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/stringTable.hpp"
27#include "gc/cms/cmsHeap.inline.hpp"
28#include "gc/cms/compactibleFreeListSpace.hpp"
29#include "gc/cms/concurrentMarkSweepGeneration.hpp"
30#include "gc/cms/parNewGeneration.inline.hpp"
31#include "gc/cms/parOopClosures.inline.hpp"
32#include "gc/serial/defNewGeneration.inline.hpp"
33#include "gc/shared/adaptiveSizePolicy.hpp"
34#include "gc/shared/ageTable.inline.hpp"
35#include "gc/shared/copyFailedInfo.hpp"
36#include "gc/shared/gcHeapSummary.hpp"
37#include "gc/shared/gcTimer.hpp"
38#include "gc/shared/gcTrace.hpp"
39#include "gc/shared/gcTraceTime.inline.hpp"
40#include "gc/shared/genOopClosures.inline.hpp"
41#include "gc/shared/generation.hpp"
42#include "gc/shared/plab.inline.hpp"
43#include "gc/shared/preservedMarks.inline.hpp"
44#include "gc/shared/referencePolicy.hpp"
45#include "gc/shared/referenceProcessorPhaseTimes.hpp"
46#include "gc/shared/space.hpp"
47#include "gc/shared/spaceDecorator.hpp"
48#include "gc/shared/strongRootsScope.hpp"
49#include "gc/shared/taskqueue.inline.hpp"
50#include "gc/shared/weakProcessor.hpp"
51#include "gc/shared/workgroup.hpp"
52#include "gc/shared/workerPolicy.hpp"
53#include "logging/log.hpp"
54#include "logging/logStream.hpp"
55#include "memory/iterator.inline.hpp"
56#include "memory/resourceArea.hpp"
57#include "oops/access.inline.hpp"
58#include "oops/compressedOops.inline.hpp"
59#include "oops/objArrayOop.hpp"
60#include "oops/oop.inline.hpp"
61#include "runtime/atomic.hpp"
62#include "runtime/handles.inline.hpp"
63#include "runtime/java.hpp"
64#include "runtime/thread.inline.hpp"
65#include "utilities/copy.hpp"
66#include "utilities/globalDefinitions.hpp"
67#include "utilities/stack.inline.hpp"
68
69ParScanThreadState::ParScanThreadState(Space* to_space_,
70 ParNewGeneration* young_gen_,
71 Generation* old_gen_,
72 int thread_num_,
73 ObjToScanQueueSet* work_queue_set_,
74 Stack<oop, mtGC>* overflow_stacks_,
75 PreservedMarks* preserved_marks_,
76 size_t desired_plab_sz_,
77 TaskTerminator& term_) :
78 _work_queue(work_queue_set_->queue(thread_num_)),
79 _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL),
80 _preserved_marks(preserved_marks_),
81 _to_space_alloc_buffer(desired_plab_sz_),
82 _to_space_closure(young_gen_, this),
83 _old_gen_closure(young_gen_, this),
84 _to_space_root_closure(young_gen_, this),
85 _older_gen_closure(young_gen_, this),
86 _old_gen_root_closure(young_gen_, this),
87 _evacuate_followers(this, &_to_space_closure, &_old_gen_closure,
88 &_to_space_root_closure, young_gen_, &_old_gen_root_closure,
89 work_queue_set_, term_.terminator()),
90 _is_alive_closure(young_gen_),
91 _scan_weak_ref_closure(young_gen_, this),
92 _keep_alive_closure(&_scan_weak_ref_closure),
93 _to_space(to_space_),
94 _young_gen(young_gen_),
95 _old_gen(old_gen_),
96 _young_old_boundary(NULL),
97 _thread_num(thread_num_),
98 _ageTable(false), // false ==> not the global age table, no perf data.
99 _to_space_full(false),
100 _strong_roots_time(0.0),
101 _term_time(0.0)
102{
103 #if TASKQUEUE_STATS
104 _term_attempts = 0;
105 _overflow_refills = 0;
106 _overflow_refill_objs = 0;
107 #endif // TASKQUEUE_STATS
108
109 _survivor_chunk_array = (ChunkArray*) old_gen()->get_data_recorder(thread_num());
110 _start = os::elapsedTime();
111 _old_gen_closure.set_generation(old_gen_);
112 _old_gen_root_closure.set_generation(old_gen_);
113}
114
115void ParScanThreadState::record_survivor_plab(HeapWord* plab_start,
116 size_t plab_word_size) {
117 ChunkArray* sca = survivor_chunk_array();
118 if (sca != NULL) {
119 // A non-null SCA implies that we want the PLAB data recorded.
120 sca->record_sample(plab_start, plab_word_size);
121 }
122}
123
124bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const {
125 return new_obj->is_objArray() &&
126 arrayOop(new_obj)->length() > ParGCArrayScanChunk &&
127 new_obj != old_obj;
128}
129
130void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) {
131 assert(old->is_objArray(), "must be obj array");
132 assert(old->is_forwarded(), "must be forwarded");
133 assert(CMSHeap::heap()->is_in_reserved(old), "must be in heap.");
134 assert(!old_gen()->is_in(old), "must be in young generation.");
135
136 objArrayOop obj = objArrayOop(old->forwardee());
137 // Process ParGCArrayScanChunk elements now
138 // and push the remainder back onto queue
139 int start = arrayOop(old)->length();
140 int end = obj->length();
141 int remainder = end - start;
142 assert(start <= end, "just checking");
143 if (remainder > 2 * ParGCArrayScanChunk) {
144 // Test above combines last partial chunk with a full chunk
145 end = start + ParGCArrayScanChunk;
146 arrayOop(old)->set_length(end);
147 // Push remainder.
148 bool ok = work_queue()->push(old);
149 assert(ok, "just popped, push must be okay");
150 } else {
151 // Restore length so that it can be used if there
152 // is a promotion failure and forwarding pointers
153 // must be removed.
154 arrayOop(old)->set_length(end);
155 }
156
157 // process our set of indices (include header in first chunk)
158 // should make sure end is even (aligned to HeapWord in case of compressed oops)
159 if ((HeapWord *)obj < young_old_boundary()) {
160 // object is in to_space
161 obj->oop_iterate_range(&_to_space_closure, start, end);
162 } else {
163 // object is in old generation
164 obj->oop_iterate_range(&_old_gen_closure, start, end);
165 }
166}
167
168void ParScanThreadState::trim_queues(int max_size) {
169 ObjToScanQueue* queue = work_queue();
170 do {
171 while (queue->size() > (juint)max_size) {
172 oop obj_to_scan;
173 if (queue->pop_local(obj_to_scan)) {
174 if ((HeapWord *)obj_to_scan < young_old_boundary()) {
175 if (obj_to_scan->is_objArray() &&
176 obj_to_scan->is_forwarded() &&
177 obj_to_scan->forwardee() != obj_to_scan) {
178 scan_partial_array_and_push_remainder(obj_to_scan);
179 } else {
180 // object is in to_space
181 obj_to_scan->oop_iterate(&_to_space_closure);
182 }
183 } else {
184 // object is in old generation
185 obj_to_scan->oop_iterate(&_old_gen_closure);
186 }
187 }
188 }
189 // For the case of compressed oops, we have a private, non-shared
190 // overflow stack, so we eagerly drain it so as to more evenly
191 // distribute load early. Note: this may be good to do in
192 // general rather than delay for the final stealing phase.
