1 #ifdef USE_PRAGMA_IDENT_HDR
2 #pragma ident "@(#)concurrentMarkSweepGeneration.hpp 1.163 08/09/25 13:47:54 JVM"
3 #endif
4 /*
5 * Copyright 2001-2007 Sun Microsystems, Inc. All Rights Reserved.
6 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
7 *
8 * This code is free software; you can redistribute it and/or modify it
9 * under the terms of the GNU General Public License version 2 only, as
10 * published by the Free Software Foundation.
11 *
12 * This code is distributed in the hope that it will be useful, but WITHOUT
13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 * version 2 for more details (a copy is included in the LICENSE file that
16 * accompanied this code).
17 *
18 * You should have received a copy of the GNU General Public License version
19 * 2 along with this work; if not, write to the Free Software Foundation,
20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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22 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
23 * CA 95054 USA or visit www.sun.com if you need additional information or
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26 */
27
28 // ConcurrentMarkSweepGeneration is in support of a concurrent
29 // mark-sweep old generation in the Detlefs-Printezis--Boehm-Demers-Schenker
30 // style. We assume, for now, that this generation is always the
31 // seniormost generation (modulo the PermGeneration), and for simplicity
32 // in the first implementation, that this generation is a single compactible
33 // space. Neither of these restrictions appears essential, and will be
34 // relaxed in the future when more time is available to implement the
35 // greater generality (and there's a need for it).
36 //
37 // Concurrent mode failures are currently handled by
38 // means of a sliding mark-compact.
39
40 class CMSAdaptiveSizePolicy;
41 class CMSConcMarkingTask;
42 class CMSGCAdaptivePolicyCounters;
43 class ConcurrentMarkSweepGeneration;
44 class ConcurrentMarkSweepPolicy;
45 class ConcurrentMarkSweepThread;
46 class CompactibleFreeListSpace;
47 class FreeChunk;
48 class PromotionInfo;
49 class ScanMarkedObjectsAgainCarefullyClosure;
50
51 // A generic CMS bit map. It's the basis for both the CMS marking bit map
52 // as well as for the mod union table (in each case only a subset of the
53 // methods are used). This is essentially a wrapper around the BitMap class,
54 // with one bit per (1<<_shifter) HeapWords. (i.e. for the marking bit map,
55 // we have _shifter == 0. and for the mod union table we have
56 // shifter == CardTableModRefBS::card_shift - LogHeapWordSize.)
57 // XXX 64-bit issues in BitMap?
58 class CMSBitMap VALUE_OBJ_CLASS_SPEC {
59 friend class VMStructs;
60
61 HeapWord* _bmStartWord; // base address of range covered by map
62 size_t _bmWordSize; // map size (in #HeapWords covered)
63 const int _shifter; // shifts to convert HeapWord to bit position
64 VirtualSpace _virtual_space; // underlying the bit map
65 BitMap _bm; // the bit map itself
66 public:
67 Mutex* const _lock; // mutex protecting _bm;
68
69 public:
70 // constructor
71 CMSBitMap(int shifter, int mutex_rank, const char* mutex_name);
72
73 // allocates the actual storage for the map
74 bool allocate(MemRegion mr);
75 // field getter
76 Mutex* lock() const { return _lock; }
77 // locking verifier convenience function
78 void assert_locked() const PRODUCT_RETURN;
79
80 // inquiries
81 HeapWord* startWord() const { return _bmStartWord; }
82 size_t sizeInWords() const { return _bmWordSize; }
83 size_t sizeInBits() const { return _bm.size(); }
84 // the following is one past the last word in space
85 HeapWord* endWord() const { return _bmStartWord + _bmWordSize; }
86
87 // reading marks
88 bool isMarked(HeapWord* addr) const;
89 bool par_isMarked(HeapWord* addr) const; // do not lock checks
90 bool isUnmarked(HeapWord* addr) const;
91 bool isAllClear() const;
92
93 // writing marks
94 void mark(HeapWord* addr);
95 // For marking by parallel GC threads;
96 // returns true if we did, false if another thread did
97 bool par_mark(HeapWord* addr);
98
99 void mark_range(MemRegion mr);
100 void par_mark_range(MemRegion mr);
101 void mark_large_range(MemRegion mr);
102 void par_mark_large_range(MemRegion mr);
103 void par_clear(HeapWord* addr); // For unmarking by parallel GC threads.
104 void clear_range(MemRegion mr);
105 void par_clear_range(MemRegion mr);
106 void clear_large_range(MemRegion mr);
107 void par_clear_large_range(MemRegion mr);
108 void clear_all();
109 void clear_all_incrementally(); // Not yet implemented!!
110
111 NOT_PRODUCT(
112 // checks the memory region for validity
113 void region_invariant(MemRegion mr);
114 )
115
116 // iteration
117 void iterate(BitMapClosure* cl) {
118 _bm.iterate(cl);
119 }
120 void iterate(BitMapClosure* cl, HeapWord* left, HeapWord* right);
121 void dirty_range_iterate_clear(MemRegionClosure* cl);
122 void dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl);
123
124 // auxiliary support for iteration
125 HeapWord* getNextMarkedWordAddress(HeapWord* addr) const;
126 HeapWord* getNextMarkedWordAddress(HeapWord* start_addr,
127 HeapWord* end_addr) const;
128 HeapWord* getNextUnmarkedWordAddress(HeapWord* addr) const;
129 HeapWord* getNextUnmarkedWordAddress(HeapWord* start_addr,
130 HeapWord* end_addr) const;
131 MemRegion getAndClearMarkedRegion(HeapWord* addr);
132 MemRegion getAndClearMarkedRegion(HeapWord* start_addr,
133 HeapWord* end_addr);
134
135 // conversion utilities
136 HeapWord* offsetToHeapWord(size_t offset) const;
137 size_t heapWordToOffset(HeapWord* addr) const;
138 size_t heapWordDiffToOffsetDiff(size_t diff) const;
139
140 // debugging
141 // is this address range covered by the bit-map?
142 NOT_PRODUCT(
143 bool covers(MemRegion mr) const;
144 bool covers(HeapWord* start, size_t size = 0) const;
145 )
146 void verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) PRODUCT_RETURN;
147 };
148
149 // Represents a marking stack used by the CMS collector.
