6552 | |
| 6553 | // Yield in response to a request from VM Thread or |
| 6554 | // from mutators. |
| 6555 | void ParMarkFromRootsClosure::do_yield_work() { |
| 6556 | assert(_task != NULL, "sanity"); |
| 6557 | _task->yield(); |
| 6558 | } |
| 6559 | |
| 6560 | // A variant of the above used for verifying CMS marking work. |
| 6561 | MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector, |
| 6562 | MemRegion span, |
| 6563 | CMSBitMap* verification_bm, CMSBitMap* cms_bm, |
| 6564 | CMSMarkStack* mark_stack): |
| 6565 | _collector(collector), |
| 6566 | _span(span), |
| 6567 | _verification_bm(verification_bm), |
| 6568 | _cms_bm(cms_bm), |
| 6569 | _mark_stack(mark_stack), |
| 6570 | _pam_verify_closure(collector, span, verification_bm, cms_bm, |
| 6571 | mark_stack) |
| 6572 | { |
| 6573 | assert(_mark_stack->isEmpty(), "stack should be empty"); |
| 6574 | _finger = _verification_bm->startWord(); |
| 6575 | assert(_collector->_restart_addr == NULL, "Sanity check"); |
| 6576 | assert(_span.contains(_finger), "Out of bounds _finger?"); |
| 6577 | } |
| 6578 | |
| 6579 | void MarkFromRootsVerifyClosure::reset(HeapWord* addr) { |
| 6580 | assert(_mark_stack->isEmpty(), "would cause duplicates on stack"); |
| 6581 | assert(_span.contains(addr), "Out of bounds _finger?"); |
| 6582 | _finger = addr; |
| 6583 | } |
| 6584 | |
| 6585 | // Should revisit to see if this should be restructured for |
| 6586 | // greater efficiency. |
| 6587 | bool MarkFromRootsVerifyClosure::do_bit(size_t offset) { |
| 6588 | // convert offset into a HeapWord* |
| 6589 | HeapWord* addr = _verification_bm->startWord() + offset; |
| 6590 | assert(_verification_bm->endWord() && addr < _verification_bm->endWord(), |
| 6591 | "address out of range"); |
| 6592 | assert(_verification_bm->isMarked(addr), "tautology"); |
| 6593 | assert(_cms_bm->isMarked(addr), "tautology"); |
| 6594 | |
| 6595 | assert(_mark_stack->isEmpty(), |
| 6596 | "should drain stack to limit stack usage"); |
| 6597 | // convert addr to an oop preparatory to scanning |
| 6598 | oop obj = oop(addr); |
| 6599 | assert(oopDesc::is_oop(obj), "should be an oop"); |
| 6600 | assert(_finger <= addr, "_finger runneth ahead"); |
| 6601 | // advance the finger to right end of this object |
| 6602 | _finger = addr + obj->size(); |
| 6603 | assert(_finger > addr, "we just incremented it above"); |
| 6604 | // Note: the finger doesn't advance while we drain |
| 6605 | // the stack below. |
| 6606 | bool res = _mark_stack->push(obj); |
| 6607 | assert(res, "Empty non-zero size stack should have space for single push"); |
| 6608 | while (!_mark_stack->isEmpty()) { |
| 6609 | oop new_oop = _mark_stack->pop(); |
| 6610 | assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop"); |
| 6611 | // now scan this oop's oops |
| 6612 | new_oop->oop_iterate(&_pam_verify_closure); |
| 6613 | } |
| 6614 | assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition"); |
| 6615 | return true; |
| 6616 | } |
| 6617 | |
| 6618 | PushAndMarkVerifyClosure::PushAndMarkVerifyClosure( |
| 6619 | CMSCollector* collector, MemRegion span, |
| 6620 | CMSBitMap* verification_bm, CMSBitMap* cms_bm, |
| 6621 | CMSMarkStack* mark_stack): |
| 6622 | MetadataVisitingOopIterateClosure(collector->ref_processor()), |
| 6623 | _collector(collector), |
| 6624 | _span(span), |
| 6625 | _verification_bm(verification_bm), |
| 6626 | _cms_bm(cms_bm), |
| 6627 | _mark_stack(mark_stack) |
| 6628 | { } |
| 6629 | |
| 6630 | template <class T> void PushAndMarkVerifyClosure::do_oop_work(T *p) { |
| 6631 | oop obj = RawAccess<>::oop_load(p); |
| 6632 | do_oop(obj); |
| 6633 | } |
| 6634 | |
| 6635 | void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); } |
| 6636 | void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); } |
| 6637 | |
| 6638 | // Upon stack overflow, we discard (part of) the stack, |
| 6639 | // remembering the least address amongst those discarded |
| 6640 | // in CMSCollector's _restart_address. |
| 6641 | void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) { |
| 6642 | // Remember the least grey address discarded |
| 6643 | HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost); |
| 6644 | _collector->lower_restart_addr(ra); |
| 6645 | _mark_stack->reset(); // discard stack contents |
| 6646 | _mark_stack->expand(); // expand the stack if possible |
| 6647 | } |
| 6648 | |
| 6649 | void PushAndMarkVerifyClosure::do_oop(oop obj) { |
| 6650 | assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at "PTR_FORMAT, p2i(obj)); |
| 6651 | HeapWord* addr = (HeapWord*)obj; |
| 6652 | if (_span.contains(addr) && !_verification_bm->isMarked(addr)) { |
| 6653 | // Oop lies in _span and isn't yet grey or black |
| 6654 | _verification_bm->mark(addr); // now grey |
| 6655 | if (!_cms_bm->isMarked(addr)) { |
| 6656 | Log(gc, verify) log; |
| 6657 | ResourceMark rm; |
| 6658 | LogStream ls(log.error()); |
| 6659 | oop(addr)->print_on(&ls); |
| 6660 | log.error(" ("INTPTR_FORMAT " should have been marked)", p2i(addr)); |
| 6661 | fatal("... aborting"); |
| 6662 | } |
| 6663 | |
| 6664 | if (!_mark_stack->push(obj)) { // stack overflow |
| 6665 | log_trace(gc)("CMS marking stack overflow (benign) at "SIZE_FORMAT, _mark_stack->capacity()); |
| 6666 | assert(_mark_stack->isFull(), "Else push should have succeeded"); |
| 6667 | handle_stack_overflow(addr); |
| 6668 | } |
| 6669 | // anything including and to the right of _finger |
| 6670 | // will be scanned as we iterate over the remainder of the |
| 6671 | // bit map |
| 6672 | } |
| 6673 | } |
| 6674 | |
| 6675 | PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector, |
| 6676 | MemRegion span, |
| 6677 | CMSBitMap* bitMap, CMSMarkStack* markStack, |
| 6678 | HeapWord* finger, MarkFromRootsClosure* parent) : |
| 6679 | MetadataVisitingOopIterateClosure(collector->ref_processor()), |
| 6680 | _collector(collector), |
| 6681 | _span(span), |
| 6682 | _bitMap(bitMap), |
| 6683 | _markStack(markStack), |
| 6684 | _finger(finger), |
| 6685 | _parent(parent) |
| 6686 | { } |
| 6687 | |
| 6688 | ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector, |
| 6689 | MemRegion span, |
| 6690 | CMSBitMap* bit_map, |
| 6691 | OopTaskQueue* work_queue, |
| 6692 | CMSMarkStack* overflow_stack, |
| 6693 | HeapWord* finger, |
| 6694 | HeapWord* volatile* global_finger_addr, |
| 6695 | ParMarkFromRootsClosure* parent) : |
| 6696 | MetadataVisitingOopIterateClosure(collector->ref_processor()), |
| 6697 | _collector(collector), |
| 6698 | _whole_span(collector->_span), |
| 6699 | _span(span), |
| 6700 | _bit_map(bit_map), |
| 6701 | _work_queue(work_queue), |
| 6702 | _overflow_stack(overflow_stack), |
| 6703 | _finger(finger), |
| 6704 | _global_finger_addr(global_finger_addr), |
| 6705 | _parent(parent) |
| 6706 | { } |
| 6707 | |
| 6708 | // Assumes thread-safe access by callers, who are |
| 6709 | // responsible for mutual exclusion. |
| 6710 | void CMSCollector::lower_restart_addr(HeapWord* low) { |
| 6711 | assert(_span.contains(low), "Out of bounds addr"); |
| 6712 | if (_restart_addr == NULL) { |
| 6713 | _restart_addr = low; |
| 6714 | } else { |
| 6715 | _restart_addr = MIN2(_restart_addr, low); |
| 6716 | } |
| 6717 | } |
| 6718 | |
| 6719 | // Upon stack overflow, we discard (part of) the stack, |
| 6720 | // remembering the least address amongst those discarded |
| 6721 | // in CMSCollector's _restart_address. |
| 6722 | void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { |
| 6723 | // Remember the least grey address discarded |
| 6724 | HeapWord* ra = (HeapWord*)_markStack->least_value(lost); |
| 6725 | _collector->lower_restart_addr(ra); |
| 6726 | _markStack->reset(); // discard stack contents |
| 6727 | _markStack->expand(); // expand the stack if possible |
| 6728 | } |
| 6729 | |
| 6730 | // Upon stack overflow, we discard (part of) the stack, |
| 6731 | // remembering the least address amongst those discarded |
| 6732 | // in CMSCollector's _restart_address. |
| 6733 | void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { |
| 6734 | // We need to do this under a mutex to prevent other |
| 6735 | // workers from interfering with the work done below. |
| 6736 | MutexLocker ml(_overflow_stack->par_lock(), |
| 6737 | Mutex::_no_safepoint_check_flag); |
| 6738 | // Remember the least grey address discarded |
| 6739 | HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); |
| 6740 | _collector->lower_restart_addr(ra); |
| 6741 | _overflow_stack->reset(); // discard stack contents |
| 6742 | _overflow_stack->expand(); // expand the stack if possible |
| 6743 | } |
| 6744 | |
| 6745 | void PushOrMarkClosure::do_oop(oop obj) { |
| 6746 | // Ignore mark word because we are running concurrent with mutators. |
| 6747 | assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at "PTR_FORMAT, p2i(obj)); |
| 6748 | HeapWord* addr = (HeapWord*)obj; |
| 6749 | if (_span.contains(addr) && !_bitMap->isMarked(addr)) { |
| 6750 | // Oop lies in _span and isn't yet grey or black |
| 6751 | _bitMap->mark(addr); // now grey |
| 6752 | if (addr < _finger) { |
| 6753 | // the bit map iteration has already either passed, or |
| 6754 | // sampled, this bit in the bit map; we'll need to |
| 6755 | // use the marking stack to scan this oop's oops. |