193 // If applicable, we'll transfer a set of objects over to our
194 // work queue, allowing them to be stolen and draining our
195 // private overflow stack.
196 } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this));
197}
198
199bool ParScanThreadState::take_from_overflow_stack() {
200 assert(ParGCUseLocalOverflow, "Else should not call");
201 assert(young_gen()->overflow_list() == NULL, "Error");
202 ObjToScanQueue* queue = work_queue();
203 Stack<oop, mtGC>* const of_stack = overflow_stack();
204 const size_t num_overflow_elems = of_stack->size();
205 const size_t space_available = queue->max_elems() - queue->size();
206 const size_t num_take_elems = MIN3(space_available / 4,
207 (size_t)ParGCDesiredObjsFromOverflowList,
208 num_overflow_elems);
209 // Transfer the most recent num_take_elems from the overflow
210 // stack to our work queue.
211 for (size_t i = 0; i != num_take_elems; i++) {
212 oop cur = of_stack->pop();
213 oop obj_to_push = cur->forwardee();
214 assert(CMSHeap::heap()->is_in_reserved(cur), "Should be in heap");
215 assert(!old_gen()->is_in_reserved(cur), "Should be in young gen");
216 assert(CMSHeap::heap()->is_in_reserved(obj_to_push), "Should be in heap");
217 if (should_be_partially_scanned(obj_to_push, cur)) {
218 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
219 obj_to_push = cur;
220 }
221 bool ok = queue->push(obj_to_push);
222 assert(ok, "Should have succeeded");
223 }
224 assert(young_gen()->overflow_list() == NULL, "Error");
225 return num_take_elems > 0; // was something transferred?
226}
227
228void ParScanThreadState::push_on_overflow_stack(oop p) {
229 assert(ParGCUseLocalOverflow, "Else should not call");
230 overflow_stack()->push(p);
231 assert(young_gen()->overflow_list() == NULL, "Error");
232}
233
234HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) {
235 // If the object is small enough, try to reallocate the buffer.
236 HeapWord* obj = NULL;
237 if (!_to_space_full) {
238 PLAB* const plab = to_space_alloc_buffer();
239 Space* const sp = to_space();
240 if (word_sz * 100 < ParallelGCBufferWastePct * plab->word_sz()) {
241 // Is small enough; abandon this buffer and start a new one.
242 plab->retire();
243 // The minimum size has to be twice SurvivorAlignmentInBytes to
244 // allow for padding used in the alignment of 1 word. A padding
245 // of 1 is too small for a filler word so the padding size will
246 // be increased by SurvivorAlignmentInBytes.
247 size_t min_usable_size = 2 * static_cast<size_t>(SurvivorAlignmentInBytes >> LogHeapWordSize);
248 size_t buf_size = MAX2(plab->word_sz(), min_usable_size);
249 HeapWord* buf_space = sp->par_allocate(buf_size);
250 if (buf_space == NULL) {
251 const size_t min_bytes = MAX2(PLAB::min_size(), min_usable_size) << LogHeapWordSize;
252 size_t free_bytes = sp->free();
253 while(buf_space == NULL && free_bytes >= min_bytes) {
254 buf_size = free_bytes >> LogHeapWordSize;
255 assert(buf_size == (size_t)align_object_size(buf_size), "Invariant");
256 buf_space = sp->par_allocate(buf_size);
257 free_bytes = sp->free();
258 }
259 }
260 if (buf_space != NULL) {
261 plab->set_buf(buf_space, buf_size);
262 record_survivor_plab(buf_space, buf_size);
263 obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes);
264 // Note that we cannot compare buf_size < word_sz below
265 // because of AlignmentReserve (see PLAB::allocate()).
266 assert(obj != NULL || plab->words_remaining() < word_sz,
267 "Else should have been able to allocate requested object size "
268 SIZE_FORMAT ", PLAB size " SIZE_FORMAT ", SurvivorAlignmentInBytes "
269 SIZE_FORMAT ", words_remaining " SIZE_FORMAT,
270 word_sz, buf_size, SurvivorAlignmentInBytes, plab->words_remaining());
271 // It's conceivable that we may be able to use the
272 // buffer we just grabbed for subsequent small requests
273 // even if not for this one.
274 } else {
275 // We're used up.
276 _to_space_full = true;
277 }
278 } else {
279 // Too large; allocate the object individually.
280 obj = sp->par_allocate(word_sz);
281 }
282 }
283 return obj;
284}
285
286void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj, size_t word_sz) {
287 to_space_alloc_buffer()->undo_allocation(obj, word_sz);
288}
289
290void ParScanThreadState::print_promotion_failure_size() {
291 if (_promotion_failed_info.has_failed()) {
292 log_trace(gc, promotion)(" (%d: promotion failure size = " SIZE_FORMAT ") ",
293 _thread_num, _promotion_failed_info.first_size());
294 }
295}
296
297class ParScanThreadStateSet: StackObj {
298public:
299 // Initializes states for the specified number of threads;
300 ParScanThreadStateSet(int num_threads,
301 Space& to_space,
302 ParNewGeneration& young_gen,
303 Generation& old_gen,
304 ObjToScanQueueSet& queue_set,
305 Stack<oop, mtGC>* overflow_stacks_,
306 PreservedMarksSet& preserved_marks_set,
307 size_t desired_plab_sz,
308 TaskTerminator& term);
309
310 ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); }
311
312 inline ParScanThreadState& thread_state(int i);
313
314 void trace_promotion_failed(const YoungGCTracer* gc_tracer);
315 void reset(uint active_workers, bool promotion_failed);
316 void flush();
317
318 #if TASKQUEUE_STATS
319 static void
320 print_termination_stats_hdr(outputStream* const st);
321 void print_termination_stats();
322 static void
323 print_taskqueue_stats_hdr(outputStream* const st);
324 void print_taskqueue_stats();
325 void reset_stats();
326 #endif // TASKQUEUE_STATS
327
328private:
329 TaskTerminator& _term;
330 ParNewGeneration& _young_gen;
331 Generation& _old_gen;
332 ParScanThreadState* _per_thread_states;
333 const int _num_threads;
334 public:
335 bool is_valid(int id) const { return id < _num_threads; }
336 ParallelTaskTerminator* terminator() { return _term.terminator(); }
337};
338
339ParScanThreadStateSet::ParScanThreadStateSet(int num_threads,
340 Space& to_space,
341 ParNewGeneration& young_gen,
342 Generation& old_gen,
343 ObjToScanQueueSet& queue_set,
344 Stack<oop, mtGC>* overflow_stacks,
345 PreservedMarksSet& preserved_marks_set,
346 size_t desired_plab_sz,
347 TaskTerminator& term)
348 : _term(term),
349 _young_gen(young_gen),
350 _old_gen(old_gen),
351 _per_thread_states(NEW_RESOURCE_ARRAY(ParScanThreadState, num_threads)),
352 _num_threads(num_threads)
353{
354 assert(num_threads > 0, "sanity check!");
355 assert(ParGCUseLocalOverflow == (overflow_stacks != NULL),
356 "overflow_stack allocation mismatch");
357 // Initialize states.
