1/*
2 * Copyright (c) 1997, 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#ifndef SHARE_GC_SHARED_GENERATION_HPP
26#define SHARE_GC_SHARED_GENERATION_HPP
27
28#include "gc/shared/collectorCounters.hpp"
29#include "gc/shared/referenceProcessor.hpp"
30#include "logging/log.hpp"
31#include "memory/allocation.hpp"
32#include "memory/memRegion.hpp"
33#include "memory/virtualspace.hpp"
34#include "runtime/mutex.hpp"
35#include "runtime/perfData.hpp"
36
37// A Generation models a heap area for similarly-aged objects.
38// It will contain one ore more spaces holding the actual objects.
39//
40// The Generation class hierarchy:
41//
42// Generation - abstract base class
43// - DefNewGeneration - allocation area (copy collected)
44// - ParNewGeneration - a DefNewGeneration that is collected by
45// several threads
46// - CardGeneration - abstract class adding offset array behavior
47// - TenuredGeneration - tenured (old object) space (markSweepCompact)
48// - ConcurrentMarkSweepGeneration - Mostly Concurrent Mark Sweep Generation
49// (Detlefs-Printezis refinement of
50// Boehm-Demers-Schenker)
51//
52// The system configurations currently allowed are:
53//
54// DefNewGeneration + TenuredGeneration
55//
56// ParNewGeneration + ConcurrentMarkSweepGeneration
57//
58
59class DefNewGeneration;
60class GCMemoryManager;
61class GenerationSpec;
62class CompactibleSpace;
63class ContiguousSpace;
64class CompactPoint;
65class OopsInGenClosure;
66class OopClosure;
67class ScanClosure;
68class FastScanClosure;
69class GenCollectedHeap;
70class GCStats;
71
72// A "ScratchBlock" represents a block of memory in one generation usable by
73// another. It represents "num_words" free words, starting at and including
74// the address of "this".
75struct ScratchBlock {
76 ScratchBlock* next;
77 size_t num_words;
78 HeapWord scratch_space[1]; // Actually, of size "num_words-2" (assuming
79 // first two fields are word-sized.)
80};
81
82class Generation: public CHeapObj<mtGC> {
83 friend class VMStructs;
84 private:
85 jlong _time_of_last_gc; // time when last gc on this generation happened (ms)
86 MemRegion _prev_used_region; // for collectors that want to "remember" a value for
87 // used region at some specific point during collection.
88
89 GCMemoryManager* _gc_manager;
90
91 protected:
92 // Minimum and maximum addresses for memory reserved (not necessarily
93 // committed) for generation.
94 // Used by card marking code. Must not overlap with address ranges of
95 // other generations.
96 MemRegion _reserved;
97
98 // Memory area reserved for generation
99 VirtualSpace _virtual_space;
100
101 // ("Weak") Reference processing support
102 SpanSubjectToDiscoveryClosure _span_based_discoverer;
103 ReferenceProcessor* _ref_processor;
104
105 // Performance Counters
106 CollectorCounters* _gc_counters;
107
108 // Statistics for garbage collection
109 GCStats* _gc_stats;
110
111 // Initialize the generation.
112 Generation(ReservedSpace rs, size_t initial_byte_size);
113
114 // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in
115 // "sp" that point into younger generations.
116 // The iteration is only over objects allocated at the start of the
117 // iterations; objects allocated as a result of applying the closure are
118 // not included.
119 void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl, uint n_threads);
120
121 public:
122 // The set of possible generation kinds.
123 enum Name {
124 DefNew,
125 ParNew,
126 MarkSweepCompact,
127 ConcurrentMarkSweep,
128 Other
129 };
130
131 enum SomePublicConstants {
132 // Generations are GenGrain-aligned and have size that are multiples of
133 // GenGrain.
134 // Note: on ARM we add 1 bit for card_table_base to be properly aligned
135 // (we expect its low byte to be zero - see implementation of post_barrier)
136 LogOfGenGrain = 16 ARM32_ONLY(+1),
137 GenGrain = 1 << LogOfGenGrain
138 };
139
140 // allocate and initialize ("weak") refs processing support
141 virtual void ref_processor_init();
142 void set_ref_processor(ReferenceProcessor* rp) {
143 assert(_ref_processor == NULL, "clobbering existing _ref_processor");
144 _ref_processor = rp;
145 }
146
147 virtual Generation::Name kind() { return Generation::Other; }
148
149 // This properly belongs in the collector, but for now this
150 // will do.