| 6756 | bool simulate_overflow = false; |
| 6757 | NOT_PRODUCT( |
| 6758 | if (CMSMarkStackOverflowALot && |
| 6759 | _collector->simulate_overflow()) { |
| 6760 | // simulate a stack overflow |
| 6761 | simulate_overflow = true; |
| 6762 | } |
| 6763 | ) |
| 6764 | if (simulate_overflow || !_markStack->push(obj)) { // stack overflow |
| 6765 | log_trace(gc)("CMS marking stack overflow (benign) at "SIZE_FORMAT, _markStack->capacity()); |
| 6766 | assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded"); |
| 6767 | handle_stack_overflow(addr); |
| 6768 | } |
| 6769 | } |
| 6770 | // anything including and to the right of _finger |
| 6771 | // will be scanned as we iterate over the remainder of the |
| 6772 | // bit map |
| 6773 | do_yield_check(); |
| 6774 | } |
| 6775 | } |
| 6776 | |
| 6777 | void ParPushOrMarkClosure::do_oop(oop obj) { |
| 6778 | // Ignore mark word because we are running concurrent with mutators. |
| 6779 | assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at "PTR_FORMAT, p2i(obj)); |
| 6780 | HeapWord* addr = (HeapWord*)obj; |
| 6781 | if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) { |
| 6782 | // Oop lies in _span and isn't yet grey or black |
| 6783 | // We read the global_finger (volatile read) strictly after marking oop |
| 6784 | bool res = _bit_map->par_mark(addr); // now grey |
| 6785 | volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr; |
| 6786 | // Should we push this marked oop on our stack? |
| 6787 | // -- if someone else marked it, nothing to do |
| 6788 | // -- if target oop is above global finger nothing to do |
| 6789 | // -- if target oop is in chunk and above local finger |
| 6790 | // then nothing to do |
| 6791 | // -- else push on work queue |
| 6792 | if ( !res // someone else marked it, they will deal with it |
| 6793 | || (addr >= *gfa) // will be scanned in a later task |
| 6794 | || (_span.contains(addr) && addr >= _finger)) { // later in this chunk |
| 6795 | return; |
| 6796 | } |
| 6797 | // the bit map iteration has already either passed, or |
| 6798 | // sampled, this bit in the bit map; we'll need to |
| 6799 | // use the marking stack to scan this oop's oops. |
| 6800 | bool simulate_overflow = false; |
| 6801 | NOT_PRODUCT( |
| 6802 | if (CMSMarkStackOverflowALot && |
| 6803 | _collector->simulate_overflow()) { |
| 6804 | // simulate a stack overflow |
| 6805 | simulate_overflow = true; |
| 6806 | } |
| 6807 | ) |
| 6808 | if (simulate_overflow || |
| 6809 | !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) { |
| 6810 | // stack overflow |
| 6811 | log_trace(gc)("CMS marking stack overflow (benign) at "SIZE_FORMAT, _overflow_stack->capacity()); |
| 6812 | // We cannot assert that the overflow stack is full because |
| 6813 | // it may have been emptied since. |
| 6814 | assert(simulate_overflow || |
| 6815 | _work_queue->size() == _work_queue->max_elems(), |
| 6816 | "Else push should have succeeded"); |
| 6817 | handle_stack_overflow(addr); |
| 6818 | } |
| 6819 | do_yield_check(); |
| 6820 | } |
| 6821 | } |
| 6822 | |
| 6823 | PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector, |
| 6824 | MemRegion span, |
| 6825 | ReferenceDiscoverer* rd, |
| 6826 | CMSBitMap* bit_map, |
| 6827 | CMSBitMap* mod_union_table, |
| 6828 | CMSMarkStack* mark_stack, |
| 6829 | bool concurrent_precleaning): |
| 6830 | MetadataVisitingOopIterateClosure(rd), |
| 6831 | _collector(collector), |
| 6832 | _span(span), |
| 6833 | _bit_map(bit_map), |
| 6834 | _mod_union_table(mod_union_table), |
| 6835 | _mark_stack(mark_stack), |
| 6836 | _concurrent_precleaning(concurrent_precleaning) |
| 6837 | { |
| 6838 | assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL"); |
| 6839 | } |
| 6840 | |
| 6841 | // Grey object rescan during pre-cleaning and second checkpoint phases -- |
| 6842 | // the non-parallel version (the parallel version appears further below.) |
| 6843 | void PushAndMarkClosure::do_oop(oop obj) { |
| 6844 | // Ignore mark word verification. If during concurrent precleaning, |
| 6845 | // the object monitor may be locked. If during the checkpoint |
| 6846 | // phases, the object may already have been reached by a different |
| 6847 | // path and may be at the end of the global overflow list (so |
| 6848 | // the mark word may be NULL). |
| 6849 | assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */), |
| 6850 | "Expected an oop or NULL at "PTR_FORMAT, p2i(obj)); |
| 6851 | HeapWord* addr = (HeapWord*)obj; |
| 6852 | // Check if oop points into the CMS generation |
| 6853 | // and is not marked |
| 6854 | if (_span.contains(addr) && !_bit_map->isMarked(addr)) { |
| 6855 | // a white object ... |
| 6856 | _bit_map->mark(addr); // ... now grey |
| 6857 | // push on the marking stack (grey set) |
| 6858 | bool simulate_overflow = false; |
| 6859 | NOT_PRODUCT( |
| 6860 | if (CMSMarkStackOverflowALot && |
| 6861 | _collector->simulate_overflow()) { |
| 6862 | // simulate a stack overflow |
| 6863 | simulate_overflow = true; |
| 6864 | } |
| 6865 | ) |
| 6866 | if (simulate_overflow || !_mark_stack->push(obj)) { |
| 6867 | if (_concurrent_precleaning) { |
| 6868 | // During precleaning we can just dirty the appropriate card(s) |
| 6869 | // in the mod union table, thus ensuring that the object remains |
| 6870 | // in the grey set and continue. In the case of object arrays |
| 6871 | // we need to dirty all of the cards that the object spans, |
| 6872 | // since the rescan of object arrays will be limited to the |
| 6873 | // dirty cards. |
| 6874 | // Note that no one can be interfering with us in this action |
| 6875 | // of dirtying the mod union table, so no locking or atomics |
| 6876 | // are required. |
| 6877 | if (obj->is_objArray()) { |
| 6878 | size_t sz = obj->size(); |
| 6879 | HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size); |
| 6880 | MemRegion redirty_range = MemRegion(addr, end_card_addr); |
| 6881 | assert(!redirty_range.is_empty(), "Arithmetical tautology"); |
| 6882 | _mod_union_table->mark_range(redirty_range); |
| 6883 | } else { |
| 6884 | _mod_union_table->mark(addr); |
| 6885 | } |
| 6886 | _collector->_ser_pmc_preclean_ovflw++; |
| 6887 | } else { |
| 6888 | // During the remark phase, we need to remember this oop |
| 6889 | // in the overflow list. |
| 6890 | _collector->push_on_overflow_list(obj); |
| 6891 | _collector->_ser_pmc_remark_ovflw++; |
| 6892 | } |
| 6893 | } |
| 6894 | } |
| 6895 | } |
| 6896 | |
| 6897 | ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector, |
| 6898 | MemRegion span, |
| 6899 | ReferenceDiscoverer* rd, |
| 6900 | CMSBitMap* bit_map, |
| 6901 | OopTaskQueue* work_queue): |
| 6902 | MetadataVisitingOopIterateClosure(rd), |
| 6903 | _collector(collector), |
| 6904 | _span(span), |
| 6905 | _bit_map(bit_map), |
| 6906 | _work_queue(work_queue) |
| 6907 | { |
| 6908 | assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL"); |
| 6909 | } |
| 6910 | |
| 6911 | // Grey object rescan during second checkpoint phase -- |
| 6912 | // the parallel version. |
| 6913 | void ParPushAndMarkClosure::do_oop(oop obj) { |
| 6914 | // In the assert below, we ignore the mark word because |
| 6915 | // this oop may point to an already visited object that is |
| 6916 | // on the overflow stack (in which case the mark word has |
| 6917 | // been hijacked for chaining into the overflow stack -- |
| 6918 | // if this is the last object in the overflow stack then |
| 6919 | // its mark word will be NULL). Because this object may |
| 6920 | // have been subsequently popped off the global overflow |
| 6921 | // stack, and the mark word possibly restored to the prototypical |
| 6922 | // value, by the time we get to examined this failing assert in |
| 6923 | // the debugger, is_oop_or_null(false) may subsequently start |
| 6924 | // to hold. |
| 6925 | assert(oopDesc::is_oop_or_null(obj, true), |
| 6926 | "Expected an oop or NULL at "PTR_FORMAT, p2i(obj)); |
| 6927 | HeapWord* addr = (HeapWord*)obj; |
| 6928 | // Check if oop points into the CMS generation |
| 6929 | // and is not marked |
| 6930 | if (_span.contains(addr) && !_bit_map->isMarked(addr)) { |
| 6931 | // a white object ... |
| 6932 | // If we manage to "claim" the object, by being the |
| 6933 | // first thread to mark it, then we push it on our |
| 6934 | // marking stack |
| 6935 | if (_bit_map->par_mark(addr)) { // ... now grey |
| 6936 | // push on work queue (grey set) |
| 6937 | bool simulate_overflow = false; |
| 6938 | NOT_PRODUCT( |
| 6939 | if (CMSMarkStackOverflowALot && |
| 6940 | _collector->par_simulate_overflow()) { |
| 6941 | // simulate a stack overflow |
| 6942 | simulate_overflow = true; |
| 6943 | } |
| 6944 | ) |
| 6945 | if (simulate_overflow || !_work_queue->push(obj)) { |
| 6946 | _collector->par_push_on_overflow_list(obj); |
| 6947 | _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS |
| 6948 | } |
| 6949 | } // Else, some other thread got there first |
| 6950 | } |
| 6951 | } |
| 6952 | |
| 6953 | void CMSPrecleanRefsYieldClosure::do_yield_work() { |
| 6954 | Mutex* bml = _collector->bitMapLock(); |
| 6955 | assert_lock_strong(bml); |
| 6956 | assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| 6957 | "CMS thread should hold CMS token"); |
| 6958 | |
| 6959 | bml->unlock(); |