150 // Ideally this should be GrowableArray<> just like MSC's marking stack(s).
151 class CMSMarkStack: public CHeapObj {
152 //
153 friend class CMSCollector; // to get at expasion stats further below
154 //
155
156 VirtualSpace _virtual_space; // space for the stack
157 oop* _base; // bottom of stack
158 size_t _index; // one more than last occupied index
159 size_t _capacity; // max #elements
160 Mutex _par_lock; // an advisory lock used in case of parallel access
161 NOT_PRODUCT(size_t _max_depth;) // max depth plumbed during run
162
163 protected:
164 size_t _hit_limit; // we hit max stack size limit
165 size_t _failed_double; // we failed expansion before hitting limit
166
167 public:
168 CMSMarkStack():
169 _par_lock(Mutex::event, "CMSMarkStack._par_lock", true),
170 _hit_limit(0),
171 _failed_double(0) {}
172
173 bool allocate(size_t size);
174
175 size_t capacity() const { return _capacity; }
176
177 oop pop() {
178 if (!isEmpty()) {
179 return _base[--_index] ;
180 }
181 return NULL;
182 }
183
184 bool push(oop ptr) {
185 if (isFull()) {
186 return false;
187 } else {
188 _base[_index++] = ptr;
189 NOT_PRODUCT(_max_depth = MAX2(_max_depth, _index));
190 return true;
191 }
192 }
193
194 bool isEmpty() const { return _index == 0; }
195 bool isFull() const {
196 assert(_index <= _capacity, "buffer overflow");
197 return _index == _capacity;
198 }
199
200 size_t length() { return _index; }
201
202 // "Parallel versions" of some of the above
203 oop par_pop() {
204 // lock and pop
205 MutexLockerEx x(&_par_lock, Mutex::_no_safepoint_check_flag);
206 return pop();
207 }
208
209 bool par_push(oop ptr) {
210 // lock and push
211 MutexLockerEx x(&_par_lock, Mutex::_no_safepoint_check_flag);
212 return push(ptr);
213 }
214
215 // Forcibly reset the stack, losing all of its contents.
216 void reset() {
217 _index = 0;
218 }
219
220 // Expand the stack, typically in response to an overflow condition
221 void expand();
222
223 // Compute the least valued stack element.
224 oop least_value(HeapWord* low) {
225 oop least = (oop)low;
226 for (size_t i = 0; i < _index; i++) {
227 least = MIN2(least, _base[i]);
228 }
229 return least;
230 }
231
232 // Exposed here to allow stack expansion in || case
233 Mutex* par_lock() { return &_par_lock; }
234 };
235
236 class CardTableRS;
237 class CMSParGCThreadState;
238
239 class ModUnionClosure: public MemRegionClosure {
240 protected:
241 CMSBitMap* _t;
242 public:
243 ModUnionClosure(CMSBitMap* t): _t(t) { }
244 void do_MemRegion(MemRegion mr);
245 };
246
247 class ModUnionClosurePar: public ModUnionClosure {
248 public:
249 ModUnionClosurePar(CMSBitMap* t): ModUnionClosure(t) { }
250 void do_MemRegion(MemRegion mr);
251 };
252
253 // Survivor Chunk Array in support of parallelization of
254 // Survivor Space rescan.
255 class ChunkArray: public CHeapObj {
256 size_t _index;
257 size_t _capacity;
258 HeapWord** _array; // storage for array
259
260 public:
261 ChunkArray() : _index(0), _capacity(0), _array(NULL) {}
262 ChunkArray(HeapWord** a, size_t c):
263 _index(0), _capacity(c), _array(a) {}
264
265 HeapWord** array() { return _array; }
266 void set_array(HeapWord** a) { _array = a; }
267
268 size_t capacity() { return _capacity; }
269 void set_capacity(size_t c) { _capacity = c; }
270
271 size_t end() {
272 assert(_index < capacity(), "_index out of bounds");
273 return _index;
274 } // exclusive
275
276 HeapWord* nth(size_t n) {
277 assert(n < end(), "Out of bounds access");
278 return _array[n];
279 }
280
281 void reset() {
282 _index = 0;
283 }
284
285 void record_sample(HeapWord* p, size_t sz) {
286 // For now we do not do anything with the size
287 if (_index < _capacity) {
288 _array[_index++] = p;
289 }
290 }
291 };
292
293 //
294 // Timing, allocation and promotion statistics for gc scheduling and incremental
295 // mode pacing. Most statistics are exponential averages.
296 //
297 class CMSStats VALUE_OBJ_CLASS_SPEC {
298 private:
299 ConcurrentMarkSweepGeneration* const _cms_gen; // The cms (old) gen.
300
301 // The following are exponential averages with factor alpha:
302 // avg = (100 - alpha) * avg + alpha * cur_sample
303 //
304 // The durations measure: end_time[n] - start_time[n]
305 // The periods measure: start_time[n] - start_time[n-1]
306 //
307 // The cms period and duration include only concurrent collections; time spent
308 // in foreground cms collections due to System.gc() or because of a failure to
309 // keep up are not included.
310 //
311 // There are 3 alphas to "bootstrap" the statistics. The _saved_alpha is the
312 // real value, but is used only after the first period. A value of 100 is
313 // used for the first sample so it gets the entire weight.
314 unsigned int _saved_alpha; // 0-100
315 unsigned int _gc0_alpha;
316 unsigned int _cms_alpha;
317
318 double _gc0_duration;
319 double _gc0_period;
320 size_t _gc0_promoted; // bytes promoted per gc0
321 double _cms_duration;
322 double _cms_duration_pre_sweep; // time from initiation to start of sweep
323 double _cms_duration_per_mb;
324 double _cms_period;
325 size_t _cms_allocated; // bytes of direct allocation per gc0 period
326
327 // Timers.
328 elapsedTimer _cms_timer;
329 TimeStamp _gc0_begin_time;
330 TimeStamp _cms_begin_time;
331 TimeStamp _cms_end_time;
332
333 // Snapshots of the amount used in the CMS generation.