358 for (int i = 0; i < num_threads; ++i) {
359 new(_per_thread_states + i)
360 ParScanThreadState(&to_space, &young_gen, &old_gen, i, &queue_set,
361 overflow_stacks, preserved_marks_set.get(i),
362 desired_plab_sz, term);
363 }
364}
365
366inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i) {
367 assert(i >= 0 && i < _num_threads, "sanity check!");
368 return _per_thread_states[i];
369}
370
371void ParScanThreadStateSet::trace_promotion_failed(const YoungGCTracer* gc_tracer) {
372 for (int i = 0; i < _num_threads; ++i) {
373 if (thread_state(i).promotion_failed()) {
374 gc_tracer->report_promotion_failed(thread_state(i).promotion_failed_info());
375 thread_state(i).promotion_failed_info().reset();
376 }
377 }
378}
379
380void ParScanThreadStateSet::reset(uint active_threads, bool promotion_failed) {
381 _term.terminator()->reset_for_reuse(active_threads);
382 if (promotion_failed) {
383 for (int i = 0; i < _num_threads; ++i) {
384 thread_state(i).print_promotion_failure_size();
385 }
386 }
387}
388
389#if TASKQUEUE_STATS
390void ParScanThreadState::reset_stats() {
391 taskqueue_stats().reset();
392 _term_attempts = 0;
393 _overflow_refills = 0;
394 _overflow_refill_objs = 0;
395}
396
397void ParScanThreadStateSet::reset_stats() {
398 for (int i = 0; i < _num_threads; ++i) {
399 thread_state(i).reset_stats();
400 }
401}
402
403void ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st) {
404 st->print_raw_cr("GC Termination Stats");
405 st->print_raw_cr(" elapsed --strong roots-- -------termination-------");
406 st->print_raw_cr("thr ms ms % ms % attempts");
407 st->print_raw_cr("--- --------- --------- ------ --------- ------ --------");
408}
409
410void ParScanThreadStateSet::print_termination_stats() {
411 Log(gc, task, stats) log;
412 if (!log.is_debug()) {
413 return;
414 }
415
416 ResourceMark rm;
417 LogStream ls(log.debug());
418 outputStream* st = &ls;
419
420 print_termination_stats_hdr(st);
421
422 for (int i = 0; i < _num_threads; ++i) {
423 const ParScanThreadState & pss = thread_state(i);
424 const double elapsed_ms = pss.elapsed_time() * 1000.0;
425 const double s_roots_ms = pss.strong_roots_time() * 1000.0;
426 const double term_ms = pss.term_time() * 1000.0;
427 st->print_cr("%3d %9.2f %9.2f %6.2f %9.2f %6.2f " SIZE_FORMAT_W(8),
428 i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms,
429 term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts());
430 }
431}
432
433// Print stats related to work queue activity.
434void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st) {
435 st->print_raw_cr("GC Task Stats");
436 st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();
437 st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();
438}
439
440void ParScanThreadStateSet::print_taskqueue_stats() {
441 if (!log_is_enabled(Trace, gc, task, stats)) {
442 return;
443 }
444 Log(gc, task, stats) log;
445 ResourceMark rm;
446 LogStream ls(log.trace());
447 outputStream* st = &ls;
448 print_taskqueue_stats_hdr(st);
449
450 TaskQueueStats totals;
451 for (int i = 0; i < _num_threads; ++i) {
452 const ParScanThreadState & pss = thread_state(i);
453 const TaskQueueStats & stats = pss.taskqueue_stats();
454 st->print("%3d ", i); stats.print(st); st->cr();
455 totals += stats;
456
457 if (pss.overflow_refills() > 0) {
458 st->print_cr(" " SIZE_FORMAT_W(10) " overflow refills "
459 SIZE_FORMAT_W(10) " overflow objects",
460 pss.overflow_refills(), pss.overflow_refill_objs());
461 }
462 }
463 st->print("tot "); totals.print(st); st->cr();
464
465 DEBUG_ONLY(totals.verify());
466}
467#endif // TASKQUEUE_STATS
468
469void ParScanThreadStateSet::flush() {
470 // Work in this loop should be kept as lightweight as
471 // possible since this might otherwise become a bottleneck
472 // to scaling. Should we add heavy-weight work into this
473 // loop, consider parallelizing the loop into the worker threads.
474 for (int i = 0; i < _num_threads; ++i) {
475 ParScanThreadState& par_scan_state = thread_state(i);
476
477 // Flush stats related to To-space PLAB activity and
478 // retire the last buffer.
479 par_scan_state.to_space_alloc_buffer()->flush_and_retire_stats(_young_gen.plab_stats());
480
481 // Every thread has its own age table. We need to merge
482 // them all into one.
483 AgeTable *local_table = par_scan_state.age_table();
484 _young_gen.age_table()->merge(local_table);
485
486 // Inform old gen that we're done.
487 _old_gen.par_promote_alloc_done(i);
488 }
489
490 if (UseConcMarkSweepGC) {
491 // We need to call this even when ResizeOldPLAB is disabled
492 // so as to avoid breaking some asserts. While we may be able
493 // to avoid this by reorganizing the code a bit, I am loathe
494 // to do that unless we find cases where ergo leads to bad
495 // performance.
496 CompactibleFreeListSpaceLAB::compute_desired_plab_size();
497 }
498}
499
500ParScanClosure::ParScanClosure(ParNewGeneration* g,
501 ParScanThreadState* par_scan_state) :
502 OopsInClassLoaderDataOrGenClosure(g), _par_scan_state(par_scan_state), _g(g) {
503 _boundary = _g->reserved().end();
504}
505
506void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, true); }
507void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); }
508
509void ParRootScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, true); }
510void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); }
511
512ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g,
513 ParScanThreadState* par_scan_state)
514 : ScanWeakRefClosure(g), _par_scan_state(par_scan_state)
515{}
516
517#ifdef WIN32
518#pragma warning(disable: 4786) /* identifier was truncated to '255' characters in the browser information */
519#endif
520
521ParEvacuateFollowersClosure::ParEvacuateFollowersClosure(
522 ParScanThreadState* par_scan_state_,
523 ParScanWithoutBarrierClosure* to_space_closure_,
524 ParScanWithBarrierClosure* old_gen_closure_,
525 ParRootScanWithoutBarrierClosure* to_space_root_closure_,
526 ParNewGeneration* par_gen_,
527 ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_,
528 ObjToScanQueueSet* task_queues_,
529 ParallelTaskTerminator* terminator_) :
530
531 _par_scan_state(par_scan_state_),
532 _to_space_closure(to_space_closure_),
533 _to_space_root_closure(to_space_root_closure_),
534 _old_gen_closure(old_gen_closure_),
535 _old_gen_root_closure(old_gen_root_closure_),
536 _par_gen(par_gen_),
537 _task_queues(task_queues_),
538 _terminator(terminator_)
539{}
540
541void ParEvacuateFollowersClosure::do_void() {
542 ObjToScanQueue* work_q = par_scan_state()->work_queue();
543
544 while (true) {
545 // Scan to-space and old-gen objs until we run out of both.