| 6960 | ConcurrentMarkSweepThread::desynchronize(true); |
| 6961 | |
| 6962 | _collector->stopTimer(); |
| 6963 | _collector->incrementYields(); |
| 6964 | |
| 6965 | // See the comment in coordinator_yield() |
| 6966 | for (unsigned i = 0; i < CMSYieldSleepCount && |
| 6967 | ConcurrentMarkSweepThread::should_yield() && |
| 6968 | !CMSCollector::foregroundGCIsActive(); ++i) { |
| 6969 | os::sleep(Thread::current(), 1, false); |
| 6970 | } |
| 6971 | |
| 6972 | ConcurrentMarkSweepThread::synchronize(true); |
| 6973 | bml->lock(); |
| 6974 | |
| 6975 | _collector->startTimer(); |
| 6976 | } |
| 6977 | |
| 6978 | bool CMSPrecleanRefsYieldClosure::should_return() { |
| 6979 | if (ConcurrentMarkSweepThread::should_yield()) { |
| 6980 | do_yield_work(); |
| 6981 | } |
| 6982 | return _collector->foregroundGCIsActive(); |
| 6983 | } |
| 6984 | |
| 6985 | void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) { |
| 6986 | assert(((size_t)mr.start())%CardTable::card_size_in_words == 0, |
| 6987 | "mr should be aligned to start at a card boundary"); |
| 6988 | // We'd like to assert: |
| 6989 | // assert(mr.word_size()%CardTable::card_size_in_words == 0, |
| 6990 | // "mr should be a range of cards"); |
| 6991 | // However, that would be too strong in one case -- the last |
| 6992 | // partition ends at _unallocated_block which, in general, can be |
| 6993 | // an arbitrary boundary, not necessarily card aligned. |
| 6994 | _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words; |
| 6995 | _space->object_iterate_mem(mr, &_scan_cl); |
| 6996 | } |
| 6997 | |
| 6998 | SweepClosure::SweepClosure(CMSCollector* collector, |
| 6999 | ConcurrentMarkSweepGeneration* g, |
| 7000 | CMSBitMap* bitMap, bool should_yield) : |
| 7001 | _collector(collector), |
| 7002 | _g(g), |
| 7003 | _sp(g->cmsSpace()), |
| 7004 | _limit(_sp->sweep_limit()), |
| 7005 | _freelistLock(_sp->freelistLock()), |
| 7006 | _bitMap(bitMap), |
| 7007 | _inFreeRange(false), // No free range at beginning of sweep |
| 7008 | _freeRangeInFreeLists(false), // No free range at beginning of sweep |
| 7009 | _lastFreeRangeCoalesced(false), |
| 7010 | _yield(should_yield), |
| 7011 | _freeFinger(g->used_region().start()) |
| 7012 | { |
| 7013 | NOT_PRODUCT( |
| 7014 | _numObjectsFreed = 0; |
| 7015 | _numWordsFreed = 0; |
| 7016 | _numObjectsLive = 0; |
| 7017 | _numWordsLive = 0; |
| 7018 | _numObjectsAlreadyFree = 0; |
| 7019 | _numWordsAlreadyFree = 0; |
| 7020 | _last_fc = NULL; |
| 7021 | |
| 7022 | _sp->initializeIndexedFreeListArrayReturnedBytes(); |
| 7023 | _sp->dictionary()->initialize_dict_returned_bytes(); |
| 7024 | ) |
| 7025 | assert(_limit >= _sp->bottom() && _limit <= _sp->end(), |
| 7026 | "sweep _limit out of bounds"); |
| 7027 | log_develop_trace(gc, sweep)("===================="); |
| 7028 | log_develop_trace(gc, sweep)("Starting new sweep with limit "PTR_FORMAT, p2i(_limit)); |
| 7029 | } |
| 7030 | |
| 7031 | void SweepClosure::print_on(outputStream* st) const { |
| 7032 | st->print_cr("_sp = ["PTR_FORMAT ","PTR_FORMAT ")", |
| 7033 | p2i(_sp->bottom()), p2i(_sp->end())); |
| 7034 | st->print_cr("_limit = "PTR_FORMAT, p2i(_limit)); |
| 7035 | st->print_cr("_freeFinger = "PTR_FORMAT, p2i(_freeFinger)); |
| 7036 | NOT_PRODUCT(st->print_cr("_last_fc = "PTR_FORMAT, p2i(_last_fc));) |
| 7037 | st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d", |
| 7038 | _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced); |
| 7039 | } |
| 7040 | |
| 7041 | #ifndef PRODUCT |
| 7042 | // Assertion checking only: no useful work in product mode -- |
| 7043 | // however, if any of the flags below become product flags, |
| 7044 | // you may need to review this code to see if it needs to be |
| 7045 | // enabled in product mode. |
| 7046 | SweepClosure::~SweepClosure() { |
| 7047 | assert_lock_strong(_freelistLock); |
| 7048 | assert(_limit >= _sp->bottom() && _limit <= _sp->end(), |
| 7049 | "sweep _limit out of bounds"); |
| 7050 | if (inFreeRange()) { |
| 7051 | Log(gc, sweep) log; |
| 7052 | log.error("inFreeRange() should have been reset; dumping state of SweepClosure"); |
| 7053 | ResourceMark rm; |
| 7054 | LogStream ls(log.error()); |
| 7055 | print_on(&ls); |
| 7056 | ShouldNotReachHere(); |
| 7057 | } |
| 7058 | |
| 7059 | if (log_is_enabled(Debug, gc, sweep)) { |
| 7060 | log_debug(gc, sweep)("Collected "SIZE_FORMAT " objects, "SIZE_FORMAT " bytes", |
| 7061 | _numObjectsFreed, _numWordsFreed*sizeof(HeapWord)); |
| 7062 | log_debug(gc, sweep)("Live "SIZE_FORMAT " objects, "SIZE_FORMAT " bytes Already free "SIZE_FORMAT " objects, "SIZE_FORMAT " bytes", |
| 7063 | _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord)); |
| 7064 | size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord); |
| 7065 | log_debug(gc, sweep)("Total sweep: "SIZE_FORMAT " bytes", totalBytes); |
| 7066 | } |
| 7067 | |
| 7068 | if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) { |
| 7069 | size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes(); |
| 7070 | size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes(); |
| 7071 | size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes; |
| 7072 | log_trace(gc, sweep)("Returned "SIZE_FORMAT " bytes Indexed List Returned "SIZE_FORMAT " bytes Dictionary Returned "SIZE_FORMAT " bytes", |
| 7073 | returned_bytes, indexListReturnedBytes, dict_returned_bytes); |
| 7074 | } |
| 7075 | log_develop_trace(gc, sweep)("end of sweep with _limit = "PTR_FORMAT, p2i(_limit)); |
| 7076 | log_develop_trace(gc, sweep)("================"); |
| 7077 | } |
| 7078 | #endif // PRODUCT |
| 7079 | |
| 7080 | void SweepClosure::initialize_free_range(HeapWord* freeFinger, |
| 7081 | bool freeRangeInFreeLists) { |
| 7082 | log_develop_trace(gc, sweep)("---- Start free range at "PTR_FORMAT " with free block (%d)", |
| 7083 | p2i(freeFinger), freeRangeInFreeLists); |
| 7084 | assert(!inFreeRange(), "Trampling existing free range"); |
| 7085 | set_inFreeRange(true); |
| 7086 | set_lastFreeRangeCoalesced(false); |
| 7087 | |
| 7088 | set_freeFinger(freeFinger); |
| 7089 | set_freeRangeInFreeLists(freeRangeInFreeLists); |
| 7090 | if (CMSTestInFreeList) { |
| 7091 | if (freeRangeInFreeLists) { |
| 7092 | FreeChunk* fc = (FreeChunk*) freeFinger; |
| 7093 | assert(fc->is_free(), "A chunk on the free list should be free."); |
| 7094 | assert(fc->size() > 0, "Free range should have a size"); |
| 7095 | assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists"); |
| 7096 | } |
| 7097 | } |
| 7098 | } |
| 7099 | |
| 7100 | // Note that the sweeper runs concurrently with mutators. Thus, |
| 7101 | // it is possible for direct allocation in this generation to happen |
| 7102 | // in the middle of the sweep. Note that the sweeper also coalesces |
| 7103 | // contiguous free blocks. Thus, unless the sweeper and the allocator |
| 7104 | // synchronize appropriately freshly allocated blocks may get swept up. |
| 7105 | // This is accomplished by the sweeper locking the free lists while |
| 7106 | // it is sweeping. Thus blocks that are determined to be free are |
| 7107 | // indeed free. There is however one additional complication: |
| 7108 | // blocks that have been allocated since the final checkpoint and |
| 7109 | // mark, will not have been marked and so would be treated as |
| 7110 | // unreachable and swept up. To prevent this, the allocator marks |
| 7111 | // the bit map when allocating during the sweep phase. This leads, |
| 7112 | // however, to a further complication -- objects may have been allocated |
| 7113 | // but not yet initialized -- in the sense that the header isn't yet |
| 7114 | // installed. The sweeper can not then determine the size of the block |
| 7115 | // in order to skip over it. To deal with this case, we use a technique |
| 7116 | // (due to Printezis) to encode such uninitialized block sizes in the |
| 7117 | // bit map. Since the bit map uses a bit per every HeapWord, but the |
| 7118 | // CMS generation has a minimum object size of 3 HeapWords, it follows |
| 7119 | // that "normal marks" won't be adjacent in the bit map (there will |
| 7120 | // always be at least two 0 bits between successive 1 bits). We make use |
| 7121 | // of these "unused" bits to represent uninitialized blocks -- the bit |
| 7122 | // corresponding to the start of the uninitialized object and the next |
| 7123 | // bit are both set. Finally, a 1 bit marks the end of the object that |
| 7124 | // started with the two consecutive 1 bits to indicate its potentially |
| 7125 | // uninitialized state. |
| 7126 | |
| 7127 | size_t SweepClosure::do_blk_careful(HeapWord* addr) { |
| 7128 | FreeChunk* fc = (FreeChunk*)addr; |
| 7129 | size_t res; |
| 7130 | |
| 7131 | // Check if we are done sweeping. Below we check "addr >= _limit" rather |
| 7132 | // than "addr == _limit" because although _limit was a block boundary when |
| 7133 | // we started the sweep, it may no longer be one because heap expansion |
| 7134 | // may have caused us to coalesce the block ending at the address _limit |
| 7135 | // with a newly expanded chunk (this happens when _limit was set to the |
| 7136 | // previous _end of the space), so we may have stepped past _limit: |
| 7137 | // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740. |