334 size_t _cms_used_at_gc0_begin;
335 size_t _cms_used_at_gc0_end;
336 size_t _cms_used_at_cms_begin;
337
338 // Used to prevent the duty cycle from being reduced in the middle of a cms
339 // cycle.
340 bool _allow_duty_cycle_reduction;
341
342 enum {
343 _GC0_VALID = 0x1,
344 _CMS_VALID = 0x2,
345 _ALL_VALID = _GC0_VALID | _CMS_VALID
346 };
347
348 unsigned int _valid_bits;
349
350 unsigned int _icms_duty_cycle; // icms duty cycle (0-100).
351
352 protected:
353
354 // Return a duty cycle that avoids wild oscillations, by limiting the amount
355 // of change between old_duty_cycle and new_duty_cycle (the latter is treated
356 // as a recommended value).
357 static unsigned int icms_damped_duty_cycle(unsigned int old_duty_cycle,
358 unsigned int new_duty_cycle);
359 unsigned int icms_update_duty_cycle_impl();
360
361 public:
362 CMSStats(ConcurrentMarkSweepGeneration* cms_gen,
363 unsigned int alpha = CMSExpAvgFactor);
364
365 // Whether or not the statistics contain valid data; higher level statistics
366 // cannot be called until this returns true (they require at least one young
367 // gen and one cms cycle to have completed).
368 bool valid() const;
369
370 // Record statistics.
371 void record_gc0_begin();
372 void record_gc0_end(size_t cms_gen_bytes_used);
373 void record_cms_begin();
374 void record_cms_end();
375
376 // Allow management of the cms timer, which must be stopped/started around
377 // yield points.
378 elapsedTimer& cms_timer() { return _cms_timer; }
379 void start_cms_timer() { _cms_timer.start(); }
380 void stop_cms_timer() { _cms_timer.stop(); }
381
382 // Basic statistics; units are seconds or bytes.
383 double gc0_period() const { return _gc0_period; }
384 double gc0_duration() const { return _gc0_duration; }
385 size_t gc0_promoted() const { return _gc0_promoted; }
386 double cms_period() const { return _cms_period; }
387 double cms_duration() const { return _cms_duration; }
388 double cms_duration_per_mb() const { return _cms_duration_per_mb; }
389 size_t cms_allocated() const { return _cms_allocated; }
390
391 size_t cms_used_at_gc0_end() const { return _cms_used_at_gc0_end;}
392
393 // Seconds since the last background cms cycle began or ended.
394 double cms_time_since_begin() const;
395 double cms_time_since_end() const;
396
397 // Higher level statistics--caller must check that valid() returns true before
398 // calling.
399
400 // Returns bytes promoted per second of wall clock time.
401 double promotion_rate() const;
402
403 // Returns bytes directly allocated per second of wall clock time.
404 double cms_allocation_rate() const;
405
406 // Rate at which space in the cms generation is being consumed (sum of the
407 // above two).
408 double cms_consumption_rate() const;
409
410 // Returns an estimate of the number of seconds until the cms generation will
411 // fill up, assuming no collection work is done.
412 double time_until_cms_gen_full() const;
413
414 // Returns an estimate of the number of seconds remaining until
415 // the cms generation collection should start.
416 double time_until_cms_start() const;
417
418 // End of higher level statistics.
419
420 // Returns the cms incremental mode duty cycle, as a percentage (0-100).
421 unsigned int icms_duty_cycle() const { return _icms_duty_cycle; }
422
423 // Update the duty cycle and return the new value.
424 unsigned int icms_update_duty_cycle();
425
426 // Debugging.
427 void print_on(outputStream* st) const PRODUCT_RETURN;
428 void print() const { print_on(gclog_or_tty); }
429 };
430
431 // A closure related to weak references processing which
432 // we embed in the CMSCollector, since we need to pass
433 // it to the reference processor for secondary filtering
434 // of references based on reachability of referent;
435 // see role of _is_alive_non_header closure in the
436 // ReferenceProcessor class.
437 // For objects in the CMS generation, this closure checks
438 // if the object is "live" (reachable). Used in weak
439 // reference processing.
440 class CMSIsAliveClosure: public BoolObjectClosure {
441 const MemRegion _span;
442 const CMSBitMap* _bit_map;
443
444 friend class CMSCollector;
445 public:
446 CMSIsAliveClosure(MemRegion span,
447 CMSBitMap* bit_map):
448 _span(span),
449 _bit_map(bit_map) {
450 assert(!span.is_empty(), "Empty span could spell trouble");
451 }
452
453 void do_object(oop obj) {
454 assert(false, "not to be invoked");
455 }
456 bool do_object_b(oop obj);
457 };
458
459
460 // Implements AbstractRefProcTaskExecutor for CMS.
461 class CMSRefProcTaskExecutor: public AbstractRefProcTaskExecutor {
462 public:
463
464 CMSRefProcTaskExecutor(CMSCollector& collector)
465 : _collector(collector)
466 { }
467
468 // Executes a task using worker threads.
469 virtual void execute(ProcessTask& task);
470 virtual void execute(EnqueueTask& task);
471 private:
472 CMSCollector& _collector;
473 };
474
475
476 class CMSCollector: public CHeapObj {
477 friend class VMStructs;
478 friend class ConcurrentMarkSweepThread;
479 friend class ConcurrentMarkSweepGeneration;
480 friend class CompactibleFreeListSpace;
481 friend class CMSParRemarkTask;
482 friend class CMSConcMarkingTask;
483 friend class CMSRefProcTaskProxy;
484 friend class CMSRefProcTaskExecutor;
485 friend class ScanMarkedObjectsAgainCarefullyClosure; // for sampling eden
486 friend class SurvivorSpacePrecleanClosure; // --- ditto -------
487 friend class PushOrMarkClosure; // to access _restart_addr
488 friend class Par_PushOrMarkClosure; // to access _restart_addr
489 friend class MarkFromRootsClosure; // -- ditto --
490 // ... and for clearing cards
491 friend class Par_MarkFromRootsClosure; // to access _restart_addr
492 // ... and for clearing cards
493 friend class Par_ConcMarkingClosure; // to access _restart_addr etc.
