Mon, 26 Jan 2009 12:47:21 -0800
6786503: Overflow list performance can be improved
Summary: Avoid overflow list walk in CMS & ParNew when it is unnecessary. Fix a couple of correctness issues, including a C-heap leak, in ParNew at the intersection of promotion failure, work queue overflow and object array chunking. Add stress testing option and related assertion checking.
Reviewed-by: jmasa
1 /*
2 * Copyright 1997-2008 Sun Microsystems, Inc. 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.
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
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22 *
23 */
25 // A Generation models a heap area for similarly-aged objects.
26 // It will contain one ore more spaces holding the actual objects.
27 //
28 // The Generation class hierarchy:
29 //
30 // Generation - abstract base class
31 // - DefNewGeneration - allocation area (copy collected)
32 // - ParNewGeneration - a DefNewGeneration that is collected by
33 // several threads
34 // - CardGeneration - abstract class adding offset array behavior
35 // - OneContigSpaceCardGeneration - abstract class holding a single
36 // contiguous space with card marking
37 // - TenuredGeneration - tenured (old object) space (markSweepCompact)
38 // - CompactingPermGenGen - reflective object area (klasses, methods, symbols, ...)
39 // - ConcurrentMarkSweepGeneration - Mostly Concurrent Mark Sweep Generation
40 // (Detlefs-Printezis refinement of
41 // Boehm-Demers-Schenker)
42 //
43 // The system configurations currently allowed are:
44 //
45 // DefNewGeneration + TenuredGeneration + PermGeneration
46 // DefNewGeneration + ConcurrentMarkSweepGeneration + ConcurrentMarkSweepPermGen
47 //
48 // ParNewGeneration + TenuredGeneration + PermGeneration
49 // ParNewGeneration + ConcurrentMarkSweepGeneration + ConcurrentMarkSweepPermGen
50 //
52 class DefNewGeneration;
53 class GenerationSpec;
54 class CompactibleSpace;
55 class ContiguousSpace;
56 class CompactPoint;
57 class OopsInGenClosure;
58 class OopClosure;
59 class ScanClosure;
60 class FastScanClosure;
61 class GenCollectedHeap;
62 class GenRemSet;
63 class GCStats;
65 // A "ScratchBlock" represents a block of memory in one generation usable by
66 // another. It represents "num_words" free words, starting at and including
67 // the address of "this".
68 struct ScratchBlock {
69 ScratchBlock* next;
70 size_t num_words;
71 HeapWord scratch_space[1]; // Actually, of size "num_words-2" (assuming
72 // first two fields are word-sized.)
73 };
76 class Generation: public CHeapObj {
77 friend class VMStructs;
78 private:
79 jlong _time_of_last_gc; // time when last gc on this generation happened (ms)
80 MemRegion _prev_used_region; // for collectors that want to "remember" a value for
81 // used region at some specific point during collection.
83 protected:
84 // Minimum and maximum addresses for memory reserved (not necessarily
85 // committed) for generation.
86 // Used by card marking code. Must not overlap with address ranges of
87 // other generations.
88 MemRegion _reserved;
90 // Memory area reserved for generation
91 VirtualSpace _virtual_space;
93 // Level in the generation hierarchy.
94 int _level;
96 // ("Weak") Reference processing support
97 ReferenceProcessor* _ref_processor;
99 // Performance Counters
100 CollectorCounters* _gc_counters;
102 // Statistics for garbage collection
103 GCStats* _gc_stats;
105 // Returns the next generation in the configuration, or else NULL if this
106 // is the highest generation.
107 Generation* next_gen() const;
109 // Initialize the generation.
110 Generation(ReservedSpace rs, size_t initial_byte_size, int level);
112 // Apply "cl->do_oop" to (the address of) (exactly) all the ref fields in
113 // "sp" that point into younger generations.
114 // The iteration is only over objects allocated at the start of the
115 // iterations; objects allocated as a result of applying the closure are
116 // not included.
117 void younger_refs_in_space_iterate(Space* sp, OopsInGenClosure* cl);
119 public:
120 // The set of possible generation kinds.
121 enum Name {
122 ASParNew,
123 ASConcurrentMarkSweep,
124 DefNew,
125 ParNew,
126 MarkSweepCompact,
127 ConcurrentMarkSweep,
128 Other
129 };
131 enum SomePublicConstants {
132 // Generations are GenGrain-aligned and have size that are multiples of
133 // GenGrain.