| 7138 | if (addr >= _limit) { // we have swept up to or past the limit: finish up |
| 7139 | assert(_limit >= _sp->bottom() && _limit <= _sp->end(), |
| 7140 | "sweep _limit out of bounds"); |
| 7141 | assert(addr < _sp->end(), "addr out of bounds"); |
| 7142 | // Flush any free range we might be holding as a single |
| 7143 | // coalesced chunk to the appropriate free list. |
| 7144 | if (inFreeRange()) { |
| 7145 | assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit, |
| 7146 | "freeFinger() "PTR_FORMAT " is out of bounds", p2i(freeFinger())); |
| 7147 | flush_cur_free_chunk(freeFinger(), |
| 7148 | pointer_delta(addr, freeFinger())); |
| 7149 | log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk "PTR_FORMAT " ("SIZE_FORMAT ") [coalesced:%d]", |
| 7150 | p2i(freeFinger()), pointer_delta(addr, freeFinger()), |
| 7151 | lastFreeRangeCoalesced() ? 1 : 0); |
| 7152 | } |
| 7153 | |
| 7154 | // help the iterator loop finish |
| 7155 | return pointer_delta(_sp->end(), addr); |
| 7156 | } |
| 7157 | |
| 7158 | assert(addr < _limit, "sweep invariant"); |
| 7159 | // check if we should yield |
| 7160 | do_yield_check(addr); |
| 7161 | if (fc->is_free()) { |
| 7162 | // Chunk that is already free |
| 7163 | res = fc->size(); |
| 7164 | do_already_free_chunk(fc); |
| 7165 | debug_only(_sp->verifyFreeLists()); |
| 7166 | // If we flush the chunk at hand in lookahead_and_flush() |
| 7167 | // and it's coalesced with a preceding chunk, then the |
| 7168 | // process of "mangling" the payload of the coalesced block |
| 7169 | // will cause erasure of the size information from the |
| 7170 | // (erstwhile) header of all the coalesced blocks but the |
| 7171 | // first, so the first disjunct in the assert will not hold |
| 7172 | // in that specific case (in which case the second disjunct |
| 7173 | // will hold). |
| 7174 | assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit, |
| 7175 | "Otherwise the size info doesn't change at this step"); |
| 7176 | NOT_PRODUCT( |
| 7177 | _numObjectsAlreadyFree++; |
| 7178 | _numWordsAlreadyFree += res; |
| 7179 | ) |
| 7180 | NOT_PRODUCT(_last_fc = fc;) |
| 7181 | } else if (!_bitMap->isMarked(addr)) { |
| 7182 | // Chunk is fresh garbage |
| 7183 | res = do_garbage_chunk(fc); |
| 7184 | debug_only(_sp->verifyFreeLists()); |
| 7185 | NOT_PRODUCT( |
| 7186 | _numObjectsFreed++; |
| 7187 | _numWordsFreed += res; |
| 7188 | ) |
| 7189 | } else { |
| 7190 | // Chunk that is alive. |
| 7191 | res = do_live_chunk(fc); |
| 7192 | debug_only(_sp->verifyFreeLists()); |
| 7193 | NOT_PRODUCT( |
| 7194 | _numObjectsLive++; |
| 7195 | _numWordsLive += res; |
| 7196 | ) |
| 7197 | } |
| 7198 | return res; |
| 7199 | } |
| 7200 | |
| 7201 | // For the smart allocation, record following |
| 7202 | // split deaths - a free chunk is removed from its free list because |
| 7203 | // it is being split into two or more chunks. |
| 7204 | // split birth - a free chunk is being added to its free list because |
| 7205 | // a larger free chunk has been split and resulted in this free chunk. |
| 7206 | // coal death - a free chunk is being removed from its free list because |
| 7207 | // it is being coalesced into a large free chunk. |
| 7208 | // coal birth - a free chunk is being added to its free list because |
| 7209 | // it was created when two or more free chunks where coalesced into |
| 7210 | // this free chunk. |
| 7211 | // |
| 7212 | // These statistics are used to determine the desired number of free |
| 7213 | // chunks of a given size. The desired number is chosen to be relative |
| 7214 | // to the end of a CMS sweep. The desired number at the end of a sweep |
| 7215 | // is the |
| 7216 | // count-at-end-of-previous-sweep (an amount that was enough) |
| 7217 | // - count-at-beginning-of-current-sweep (the excess) |
| 7218 | // + split-births (gains in this size during interval) |
| 7219 | // - split-deaths (demands on this size during interval) |
| 7220 | // where the interval is from the end of one sweep to the end of the |
| 7221 | // next. |
| 7222 | // |
| 7223 | // When sweeping the sweeper maintains an accumulated chunk which is |
| 7224 | // the chunk that is made up of chunks that have been coalesced. That |
| 7225 | // will be termed the left-hand chunk. A new chunk of garbage that |
| 7226 | // is being considered for coalescing will be referred to as the |
| 7227 | // right-hand chunk. |
| 7228 | // |
| 7229 | // When making a decision on whether to coalesce a right-hand chunk with |
| 7230 | // the current left-hand chunk, the current count vs. the desired count |
| 7231 | // of the left-hand chunk is considered. Also if the right-hand chunk |
| 7232 | // is near the large chunk at the end of the heap (see |
| 7233 | // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the |
| 7234 | // left-hand chunk is coalesced. |
| 7235 | // |
| 7236 | // When making a decision about whether to split a chunk, the desired count |
| 7237 | // vs. the current count of the candidate to be split is also considered. |
| 7238 | // If the candidate is underpopulated (currently fewer chunks than desired) |
| 7239 | // a chunk of an overpopulated (currently more chunks than desired) size may |
| 7240 | // be chosen. The "hint" associated with a free list, if non-null, points |
| 7241 | // to a free list which may be overpopulated. |
| 7242 | // |
| 7243 | |
| 7244 | void SweepClosure::do_already_free_chunk(FreeChunk* fc) { |
| 7245 | const size_t size = fc->size(); |
| 7246 | // Chunks that cannot be coalesced are not in the |
| 7247 | // free lists. |
| 7248 | if (CMSTestInFreeList && !fc->cantCoalesce()) { |
| 7249 | assert(_sp->verify_chunk_in_free_list(fc), |
| 7250 | "free chunk should be in free lists"); |
| 7251 | } |
| 7252 | // a chunk that is already free, should not have been |
| 7253 | // marked in the bit map |
| 7254 | HeapWord* const addr = (HeapWord*) fc; |
| 7255 | assert(!_bitMap->isMarked(addr), "free chunk should be unmarked"); |
| 7256 | // Verify that the bit map has no bits marked between |
| 7257 | // addr and purported end of this block. |
| 7258 | _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); |
| 7259 | |
| 7260 | // Some chunks cannot be coalesced under any circumstances. |
| 7261 | // See the definition of cantCoalesce(). |
| 7262 | if (!fc->cantCoalesce()) { |
| 7263 | // This chunk can potentially be coalesced. |
| 7264 | // All the work is done in |
| 7265 | do_post_free_or_garbage_chunk(fc, size); |
| 7266 | // Note that if the chunk is not coalescable (the else arm |
| 7267 | // below), we unconditionally flush, without needing to do |
| 7268 | // a "lookahead," as we do below. |
| 7269 | if (inFreeRange()) lookahead_and_flush(fc, size); |
| 7270 | } else { |
| 7271 | // Code path common to both original and adaptive free lists. |
| 7272 | |
| 7273 | // cant coalesce with previous block; this should be treated |
| 7274 | // as the end of a free run if any |
| 7275 | if (inFreeRange()) { |
| 7276 | // we kicked some butt; time to pick up the garbage |
| 7277 | assert(freeFinger() < addr, "freeFinger points too high"); |
| 7278 | flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); |
| 7279 | } |
| 7280 | // else, nothing to do, just continue |
| 7281 | } |
| 7282 | } |
| 7283 | |
| 7284 | size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) { |
| 7285 | // This is a chunk of garbage. It is not in any free list. |
| 7286 | // Add it to a free list or let it possibly be coalesced into |
| 7287 | // a larger chunk. |
| 7288 | HeapWord* const addr = (HeapWord*) fc; |
| 7289 | const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); |
| 7290 | |
| 7291 | // Verify that the bit map has no bits marked between |
| 7292 | // addr and purported end of just dead object. |
| 7293 | _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); |
| 7294 | do_post_free_or_garbage_chunk(fc, size); |
| 7295 | |
| 7296 | assert(_limit >= addr + size, |
| 7297 | "A freshly garbage chunk can't possibly straddle over _limit"); |
| 7298 | if (inFreeRange()) lookahead_and_flush(fc, size); |
| 7299 | return size; |
| 7300 | } |
| 7301 | |
| 7302 | size_t SweepClosure::do_live_chunk(FreeChunk* fc) { |
| 7303 | HeapWord* addr = (HeapWord*) fc; |
| 7304 | // The sweeper has just found a live object. Return any accumulated |
| 7305 | // left hand chunk to the free lists. |
| 7306 | if (inFreeRange()) { |
| 7307 | assert(freeFinger() < addr, "freeFinger points too high"); |
| 7308 | flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); |
| 7309 | } |
| 7310 | |
| 7311 | // This object is live: we'd normally expect this to be |
| 7312 | // an oop, and like to assert the following: |
| 7313 | // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop"); |
| 7314 | // However, as we commented above, this may be an object whose |
| 7315 | // header hasn't yet been initialized. |
| 7316 | size_t size; |
| 7317 | assert(_bitMap->isMarked(addr), "Tautology for this control point"); |
| 7318 | if (_bitMap->isMarked(addr + 1)) { |
| 7319 | // Determine the size from the bit map, rather than trying to |
| 7320 | // compute it from the object header. |
| 7321 | HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); |
| 7322 | size = pointer_delta(nextOneAddr + 1, addr); |