494 friend class MarkFromRootsVerifyClosure; // to access _restart_addr
495 friend class PushAndMarkVerifyClosure; // -- ditto --
496 friend class MarkRefsIntoAndScanClosure; // to access _overflow_list
497 friend class PushAndMarkClosure; // -- ditto --
498 friend class Par_PushAndMarkClosure; // -- ditto --
499 friend class CMSKeepAliveClosure; // -- ditto --
500 friend class CMSDrainMarkingStackClosure; // -- ditto --
501 friend class CMSInnerParMarkAndPushClosure; // -- ditto --
502 NOT_PRODUCT(friend class ScanMarkedObjectsAgainClosure;) // assertion on _overflow_list
503 friend class ReleaseForegroundGC; // to access _foregroundGCShouldWait
504 friend class VM_CMS_Operation;
505 friend class VM_CMS_Initial_Mark;
506 friend class VM_CMS_Final_Remark;
507
508 private:
509 jlong _time_of_last_gc;
510 void update_time_of_last_gc(jlong now) {
511 _time_of_last_gc = now;
512 }
513
514 OopTaskQueueSet* _task_queues;
515
516 // Overflow list of grey objects, threaded through mark-word
517 // Manipulated with CAS in the parallel/multi-threaded case.
518 oop _overflow_list;
519 // The following array-pair keeps track of mark words
520 // displaced for accomodating overflow list above.
521 // This code will likely be revisited under RFE#4922830.
522 GrowableArray<oop>* _preserved_oop_stack;
523 GrowableArray<markOop>* _preserved_mark_stack;
524
525 int* _hash_seed;
526
527 // In support of multi-threaded concurrent phases
528 YieldingFlexibleWorkGang* _conc_workers;
529
530 // Performance Counters
531 CollectorCounters* _gc_counters;
532
533 // Initialization Errors
534 bool _completed_initialization;
535
536 // In support of ExplicitGCInvokesConcurrent
537 static bool _full_gc_requested;
538 unsigned int _collection_count_start;
539 // Should we unload classes this concurrent cycle?
540 // Set in response to a concurrent full gc request.
541 bool _unload_classes;
542 bool _unloaded_classes_last_cycle;
543 // Did we (allow) unload classes in the previous concurrent cycle?
544 bool cms_unloaded_classes_last_cycle() const {
545 return _unloaded_classes_last_cycle || CMSClassUnloadingEnabled;
546 }
547
548 // Verification support
549 CMSBitMap _verification_mark_bm;
550 void verify_after_remark_work_1();
551 void verify_after_remark_work_2();
552
553 // true if any verification flag is on.
554 bool _verifying;
555 bool verifying() const { return _verifying; }
556 void set_verifying(bool v) { _verifying = v; }
557
558 // Collector policy
559 ConcurrentMarkSweepPolicy* _collector_policy;
560 ConcurrentMarkSweepPolicy* collector_policy() { return _collector_policy; }
561
562 // Check whether the gc time limit has been
563 // exceeded and set the size policy flag
564 // appropriately.
565 void check_gc_time_limit();
566 // XXX Move these to CMSStats ??? FIX ME !!!
567 elapsedTimer _sweep_timer;
568 AdaptivePaddedAverage _sweep_estimate;
569
570 protected:
571 ConcurrentMarkSweepGeneration* _cmsGen; // old gen (CMS)
572 ConcurrentMarkSweepGeneration* _permGen; // perm gen
573 MemRegion _span; // span covering above two
574 CardTableRS* _ct; // card table
575
576 // CMS marking support structures
577 CMSBitMap _markBitMap;
578 CMSBitMap _modUnionTable;
579 CMSMarkStack _markStack;
580 CMSMarkStack _revisitStack; // used to keep track of klassKlass objects
581 // to revisit
582 CMSBitMap _perm_gen_verify_bit_map; // Mark bit map for perm gen verification support.
583
584 HeapWord* _restart_addr; // in support of marking stack overflow
585 void lower_restart_addr(HeapWord* low);
586
587 // Counters in support of marking stack / work queue overflow handling:
588 // a non-zero value indicates certain types of overflow events during
589 // the current CMS cycle and could lead to stack resizing efforts at
590 // an opportune future time.
591 size_t _ser_pmc_preclean_ovflw;
592 size_t _ser_pmc_remark_ovflw;
593 size_t _par_pmc_remark_ovflw;
594 size_t _ser_kac_ovflw;
595 size_t _par_kac_ovflw;
596 NOT_PRODUCT(size_t _num_par_pushes;)
597
598 // ("Weak") Reference processing support
599 ReferenceProcessor* _ref_processor;
600 CMSIsAliveClosure _is_alive_closure;
601 // keep this textually after _markBitMap and _span; c'tor dependency
602
603 ConcurrentMarkSweepThread* _cmsThread; // the thread doing the work
604 ModUnionClosure _modUnionClosure;
605 ModUnionClosurePar _modUnionClosurePar;
606
607 // CMS abstract state machine
608 // initial_state: Idling
609 // next_state(Idling) = {Marking}
610 // next_state(Marking) = {Precleaning, Sweeping}
611 // next_state(Precleaning) = {AbortablePreclean, FinalMarking}
612 // next_state(AbortablePreclean) = {FinalMarking}
613 // next_state(FinalMarking) = {Sweeping}
614 // next_state(Sweeping) = {Resizing}
615 // next_state(Resizing) = {Resetting}
616 // next_state(Resetting) = {Idling}
617 // The numeric values below are chosen so that:
618 // . _collectorState <= Idling == post-sweep && pre-mark
619 // . _collectorState in (Idling, Sweeping) == {initial,final}marking ||
620 // precleaning || abortablePrecleanb
621 enum CollectorState {
622 Resizing = 0,
623 Resetting = 1,
624 Idling = 2,
625 InitialMarking = 3,
626 Marking = 4,
627 Precleaning = 5,
628 AbortablePreclean = 6,
629 FinalMarking = 7,
630 Sweeping = 8
631 };
632 static CollectorState _collectorState;
633
634 // State related to prologue/epilogue invocation for my generations
635 bool _between_prologue_and_epilogue;
636
637 // Signalling/State related to coordination between fore- and backgroud GC
638 // Note: When the baton has been passed from background GC to foreground GC,
639 // _foregroundGCIsActive is true and _foregroundGCShouldWait is false.