151 virtual bool refs_discovery_is_atomic() const { return true; }
152 virtual bool refs_discovery_is_mt() const { return false; }
153
154 // Space inquiries (results in bytes)
155 size_t initial_size();
156 virtual size_t capacity() const = 0; // The maximum number of object bytes the
157 // generation can currently hold.
158 virtual size_t used() const = 0; // The number of used bytes in the gen.
159 virtual size_t free() const = 0; // The number of free bytes in the gen.
160
161 // Support for java.lang.Runtime.maxMemory(); see CollectedHeap.
162 // Returns the total number of bytes available in a generation
163 // for the allocation of objects.
164 virtual size_t max_capacity() const;
165
166 // If this is a young generation, the maximum number of bytes that can be
167 // allocated in this generation before a GC is triggered.
168 virtual size_t capacity_before_gc() const { return 0; }
169
170 // The largest number of contiguous free bytes in the generation,
171 // including expansion (Assumes called at a safepoint.)
172 virtual size_t contiguous_available() const = 0;
173 // The largest number of contiguous free bytes in this or any higher generation.
174 virtual size_t max_contiguous_available() const;
175
176 // Returns true if promotions of the specified amount are
177 // likely to succeed without a promotion failure.
178 // Promotion of the full amount is not guaranteed but
179 // might be attempted in the worst case.
180 virtual bool promotion_attempt_is_safe(size_t max_promotion_in_bytes) const;
181
182 // For a non-young generation, this interface can be used to inform a
183 // generation that a promotion attempt into that generation failed.
184 // Typically used to enable diagnostic output for post-mortem analysis,
185 // but other uses of the interface are not ruled out.
186 virtual void promotion_failure_occurred() { /* does nothing */ }
187
188 // Return an estimate of the maximum allocation that could be performed
189 // in the generation without triggering any collection or expansion
190 // activity. It is "unsafe" because no locks are taken; the result
191 // should be treated as an approximation, not a guarantee, for use in
192 // heuristic resizing decisions.
193 virtual size_t unsafe_max_alloc_nogc() const = 0;
194
195 // Returns true if this generation cannot be expanded further
196 // without a GC. Override as appropriate.
197 virtual bool is_maximal_no_gc() const {
198 return _virtual_space.uncommitted_size() == 0;
199 }
200
201 MemRegion reserved() const { return _reserved; }
202
203 // Returns a region guaranteed to contain all the objects in the
204 // generation.
205 virtual MemRegion used_region() const { return _reserved; }
206
207 MemRegion prev_used_region() const { return _prev_used_region; }
208 virtual void save_used_region() { _prev_used_region = used_region(); }
209
210 // Returns "TRUE" iff "p" points into the committed areas in the generation.
211 // For some kinds of generations, this may be an expensive operation.
212 // To avoid performance problems stemming from its inadvertent use in
213 // product jvm's, we restrict its use to assertion checking or
214 // verification only.
215 virtual bool is_in(const void* p) const;
216
217 /* Returns "TRUE" iff "p" points into the reserved area of the generation. */
218 bool is_in_reserved(const void* p) const {
219 return _reserved.contains(p);
220 }
221
222 // If some space in the generation contains the given "addr", return a
223 // pointer to that space, else return "NULL".
224 virtual Space* space_containing(const void* addr) const;
225
226 // Iteration - do not use for time critical operations
227 virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0;
228
229 // Returns the first space, if any, in the generation that can participate
230 // in compaction, or else "NULL".
231 virtual CompactibleSpace* first_compaction_space() const = 0;
232
233 // Returns "true" iff this generation should be used to allocate an
234 // object of the given size. Young generations might
235 // wish to exclude very large objects, for example, since, if allocated
236 // often, they would greatly increase the frequency of young-gen
237 // collection.