| 7323 | assert(size == CompactibleFreeListSpace::adjustObjectSize(size), |
| 7324 | "alignment problem"); |
| 7325 | |
| 7326 | #ifdef ASSERT |
| 7327 | if (oop(addr)->klass_or_null_acquire() != NULL) { |
| 7328 | // Ignore mark word because we are running concurrent with mutators |
| 7329 | assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop"); |
| 7330 | assert(size == |
| 7331 | CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()), |
| 7332 | "P-mark and computed size do not agree"); |
| 7333 | } |
| 7334 | #endif |
| 7335 | |
| 7336 | } else { |
| 7337 | // This should be an initialized object that's alive. |
| 7338 | assert(oop(addr)->klass_or_null_acquire() != NULL, |
| 7339 | "Should be an initialized object"); |
| 7340 | // Ignore mark word because we are running concurrent with mutators |
| 7341 | assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop"); |
| 7342 | // Verify that the bit map has no bits marked between |
| 7343 | // addr and purported end of this block. |
| 7344 | size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); |
| 7345 | assert(size >= 3, "Necessary for Printezis marks to work"); |
| 7346 | assert(!_bitMap->isMarked(addr+1), "Tautology for this control point"); |
| 7347 | DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);) |
| 7348 | } |
| 7349 | return size; |
| 7350 | } |
| 7351 | |
| 7352 | void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc, |
| 7353 | size_t chunkSize) { |
| 7354 | // do_post_free_or_garbage_chunk() should only be called in the case |
| 7355 | // of the adaptive free list allocator. |
| 7356 | const bool fcInFreeLists = fc->is_free(); |
| 7357 | assert((HeapWord*)fc <= _limit, "sweep invariant"); |
| 7358 | if (CMSTestInFreeList && fcInFreeLists) { |
| 7359 | assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists"); |
| 7360 | } |
| 7361 | |
| 7362 | log_develop_trace(gc, sweep)(" -- pick up another chunk at "PTR_FORMAT " ("SIZE_FORMAT ")", p2i(fc), chunkSize); |
| 7363 | |
| 7364 | HeapWord* const fc_addr = (HeapWord*) fc; |
| 7365 | |
| 7366 | bool coalesce = false; |
| 7367 | const size_t left = pointer_delta(fc_addr, freeFinger()); |
| 7368 | const size_t right = chunkSize; |
| 7369 | switch (FLSCoalescePolicy) { |
| 7370 | // numeric value forms a coalition aggressiveness metric |
| 7371 | case 0: { // never coalesce |
| 7372 | coalesce = false; |
| 7373 | break; |
| 7374 | } |
| 7375 | case 1: { // coalesce if left & right chunks on overpopulated lists |
| 7376 | coalesce = _sp->coalOverPopulated(left) && |
| 7377 | _sp->coalOverPopulated(right); |
| 7378 | break; |
| 7379 | } |
| 7380 | case 2: { // coalesce if left chunk on overpopulated list (default) |
| 7381 | coalesce = _sp->coalOverPopulated(left); |
| 7382 | break; |
| 7383 | } |
| 7384 | case 3: { // coalesce if left OR right chunk on overpopulated list |
| 7385 | coalesce = _sp->coalOverPopulated(left) || |
| 7386 | _sp->coalOverPopulated(right); |
| 7387 | break; |
| 7388 | } |
| 7389 | case 4: { // always coalesce |
| 7390 | coalesce = true; |
| 7391 | break; |
| 7392 | } |
| 7393 | default: |
| 7394 | ShouldNotReachHere(); |
| 7395 | } |
| 7396 | |
| 7397 | // Should the current free range be coalesced? |
| 7398 | // If the chunk is in a free range and either we decided to coalesce above |
| 7399 | // or the chunk is near the large block at the end of the heap |
| 7400 | // (isNearLargestChunk() returns true), then coalesce this chunk. |
| 7401 | const bool doCoalesce = inFreeRange() |
| 7402 | && (coalesce || _g->isNearLargestChunk(fc_addr)); |
| 7403 | if (doCoalesce) { |
| 7404 | // Coalesce the current free range on the left with the new |
| 7405 | // chunk on the right. If either is on a free list, |
| 7406 | // it must be removed from the list and stashed in the closure. |
| 7407 | if (freeRangeInFreeLists()) { |
| 7408 | FreeChunk* const ffc = (FreeChunk*)freeFinger(); |
| 7409 | assert(ffc->size() == pointer_delta(fc_addr, freeFinger()), |
| 7410 | "Size of free range is inconsistent with chunk size."); |
| 7411 | if (CMSTestInFreeList) { |
| 7412 | assert(_sp->verify_chunk_in_free_list(ffc), |
| 7413 | "Chunk is not in free lists"); |
| 7414 | } |
| 7415 | _sp->coalDeath(ffc->size()); |
| 7416 | _sp->removeFreeChunkFromFreeLists(ffc); |
| 7417 | set_freeRangeInFreeLists(false); |
| 7418 | } |
| 7419 | if (fcInFreeLists) { |
| 7420 | _sp->coalDeath(chunkSize); |
| 7421 | assert(fc->size() == chunkSize, |
| 7422 | "The chunk has the wrong size or is not in the free lists"); |
| 7423 | _sp->removeFreeChunkFromFreeLists(fc); |
| 7424 | } |
| 7425 | set_lastFreeRangeCoalesced(true); |
| 7426 | print_free_block_coalesced(fc); |
| 7427 | } else { // not in a free range and/or should not coalesce |
| 7428 | // Return the current free range and start a new one. |
| 7429 | if (inFreeRange()) { |
| 7430 | // In a free range but cannot coalesce with the right hand chunk. |
| 7431 | // Put the current free range into the free lists. |
| 7432 | flush_cur_free_chunk(freeFinger(), |
| 7433 | pointer_delta(fc_addr, freeFinger())); |
| 7434 | } |
| 7435 | // Set up for new free range. Pass along whether the right hand |
| 7436 | // chunk is in the free lists. |
| 7437 | initialize_free_range((HeapWord*)fc, fcInFreeLists); |
| 7438 | } |
| 7439 | } |
| 7440 | |
| 7441 | // Lookahead flush: |
| 7442 | // If we are tracking a free range, and this is the last chunk that |
| 7443 | // we'll look at because its end crosses past _limit, we'll preemptively |
| 7444 | // flush it along with any free range we may be holding on to. Note that |
| 7445 | // this can be the case only for an already free or freshly garbage |
| 7446 | // chunk. If this block is an object, it can never straddle |
| 7447 | // over _limit. The "straddling" occurs when _limit is set at |
| 7448 | // the previous end of the space when this cycle started, and |
| 7449 | // a subsequent heap expansion caused the previously co-terminal |
| 7450 | // free block to be coalesced with the newly expanded portion, |
| 7451 | // thus rendering _limit a non-block-boundary making it dangerous |
| 7452 | // for the sweeper to step over and examine. |
| 7453 | void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) { |
| 7454 | assert(inFreeRange(), "Should only be called if currently in a free range."); |
| 7455 | HeapWord* const eob = ((HeapWord*)fc) + chunk_size; |
| 7456 | assert(_sp->used_region().contains(eob - 1), |
| 7457 | "eob = "PTR_FORMAT " eob-1 = "PTR_FORMAT " _limit = "PTR_FORMAT |
| 7458 | " out of bounds wrt _sp = ["PTR_FORMAT ","PTR_FORMAT ")" |
| 7459 | " when examining fc = "PTR_FORMAT "("SIZE_FORMAT ")", |
| 7460 | p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size); |
| 7461 | if (eob >= _limit) { |
| 7462 | assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit"); |
| 7463 | log_develop_trace(gc, sweep)("_limit "PTR_FORMAT " reached or crossed by block " |
| 7464 | "["PTR_FORMAT ","PTR_FORMAT ") in space " |
| 7465 | "["PTR_FORMAT ","PTR_FORMAT ")", |
| 7466 | p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end())); |
| 7467 | // Return the storage we are tracking back into the free lists. |
| 7468 | log_develop_trace(gc, sweep)("Flushing ... "); |
| 7469 | assert(freeFinger() < eob, "Error"); |
| 7470 | flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger())); |
| 7471 | } |
| 7472 | } |
| 7473 | |
| 7474 | void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) { |
| 7475 | assert(inFreeRange(), "Should only be called if currently in a free range."); |
| 7476 | assert(size > 0, |
| 7477 | "A zero sized chunk cannot be added to the free lists."); |
| 7478 | if (!freeRangeInFreeLists()) { |
| 7479 | if (CMSTestInFreeList) { |
| 7480 | FreeChunk* fc = (FreeChunk*) chunk; |
| 7481 | fc->set_size(size); |
| 7482 | assert(!_sp->verify_chunk_in_free_list(fc), |
| 7483 | "chunk should not be in free lists yet"); |
| 7484 | } |
| 7485 | log_develop_trace(gc, sweep)(" -- add free block "PTR_FORMAT " ("SIZE_FORMAT ") to free lists", p2i(chunk), size); |
| 7486 | // A new free range is going to be starting. The current |
| 7487 | // free range has not been added to the free lists yet or |
| 7488 | // was removed so add it back. |
| 7489 | // If the current free range was coalesced, then the death |
| 7490 | // of the free range was recorded. Record a birth now. |
| 7491 | if (lastFreeRangeCoalesced()) { |
| 7492 | _sp->coalBirth(size); |
| 7493 | } |
| 7494 | _sp->addChunkAndRepairOffsetTable(chunk, size, |
| 7495 | lastFreeRangeCoalesced()); |
| 7496 | } else { |
| 7497 | log_develop_trace(gc, sweep)("Already in free list: nothing to flush"); |
| 7498 | } |
| 7499 | set_inFreeRange(false); |
| 7500 | set_freeRangeInFreeLists(false); |
| 7501 | } |
| 7502 | |
| 7503 | // We take a break if we've been at this for a while, |
| 7504 | // so as to avoid monopolizing the locks involved. |
| 7505 | void SweepClosure::do_yield_work(HeapWord* addr) { |
| 7506 | // Return current free chunk being used for coalescing (if any) |
| 7507 | // to the appropriate freelist. After yielding, the next |
| 7508 | // free block encountered will start a coalescing range of |
| 7509 | // free blocks. If the next free block is adjacent to the |