134 LogOfGenGrain = 16,
135 GenGrain = 1 << LogOfGenGrain
136 };
138 // allocate and initialize ("weak") refs processing support
139 virtual void ref_processor_init();
140 void set_ref_processor(ReferenceProcessor* rp) {
141 assert(_ref_processor == NULL, "clobbering existing _ref_processor");
142 _ref_processor = rp;
143 }
145 virtual Generation::Name kind() { return Generation::Other; }
146 GenerationSpec* spec();
148 // This properly belongs in the collector, but for now this
149 // will do.
150 virtual bool refs_discovery_is_atomic() const { return true; }
151 virtual bool refs_discovery_is_mt() const { return false; }
153 // Space enquiries (results in bytes)
154 virtual size_t capacity() const = 0; // The maximum number of object bytes the
155 // generation can currently hold.
156 virtual size_t used() const = 0; // The number of used bytes in the gen.
157 virtual size_t free() const = 0; // The number of free bytes in the gen.
159 // Support for java.lang.Runtime.maxMemory(); see CollectedHeap.
160 // Returns the total number of bytes available in a generation
161 // for the allocation of objects.
162 virtual size_t max_capacity() const;
164 // If this is a young generation, the maximum number of bytes that can be
165 // allocated in this generation before a GC is triggered.
166 virtual size_t capacity_before_gc() const { return 0; }
168 // The largest number of contiguous free bytes in the generation,
169 // including expansion (Assumes called at a safepoint.)
170 virtual size_t contiguous_available() const = 0;
171 // The largest number of contiguous free bytes in this or any higher generation.
172 virtual size_t max_contiguous_available() const;
174 // Returns true if promotions of the specified amount can
175 // be attempted safely (without a vm failure).
176 // Promotion of the full amount is not guaranteed but
177 // can be attempted.
178 // younger_handles_promotion_failure
179 // is true if the younger generation handles a promotion
180 // failure.
181 virtual bool promotion_attempt_is_safe(size_t promotion_in_bytes,
182 bool younger_handles_promotion_failure) const;
184 // Return an estimate of the maximum allocation that could be performed
185 // in the generation without triggering any collection or expansion
186 // activity. It is "unsafe" because no locks are taken; the result
187 // should be treated as an approximation, not a guarantee, for use in
188 // heuristic resizing decisions.
189 virtual size_t unsafe_max_alloc_nogc() const = 0;
191 // Returns true if this generation cannot be expanded further
192 // without a GC. Override as appropriate.
193 virtual bool is_maximal_no_gc() const {
194 return _virtual_space.uncommitted_size() == 0;
195 }
197 MemRegion reserved() const { return _reserved; }
199 // Returns a region guaranteed to contain all the objects in the
200 // generation.
201 virtual MemRegion used_region() const { return _reserved; }
203 MemRegion prev_used_region() const { return _prev_used_region; }
204 virtual void save_used_region() { _prev_used_region = used_region(); }
206 // Returns "TRUE" iff "p" points into an allocated object in the generation.
207 // For some kinds of generations, this may be an expensive operation.
208 // To avoid performance problems stemming from its inadvertent use in
209 // product jvm's, we restrict its use to assertion checking or
210 // verification only.
211 virtual bool is_in(const void* p) const;
213 /* Returns "TRUE" iff "p" points into the reserved area of the generation. */
214 bool is_in_reserved(const void* p) const {
215 return _reserved.contains(p);
216 }
218 // Check that the generation kind is DefNewGeneration or a sub
219 // class of DefNewGeneration and return a DefNewGeneration*
220 DefNewGeneration* as_DefNewGeneration();
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;
226 // Iteration - do not use for time critical operations
227 virtual void space_iterate(SpaceClosure* blk, bool usedOnly = false) = 0;
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;
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 }
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;
251 // Like "allocate", but performs any necessary locking internally.
252 virtual HeapWord* par_allocate(size_t word_size, bool is_tlab) = 0;
254 // A 'younger' gen has reached an allocation limit, and uses this to notify
255 // the next older gen. The return value is a new limit, or NULL if none. The
256 // caller must do the necessary locking.
257 virtual HeapWord* allocation_limit_reached(Space* space, HeapWord* top,
258 size_t word_size) {
259 return NULL;
260 }
262 // Some generation may offer a region for shared, contiguous allocation,
263 // via inlined code (by exporting the address of the top and end fields
264 // defining the extent of the contiguous allocation region.)
266 // This function returns "true" iff the heap supports this kind of
267 // allocation. (More precisely, this means the style of allocation that
268 // increments *top_addr()" with a CAS.) (Default is "no".)