238 virtual bool should_allocate(size_t word_size, bool is_tlab) {
239 bool result = false;
240 size_t overflow_limit = (size_t)1 << (BitsPerSize_t - LogHeapWordSize);
241 if (!is_tlab || supports_tlab_allocation()) {
242 result = (word_size > 0) && (word_size < overflow_limit);
243 }
244 return result;
245 }
246
247 // Allocate and returns a block of the requested size, or returns "NULL".
248 // Assumes the caller has done any necessary locking.
249 virtual HeapWord* allocate(size_t word_size, bool is_tlab) = 0;
250
251 // Like "allocate", but performs any necessary locking internally.
252 virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0;
253
254 // Some generation may offer a region for shared, contiguous allocation,
255 // via inlined code (by exporting the address of the top and end fields
256 // defining the extent of the contiguous allocation region.)
257
258 // This function returns "true" iff the heap supports this kind of
259 // allocation. (More precisely, this means the style of allocation that
260 // increments *top_addr()" with a CAS.) (Default is "no".)
261 // A generation that supports this allocation style must use lock-free
262 // allocation for *all* allocation, since there are times when lock free
263 // allocation will be concurrent with plain "allocate" calls.
264 virtual bool supports_inline_contig_alloc() const { return false; }
265
266 // These functions return the addresses of the fields that define the
267 // boundaries of the contiguous allocation area. (These fields should be
268 // physically near to one another.)
269 virtual HeapWord* volatile* top_addr() const { return NULL; }
270 virtual HeapWord** end_addr() const { return NULL; }
271
272 // Thread-local allocation buffers
273 virtual bool supports_tlab_allocation() const { return false; }
274 virtual size_t tlab_capacity() const {
275 guarantee(false, "Generation doesn't support thread local allocation buffers");
276 return 0;
277 }
278 virtual size_t tlab_used() const {
279 guarantee(false, "Generation doesn't support thread local allocation buffers");
280 return 0;
281 }
282 virtual size_t unsafe_max_tlab_alloc() const {
283 guarantee(false, "Generation doesn't support thread local allocation buffers");
284 return 0;
285 }
286
287 // "obj" is the address of an object in a younger generation. Allocate space
288 // for "obj" in the current (or some higher) generation, and copy "obj" into
289 // the newly allocated space, if possible, returning the result (or NULL if
290 // the allocation failed).
291 //
292 // The "obj_size" argument is just obj->size(), passed along so the caller can
293 // avoid repeating the virtual call to retrieve it.
294 virtual oop promote(oop obj, size_t obj_size);
295
296 // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote
297 // object "obj", whose original mark word was "m", and whose size is
298 // "word_sz". If possible, allocate space for "obj", copy obj into it
299 // (taking care to copy "m" into the mark word when done, since the mark
300 // word of "obj" may have been overwritten with a forwarding pointer, and
301 // also taking care to copy the klass pointer *last*. Returns the new
302 // object if successful, or else NULL.
303 virtual oop par_promote(int thread_num, oop obj, markOop m, size_t word_sz);
304
305 // Informs the current generation that all par_promote_alloc's in the
306 // collection have been completed; any supporting data structures can be
307 // reset. Default is to do nothing.
308 virtual void par_promote_alloc_done(int thread_num) {}
309
310 // Informs the current generation that all oop_since_save_marks_iterates
311 // performed by "thread_num" in the current collection, if any, have been
312 // completed; any supporting data structures can be reset. Default is to
313 // do nothing.
314 virtual void par_oop_since_save_marks_iterate_done(int thread_num) {}
315
316 // Returns "true" iff collect() should subsequently be called on this
317 // this generation. See comment below.
318 // This is a generic implementation which can be overridden.
319 //
320 // Note: in the current (1.4) implementation, when genCollectedHeap's
321 // incremental_collection_will_fail flag is set, all allocations are
322 // slow path (the only fast-path place to allocate is DefNew, which
323 // will be full if the flag is set).
324 // Thus, older generations which collect younger generations should
325 // test this flag and collect if it is set.
326 virtual bool should_collect(bool full,
327 size_t word_size,
328 bool is_tlab) {
329 return (full || should_allocate(word_size, is_tlab));
330 }
331
332 // Returns true if the collection is likely to be safely
333 // completed. Even if this method returns true, a collection
334 // may not be guaranteed to succeed, and the system should be
335 // able to safely unwind and recover from that failure, albeit
336 // at some additional cost.