| 7510 | // chunk just flushed, they will need to wait for the next |
| 7511 | // sweep to be coalesced. |
| 7512 | if (inFreeRange()) { |
| 7513 | flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); |
| 7514 | } |
| 7515 | |
| 7516 | // First give up the locks, then yield, then re-lock. |
| 7517 | // We should probably use a constructor/destructor idiom to |
| 7518 | // do this unlock/lock or modify the MutexUnlocker class to |
| 7519 | // serve our purpose. XXX |
| 7520 | assert_lock_strong(_bitMap->lock()); |
| 7521 | assert_lock_strong(_freelistLock); |
| 7522 | assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), |
| 7523 | "CMS thread should hold CMS token"); |
| 7524 | _bitMap->lock()->unlock(); |
| 7525 | _freelistLock->unlock(); |
| 7526 | ConcurrentMarkSweepThread::desynchronize(true); |
| 7527 | _collector->stopTimer(); |
| 7528 | _collector->incrementYields(); |
| 7529 | |
| 7530 | // See the comment in coordinator_yield() |
| 7531 | for (unsigned i = 0; i < CMSYieldSleepCount && |
| 7532 | ConcurrentMarkSweepThread::should_yield() && |
| 7533 | !CMSCollector::foregroundGCIsActive(); ++i) { |
| 7534 | os::sleep(Thread::current(), 1, false); |
| 7535 | } |
| 7536 | |
| 7537 | ConcurrentMarkSweepThread::synchronize(true); |
| 7538 | _freelistLock->lock_without_safepoint_check(); |
| 7539 | _bitMap->lock()->lock_without_safepoint_check(); |
| 7540 | _collector->startTimer(); |
| 7541 | } |
| 7542 | |
| 7543 | #ifndef PRODUCT |
| 7544 | // This is actually very useful in a product build if it can |
| 7545 | // be called from the debugger. Compile it into the product |
| 7546 | // as needed. |
| 7547 | bool debug_verify_chunk_in_free_list(FreeChunk* fc) { |
| 7548 | return debug_cms_space->verify_chunk_in_free_list(fc); |
| 7549 | } |
| 7550 | #endif |
| 7551 | |
| 7552 | void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const { |
| 7553 | log_develop_trace(gc, sweep)("Sweep:coal_free_blk "PTR_FORMAT " ("SIZE_FORMAT ")", |
| 7554 | p2i(fc), fc->size()); |
| 7555 | } |
| 7556 | |
| 7557 | // CMSIsAliveClosure |
| 7558 | bool CMSIsAliveClosure::do_object_b(oop obj) { |
| 7559 | HeapWord* addr = (HeapWord*)obj; |
| 7560 | return addr != NULL && |
| 7561 | (!_span.contains(addr) || _bit_map->isMarked(addr)); |
| 7562 | } |
| 7563 | |
| 7564 | CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector, |
| 7565 | MemRegion span, |
| 7566 | CMSBitMap* bit_map, CMSMarkStack* mark_stack, |
| 7567 | bool cpc): |
| 7568 | _collector(collector), |
| 7569 | _span(span), |
| 7570 | _mark_stack(mark_stack), |
| 7571 | _bit_map(bit_map), |
| 7572 | _concurrent_precleaning(cpc) { |
| 7573 | assert(!_span.is_empty(), "Empty span could spell trouble"); |
| 7574 | } |
| 7575 | |
| 7576 | |
| 7577 | // CMSKeepAliveClosure: the serial version |
| 7578 | void CMSKeepAliveClosure::do_oop(oop obj) { |
| 7579 | HeapWord* addr = (HeapWord*)obj; |
| 7580 | if (_span.contains(addr) && |
| 7581 | !_bit_map->isMarked(addr)) { |
| 7582 | _bit_map->mark(addr); |
| 7583 | bool simulate_overflow = false; |
| 7584 | NOT_PRODUCT( |
| 7585 | if (CMSMarkStackOverflowALot && |
| 7586 | _collector->simulate_overflow()) { |
| 7587 | // simulate a stack overflow |
| 7588 | simulate_overflow = true; |
| 7589 | } |
| 7590 | ) |
| 7591 | if (simulate_overflow || !_mark_stack->push(obj)) { |
| 7592 | if (_concurrent_precleaning) { |
| 7593 | // We dirty the overflown object and let the remark |
| 7594 | // phase deal with it. |
| 7595 | assert(_collector->overflow_list_is_empty(), "Error"); |
| 7596 | // In the case of object arrays, we need to dirty all of |
| 7597 | // the cards that the object spans. No locking or atomics |
| 7598 | // are needed since no one else can be mutating the mod union |
| 7599 | // table. |
| 7600 | if (obj->is_objArray()) { |
| 7601 | size_t sz = obj->size(); |
| 7602 | HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size); |
| 7603 | MemRegion redirty_range = MemRegion(addr, end_card_addr); |
| 7604 | assert(!redirty_range.is_empty(), "Arithmetical tautology"); |
| 7605 | _collector->_modUnionTable.mark_range(redirty_range); |
| 7606 | } else { |
| 7607 | _collector->_modUnionTable.mark(addr); |
| 7608 | } |
| 7609 | _collector->_ser_kac_preclean_ovflw++; |
| 7610 | } else { |
| 7611 | _collector->push_on_overflow_list(obj); |
| 7612 | _collector->_ser_kac_ovflw++; |
| 7613 | } |
| 7614 | } |
| 7615 | } |
| 7616 | } |
| 7617 | |
| 7618 | // CMSParKeepAliveClosure: a parallel version of the above. |
| 7619 | // The work queues are private to each closure (thread), |
| 7620 | // but (may be) available for stealing by other threads. |
| 7621 | void CMSParKeepAliveClosure::do_oop(oop obj) { |
| 7622 | HeapWord* addr = (HeapWord*)obj; |
| 7623 | if (_span.contains(addr) && |
| 7624 | !_bit_map->isMarked(addr)) { |
| 7625 | // In general, during recursive tracing, several threads |
| 7626 | // may be concurrently getting here; the first one to |
| 7627 | // "tag" it, claims it. |
| 7628 | if (_bit_map->par_mark(addr)) { |
| 7629 | bool res = _work_queue->push(obj); |
| 7630 | assert(res, "Low water mark should be much less than capacity"); |
| 7631 | // Do a recursive trim in the hope that this will keep |
| 7632 | // stack usage lower, but leave some oops for potential stealers |
| 7633 | trim_queue(_low_water_mark); |
| 7634 | } // Else, another thread got there first |
| 7635 | } |
| 7636 | } |
| 7637 | |
| 7638 | void CMSParKeepAliveClosure::trim_queue(uint max) { |
| 7639 | while (_work_queue->size() > max) { |
| 7640 | oop new_oop; |
| 7641 | if (_work_queue->pop_local(new_oop)) { |
| 7642 | assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop"); |
| 7643 | assert(_bit_map->isMarked((HeapWord*)new_oop), |
| 7644 | "no white objects on this stack!"); |
| 7645 | assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); |
| 7646 | // iterate over the oops in this oop, marking and pushing |
| 7647 | // the ones in CMS heap (i.e. in _span). |
| 7648 | new_oop->oop_iterate(&_mark_and_push); |
| 7649 | } |
| 7650 | } |
| 7651 | } |
| 7652 | |
| 7653 | CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure( |
| 7654 | CMSCollector* collector, |
| 7655 | MemRegion span, CMSBitMap* bit_map, |
| 7656 | OopTaskQueue* work_queue): |
| 7657 | _collector(collector), |
| 7658 | _span(span), |
| 7659 | _work_queue(work_queue), |
| 7660 | _bit_map(bit_map) { } |
| 7661 | |
| 7662 | void CMSInnerParMarkAndPushClosure::do_oop(oop obj) { |
| 7663 | HeapWord* addr = (HeapWord*)obj; |
| 7664 | if (_span.contains(addr) && |
| 7665 | !_bit_map->isMarked(addr)) { |
| 7666 | if (_bit_map->par_mark(addr)) { |
| 7667 | bool simulate_overflow = false; |
| 7668 | NOT_PRODUCT( |
| 7669 | if (CMSMarkStackOverflowALot && |
| 7670 | _collector->par_simulate_overflow()) { |
| 7671 | // simulate a stack overflow |
| 7672 | simulate_overflow = true; |
| 7673 | } |
| 7674 | ) |
| 7675 | if (simulate_overflow || !_work_queue->push(obj)) { |
| 7676 | _collector->par_push_on_overflow_list(obj); |
| 7677 | _collector->_par_kac_ovflw++; |
| 7678 | } |
| 7679 | } // Else another thread got there already |
| 7680 | } |
| 7681 | } |
| 7682 | |
| 7683 | ////////////////////////////////////////////////////////////////// |
| 7684 | // CMSExpansionCause ///////////////////////////// |
| 7685 | ////////////////////////////////////////////////////////////////// |
| 7686 | const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) { |
| 7687 | switch (cause) { |
| 7688 | case _no_expansion: |
| 7689 | return "No expansion"; |
| 7690 | case _satisfy_free_ratio: |
| 7691 | return "Free ratio"; |
| 7692 | case _satisfy_promotion: |
| 7693 | return "Satisfy promotion"; |
| 7694 | case _satisfy_allocation: |
| 7695 | return "allocation"; |
| 7696 | case _allocate_par_lab: |
| 7697 | return "Par LAB"; |
| 7698 | case _allocate_par_spooling_space: |
| 7699 | return "Par Spooling Space"; |
| 7700 | case _adaptive_size_policy: |
| 7701 | return "Ergonomics"; |
| 7702 | default: |
| 7703 | return "unknown"; |
| 7704 | } |
| 7705 | } |
| 7706 | |
| 7707 | void CMSDrainMarkingStackClosure::do_void() { |
| 7708 | // the max number to take from overflow list at a time |
| 7709 | const size_t num = _mark_stack->capacity()/4; |
| 7710 | assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(), |
| 7711 | "Overflow list should be NULL during concurrent phases"); |
| 7712 | while (!_mark_stack->isEmpty() || |
| 7713 | // if stack is empty, check the overflow list |
| 7714 | _collector->take_from_overflow_list(num, _mark_stack)) { |
| 7715 | oop obj = _mark_stack->pop(); |
| 7716 | HeapWord* addr = (HeapWord*)obj; |
| 7717 | assert(_span.contains(addr), "Should be within span"); |
| 7718 | assert(_bit_map->isMarked(addr), "Should be marked"); |
| 7719 | assert(oopDesc::is_oop(obj), "Should be an oop"); |
| 7720 | obj->oop_iterate(_keep_alive); |
| 7721 | } |
| 7722 | } |
| 7723 | |
| 7724 | void CMSParDrainMarkingStackClosure::do_void() { |
| 7725 | // drain queue |
| 7726 | trim_queue(0); |
| 7727 | } |
| 7728 | |
| 7729 | // Trim our work_queue so its length is below max at return |
| 7730 | void CMSParDrainMarkingStackClosure::trim_queue(uint max) { |
| 7731 | while (_work_queue->size() > max) { |
| 7732 | oop new_oop; |
| 7733 | if (_work_queue->pop_local(new_oop)) { |