546 oop obj_to_scan;
547 par_scan_state()->trim_queues(0);
548
549 // We have no local work, attempt to steal from other threads.
550
551 // Attempt to steal work from promoted.
552 if (task_queues()->steal(par_scan_state()->thread_num(),
553 obj_to_scan)) {
554 bool res = work_q->push(obj_to_scan);
555 assert(res, "Empty queue should have room for a push.");
556
557 // If successful, goto Start.
558 continue;
559
560 // Try global overflow list.
561 } else if (par_gen()->take_from_overflow_list(par_scan_state())) {
562 continue;
563 }
564
565 // Otherwise, offer termination.
566 par_scan_state()->start_term_time();
567 if (terminator()->offer_termination()) break;
568 par_scan_state()->end_term_time();
569 }
570 assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0,
571 "Broken overflow list?");
572 // Finish the last termination pause.
573 par_scan_state()->end_term_time();
574}
575
576ParNewGenTask::ParNewGenTask(ParNewGeneration* young_gen,
577 Generation* old_gen,
578 HeapWord* young_old_boundary,
579 ParScanThreadStateSet* state_set,
580 StrongRootsScope* strong_roots_scope) :
581 AbstractGangTask("ParNewGeneration collection"),
582 _young_gen(young_gen), _old_gen(old_gen),
583 _young_old_boundary(young_old_boundary),
584 _state_set(state_set),
585 _strong_roots_scope(strong_roots_scope)
586{}
587
588void ParNewGenTask::work(uint worker_id) {
589 CMSHeap* heap = CMSHeap::heap();
590 // Since this is being done in a separate thread, need new resource
591 // and handle marks.
592 ResourceMark rm;
593 HandleMark hm;
594
595 ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id);
596 assert(_state_set->is_valid(worker_id), "Should not have been called");
597
598 par_scan_state.set_young_old_boundary(_young_old_boundary);
599
600 CLDScanClosure cld_scan_closure(&par_scan_state.to_space_root_closure(),
601 heap->rem_set()->cld_rem_set()->accumulate_modified_oops());
602
603 par_scan_state.start_strong_roots();
604 heap->young_process_roots(_strong_roots_scope,
605 &par_scan_state.to_space_root_closure(),
606 &par_scan_state.older_gen_closure(),
607 &cld_scan_closure);
608
609 par_scan_state.end_strong_roots();
610
611 // "evacuate followers".
612 par_scan_state.evacuate_followers_closure().do_void();
613
614 // This will collapse this worker's promoted object list that's
615 // created during the main ParNew parallel phase of ParNew. This has
616 // to be called after all workers have finished promoting objects
617 // and scanning promoted objects. It should be safe calling it from
618 // here, given that we can only reach here after all thread have
619 // offered termination, i.e., after there is no more work to be
620 // done. It will also disable promotion tracking for the rest of
621 // this GC as it's not necessary to be on during reference processing.
622 _old_gen->par_oop_since_save_marks_iterate_done((int) worker_id);
623}
624
625ParNewGeneration::ParNewGeneration(ReservedSpace rs,
626 size_t initial_byte_size,
627 size_t min_byte_size,
628 size_t max_byte_size)
629 : DefNewGeneration(rs, initial_byte_size, min_byte_size, max_byte_size, "CMS young collection pauses"),
630 _plab_stats("Young", YoungPLABSize, PLABWeight),
631 _overflow_list(NULL),
632 _is_alive_closure(this)
633{
634 NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)
635 NOT_PRODUCT(_num_par_pushes = 0;)
636 _task_queues = new ObjToScanQueueSet(ParallelGCThreads);
637 guarantee(_task_queues != NULL, "task_queues allocation failure.");
638
639 for (uint i = 0; i < ParallelGCThreads; i++) {
640 ObjToScanQueue *q = new ObjToScanQueue();
641 guarantee(q != NULL, "work_queue Allocation failure.");
642 _task_queues->register_queue(i, q);
643 }
644
645 for (uint i = 0; i < ParallelGCThreads; i++) {
646 _task_queues->queue(i)->initialize();
647 }
648
649 _overflow_stacks = NULL;
650 if (ParGCUseLocalOverflow) {
651 // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal with ','
652 typedef Stack<oop, mtGC> GCOopStack;
653
654 _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC);
655 for (size_t i = 0; i < ParallelGCThreads; ++i) {
656 new (_overflow_stacks + i) Stack<oop, mtGC>();
657 }
658 }
659
660 if (UsePerfData) {
661 EXCEPTION_MARK;
662 ResourceMark rm;
663
664 const char* cname =
665 PerfDataManager::counter_name(_gen_counters->name_space(), "threads");
666 PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None,
667 ParallelGCThreads, CHECK);
668 }
669}
670
671// ParNewGeneration::
672ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :
673 DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {}
674
675template <class T>
676void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) {
677#ifdef ASSERT
678 {
679 oop obj = RawAccess<IS_NOT_NULL>::oop_load(p);
680 // We never expect to see a null reference being processed
681 // as a weak reference.
682 assert(oopDesc::is_oop(obj), "expected an oop while scanning weak refs");
683 }
684#endif // ASSERT
685
686 Devirtualizer::do_oop_no_verify(_par_cl, p);
687
688 if (CMSHeap::heap()->is_in_reserved(p)) {
689 oop obj = RawAccess<IS_NOT_NULL>::oop_load(p);;
690 _rs->write_ref_field_gc_par(p, obj);
691 }
692}
693
694void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); }
695void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); }
696
697// ParNewGeneration::
698KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) :
699 DefNewGeneration::KeepAliveClosure(cl) {}
700
701template <class T>
702void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) {
703#ifdef ASSERT
704 {
705 oop obj = RawAccess<IS_NOT_NULL>::oop_load(p);
706 // We never expect to see a null reference being processed
707 // as a weak reference.
708 assert(oopDesc::is_oop(obj), "expected an oop while scanning weak refs");
709 }
710#endif // ASSERT
711
712 Devirtualizer::do_oop_no_verify(_cl, p);
713
714 if (CMSHeap::heap()->is_in_reserved(p)) {
715 oop obj = RawAccess<IS_NOT_NULL>::oop_load(p);
716 _rs->write_ref_field_gc_par(p, obj);
717 }
718}
719
720void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); }
721void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); }
722
723template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) {
724 T heap_oop = RawAccess<>::oop_load(p);
725 if (!CompressedOops::is_null(heap_oop)) {
726 oop obj = CompressedOops::decode_not_null(heap_oop);
727 if ((HeapWord*)obj < _boundary) {
728 assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?");
729 oop new_obj = obj->is_forwarded()
730 ? obj->forwardee()
731 : _g->DefNewGeneration::copy_to_survivor_space(obj);
732 RawAccess<IS_NOT_NULL>::oop_store(p, new_obj);
733 }
734 if (_gc_barrier) {
735 // If p points to a younger generation, mark the card.