337 virtual bool collection_attempt_is_safe() {
338 guarantee(false, "Are you sure you want to call this method?");
339 return true;
340 }
341
342 // Perform a garbage collection.
343 // If full is true attempt a full garbage collection of this generation.
344 // Otherwise, attempting to (at least) free enough space to support an
345 // allocation of the given "word_size".
346 virtual void collect(bool full,
347 bool clear_all_soft_refs,
348 size_t word_size,
349 bool is_tlab) = 0;
350
351 // Perform a heap collection, attempting to create (at least) enough
352 // space to support an allocation of the given "word_size". If
353 // successful, perform the allocation and return the resulting
354 // "oop" (initializing the allocated block). If the allocation is
355 // still unsuccessful, return "NULL".
356 virtual HeapWord* expand_and_allocate(size_t word_size,
357 bool is_tlab,
358 bool parallel = false) = 0;
359
360 // Some generations may require some cleanup or preparation actions before
361 // allowing a collection. The default is to do nothing.
362 virtual void gc_prologue(bool full) {}
363
364 // Some generations may require some cleanup actions after a collection.
365 // The default is to do nothing.
366 virtual void gc_epilogue(bool full) {}
367
368 // Save the high water marks for the used space in a generation.
369 virtual void record_spaces_top() {}
370
371 // Some generations may need to be "fixed-up" after some allocation
372 // activity to make them parsable again. The default is to do nothing.
373 virtual void ensure_parsability() {}
374
375 // Time (in ms) when we were last collected or now if a collection is
376 // in progress.
377 virtual jlong time_of_last_gc(jlong now) {
378 // Both _time_of_last_gc and now are set using a time source
379 // that guarantees monotonically non-decreasing values provided
380 // the underlying platform provides such a source. So we still
381 // have to guard against non-monotonicity.
382 NOT_PRODUCT(
383 if (now < _time_of_last_gc) {
384 log_warning(gc)("time warp: " JLONG_FORMAT " to " JLONG_FORMAT, _time_of_last_gc, now);
385 }
386 )
387 return _time_of_last_gc;
388 }
389
390 virtual void update_time_of_last_gc(jlong now) {
391 _time_of_last_gc = now;
392 }
393
394 // Generations may keep statistics about collection. This method
395 // updates those statistics. current_generation is the generation
396 // that was most recently collected. This allows the generation to
397 // decide what statistics are valid to collect. For example, the
398 // generation can decide to gather the amount of promoted data if
399 // the collection of the young generation has completed.
400 GCStats* gc_stats() const { return _gc_stats; }
401 virtual void update_gc_stats(Generation* current_generation, bool full) {}
402
403#if INCLUDE_SERIALGC
404 // Mark sweep support phase2
405 virtual void prepare_for_compaction(CompactPoint* cp);
406 // Mark sweep support phase3
407 virtual void adjust_pointers();
408 // Mark sweep support phase4
409 virtual void compact();
410 virtual void post_compact() { ShouldNotReachHere(); }
411#endif
412
413 // Support for CMS's rescan. In this general form we return a pointer
414 // to an abstract object that can be used, based on specific previously
415 // decided protocols, to exchange information between generations,
416 // information that may be useful for speeding up certain types of
417 // garbage collectors. A NULL value indicates to the client that
418 // no data recording is expected by the provider. The data-recorder is
419 // expected to be GC worker thread-local, with the worker index
420 // indicated by "thr_num".
421 virtual void* get_data_recorder(int thr_num) { return NULL; }
422 virtual void sample_eden_chunk() {}
423
424 // Some generations may require some cleanup actions before allowing
425 // a verification.
426 virtual void prepare_for_verify() {}
427
428 // Accessing "marks".
429
430 // This function gives a generation a chance to note a point between
431 // collections. For example, a contiguous generation might note the
432 // beginning allocation point post-collection, which might allow some later
433 // operations to be optimized.
434 virtual void save_marks() {}
435
436 // This function allows generations to initialize any "saved marks". That
437 // is, should only be called when the generation is empty.
438 virtual void reset_saved_marks() {}
439
440 // This function is "true" iff any no allocations have occurred in the
441 // generation since the last call to "save_marks".