| 7734 | assert(oopDesc::is_oop(new_oop), "Expected an oop"); |
| 7735 | assert(_bit_map->isMarked((HeapWord*)new_oop), |
| 7736 | "no white objects on this stack!"); |
| 7737 | assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); |
| 7738 | // iterate over the oops in this oop, marking and pushing |
| 7739 | // the ones in CMS heap (i.e. in _span). |
| 7740 | new_oop->oop_iterate(&_mark_and_push); |
| 7741 | } |
| 7742 | } |
| 7743 | } |
| 7744 | |
| 7745 | //////////////////////////////////////////////////////////////////// |
| 7746 | // Support for Marking Stack Overflow list handling and related code |
| 7747 | //////////////////////////////////////////////////////////////////// |
| 7748 | // Much of the following code is similar in shape and spirit to the |
| 7749 | // code used in ParNewGC. We should try and share that code |
| 7750 | // as much as possible in the future. |
| 7751 | |
| 7752 | #ifndef PRODUCT |
| 7753 | // Debugging support for CMSStackOverflowALot |
| 7754 | |
| 7755 | // It's OK to call this multi-threaded; the worst thing |
| 7756 | // that can happen is that we'll get a bunch of closely |
| 7757 | // spaced simulated overflows, but that's OK, in fact |
| 7758 | // probably good as it would exercise the overflow code |
| 7759 | // under contention. |
| 7760 | bool CMSCollector::simulate_overflow() { |
| 7761 | if (_overflow_counter-- <= 0) { // just being defensive |
| 7762 | _overflow_counter = CMSMarkStackOverflowInterval; |
| 7763 | return true; |
| 7764 | } else { |
| 7765 | return false; |
| 7766 | } |
| 7767 | } |
| 7768 | |
| 7769 | bool CMSCollector::par_simulate_overflow() { |
| 7770 | return simulate_overflow(); |
| 7771 | } |
| 7772 | #endif |
| 7773 | |
| 7774 | // Single-threaded |
| 7775 | bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) { |
| 7776 | assert(stack->isEmpty(), "Expected precondition"); |
| 7777 | assert(stack->capacity() > num, "Shouldn't bite more than can chew"); |
| 7778 | size_t i = num; |
| 7779 | oop cur = _overflow_list; |
| 7780 | const markOop proto = markOopDesc::prototype(); |
| 7781 | NOT_PRODUCT(ssize_t n = 0;) |
| 7782 | for (oop next; i > 0 && cur != NULL; cur = next, i--) { |
| 7783 | next = oop(cur->mark_raw()); |
| 7784 | cur->set_mark_raw(proto); // until proven otherwise |
| 7785 | assert(oopDesc::is_oop(cur), "Should be an oop"); |
| 7786 | bool res = stack->push(cur); |
| 7787 | assert(res, "Bit off more than can chew?"); |
| 7788 | NOT_PRODUCT(n++;) |
| 7789 | } |
| 7790 | _overflow_list = cur; |
| 7791 | #ifndef PRODUCT |
| 7792 | assert(_num_par_pushes >= n, "Too many pops?"); |
| 7793 | _num_par_pushes -=n; |
| 7794 | #endif |
| 7795 | return !stack->isEmpty(); |
| 7796 | } |
| 7797 | |
| 7798 | #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff)) |
| 7799 | // (MT-safe) Get a prefix of at most "num" from the list. |
| 7800 | // The overflow list is chained through the mark word of |
| 7801 | // each object in the list. We fetch the entire list, |
| 7802 | // break off a prefix of the right size and return the |
| 7803 | // remainder. If other threads try to take objects from |
| 7804 | // the overflow list at that time, they will wait for |
| 7805 | // some time to see if data becomes available. If (and |
| 7806 | // only if) another thread places one or more object(s) |
| 7807 | // on the global list before we have returned the suffix |
| 7808 | // to the global list, we will walk down our local list |
| 7809 | // to find its end and append the global list to |
| 7810 | // our suffix before returning it. This suffix walk can |
| 7811 | // prove to be expensive (quadratic in the amount of traffic) |
| 7812 | // when there are many objects in the overflow list and |
| 7813 | // there is much producer-consumer contention on the list. |
| 7814 | // *NOTE*: The overflow list manipulation code here and |
| 7815 | // in ParNewGeneration:: are very similar in shape, |
| 7816 | // except that in the ParNew case we use the old (from/eden) |
| 7817 | // copy of the object to thread the list via its klass word. |
| 7818 | // Because of the common code, if you make any changes in |
| 7819 | // the code below, please check the ParNew version to see if |
| 7820 | // similar changes might be needed. |
| 7821 | // CR 6797058 has been filed to consolidate the common code. |
| 7822 | bool CMSCollector::par_take_from_overflow_list(size_t num, |
| 7823 | OopTaskQueue* work_q, |
| 7824 | int no_of_gc_threads) { |
| 7825 | assert(work_q->size() == 0, "First empty local work queue"); |
| 7826 | assert(num < work_q->max_elems(), "Can't bite more than we can chew"); |
| 7827 | if (_overflow_list == NULL) { |
| 7828 | return false; |
| 7829 | } |
| 7830 | // Grab the entire list; we'll put back a suffix |
| 7831 | oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list)); |
| 7832 | Thread* tid = Thread::current(); |
| 7833 | // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was |
| 7834 | // set to ParallelGCThreads. |
| 7835 | size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads; |
| 7836 | size_t sleep_time_millis = MAX2((size_t)1, num/100); |
| 7837 | // If the list is busy, we spin for a short while, |
| 7838 | // sleeping between attempts to get the list. |
| 7839 | for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) { |
| 7840 | os::sleep(tid, sleep_time_millis, false); |
| 7841 | if (_overflow_list == NULL) { |
| 7842 | // Nothing left to take |
| 7843 | return false; |
| 7844 | } else if (_overflow_list != BUSY) { |
| 7845 | // Try and grab the prefix |
| 7846 | prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list)); |
| 7847 | } |
| 7848 | } |
| 7849 | // If the list was found to be empty, or we spun long |
| 7850 | // enough, we give up and return empty-handed. If we leave |
| 7851 | // the list in the BUSY state below, it must be the case that |
| 7852 | // some other thread holds the overflow list and will set it |
| 7853 | // to a non-BUSY state in the future. |
| 7854 | if (prefix == NULL || prefix == BUSY) { |
| 7855 | // Nothing to take or waited long enough |
| 7856 | if (prefix == NULL) { |
| 7857 | // Write back the NULL in case we overwrote it with BUSY above |
| 7858 | // and it is still the same value. |
| 7859 | Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY); |
| 7860 | } |
| 7861 | return false; |
| 7862 | } |
| 7863 | assert(prefix != NULL && prefix != BUSY, "Error"); |
| 7864 | size_t i = num; |
| 7865 | oop cur = prefix; |
| 7866 | // Walk down the first "num" objects, unless we reach the end. |
| 7867 | for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--); |
| 7868 | if (cur->mark_raw() == NULL) { |
| 7869 | // We have "num" or fewer elements in the list, so there |
| 7870 | // is nothing to return to the global list. |
| 7871 | // Write back the NULL in lieu of the BUSY we wrote |
| 7872 | // above, if it is still the same value. |
| 7873 | if (_overflow_list == BUSY) { |
| 7874 | Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY); |
| 7875 | } |
| 7876 | } else { |
| 7877 | // Chop off the suffix and return it to the global list. |
| 7878 | assert(cur->mark_raw() != BUSY, "Error"); |
| 7879 | oop suffix_head = cur->mark_raw(); // suffix will be put back on global list |
| 7880 | cur->set_mark_raw(NULL); // break off suffix |
| 7881 | // It's possible that the list is still in the empty(busy) state |
| 7882 | // we left it in a short while ago; in that case we may be |
| 7883 | // able to place back the suffix without incurring the cost |
| 7884 | // of a walk down the list. |
| 7885 | oop observed_overflow_list = _overflow_list; |
| 7886 | oop cur_overflow_list = observed_overflow_list; |
| 7887 | bool attached = false; |
| 7888 | while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { |
| 7889 | observed_overflow_list = |
| 7890 | Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list); |
| 7891 | if (cur_overflow_list == observed_overflow_list) { |
| 7892 | attached = true; |
| 7893 | break; |
| 7894 | } else cur_overflow_list = observed_overflow_list; |
| 7895 | } |
| 7896 | if (!attached) { |
| 7897 | // Too bad, someone else sneaked in (at least) an element; we'll need |
| 7898 | // to do a splice. Find tail of suffix so we can prepend suffix to global |
| 7899 | // list. |
| 7900 | for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw())); |
| 7901 | oop suffix_tail = cur; |
| 7902 | assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL, |
| 7903 | "Tautology"); |
| 7904 | observed_overflow_list = _overflow_list; |
| 7905 | do { |
| 7906 | cur_overflow_list = observed_overflow_list; |
| 7907 | if (cur_overflow_list != BUSY) { |
| 7908 | // Do the splice ... |
| 7909 | suffix_tail->set_mark_raw(markOop(cur_overflow_list)); |
| 7910 | } else { // cur_overflow_list == BUSY |
| 7911 | suffix_tail->set_mark_raw(NULL); |
| 7912 | } |
| 7913 | // ... and try to place spliced list back on overflow_list ... |
| 7914 | observed_overflow_list = |
| 7915 | Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list); |
| 7916 | } while (cur_overflow_list != observed_overflow_list); |
| 7917 | // ... until we have succeeded in doing so. |
| 7918 | } |
| 7919 | } |
| 7920 | |
| 7921 | // Push the prefix elements on work_q |