269 // A generation that supports this allocation style must use lock-free
270 // allocation for *all* allocation, since there are times when lock free
271 // allocation will be concurrent with plain "allocate" calls.
272 virtual bool supports_inline_contig_alloc() const { return false; }
274 // These functions return the addresses of the fields that define the
275 // boundaries of the contiguous allocation area. (These fields should be
276 // physicall near to one another.)
277 virtual HeapWord** top_addr() const { return NULL; }
278 virtual HeapWord** end_addr() const { return NULL; }
280 // Thread-local allocation buffers
281 virtual bool supports_tlab_allocation() const { return false; }
282 virtual size_t tlab_capacity() const {
283 guarantee(false, "Generation doesn't support thread local allocation buffers");
284 return 0;
285 }
286 virtual size_t unsafe_max_tlab_alloc() const {
287 guarantee(false, "Generation doesn't support thread local allocation buffers");
288 return 0;
289 }
291 // "obj" is the address of an object in a younger generation. Allocate space
292 // for "obj" in the current (or some higher) generation, and copy "obj" into
293 // the newly allocated space, if possible, returning the result (or NULL if
294 // the allocation failed).
295 //
296 // The "obj_size" argument is just obj->size(), passed along so the caller can
297 // avoid repeating the virtual call to retrieve it.
298 virtual oop promote(oop obj, size_t obj_size);
300 // Thread "thread_num" (0 <= i < ParalleGCThreads) wants to promote
301 // object "obj", whose original mark word was "m", and whose size is
302 // "word_sz". If possible, allocate space for "obj", copy obj into it
303 // (taking care to copy "m" into the mark word when done, since the mark
304 // word of "obj" may have been overwritten with a forwarding pointer, and
305 // also taking care to copy the klass pointer *last*. Returns the new
306 // object if successful, or else NULL.
307 virtual oop par_promote(int thread_num,
308 oop obj, markOop m, size_t word_sz);
310 // Undo, if possible, the most recent par_promote_alloc allocation by
311 // "thread_num" ("obj", of "word_sz").
312 virtual void par_promote_alloc_undo(int thread_num,
313 HeapWord* obj, size_t word_sz);
315 // Informs the current generation that all par_promote_alloc's in the
316 // collection have been completed; any supporting data structures can be
317 // reset. Default is to do nothing.
318 virtual void par_promote_alloc_done(int thread_num) {}
320 // Informs the current generation that all oop_since_save_marks_iterates
321 // performed by "thread_num" in the current collection, if any, have been
322 // completed; any supporting data structures can be reset. Default is to
323 // do nothing.
324 virtual void par_oop_since_save_marks_iterate_done(int thread_num) {}
326 // This generation will collect all younger generations
327 // during a full collection.
328 virtual bool full_collects_younger_generations() const { return false; }
330 // This generation does in-place marking, meaning that mark words
331 // are mutated during the marking phase and presumably reinitialized
332 // to a canonical value after the GC. This is currently used by the
333 // biased locking implementation to determine whether additional
334 // work is required during the GC prologue and epilogue.
335 virtual bool performs_in_place_marking() const { return true; }
337 // Returns "true" iff collect() should subsequently be called on this
338 // this generation. See comment below.
339 // This is a generic implementation which can be overridden.
340 //
341 // Note: in the current (1.4) implementation, when genCollectedHeap's
342 // incremental_collection_will_fail flag is set, all allocations are
343 // slow path (the only fast-path place to allocate is DefNew, which
344 // will be full if the flag is set).
345 // Thus, older generations which collect younger generations should
346 // test this flag and collect if it is set.
347 virtual bool should_collect(bool full,
348 size_t word_size,
349 bool is_tlab) {
350 return (full || should_allocate(word_size, is_tlab));
351 }
353 // Perform a garbage collection.
354 // If full is true attempt a full garbage collection of this generation.
355 // Otherwise, attempting to (at least) free enough space to support an
356 // allocation of the given "word_size".
357 virtual void collect(bool full,
358 bool clear_all_soft_refs,
359 size_t word_size,
360 bool is_tlab) = 0;
362 // Perform a heap collection, attempting to create (at least) enough
363 // space to support an allocation of the given "word_size". If
364 // successful, perform the allocation and return the resulting
365 // "oop" (initializing the allocated block). If the allocation is
366 // still unsuccessful, return "NULL".