442 virtual bool no_allocs_since_save_marks() = 0;
443
444 // The "requestor" generation is performing some garbage collection
445 // action for which it would be useful to have scratch space. If
446 // the target is not the requestor, no gc actions will be required
447 // of the target. The requestor promises to allocate no more than
448 // "max_alloc_words" in the target generation (via promotion say,
449 // if the requestor is a young generation and the target is older).
450 // If the target generation can provide any scratch space, it adds
451 // it to "list", leaving "list" pointing to the head of the
452 // augmented list. The default is to offer no space.
453 virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor,
454 size_t max_alloc_words) {}
455
456 // Give each generation an opportunity to do clean up for any
457 // contributed scratch.
458 virtual void reset_scratch() {}
459
460 // When an older generation has been collected, and perhaps resized,
461 // this method will be invoked on all younger generations (from older to
462 // younger), allowing them to resize themselves as appropriate.
463 virtual void compute_new_size() = 0;
464
465 // Printing
466 virtual const char* name() const = 0;
467 virtual const char* short_name() const = 0;
468
469 // Reference Processing accessor
470 ReferenceProcessor* const ref_processor() { return _ref_processor; }
471
472 // Iteration.
473
474 // Iterate over all the ref-containing fields of all objects in the
475 // generation, calling "cl.do_oop" on each.
476 virtual void oop_iterate(OopIterateClosure* cl);
477
478 // Iterate over all objects in the generation, calling "cl.do_object" on
479 // each.
480 virtual void object_iterate(ObjectClosure* cl);
481
482 // Iterate over all safe objects in the generation, calling "cl.do_object" on
483 // each. An object is safe if its references point to other objects in
484 // the heap. This defaults to object_iterate() unless overridden.
485 virtual void safe_object_iterate(ObjectClosure* cl);
486
487 // Apply "cl->do_oop" to (the address of) all and only all the ref fields
488 // in the current generation that contain pointers to objects in younger
489 // generations. Objects allocated since the last "save_marks" call are
490 // excluded.
491 virtual void younger_refs_iterate(OopsInGenClosure* cl, uint n_threads) = 0;
492
493 // Inform a generation that it longer contains references to objects
494 // in any younger generation. [e.g. Because younger gens are empty,
495 // clear the card table.]
496 virtual void clear_remembered_set() { }
497
498 // Inform a generation that some of its objects have moved. [e.g. The
499 // generation's spaces were compacted, invalidating the card table.]
500 virtual void invalidate_remembered_set() { }
501
502 // Block abstraction.
503
504 // Returns the address of the start of the "block" that contains the
505 // address "addr". We say "blocks" instead of "object" since some heaps
506 // may not pack objects densely; a chunk may either be an object or a
507 // non-object.
508 virtual HeapWord* block_start(const void* addr) const;
509
510 // Requires "addr" to be the start of a chunk, and returns its size.
511 // "addr + size" is required to be the start of a new chunk, or the end
512 // of the active area of the heap.
513 virtual size_t block_size(const HeapWord* addr) const ;
514
515 // Requires "addr" to be the start of a block, and returns "TRUE" iff
516 // the block is an object.
517 virtual bool block_is_obj(const HeapWord* addr) const;
518
519 void print_heap_change(size_t prev_used) const;
520
521 virtual void print() const;
522 virtual void print_on(outputStream* st) const;
523
524 virtual void verify() = 0;
525
526 struct StatRecord {
527 int invocations;
528 elapsedTimer accumulated_time;
529 StatRecord() :
530 invocations(0),
531 accumulated_time(elapsedTimer()) {}
532 };
533private:
534 StatRecord _stat_record;
535public:
536 StatRecord* stat_record() { return &_stat_record; }
537
538 virtual void print_summary_info_on(outputStream* st);
539
540 // Performance Counter support
541 virtual void update_counters() = 0;
542 virtual CollectorCounters* counters() { return _gc_counters; }
543
544 GCMemoryManager* gc_manager() const {
545 assert(_gc_manager != NULL, "not initialized yet");
546 return _gc_manager;
547 }
548
549 void set_gc_manager(GCMemoryManager* gc_manager) {
550 _gc_manager = gc_manager;
551 }
552
553};
554
555#endif // SHARE_GC_SHARED_GENERATION_HPP
556