640 static bool _foregroundGCIsActive; // true iff foreground collector is active or
641 // wants to go active
642 static bool _foregroundGCShouldWait; // true iff background GC is active and has not
643 // yet passed the baton to the foreground GC
644
645 // Support for CMSScheduleRemark (abortable preclean)
646 bool _abort_preclean;
647 bool _start_sampling;
648
649 int _numYields;
650 size_t _numDirtyCards;
651 uint _sweepCount;
652 // number of full gc's since the last concurrent gc.
653 uint _full_gcs_since_conc_gc;
654
655 // if occupancy exceeds this, start a new gc cycle
656 double _initiatingOccupancy;
657 // occupancy used for bootstrapping stats
658 double _bootstrap_occupancy;
659
660 // timer
661 elapsedTimer _timer;
662
663 // Timing, allocation and promotion statistics, used for scheduling.
664 CMSStats _stats;
665
666 // Allocation limits installed in the young gen, used only in
667 // CMSIncrementalMode. When an allocation in the young gen would cross one of
668 // these limits, the cms generation is notified and the cms thread is started
669 // or stopped, respectively.
670 HeapWord* _icms_start_limit;
671 HeapWord* _icms_stop_limit;
672
673 enum CMS_op_type {
674 CMS_op_checkpointRootsInitial,
675 CMS_op_checkpointRootsFinal
676 };
677
678 void do_CMS_operation(CMS_op_type op);
679 bool stop_world_and_do(CMS_op_type op);
680
681 OopTaskQueueSet* task_queues() { return _task_queues; }
682 int* hash_seed(int i) { return &_hash_seed[i]; }
683 YieldingFlexibleWorkGang* conc_workers() { return _conc_workers; }
684
685 // Support for parallelizing Eden rescan in CMS remark phase
686 void sample_eden(); // ... sample Eden space top
687
688 private:
689 // Support for parallelizing young gen rescan in CMS remark phase
690 Generation* _young_gen; // the younger gen
691 HeapWord** _top_addr; // ... Top of Eden
692 HeapWord** _end_addr; // ... End of Eden
693 HeapWord** _eden_chunk_array; // ... Eden partitioning array
694 size_t _eden_chunk_index; // ... top (exclusive) of array
695 size_t _eden_chunk_capacity; // ... max entries in array
696
697 // Support for parallelizing survivor space rescan
698 HeapWord** _survivor_chunk_array;
699 size_t _survivor_chunk_index;
700 size_t _survivor_chunk_capacity;
701 size_t* _cursor;
702 ChunkArray* _survivor_plab_array;
703
704 // Support for marking stack overflow handling
705 bool take_from_overflow_list(size_t num, CMSMarkStack* to_stack);
706 bool par_take_from_overflow_list(size_t num, OopTaskQueue* to_work_q);
707 void push_on_overflow_list(oop p);
708 void par_push_on_overflow_list(oop p);
709 // the following is, obviously, not, in general, "MT-stable"
710 bool overflow_list_is_empty() const;
711
712 void preserve_mark_if_necessary(oop p);
713 void par_preserve_mark_if_necessary(oop p);
714 void preserve_mark_work(oop p, markOop m);
715 void restore_preserved_marks_if_any();
716 NOT_PRODUCT(bool no_preserved_marks() const;)
717 // in support of testing overflow code
718 NOT_PRODUCT(int _overflow_counter;)
719 NOT_PRODUCT(bool simulate_overflow();) // sequential
720 NOT_PRODUCT(bool par_simulate_overflow();) // MT version
721
722 int _roots_scanning_options;
723 int roots_scanning_options() const { return _roots_scanning_options; }
724 void add_root_scanning_option(int o) { _roots_scanning_options |= o; }
725 void remove_root_scanning_option(int o) { _roots_scanning_options &= ~o; }
726
727 // CMS work methods
728 void checkpointRootsInitialWork(bool asynch); // initial checkpoint work
729
730 // a return value of false indicates failure due to stack overflow
731 bool markFromRootsWork(bool asynch); // concurrent marking work
732
733 public: // FIX ME!!! only for testing
734 bool do_marking_st(bool asynch); // single-threaded marking
735 bool do_marking_mt(bool asynch); // multi-threaded marking
736
737 private:
738
739 // concurrent precleaning work
740 size_t preclean_mod_union_table(ConcurrentMarkSweepGeneration* gen,
741 ScanMarkedObjectsAgainCarefullyClosure* cl);
742 size_t preclean_card_table(ConcurrentMarkSweepGeneration* gen,
743 ScanMarkedObjectsAgainCarefullyClosure* cl);
744 // Does precleaning work, returning a quantity indicative of
745 // the amount of "useful work" done.
746 size_t preclean_work(bool clean_refs, bool clean_survivors);
747 void abortable_preclean(); // Preclean while looking for possible abort
748 void initialize_sequential_subtasks_for_young_gen_rescan(int i);
749 // Helper function for above; merge-sorts the per-thread plab samples
750 void merge_survivor_plab_arrays(ContiguousSpace* surv);
751 // Resets (i.e. clears) the per-thread plab sample vectors
752 void reset_survivor_plab_arrays();
753
754 // final (second) checkpoint work
755 void checkpointRootsFinalWork(bool asynch, bool clear_all_soft_refs,
756 bool init_mark_was_synchronous);
757 // work routine for parallel version of remark
758 void do_remark_parallel();
759 // work routine for non-parallel version of remark
760 void do_remark_non_parallel();
761 // reference processing work routine (during second checkpoint)
762 void refProcessingWork(bool asynch, bool clear_all_soft_refs);
763
764 // concurrent sweeping work
765 void sweepWork(ConcurrentMarkSweepGeneration* gen, bool asynch);
766
767 // (concurrent) resetting of support data structures
768 void reset(bool asynch);
769
770 // Clear _expansion_cause fields of constituent generations
771 void clear_expansion_cause();
772
773 // An auxilliary method used to record the ends of
774 // used regions of each generation to limit the extent of sweep
775 void save_sweep_limits();
776
777 // Resize the generations included in the collector.