367 virtual HeapWord* expand_and_allocate(size_t word_size,
368 bool is_tlab,
369 bool parallel = false) = 0;
371 // Some generations may require some cleanup or preparation actions before
372 // allowing a collection. The default is to do nothing.
373 virtual void gc_prologue(bool full) {};
375 // Some generations may require some cleanup actions after a collection.
376 // The default is to do nothing.
377 virtual void gc_epilogue(bool full) {};
379 // Save the high water marks for the used space in a generation.
380 virtual void record_spaces_top() {};
382 // Some generations may need to be "fixed-up" after some allocation
383 // activity to make them parsable again. The default is to do nothing.
384 virtual void ensure_parsability() {};
386 // Time (in ms) when we were last collected or now if a collection is
387 // in progress.
388 virtual jlong time_of_last_gc(jlong now) {
389 // XXX See note in genCollectedHeap::millis_since_last_gc()
390 NOT_PRODUCT(
391 if (now < _time_of_last_gc) {
392 warning("time warp: %d to %d", _time_of_last_gc, now);
393 }
394 )
395 return _time_of_last_gc;
396 }
398 virtual void update_time_of_last_gc(jlong now) {
399 _time_of_last_gc = now;
400 }
402 // Generations may keep statistics about collection. This
403 // method updates those statistics. current_level is
404 // the level of the collection that has most recently
405 // occurred. This allows the generation to decide what
406 // statistics are valid to collect. For example, the
407 // generation can decide to gather the amount of promoted data
408 // if the collection of the younger generations has completed.
409 GCStats* gc_stats() const { return _gc_stats; }
410 virtual void update_gc_stats(int current_level, bool full) {}
412 // Mark sweep support phase2
413 virtual void prepare_for_compaction(CompactPoint* cp);
414 // Mark sweep support phase3
415 virtual void pre_adjust_pointers() {ShouldNotReachHere();}
416 virtual void adjust_pointers();
417 // Mark sweep support phase4
418 virtual void compact();
419 virtual void post_compact() {ShouldNotReachHere();}
421 // Support for CMS's rescan. In this general form we return a pointer
422 // to an abstract object that can be used, based on specific previously
423 // decided protocols, to exchange information between generations,
424 // information that may be useful for speeding up certain types of
425 // garbage collectors. A NULL value indicates to the client that
426 // no data recording is expected by the provider. The data-recorder is
427 // expected to be GC worker thread-local, with the worker index
428 // indicated by "thr_num".
429 virtual void* get_data_recorder(int thr_num) { return NULL; }
431 // Some generations may require some cleanup actions before allowing
432 // a verification.
433 virtual void prepare_for_verify() {};
435 // Accessing "marks".
437 // This function gives a generation a chance to note a point between
438 // collections. For example, a contiguous generation might note the
439 // beginning allocation point post-collection, which might allow some later
440 // operations to be optimized.
441 virtual void save_marks() {}
443 // This function allows generations to initialize any "saved marks". That
444 // is, should only be called when the generation is empty.
445 virtual void reset_saved_marks() {}
447 // This function is "true" iff any no allocations have occurred in the
448 // generation since the last call to "save_marks".
449 virtual bool no_allocs_since_save_marks() = 0;
451 // Apply "cl->apply" to (the addresses of) all reference fields in objects
452 // allocated in the current generation since the last call to "save_marks".
453 // If more objects are allocated in this generation as a result of applying
454 // the closure, iterates over reference fields in those objects as well.
455 // Calls "save_marks" at the end of the iteration.
456 // General signature...
457 virtual void oop_since_save_marks_iterate_v(OopsInGenClosure* cl) = 0;
458 // ...and specializations for de-virtualization. (The general
459 // implemention of the _nv versions call the virtual version.
460 // Note that the _nv suffix is not really semantically necessary,
461 // but it avoids some not-so-useful warnings on Solaris.)
462 #define Generation_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \
463 virtual void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
464 oop_since_save_marks_iterate_v((OopsInGenClosure*)cl); \
465 }
466 SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(Generation_SINCE_SAVE_MARKS_DECL)
468 #undef Generation_SINCE_SAVE_MARKS_DECL
470 // The "requestor" generation is performing some garbage collection
471 // action for which it would be useful to have scratch space. If
472 // the target is not the requestor, no gc actions will be required
473 // of the target. The requestor promises to allocate no more than
474 // "max_alloc_words" in the target generation (via promotion say,
475 // if the requestor is a young generation and the target is older).