736 if ((HeapWord*)obj < _gen_boundary) {
737 _rs->write_ref_field_gc_par(p, obj);
738 }
739 }
740 }
741}
742
743void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
744void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
745
746class ParNewRefProcTaskProxy: public AbstractGangTask {
747 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
748public:
749 ParNewRefProcTaskProxy(ProcessTask& task,
750 ParNewGeneration& young_gen,
751 Generation& old_gen,
752 HeapWord* young_old_boundary,
753 ParScanThreadStateSet& state_set);
754
755private:
756 virtual void work(uint worker_id);
757private:
758 ParNewGeneration& _young_gen;
759 ProcessTask& _task;
760 Generation& _old_gen;
761 HeapWord* _young_old_boundary;
762 ParScanThreadStateSet& _state_set;
763};
764
765ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(ProcessTask& task,
766 ParNewGeneration& young_gen,
767 Generation& old_gen,
768 HeapWord* young_old_boundary,
769 ParScanThreadStateSet& state_set)
770 : AbstractGangTask("ParNewGeneration parallel reference processing"),
771 _young_gen(young_gen),
772 _task(task),
773 _old_gen(old_gen),
774 _young_old_boundary(young_old_boundary),
775 _state_set(state_set)
776{ }
777
778void ParNewRefProcTaskProxy::work(uint worker_id) {
779 ResourceMark rm;
780 HandleMark hm;
781 ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id);
782 par_scan_state.set_young_old_boundary(_young_old_boundary);
783 _task.work(worker_id, par_scan_state.is_alive_closure(),
784 par_scan_state.keep_alive_closure(),
785 par_scan_state.evacuate_followers_closure());
786}
787
788void ParNewRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers) {
789 CMSHeap* gch = CMSHeap::heap();
790 WorkGang* workers = gch->workers();
791 assert(workers != NULL, "Need parallel worker threads.");
792 assert(workers->active_workers() == ergo_workers,
793 "Ergonomically chosen workers (%u) must be equal to active workers (%u)",
794 ergo_workers, workers->active_workers());
795 _state_set.reset(workers->active_workers(), _young_gen.promotion_failed());
796 ParNewRefProcTaskProxy rp_task(task, _young_gen, _old_gen,
797 _young_gen.reserved().end(), _state_set);
798 workers->run_task(&rp_task, workers->active_workers());
799 _state_set.reset(0 /* bad value in debug if not reset */,
800 _young_gen.promotion_failed());
801}
802
803void ParNewRefProcTaskExecutor::set_single_threaded_mode() {
804 _state_set.flush();
805 CMSHeap* heap = CMSHeap::heap();
806 heap->save_marks();
807}
808
809ScanClosureWithParBarrier::
810ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :
811 OopsInClassLoaderDataOrGenClosure(g), _g(g), _boundary(g->reserved().end()), _gc_barrier(gc_barrier)
812{ }
813
814template <typename OopClosureType1, typename OopClosureType2>
815EvacuateFollowersClosureGeneral<OopClosureType1, OopClosureType2>::
816EvacuateFollowersClosureGeneral(CMSHeap* heap,
817 OopClosureType1* cur,
818 OopClosureType2* older) :
819 _heap(heap),
820 _scan_cur_or_nonheap(cur), _scan_older(older)
821{ }
822
823template <typename OopClosureType1, typename OopClosureType2>
824void EvacuateFollowersClosureGeneral<OopClosureType1, OopClosureType2>::do_void() {
825 do {
826 _heap->oop_since_save_marks_iterate(_scan_cur_or_nonheap,
827 _scan_older);
828 } while (!_heap->no_allocs_since_save_marks());
829}
830
831// A Generation that does parallel young-gen collection.
832
833void ParNewGeneration::handle_promotion_failed(CMSHeap* gch, ParScanThreadStateSet& thread_state_set) {
834 assert(_promo_failure_scan_stack.is_empty(), "post condition");
835 _promo_failure_scan_stack.clear(true); // Clear cached segments.
836
837 remove_forwarding_pointers();
838 log_info(gc, promotion)("Promotion failed");
839 // All the spaces are in play for mark-sweep.
840 swap_spaces(); // Make life simpler for CMS || rescan; see 6483690.
841 from()->set_next_compaction_space(to());
842 gch->set_incremental_collection_failed();
843 // Inform the next generation that a promotion failure occurred.
844 _old_gen->promotion_failure_occurred();
845
846 // Trace promotion failure in the parallel GC threads
847 thread_state_set.trace_promotion_failed(gc_tracer());
848 // Single threaded code may have reported promotion failure to the global state
849 if (_promotion_failed_info.has_failed()) {
850 _gc_tracer.report_promotion_failed(_promotion_failed_info);
851 }
852 // Reset the PromotionFailureALot counters.
853 NOT_PRODUCT(gch->reset_promotion_should_fail();)
854}
855
856void ParNewGeneration::collect(bool full,
857 bool clear_all_soft_refs,
858 size_t size,
859 bool is_tlab) {
860 assert(full || size > 0, "otherwise we don't want to collect");
861
862 CMSHeap* gch = CMSHeap::heap();
863
864 _gc_timer->register_gc_start();
865
866 AdaptiveSizePolicy* size_policy = gch->size_policy();
867 WorkGang* workers = gch->workers();
868 assert(workers != NULL, "Need workgang for parallel work");
869 uint active_workers =
870 WorkerPolicy::calc_active_workers(workers->total_workers(),
871 workers->active_workers(),
872 Threads::number_of_non_daemon_threads());
873 active_workers = workers->update_active_workers(active_workers);
874 log_info(gc,task)("Using %u workers of %u for evacuation", active_workers, workers->total_workers());
875
876 _old_gen = gch->old_gen();
877
878 // If the next generation is too full to accommodate worst-case promotion
879 // from this generation, pass on collection; let the next generation
880 // do it.
881 if (!collection_attempt_is_safe()) {
882 gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one
883 return;
884 }
885 assert(to()->is_empty(), "Else not collection_attempt_is_safe");
886
887 _gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());
888 gch->trace_heap_before_gc(gc_tracer());
889
890 init_assuming_no_promotion_failure();
891
892 GCTraceTime(Trace, gc, phases) t1("ParNew", NULL, gch->gc_cause());
893
894 age_table()->clear();
895 to()->clear(SpaceDecorator::Mangle);
896
897 gch->save_marks();
898
899 // Set the correct parallelism (number of queues) in the reference processor
900 ref_processor()->set_active_mt_degree(active_workers);
901
902 // Need to initialize the preserved marks before the ThreadStateSet c'tor.
903 _preserved_marks_set.init(active_workers);
904
905 // Always set the terminator for the active number of workers
906 // because only those workers go through the termination protocol.
907 TaskTerminator _term(active_workers, task_queues());
908 ParScanThreadStateSet thread_state_set(active_workers,
909 *to(), *this, *_old_gen, *task_queues(),
910 _overflow_stacks, _preserved_marks_set,
911 desired_plab_sz(), _term);
912
913 thread_state_set.reset(active_workers, promotion_failed());
914
915 {
916 StrongRootsScope srs(active_workers);
917
918 ParNewGenTask tsk(this, _old_gen, reserved().end(), &thread_state_set, &srs);
919 gch->rem_set()->prepare_for_younger_refs_iterate(true);
920 // It turns out that even when we're using 1 thread, doing the work in a
921 // separate thread causes wide variance in run times. We can't help this
922 // in the multi-threaded case, but we special-case n=1 here to get
923 // repeatable measurements of the 1-thread overhead of the parallel code.