778 void compute_new_size();
779
780 // A work method used by foreground collection to determine
781 // what type of collection (compacting or not, continuing or fresh)
782 // it should do.
783 void decide_foreground_collection_type(bool clear_all_soft_refs,
784 bool* should_compact, bool* should_start_over);
785
786 // A work method used by the foreground collector to do
787 // a mark-sweep-compact.
788 void do_compaction_work(bool clear_all_soft_refs);
789
790 // A work method used by the foreground collector to do
791 // a mark-sweep, after taking over from a possibly on-going
792 // concurrent mark-sweep collection.
793 void do_mark_sweep_work(bool clear_all_soft_refs,
794 CollectorState first_state, bool should_start_over);
795
796 // If the backgrould GC is active, acquire control from the background
797 // GC and do the collection.
798 void acquire_control_and_collect(bool full, bool clear_all_soft_refs);
799
800 // For synchronizing passing of control from background to foreground
801 // GC. waitForForegroundGC() is called by the background
802 // collector. It if had to wait for a foreground collection,
803 // it returns true and the background collection should assume
804 // that the collection was finished by the foreground
805 // collector.
806 bool waitForForegroundGC();
807
808 // Incremental mode triggering: recompute the icms duty cycle and set the
809 // allocation limits in the young gen.
810 void icms_update_allocation_limits();
811
812 size_t block_size_using_printezis_bits(HeapWord* addr) const;
813 size_t block_size_if_printezis_bits(HeapWord* addr) const;
814 HeapWord* next_card_start_after_block(HeapWord* addr) const;
815
816 void setup_cms_unloading_and_verification_state();
817 public:
818 CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
819 ConcurrentMarkSweepGeneration* permGen,
820 CardTableRS* ct,
821 ConcurrentMarkSweepPolicy* cp);
822 ConcurrentMarkSweepThread* cmsThread() { return _cmsThread; }
823
824 ReferenceProcessor* ref_processor() { return _ref_processor; }
825 void ref_processor_init();
826
827 Mutex* bitMapLock() const { return _markBitMap.lock(); }
828 static CollectorState abstract_state() { return _collectorState; }
829 double initiatingOccupancy() const { return _initiatingOccupancy; }
830
831 bool should_abort_preclean() const; // Whether preclean should be aborted.
832 size_t get_eden_used() const;
833 size_t get_eden_capacity() const;
834
835 ConcurrentMarkSweepGeneration* cmsGen() { return _cmsGen; }
836
837 // locking checks
838 NOT_PRODUCT(static bool have_cms_token();)
839
840 // XXXPERM bool should_collect(bool full, size_t size, bool tlab);
841 bool shouldConcurrentCollect();
842
843 void collect(bool full,
844 bool clear_all_soft_refs,
845 size_t size,
846 bool tlab);
847 void collect_in_background(bool clear_all_soft_refs);
848 void collect_in_foreground(bool clear_all_soft_refs);
849
850 // In support of ExplicitGCInvokesConcurrent
851 static void request_full_gc(unsigned int full_gc_count);
852 // Should we unload classes in a particular concurrent cycle?
853 bool cms_should_unload_classes() const {
854 assert(!_unload_classes || ExplicitGCInvokesConcurrentAndUnloadsClasses,
855 "Inconsistency; see CR 6541037");
856 return _unload_classes || CMSClassUnloadingEnabled;
857 }
858
859 void direct_allocated(HeapWord* start, size_t size);
860
861 // Object is dead if not marked and current phase is sweeping.
862 bool is_dead_obj(oop obj) const;
863
864 // After a promotion (of "start"), do any necessary marking.
865 // If "par", then it's being done by a parallel GC thread.
866 // The last two args indicate if we need precise marking
867 // and if so the size of the object so it can be dirtied
868 // in its entirety.
869 void promoted(bool par, HeapWord* start,
870 bool is_obj_array, size_t obj_size);
871
872 HeapWord* allocation_limit_reached(Space* space, HeapWord* top,
873 size_t word_size);
874
875 void getFreelistLocks() const;
876 void releaseFreelistLocks() const;
877 bool haveFreelistLocks() const;
878
879 // GC prologue and epilogue
880 void gc_prologue(bool full);
881 void gc_epilogue(bool full);
882
883 jlong time_of_last_gc(jlong now) {
884 if (_collectorState <= Idling) {
885 // gc not in progress
886 return _time_of_last_gc;
887 } else {
888 // collection in progress
889 return now;
890 }
891 }
892
893 // Support for parallel remark of survivor space
894 void* get_data_recorder(int thr_num);
895
896 CMSBitMap* markBitMap() { return &_markBitMap; }
897 void directAllocated(HeapWord* start, size_t size);
898
899 // main CMS steps and related support
900 void checkpointRootsInitial(bool asynch);
901 bool markFromRoots(bool asynch); // a return value of false indicates failure
902 // due to stack overflow
903 void preclean();
904 void checkpointRootsFinal(bool asynch, bool clear_all_soft_refs,
905 bool init_mark_was_synchronous);
906 void sweep(bool asynch);
907
908 // Check that the currently executing thread is the expected
909 // one (foreground collector or background collector).
910 void check_correct_thread_executing() PRODUCT_RETURN;
911 // XXXPERM void print_statistics() PRODUCT_RETURN;
912
913 bool is_cms_reachable(HeapWord* addr);
914
915 // Performance Counter Support
916 CollectorCounters* counters() { return _gc_counters; }
917
918 // timer stuff
919 void startTimer() { assert(!_timer.is_active(), "Error"); _timer.start(); }
920 void stopTimer() { assert( _timer.is_active(), "Error"); _timer.stop(); }
921 void resetTimer() { assert(!_timer.is_active(), "Error"); _timer.reset(); }
922 double timerValue() { assert(!_timer.is_active(), "Error"); return _timer.seconds(); }
923
924 int yields() { return _numYields; }
925 void resetYields() { _numYields = 0; }
926 void incrementYields() { _numYields++; }
927 void resetNumDirtyCards() { _numDirtyCards = 0; }
928 void incrementNumDirtyCards(size_t num) { _numDirtyCards += num; }
929 size_t numDirtyCards() { return _numDirtyCards; }
930
931 static bool foregroundGCShouldWait() { return _foregroundGCShouldWait; }
932 static void set_foregroundGCShouldWait(bool v) { _foregroundGCShouldWait = v; }
933 static bool foregroundGCIsActive() { return _foregroundGCIsActive; }
934 static void set_foregroundGCIsActive(bool v) { _foregroundGCIsActive = v; }
935 uint sweepCount() const { return _sweepCount; }
936 void incrementSweepCount() { _sweepCount++; }
937
938 // Timers/stats for gc scheduling and incremental mode pacing.