476 // If the target generation can provide any scratch space, it adds
477 // it to "list", leaving "list" pointing to the head of the
478 // augmented list. The default is to offer no space.
479 virtual void contribute_scratch(ScratchBlock*& list, Generation* requestor,
480 size_t max_alloc_words) {}
482 // Give each generation an opportunity to do clean up for any
483 // contributed scratch.
484 virtual void reset_scratch() {};
486 // When an older generation has been collected, and perhaps resized,
487 // this method will be invoked on all younger generations (from older to
488 // younger), allowing them to resize themselves as appropriate.
489 virtual void compute_new_size() = 0;
491 // Printing
492 virtual const char* name() const = 0;
493 virtual const char* short_name() const = 0;
495 int level() const { return _level; }
497 // Attributes
499 // True iff the given generation may only be the youngest generation.
500 virtual bool must_be_youngest() const = 0;
501 // True iff the given generation may only be the oldest generation.
502 virtual bool must_be_oldest() const = 0;
504 // Reference Processing accessor
505 ReferenceProcessor* const ref_processor() { return _ref_processor; }
507 // Iteration.
509 // Iterate over all the ref-containing fields of all objects in the
510 // generation, calling "cl.do_oop" on each.
511 virtual void oop_iterate(OopClosure* cl);
513 // Same as above, restricted to the intersection of a memory region and
514 // the generation.
515 virtual void oop_iterate(MemRegion mr, OopClosure* cl);
517 // Iterate over all objects in the generation, calling "cl.do_object" on
518 // each.
519 virtual void object_iterate(ObjectClosure* cl);
521 // Iterate over all safe objects in the generation, calling "cl.do_object" on
522 // each. An object is safe if its references point to other objects in
523 // the heap. This defaults to object_iterate() unless overridden.
524 virtual void safe_object_iterate(ObjectClosure* cl);
526 // Iterate over all objects allocated in the generation since the last
527 // collection, calling "cl.do_object" on each. The generation must have
528 // been initialized properly to support this function, or else this call
529 // will fail.
530 virtual void object_iterate_since_last_GC(ObjectClosure* cl) = 0;
532 // Apply "cl->do_oop" to (the address of) all and only all the ref fields
533 // in the current generation that contain pointers to objects in younger
534 // generations. Objects allocated since the last "save_marks" call are
535 // excluded.
536 virtual void younger_refs_iterate(OopsInGenClosure* cl) = 0;
538 // Inform a generation that it longer contains references to objects
539 // in any younger generation. [e.g. Because younger gens are empty,
540 // clear the card table.]
541 virtual void clear_remembered_set() { }
543 // Inform a generation that some of its objects have moved. [e.g. The
544 // generation's spaces were compacted, invalidating the card table.]
545 virtual void invalidate_remembered_set() { }
547 // Block abstraction.
549 // Returns the address of the start of the "block" that contains the
550 // address "addr". We say "blocks" instead of "object" since some heaps
551 // may not pack objects densely; a chunk may either be an object or a
552 // non-object.
553 virtual HeapWord* block_start(const void* addr) const;
555 // Requires "addr" to be the start of a chunk, and returns its size.
556 // "addr + size" is required to be the start of a new chunk, or the end
557 // of the active area of the heap.
558 virtual size_t block_size(const HeapWord* addr) const ;
560 // Requires "addr" to be the start of a block, and returns "TRUE" iff
561 // the block is an object.
562 virtual bool block_is_obj(const HeapWord* addr) const;
565 // PrintGC, PrintGCDetails support
566 void print_heap_change(size_t prev_used) const;
568 // PrintHeapAtGC support
569 virtual void print() const;
570 virtual void print_on(outputStream* st) const;
572 virtual void verify(bool allow_dirty) = 0;
574 struct StatRecord {
575 int invocations;
576 elapsedTimer accumulated_time;
577 StatRecord() :
578 invocations(0),
579 accumulated_time(elapsedTimer()) {}
580 };
581 private:
582 StatRecord _stat_record;
583 public:
584 StatRecord* stat_record() { return &_stat_record; }
586 virtual void print_summary_info();
587 virtual void print_summary_info_on(outputStream* st);
589 // Performance Counter support
590 virtual void update_counters() = 0;
591 virtual CollectorCounters* counters() { return _gc_counters; }
592 };
594 // Class CardGeneration is a generation that is covered by a card table,
595 // and uses a card-size block-offset array to implement block_start.