| 7922 | assert(prefix != NULL, "control point invariant"); |
| 7923 | const markOop proto = markOopDesc::prototype(); |
| 7924 | oop next; |
| 7925 | NOT_PRODUCT(ssize_t n = 0;) |
| 7926 | for (cur = prefix; cur != NULL; cur = next) { |
| 7927 | next = oop(cur->mark_raw()); |
| 7928 | cur->set_mark_raw(proto); // until proven otherwise |
| 7929 | assert(oopDesc::is_oop(cur), "Should be an oop"); |
| 7930 | bool res = work_q->push(cur); |
| 7931 | assert(res, "Bit off more than we can chew?"); |
| 7932 | NOT_PRODUCT(n++;) |
| 7933 | } |
| 7934 | #ifndef PRODUCT |
| 7935 | assert(_num_par_pushes >= n, "Too many pops?"); |
| 7936 | Atomic::sub(n, &_num_par_pushes); |
| 7937 | #endif |
| 7938 | return true; |
| 7939 | } |
| 7940 | |
| 7941 | // Single-threaded |
| 7942 | void CMSCollector::push_on_overflow_list(oop p) { |
| 7943 | NOT_PRODUCT(_num_par_pushes++;) |
| 7944 | assert(oopDesc::is_oop(p), "Not an oop"); |
| 7945 | preserve_mark_if_necessary(p); |
| 7946 | p->set_mark_raw((markOop)_overflow_list); |
| 7947 | _overflow_list = p; |
| 7948 | } |
| 7949 | |
| 7950 | // Multi-threaded; use CAS to prepend to overflow list |
| 7951 | void CMSCollector::par_push_on_overflow_list(oop p) { |
| 7952 | NOT_PRODUCT(Atomic::inc(&_num_par_pushes);) |
| 7953 | assert(oopDesc::is_oop(p), "Not an oop"); |
| 7954 | par_preserve_mark_if_necessary(p); |
| 7955 | oop observed_overflow_list = _overflow_list; |
| 7956 | oop cur_overflow_list; |
| 7957 | do { |
| 7958 | cur_overflow_list = observed_overflow_list; |
| 7959 | if (cur_overflow_list != BUSY) { |
| 7960 | p->set_mark_raw(markOop(cur_overflow_list)); |
| 7961 | } else { |
| 7962 | p->set_mark_raw(NULL); |
| 7963 | } |
| 7964 | observed_overflow_list = |
| 7965 | Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list); |
| 7966 | } while (cur_overflow_list != observed_overflow_list); |
| 7967 | } |
| 7968 | #undef BUSY |
| 7969 | |
| 7970 | // Single threaded |
| 7971 | // General Note on GrowableArray: pushes may silently fail |
| 7972 | // because we are (temporarily) out of C-heap for expanding |
| 7973 | // the stack. The problem is quite ubiquitous and affects |
| 7974 | // a lot of code in the JVM. The prudent thing for GrowableArray |
| 7975 | // to do (for now) is to exit with an error. However, that may |
| 7976 | // be too draconian in some cases because the caller may be |
| 7977 | // able to recover without much harm. For such cases, we |
| 7978 | // should probably introduce a "soft_push" method which returns |
| 7979 | // an indication of success or failure with the assumption that |
| 7980 | // the caller may be able to recover from a failure; code in |
| 7981 | // the VM can then be changed, incrementally, to deal with such |
| 7982 | // failures where possible, thus, incrementally hardening the VM |
| 7983 | // in such low resource situations. |
| 7984 | void CMSCollector::preserve_mark_work(oop p, markOop m) { |
| 7985 | _preserved_oop_stack.push(p); |
| 7986 | _preserved_mark_stack.push(m); |
| 7987 | assert(m == p->mark_raw(), "Mark word changed"); |
| 7988 | assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(), |
| 7989 | "bijection"); |
| 7990 | } |
| 7991 | |
| 7992 | // Single threaded |
| 7993 | void CMSCollector::preserve_mark_if_necessary(oop p) { |
| 7994 | markOop m = p->mark_raw(); |
| 7995 | if (m->must_be_preserved(p)) { |
| 7996 | preserve_mark_work(p, m); |
| 7997 | } |
| 7998 | } |
| 7999 | |
| 8000 | void CMSCollector::par_preserve_mark_if_necessary(oop p) { |
| 8001 | markOop m = p->mark_raw(); |
| 8002 | if (m->must_be_preserved(p)) { |
| 8003 | MutexLocker x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag); |
| 8004 | // Even though we read the mark word without holding |
| 8005 | // the lock, we are assured that it will not change |
| 8006 | // because we "own" this oop, so no other thread can |
| 8007 | // be trying to push it on the overflow list; see |
| 8008 | // the assertion in preserve_mark_work() that checks |
| 8009 | // that m == p->mark_raw(). |
| 8010 | preserve_mark_work(p, m); |
| 8011 | } |
| 8012 | } |
| 8013 | |
| 8014 | // We should be able to do this multi-threaded, |
| 8015 | // a chunk of stack being a task (this is |
| 8016 | // correct because each oop only ever appears |
| 8017 | // once in the overflow list. However, it's |
| 8018 | // not very easy to completely overlap this with |
| 8019 | // other operations, so will generally not be done |
| 8020 | // until all work's been completed. Because we |
| 8021 | // expect the preserved oop stack (set) to be small, |
| 8022 | // it's probably fine to do this single-threaded. |
| 8023 | // We can explore cleverer concurrent/overlapped/parallel |
| 8024 | // processing of preserved marks if we feel the |
| 8025 | // need for this in the future. Stack overflow should |
| 8026 | // be so rare in practice and, when it happens, its |
| 8027 | // effect on performance so great that this will |
| 8028 | // likely just be in the noise anyway. |
| 8029 | void CMSCollector::restore_preserved_marks_if_any() { |
| 8030 | assert(SafepointSynchronize::is_at_safepoint(), |
| 8031 | "world should be stopped"); |
| 8032 | assert(Thread::current()->is_ConcurrentGC_thread() || |
| 8033 | Thread::current()->is_VM_thread(), |
| 8034 | "should be single-threaded"); |
| 8035 | assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(), |
| 8036 | "bijection"); |
| 8037 | |
| 8038 | while (!_preserved_oop_stack.is_empty()) { |
| 8039 | oop p = _preserved_oop_stack.pop(); |
| 8040 | assert(oopDesc::is_oop(p), "Should be an oop"); |
| 8041 | assert(_span.contains(p), "oop should be in _span"); |
| 8042 | assert(p->mark_raw() == markOopDesc::prototype(), |
| 8043 | "Set when taken from overflow list"); |
| 8044 | markOop m = _preserved_mark_stack.pop(); |
| 8045 | p->set_mark_raw(m); |
| 8046 | } |
| 8047 | assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(), |
| 8048 | "stacks were cleared above"); |
| 8049 | } |
| 8050 | |
| 8051 | #ifndef PRODUCT |
| 8052 | bool CMSCollector::no_preserved_marks() const { |
| 8053 | return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(); |
| 8054 | } |
| 8055 | #endif |
| 8056 | |
| 8057 | // Transfer some number of overflown objects to usual marking |
| 8058 | // stack. Return true if some objects were transferred. |
| 8059 | bool MarkRefsIntoAndScanClosure::take_from_overflow_list() { |
| 8060 | size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4, |
| 8061 | (size_t)ParGCDesiredObjsFromOverflowList); |
| 8062 | |
| 8063 | bool res = _collector->take_from_overflow_list(num, _mark_stack); |
| 8064 | assert(_collector->overflow_list_is_empty() || res, |
| 8065 | "If list is not empty, we should have taken something"); |
| 8066 | assert(!res || !_mark_stack->isEmpty(), |
| 8067 | "If we took something, it should now be on our stack"); |
| 8068 | return res; |
| 8069 | } |
| 8070 | |
| 8071 | size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) { |
| 8072 | size_t res = _sp->block_size_no_stall(addr, _collector); |
| 8073 | if (_sp->block_is_obj(addr)) { |
| 8074 | if (_live_bit_map->isMarked(addr)) { |
| 8075 | // It can't have been dead in a previous cycle |
| 8076 | guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!"); |
| 8077 | } else { |
| 8078 | _dead_bit_map->mark(addr); // mark the dead object |
| 8079 | } |
| 8080 | } |
| 8081 | // Could be 0, if the block size could not be computed without stalling. |
| 8082 | return res; |
| 8083 | } |
| 8084 | |
| 8085 | TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() { |
| 8086 | GCMemoryManager* manager = CMSHeap::heap()->old_manager(); |
| 8087 | switch (phase) { |
| 8088 | case CMSCollector::InitialMarking: |
| 8089 | initialize(manager /* GC manager */ , |
| 8090 | cause /* cause of the GC */, |
| 8091 | true /* allMemoryPoolsAffected */, |
| 8092 | true /* recordGCBeginTime */, |
| 8093 | true /* recordPreGCUsage */, |
| 8094 | false /* recordPeakUsage */, |
| 8095 | false /* recordPostGCusage */, |
| 8096 | true /* recordAccumulatedGCTime */, |
| 8097 | false /* recordGCEndTime */, |
| 8098 | false /* countCollection */ ); |
| 8099 | break; |
| 8100 | |
| 8101 | case CMSCollector::FinalMarking: |
| 8102 | initialize(manager /* GC manager */ , |
| 8103 | cause /* cause of the GC */, |
| 8104 | true /* allMemoryPoolsAffected */, |
| 8105 | false /* recordGCBeginTime */, |
| 8106 | false /* recordPreGCUsage */, |
| 8107 | false /* recordPeakUsage */, |
| 8108 | false /* recordPostGCusage */, |
| 8109 | true /* recordAccumulatedGCTime */, |
| 8110 | false /* recordGCEndTime */, |
| 8111 | false /* countCollection */ ); |
| 8112 | break; |
| 8113 | |
| 8114 | case CMSCollector::Sweeping: |
| 8115 | initialize(manager /* GC manager */ , |
| 8116 | cause /* cause of the GC */, |
| 8117 | true /* allMemoryPoolsAffected */, |
| 8118 | false /* recordGCBeginTime */, |
| 8119 | false /* recordPreGCUsage */, |
| 8120 | true /* recordPeakUsage */, |
| 8121 | true /* recordPostGCusage */, |
| 8122 | false /* recordAccumulatedGCTime */, |
| 8123 | true /* recordGCEndTime */, |
| 8124 | true /* countCollection */ ); |
| 8125 | break; |
| 8126 | |
| 8127 | default: |
| 8128 | ShouldNotReachHere(); |
| 8129 | } |
| 8130 | } |
| 8131 |
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