924 // Might multiple workers ever be used? If yes, initialization
925 // has been done such that the single threaded path should not be used.
926 if (workers->total_workers() > 1) {
927 workers->run_task(&tsk);
928 } else {
929 tsk.work(0);
930 }
931 }
932
933 thread_state_set.reset(0 /* Bad value in debug if not reset */,
934 promotion_failed());
935
936 // Trace and reset failed promotion info.
937 if (promotion_failed()) {
938 thread_state_set.trace_promotion_failed(gc_tracer());
939 }
940
941 // Process (weak) reference objects found during scavenge.
942 ReferenceProcessor* rp = ref_processor();
943 IsAliveClosure is_alive(this);
944 ScanWeakRefClosure scan_weak_ref(this);
945 KeepAliveClosure keep_alive(&scan_weak_ref);
946 ScanClosure scan_without_gc_barrier(this, false);
947 ScanClosureWithParBarrier scan_with_gc_barrier(this, true);
948 set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);
949 EvacuateFollowersClosureGeneral<ScanClosure, ScanClosureWithParBarrier> evacuate_followers(
950 gch, &scan_without_gc_barrier, &scan_with_gc_barrier);
951 rp->setup_policy(clear_all_soft_refs);
952 // Can the mt_degree be set later (at run_task() time would be best)?
953 rp->set_active_mt_degree(active_workers);
954 ReferenceProcessorStats stats;
955 ReferenceProcessorPhaseTimes pt(_gc_timer, rp->max_num_queues());
956 if (rp->processing_is_mt()) {
957 ParNewRefProcTaskExecutor task_executor(*this, *_old_gen, thread_state_set);
958 stats = rp->process_discovered_references(&is_alive, &keep_alive,
959 &evacuate_followers, &task_executor,
960 &pt);
961 } else {
962 thread_state_set.flush();
963 gch->save_marks();
964 stats = rp->process_discovered_references(&is_alive, &keep_alive,
965 &evacuate_followers, NULL,
966 &pt);
967 }
968 _gc_tracer.report_gc_reference_stats(stats);
969 _gc_tracer.report_tenuring_threshold(tenuring_threshold());
970 pt.print_all_references();
971
972 assert(gch->no_allocs_since_save_marks(), "evacuation should be done at this point");
973
974 WeakProcessor::weak_oops_do(&is_alive, &keep_alive);
975
976 // Verify that the usage of keep_alive only forwarded
977 // the oops and did not find anything new to copy.
978 assert(gch->no_allocs_since_save_marks(), "unexpectedly copied objects");
979
980 if (!promotion_failed()) {
981 // Swap the survivor spaces.
982 eden()->clear(SpaceDecorator::Mangle);
983 from()->clear(SpaceDecorator::Mangle);
984 if (ZapUnusedHeapArea) {
985 // This is now done here because of the piece-meal mangling which
986 // can check for valid mangling at intermediate points in the
987 // collection(s). When a young collection fails to collect
988 // sufficient space resizing of the young generation can occur
989 // and redistribute the spaces in the young generation. Mangle
990 // here so that unzapped regions don't get distributed to
991 // other spaces.
992 to()->mangle_unused_area();
993 }
994 swap_spaces();
995
996 // A successful scavenge should restart the GC time limit count which is
997 // for full GC's.
998 size_policy->reset_gc_overhead_limit_count();
999
1000 assert(to()->is_empty(), "to space should be empty now");
1001
1002 adjust_desired_tenuring_threshold();
1003 } else {
1004 handle_promotion_failed(gch, thread_state_set);
1005 }
1006 _preserved_marks_set.reclaim();
1007 // set new iteration safe limit for the survivor spaces
1008 from()->set_concurrent_iteration_safe_limit(from()->top());
1009 to()->set_concurrent_iteration_safe_limit(to()->top());
1010
1011 plab_stats()->adjust_desired_plab_sz();
1012
1013 TASKQUEUE_STATS_ONLY(thread_state_set.print_termination_stats());
1014 TASKQUEUE_STATS_ONLY(thread_state_set.print_taskqueue_stats());
1015
1016 // We need to use a monotonically non-decreasing time in ms
1017 // or we will see time-warp warnings and os::javaTimeMillis()
1018 // does not guarantee monotonicity.
1019 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1020 update_time_of_last_gc(now);
1021
1022 rp->set_enqueuing_is_done(true);
1023 rp->verify_no_references_recorded();
1024
1025 gch->trace_heap_after_gc(gc_tracer());
1026
1027 _gc_timer->register_gc_end();
1028
1029 _gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
1030}
1031
1032size_t ParNewGeneration::desired_plab_sz() {
1033 return _plab_stats.desired_plab_sz(CMSHeap::heap()->workers()->active_workers());
1034}
1035
1036static int sum;
1037void ParNewGeneration::waste_some_time() {
1038 for (int i = 0; i < 100; i++) {
1039 sum += i;
1040 }
1041}
1042
1043static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4);
1044
1045// Because of concurrency, there are times where an object for which
1046// "is_forwarded()" is true contains an "interim" forwarding pointer
1047// value. Such a value will soon be overwritten with a real value.
1048// This method requires "obj" to have a forwarding pointer, and waits, if
1049// necessary for a real one to be inserted, and returns it.
1050
1051oop ParNewGeneration::real_forwardee(oop obj) {
1052 oop forward_ptr = obj->forwardee();
1053 if (forward_ptr != ClaimedForwardPtr) {
1054 return forward_ptr;
1055 } else {
1056 return real_forwardee_slow(obj);
1057 }
1058}
1059
1060oop ParNewGeneration::real_forwardee_slow(oop obj) {
1061 // Spin-read if it is claimed but not yet written by another thread.
1062 oop forward_ptr = obj->forwardee();
1063 while (forward_ptr == ClaimedForwardPtr) {
1064 waste_some_time();
1065 assert(obj->is_forwarded(), "precondition");
1066 forward_ptr = obj->forwardee();
1067 }
1068 return forward_ptr;
1069}
1070
1071// Multiple GC threads may try to promote an object. If the object
1072// is successfully promoted, a forwarding pointer will be installed in
1073// the object in the young generation. This method claims the right
1074// to install the forwarding pointer before it copies the object,
1075// thus avoiding the need to undo the copy as in
1076// copy_to_survivor_space_avoiding_with_undo.
1077
1078oop ParNewGeneration::copy_to_survivor_space(ParScanThreadState* par_scan_state,
1079 oop old,
1080 size_t sz,
1081 markOop m) {
1082 // In the sequential version, this assert also says that the object is
1083 // not forwarded. That might not be the case here. It is the case that
1084 // the caller observed it to be not forwarded at some time in the past.