597 // class BlockOffsetArray;
598 // class BlockOffsetArrayContigSpace;
599 class BlockOffsetSharedArray;
601 class CardGeneration: public Generation {
602 friend class VMStructs;
603 protected:
604 // This is shared with other generations.
605 GenRemSet* _rs;
606 // This is local to this generation.
607 BlockOffsetSharedArray* _bts;
609 CardGeneration(ReservedSpace rs, size_t initial_byte_size, int level,
610 GenRemSet* remset);
612 public:
614 // Attempt to expand the generation by "bytes". Expand by at a
615 // minimum "expand_bytes". Return true if some amount (not
616 // necessarily the full "bytes") was done.
617 virtual bool expand(size_t bytes, size_t expand_bytes);
619 virtual void clear_remembered_set();
621 virtual void invalidate_remembered_set();
623 virtual void prepare_for_verify();
625 // Grow generation with specified size (returns false if unable to grow)
626 virtual bool grow_by(size_t bytes) = 0;
627 // Grow generation to reserved size.
628 virtual bool grow_to_reserved() = 0;
629 };
631 // OneContigSpaceCardGeneration models a heap of old objects contained in a single
632 // contiguous space.
633 //
634 // Garbage collection is performed using mark-compact.
636 class OneContigSpaceCardGeneration: public CardGeneration {
637 friend class VMStructs;
638 // Abstractly, this is a subtype that gets access to protected fields.
639 friend class CompactingPermGen;
640 friend class VM_PopulateDumpSharedSpace;
642 protected:
643 size_t _min_heap_delta_bytes; // Minimum amount to expand.
644 ContiguousSpace* _the_space; // actual space holding objects
645 WaterMark _last_gc; // watermark between objects allocated before
646 // and after last GC.
648 // Grow generation with specified size (returns false if unable to grow)
649 virtual bool grow_by(size_t bytes);
650 // Grow generation to reserved size.
651 virtual bool grow_to_reserved();
652 // Shrink generation with specified size (returns false if unable to shrink)
653 void shrink_by(size_t bytes);
655 // Allocation failure
656 virtual bool expand(size_t bytes, size_t expand_bytes);
657 void shrink(size_t bytes);
659 // Accessing spaces
660 ContiguousSpace* the_space() const { return _the_space; }
662 public:
663 OneContigSpaceCardGeneration(ReservedSpace rs, size_t initial_byte_size,
664 size_t min_heap_delta_bytes,
665 int level, GenRemSet* remset,
666 ContiguousSpace* space) :
667 CardGeneration(rs, initial_byte_size, level, remset),
668 _the_space(space), _min_heap_delta_bytes(min_heap_delta_bytes)
669 {}
671 inline bool is_in(const void* p) const;
673 // Space enquiries
674 size_t capacity() const;
675 size_t used() const;
676 size_t free() const;
678 MemRegion used_region() const;
680 size_t unsafe_max_alloc_nogc() const;
681 size_t contiguous_available() const;
683 // Iteration
684 void object_iterate(ObjectClosure* blk);
685 void space_iterate(SpaceClosure* blk, bool usedOnly = false);
686 void object_iterate_since_last_GC(ObjectClosure* cl);
688 void younger_refs_iterate(OopsInGenClosure* blk);
690 inline CompactibleSpace* first_compaction_space() const;
692 virtual inline HeapWord* allocate(size_t word_size, bool is_tlab);
693 virtual inline HeapWord* par_allocate(size_t word_size, bool is_tlab);
695 // Accessing marks
696 inline WaterMark top_mark();
697 inline WaterMark bottom_mark();
699 #define OneContig_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \
700 void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl);
701 OneContig_SINCE_SAVE_MARKS_DECL(OopsInGenClosure,_v)
702 SPECIALIZED_SINCE_SAVE_MARKS_CLOSURES(OneContig_SINCE_SAVE_MARKS_DECL)
704 void save_marks();
705 void reset_saved_marks();
706 bool no_allocs_since_save_marks();
708 inline size_t block_size(const HeapWord* addr) const;
710 inline bool block_is_obj(const HeapWord* addr) const;
712 virtual void collect(bool full,
713 bool clear_all_soft_refs,
714 size_t size,
715 bool is_tlab);
716 HeapWord* expand_and_allocate(size_t size,
717 bool is_tlab,
718 bool parallel = false);
720 virtual void prepare_for_verify();
722 virtual void gc_epilogue(bool full);
724 virtual void record_spaces_top();
726 virtual void verify(bool allow_dirty);
727 virtual void print_on(outputStream* st) const;
728 };