939 CMSStats& stats() { return _stats; }
940
941 // Convenience methods that check whether CMSIncrementalMode is enabled and
942 // forward to the corresponding methods in ConcurrentMarkSweepThread.
943 static void start_icms();
944 static void stop_icms(); // Called at the end of the cms cycle.
945 static void disable_icms(); // Called before a foreground collection.
946 static void enable_icms(); // Called after a foreground collection.
947 void icms_wait(); // Called at yield points.
948
949 // Adaptive size policy
950 CMSAdaptiveSizePolicy* size_policy();
951 CMSGCAdaptivePolicyCounters* gc_adaptive_policy_counters();
952
953 // debugging
954 void verify(bool);
955 bool verify_after_remark();
956 void verify_ok_to_terminate() const PRODUCT_RETURN;
957 void verify_work_stacks_empty() const PRODUCT_RETURN;
958 void verify_overflow_empty() const PRODUCT_RETURN;
959
960 // convenience methods in support of debugging
961 static const size_t skip_header_HeapWords() PRODUCT_RETURN0;
962 HeapWord* block_start(const void* p) const PRODUCT_RETURN0;
963
964 // accessors
965 CMSMarkStack* verification_mark_stack() { return &_markStack; }
966 CMSBitMap* verification_mark_bm() { return &_verification_mark_bm; }
967
968 // Get the bit map with a perm gen "deadness" information.
969 CMSBitMap* perm_gen_verify_bit_map() { return &_perm_gen_verify_bit_map; }
970
971 // Initialization errors
972 bool completed_initialization() { return _completed_initialization; }
973 };
974
975 class CMSExpansionCause : public AllStatic {
976 public:
977 enum Cause {
978 _no_expansion,
979 _satisfy_free_ratio,
980 _satisfy_promotion,
981 _satisfy_allocation,
982 _allocate_par_lab,
983 _allocate_par_spooling_space,
984 _adaptive_size_policy
985 };
986 // Return a string describing the cause of the expansion.
987 static const char* to_string(CMSExpansionCause::Cause cause);
988 };
989
990 class ConcurrentMarkSweepGeneration: public CardGeneration {
991 friend class VMStructs;
992 friend class ConcurrentMarkSweepThread;
993 friend class ConcurrentMarkSweep;
994 friend class CMSCollector;
995 protected:
996 static CMSCollector* _collector; // the collector that collects us
997 CompactibleFreeListSpace* _cmsSpace; // underlying space (only one for now)
998
999 // Performance Counters
1000 GenerationCounters* _gen_counters;
1001 GSpaceCounters* _space_counters;
1002
1003 // Words directly allocated, used by CMSStats.
1004 size_t _direct_allocated_words;
1005
1006 // Non-product stat counters
1007 NOT_PRODUCT(
1008 int _numObjectsPromoted;
1009 int _numWordsPromoted;
1010 int _numObjectsAllocated;
1011 int _numWordsAllocated;
1012 )
1013
1014 // Used for sizing decisions
1015 bool _incremental_collection_failed;
1016 bool incremental_collection_failed() {
1017 return _incremental_collection_failed;
1018 }
1019 void set_incremental_collection_failed() {
1020 _incremental_collection_failed = true;
1021 }
1022 void clear_incremental_collection_failed() {
1023 _incremental_collection_failed = false;
1024 }
1025
1026 private:
1027 // For parallel young-gen GC support.
1028 CMSParGCThreadState** _par_gc_thread_states;
1029
1030 // Reason generation was expanded
1031 CMSExpansionCause::Cause _expansion_cause;
1032
1033 // accessors
1034 void set_expansion_cause(CMSExpansionCause::Cause v) { _expansion_cause = v;}
1035 CMSExpansionCause::Cause expansion_cause() { return _expansion_cause; }
1036
1037 // In support of MinChunkSize being larger than min object size
1038 const double _dilatation_factor;
1039
1040 enum CollectionTypes {
1041 Concurrent_collection_type = 0,
1042 MS_foreground_collection_type = 1,
1043 MSC_foreground_collection_type = 2,
1044 Unknown_collection_type = 3
1045 };
1046
1047 CollectionTypes _debug_collection_type;
1048
1049 protected:
1050 // Grow generation by specified size (returns false if unable to grow)
1051 bool grow_by(size_t bytes);
1052 // Grow generation to reserved size.
1053 bool grow_to_reserved();
1054 // Shrink generation by specified size (returns false if unable to shrink)
1055 virtual void shrink_by(size_t bytes);
1056
1057 // Update statistics for GC
1058 virtual void update_gc_stats(int level, bool full);
1059
1060 // Maximum available space in the generation (including uncommitted)
1061 // space.
1062 size_t max_available() const;
1063
1064 public:
1065 ConcurrentMarkSweepGeneration(ReservedSpace rs, size_t initial_byte_size,
1066 int level, CardTableRS* ct,
1067 bool use_adaptive_freelists,
1068 FreeBlockDictionary::DictionaryChoice);
1069
1070 // Accessors
1071 CMSCollector* collector() const { return _collector; }
1072 static void set_collector(CMSCollector* collector) {
1073 assert(_collector == NULL, "already set");
1074 _collector = collector;
1075 }
1076 CompactibleFreeListSpace* cmsSpace() const { return _cmsSpace; }
1077
1078 Mutex* freelistLock() const;
1079
1080 virtual Generation::Name kind() { return Generation::ConcurrentMarkSweep; }
1081
1082 // Adaptive size policy
1083 CMSAdaptiveSizePolicy* size_policy();
1084
1085 bool refs_discovery_is_atomic() const { return false; }
1086 bool refs_discovery_is_mt() const {
1087 // Note: CMS does MT-discovery during the parallel-remark
1088 // phases. Use ReferenceProcessorMTMutator to make refs
1089 // discovery MT-safe during such phases or other parallel
1090 // discovery phases in the future. This may all go away
1091 // if/when we decide that refs discovery is sufficiently
1092 // rare that the cost of the CAS's involved is in the
1093 // noise. That's a measurement that should be done, and
1094 // the code simplified if that turns out to be the case.