1085 assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1086
1087 // The sequential code read "old->age()" below. That doesn't work here,
1088 // since the age is in the mark word, and that might be overwritten with
1089 // a forwarding pointer by a parallel thread. So we must save the mark
1090 // word in a local and then analyze it.
1091 oopDesc dummyOld;
1092 dummyOld.set_mark_raw(m);
1093 assert(!dummyOld.is_forwarded(),
1094 "should not be called with forwarding pointer mark word.");
1095
1096 oop new_obj = NULL;
1097 oop forward_ptr;
1098
1099 // Try allocating obj in to-space (unless too old)
1100 if (dummyOld.age() < tenuring_threshold()) {
1101 new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1102 }
1103
1104 if (new_obj == NULL) {
1105 // Either to-space is full or we decided to promote try allocating obj tenured
1106
1107 // Attempt to install a null forwarding pointer (atomically),
1108 // to claim the right to install the real forwarding pointer.
1109 forward_ptr = old->forward_to_atomic(ClaimedForwardPtr, m);
1110 if (forward_ptr != NULL) {
1111 // someone else beat us to it.
1112 return real_forwardee(old);
1113 }
1114
1115 if (!_promotion_failed) {
1116 new_obj = _old_gen->par_promote(par_scan_state->thread_num(),
1117 old, m, sz);
1118 }
1119
1120 if (new_obj == NULL) {
1121 // promotion failed, forward to self
1122 _promotion_failed = true;
1123 new_obj = old;
1124
1125 par_scan_state->preserved_marks()->push_if_necessary(old, m);
1126 par_scan_state->register_promotion_failure(sz);
1127 }
1128
1129 old->forward_to(new_obj);
1130 forward_ptr = NULL;
1131 } else {
1132 // Is in to-space; do copying ourselves.
1133 Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1134 assert(CMSHeap::heap()->is_in_reserved(new_obj), "illegal forwarding pointer value.");
1135 forward_ptr = old->forward_to_atomic(new_obj, m);
1136 // Restore the mark word copied above.
1137 new_obj->set_mark_raw(m);
1138 // Increment age if obj still in new generation
1139 new_obj->incr_age();
1140 par_scan_state->age_table()->add(new_obj, sz);
1141 }
1142 assert(new_obj != NULL, "just checking");
1143
1144 // This code must come after the CAS test, or it will print incorrect
1145 // information.
1146 log_develop_trace(gc, scavenge)("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}",
1147 is_in_reserved(new_obj) ? "copying" : "tenuring",
1148 new_obj->klass()->internal_name(), p2i(old), p2i(new_obj), new_obj->size());
1149
1150 if (forward_ptr == NULL) {
1151 oop obj_to_push = new_obj;
1152 if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1153 // Length field used as index of next element to be scanned.
1154 // Real length can be obtained from real_forwardee()
1155 arrayOop(old)->set_length(0);
1156 obj_to_push = old;
1157 assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1158 "push forwarded object");
1159 }
1160 // Push it on one of the queues of to-be-scanned objects.
1161 bool simulate_overflow = false;
1162 NOT_PRODUCT(
1163 if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1164 // simulate a stack overflow
1165 simulate_overflow = true;
1166 }
1167 )
1168 if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1169 // Add stats for overflow pushes.
1170 log_develop_trace(gc)("Queue Overflow");
1171 push_on_overflow_list(old, par_scan_state);
1172 TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1173 }
1174
1175 return new_obj;
1176 }
1177
1178 // Oops. Someone beat us to it. Undo the allocation. Where did we
1179 // allocate it?
1180 if (is_in_reserved(new_obj)) {
1181 // Must be in to_space.
1182 assert(to()->is_in_reserved(new_obj), "Checking");
1183 if (forward_ptr == ClaimedForwardPtr) {
1184 // Wait to get the real forwarding pointer value.
1185 forward_ptr = real_forwardee(old);
1186 }
1187 par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1188 }
1189
1190 return forward_ptr;
1191}
1192
1193#ifndef PRODUCT
1194// It's OK to call this multi-threaded; the worst thing
1195// that can happen is that we'll get a bunch of closely
1196// spaced simulated overflows, but that's OK, in fact
1197// probably good as it would exercise the overflow code
1198// under contention.
1199bool ParNewGeneration::should_simulate_overflow() {
1200 if (_overflow_counter-- <= 0) { // just being defensive
1201 _overflow_counter = ParGCWorkQueueOverflowInterval;
1202 return true;
1203 } else {
1204 return false;
1205 }
1206}
1207#endif
1208
1209// In case we are using compressed oops, we need to be careful.
1210// If the object being pushed is an object array, then its length
1211// field keeps track of the "grey boundary" at which the next
1212// incremental scan will be done (see ParGCArrayScanChunk).
1213// When using compressed oops, this length field is kept in the
1214// lower 32 bits of the erstwhile klass word and cannot be used
1215// for the overflow chaining pointer (OCP below). As such the OCP
1216// would itself need to be compressed into the top 32-bits in this
1217// case. Unfortunately, see below, in the event that we have a
1218// promotion failure, the node to be pushed on the list can be
1219// outside of the Java heap, so the heap-based pointer compression
1220// would not work (we would have potential aliasing between C-heap
1221// and Java-heap pointers). For this reason, when using compressed
1222// oops, we simply use a worker-thread-local, non-shared overflow
1223// list in the form of a growable array, with a slightly different
1224// overflow stack draining strategy. If/when we start using fat
1225// stacks here, we can go back to using (fat) pointer chains
1226// (although some performance comparisons would be useful since
1227// single global lists have their own performance disadvantages
1228// as we were made painfully aware not long ago, see 6786503).
1229#define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
1230void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {
1231 assert(is_in_reserved(from_space_obj), "Should be from this generation");
1232 if (ParGCUseLocalOverflow) {
1233 // In the case of compressed oops, we use a private, not-shared
1234 // overflow stack.
1235 par_scan_state->push_on_overflow_stack(from_space_obj);
1236 } else {
1237 assert(!UseCompressedOops, "Error");
1238 // if the object has been forwarded to itself, then we cannot
1239 // use the klass pointer for the linked list. Instead we have
1240 // to allocate an oopDesc in the C-Heap and use that for the linked list.
1241 // XXX This is horribly inefficient when a promotion failure occurs
1242 // and should be fixed. XXX FIX ME !!!
1243#ifndef PRODUCT
1244 Atomic::inc(&_num_par_pushes);
1245 assert(_num_par_pushes > 0, "Tautology");
1246#endif
1247 if (from_space_obj->forwardee() == from_space_obj) {
1248 oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC);
1249 listhead->forward_to(from_space_obj);
1250 from_space_obj = listhead;
1251 }
1252 oop observed_overflow_list = _overflow_list;
1253 oop cur_overflow_list;
1254 do {
1255 cur_overflow_list = observed_overflow_list;
1256 if (cur_overflow_list != BUSY) {
1257 from_space_obj->set_klass_to_list_ptr(cur_overflow_list);
1258 } else {
1259 from_space_obj->set_klass_to_list_ptr(NULL);
1260 }
1261 observed_overflow_list =
1262 Atomic::cmpxchg((oopDesc*)from_space_obj, &_overflow_list, (oopDesc*)cur_overflow_list);
1263 } while (cur_overflow_list != observed_overflow_list);
1264 }
1265}
1266
1267bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
1268 bool res;
1269
1270 if (ParGCUseLocalOverflow) {
1271 res = par_scan_state->take_from_overflow_stack();
1272 } else {
1273 assert(!UseCompressedOops, "Error");
1274 res = take_from_overflow_list_work(par_scan_state);
1275 }
1276 return res;
1277}
1278
1279
1280// *NOTE*: The overflow list manipulation code here and
1281// in CMSCollector:: are very similar in shape,
1282// except that in the CMS case we thread the objects
1283// directly into the list via their mark word, and do
1284// not need to deal with special cases below related
1285// to chunking of object arrays and promotion failure
1286// handling.
1287// CR 6797058 has been filed to attempt consolidation of
1288// the common code.
1289// Because of the common code, if you make any changes in
1290// the code below, please check the CMS version to see if
1291// similar changes might be needed.
1292// See CMSCollector::par_take_from_overflow_list() for
1293// more extensive documentation comments.
1294bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) {
1295 ObjToScanQueue* work_q = par_scan_state->work_queue();
1296 // How many to take?
1297 size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
1298 (size_t)ParGCDesiredObjsFromOverflowList);
1299
1300 assert(!UseCompressedOops, "Error");
1301 assert(par_scan_state->overflow_stack() == NULL, "Error");
1302 if (_overflow_list == NULL) return false;
1303
1304 // Otherwise, there was something there; try claiming the list.
1305 oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
1306 // Trim off a prefix of at most objsFromOverflow items
1307 Thread* tid = Thread::current();
1308 size_t spin_count = ParallelGCThreads;
1309 size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100);
1310 for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) {
1311 // someone grabbed it before we did ...
1312 // ... we spin for a short while...
1313 os::sleep(tid, sleep_time_millis, false);
1314 if (_overflow_list == NULL) {
1315 // nothing left to take
1316 return false;
1317 } else if (_overflow_list != BUSY) {
1318 // try and grab the prefix
1319 prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
1320 }
1321 }
1322 if (prefix == NULL || prefix == BUSY) {
1323 // Nothing to take or waited long enough
1324 if (prefix == NULL) {
1325 // Write back the NULL in case we overwrote it with BUSY above
1326 // and it is still the same value.
1327 (void) Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
1328 }
1329 return false;
1330 }
1331 assert(prefix != NULL && prefix != BUSY, "Error");
1332 oop cur = prefix;
1333 for (size_t i = 1; i < objsFromOverflow; ++i) {
1334 oop next = cur->list_ptr_from_klass();
1335 if (next == NULL) break;
1336 cur = next;
1337 }
1338 assert(cur != NULL, "Loop postcondition");
1339
1340 // Reattach remaining (suffix) to overflow list
1341 oop suffix = cur->list_ptr_from_klass();
1342 if (suffix == NULL) {
1343 // Write back the NULL in lieu of the BUSY we wrote
1344 // above and it is still the same value.
1345 if (_overflow_list == BUSY) {
1346 (void) Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
1347 }
1348 } else {
1349 assert(suffix != BUSY, "Error");
1350 // suffix will be put back on global list
1351 cur->set_klass_to_list_ptr(NULL); // break off suffix
1352 // It's possible that the list is still in the empty(busy) state
1353 // we left it in a short while ago; in that case we may be
1354 // able to place back the suffix.
1355 oop observed_overflow_list = _overflow_list;
1356 oop cur_overflow_list = observed_overflow_list;
1357 bool attached = false;
1358 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
1359 observed_overflow_list =
1360 Atomic::cmpxchg((oopDesc*)suffix, &_overflow_list, (oopDesc*)cur_overflow_list);
1361 if (cur_overflow_list == observed_overflow_list) {
1362 attached = true;
1363 break;
1364 } else cur_overflow_list = observed_overflow_list;
1365 }
1366 if (!attached) {
1367 // Too bad, someone else got in in between; we'll need to do a splice.
1368 // Find the last item of suffix list
1369 oop last = suffix;
1370 while (true) {
1371 oop next = last->list_ptr_from_klass();
1372 if (next == NULL) break;
1373 last = next;
1374 }
1375 // Atomically prepend suffix to current overflow list
1376 observed_overflow_list = _overflow_list;
1377 do {
1378 cur_overflow_list = observed_overflow_list;
1379 if (cur_overflow_list != BUSY) {
1380 // Do the splice ...
1381 last->set_klass_to_list_ptr(cur_overflow_list);
1382 } else { // cur_overflow_list == BUSY
1383 last->set_klass_to_list_ptr(NULL);
1384 }
1385 observed_overflow_list =
1386 Atomic::cmpxchg((oopDesc*)suffix, &_overflow_list, (oopDesc*)cur_overflow_list);
1387 } while (cur_overflow_list != observed_overflow_list);
1388 }
1389 }
1390
1391 // Push objects on prefix list onto this thread's work queue
1392 assert(prefix != NULL && prefix != BUSY, "program logic");
1393 cur = prefix;
1394 ssize_t n = 0;
1395 while (cur != NULL) {
1396 oop obj_to_push = cur->forwardee();
1397 oop next = cur->list_ptr_from_klass();
1398 cur->set_klass(obj_to_push->klass());
1399 // This may be an array object that is self-forwarded. In that case, the list pointer
1400 // space, cur, is not in the Java heap, but rather in the C-heap and should be freed.
1401 if (!is_in_reserved(cur)) {
1402 // This can become a scaling bottleneck when there is work queue overflow coincident
1403 // with promotion failure.
1404 oopDesc* f = cur;
1405 FREE_C_HEAP_ARRAY(oopDesc, f);
1406 } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) {
1407 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
1408 obj_to_push = cur;
1409 }
1410 bool ok = work_q->push(obj_to_push);
1411 assert(ok, "Should have succeeded");
1412 cur = next;
1413 n++;
1414 }
1415 TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n));
1416#ifndef PRODUCT
1417 assert(_num_par_pushes >= n, "Too many pops?");
1418 Atomic::sub(n, &_num_par_pushes);
1419#endif
1420 return true;
1421}
1422#undef BUSY
1423
1424void ParNewGeneration::ref_processor_init() {
1425 if (_ref_processor == NULL) {
1426 // Allocate and initialize a reference processor
1427 _span_based_discoverer.set_span(_reserved);
1428 _ref_processor =
1429 new ReferenceProcessor(&_span_based_discoverer, // span
1430 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
1431 ParallelGCThreads, // mt processing degree
1432 refs_discovery_is_mt(), // mt discovery
1433 ParallelGCThreads, // mt discovery degree
1434 refs_discovery_is_atomic(), // atomic_discovery
1435 NULL, // is_alive_non_header
1436 false); // disable adjusting number of processing threads
1437 }
1438}
1439
1440const char* ParNewGeneration::name() const {
1441 return "par new generation";
1442}
1443
1444void ParNewGeneration::restore_preserved_marks() {
1445 SharedRestorePreservedMarksTaskExecutor task_executor(CMSHeap::heap()->workers());
1446 _preserved_marks_set.restore(&task_executor);
1447}
1448