1095 return false;
1096 }
1097
1098 // Override
1099 virtual void ref_processor_init();
1100
1101 void clear_expansion_cause() { _expansion_cause = CMSExpansionCause::_no_expansion; }
1102
1103 // Space enquiries
1104 size_t capacity() const;
1105 size_t used() const;
1106 size_t free() const;
1107 double occupancy() { return ((double)used())/((double)capacity()); }
1108 size_t contiguous_available() const;
1109 size_t unsafe_max_alloc_nogc() const;
1110
1111 // over-rides
1112 MemRegion used_region() const;
1113 MemRegion used_region_at_save_marks() const;
1114
1115 // Does a "full" (forced) collection invoked on this generation collect
1116 // all younger generations as well? Note that the second conjunct is a
1117 // hack to allow the collection of the younger gen first if the flag is
1118 // set. This is better than using th policy's should_collect_gen0_first()
1119 // since that causes us to do an extra unnecessary pair of restart-&-stop-world.
1120 virtual bool full_collects_younger_generations() const {
1121 return UseCMSCompactAtFullCollection && !CollectGen0First;
1122 }
1123
1124 void space_iterate(SpaceClosure* blk, bool usedOnly = false);
1125
1126 // Support for compaction
1127 CompactibleSpace* first_compaction_space() const;
1128 // Adjust quantites in the generation affected by
1129 // the compaction.
1130 void reset_after_compaction();
1131
1132 // Allocation support
1133 HeapWord* allocate(size_t size, bool tlab);
1134 HeapWord* have_lock_and_allocate(size_t size, bool tlab);
1135 oop promote(oop obj, size_t obj_size, oop* ref);
1136 HeapWord* par_allocate(size_t size, bool tlab) {
1137 return allocate(size, tlab);
1138 }
1139
1140 // Incremental mode triggering.
1141 HeapWord* allocation_limit_reached(Space* space, HeapWord* top,
1142 size_t word_size);
1143
1144 // Used by CMSStats to track direct allocation. The value is sampled and
1145 // reset after each young gen collection.
1146 size_t direct_allocated_words() const { return _direct_allocated_words; }
1147 void reset_direct_allocated_words() { _direct_allocated_words = 0; }
1148
1149 // Overrides for parallel promotion.
1150 virtual oop par_promote(int thread_num,
1151 oop obj, markOop m, size_t word_sz);
1152 // This one should not be called for CMS.
1153 virtual void par_promote_alloc_undo(int thread_num,
1154 HeapWord* obj, size_t word_sz);
1155 virtual void par_promote_alloc_done(int thread_num);
1156 virtual void par_oop_since_save_marks_iterate_done(int thread_num);
1157
1158 virtual bool promotion_attempt_is_safe(size_t promotion_in_bytes,
1159 bool younger_handles_promotion_failure) const;
1160
1161 bool should_collect(bool full, size_t size, bool tlab);
1162 // XXXPERM
1163 bool shouldConcurrentCollect(double initiatingOccupancy); // XXXPERM
1164 void collect(bool full,
1165 bool clear_all_soft_refs,
1166 size_t size,
1167 bool tlab);
1168
1169 HeapWord* expand_and_allocate(size_t word_size,
1170 bool tlab,
1171 bool parallel = false);
1172
1173 // GC prologue and epilogue
1174 void gc_prologue(bool full);
1175 void gc_prologue_work(bool full, bool registerClosure,
1176 ModUnionClosure* modUnionClosure);
1177 void gc_epilogue(bool full);
1178 void gc_epilogue_work(bool full);
1179
1180 // Time since last GC of this generation
1181 jlong time_of_last_gc(jlong now) {
1182 return collector()->time_of_last_gc(now);
1183 }
1184 void update_time_of_last_gc(jlong now) {
1185 collector()-> update_time_of_last_gc(now);
1186 }
1187
1188 // Allocation failure
1189 void expand(size_t bytes, size_t expand_bytes,
1190 CMSExpansionCause::Cause cause);
1191 void shrink(size_t bytes);
1192 HeapWord* expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz);
1193 bool expand_and_ensure_spooling_space(PromotionInfo* promo);
1194
1195 // Iteration support and related enquiries
1196 void save_marks();
1197 bool no_allocs_since_save_marks();
1198 void object_iterate_since_last_GC(ObjectClosure* cl);
1199 void younger_refs_iterate(OopsInGenClosure* cl);
1200
1201 // Iteration support specific to CMS generations
1202 void save_sweep_limit();
1203
1204 // More iteration support
1205 virtual void oop_iterate(MemRegion mr, OopClosure* cl);
1206 virtual void oop_iterate(OopClosure* cl);
1207 virtual void object_iterate(ObjectClosure* cl);
1208
1209 // Need to declare the full complement of closures, whether we'll
1210 // override them or not, or get message from the compiler:
1211 // oop_since_save_marks_iterate_nv hides virtual function...
1212 #define CMS_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \
1213 void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl);
1214 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DECL)
1215
1216 // Smart allocation XXX -- move to CFLSpace?
1217 void setNearLargestChunk();
1218 bool isNearLargestChunk(HeapWord* addr);
1219
1220 // Get the chunk at the end of the space. Delagates to
1221 // the space.
1222 FreeChunk* find_chunk_at_end();
1223
1224 // Overriding of unused functionality (sharing not yet supported with CMS)
1225 void pre_adjust_pointers();
1226 void post_compact();
1227
1228 // Debugging
1229 void prepare_for_verify();
1230 void verify(bool allow_dirty);
1231 void print_statistics() PRODUCT_RETURN;
1232
1233 // Performance Counters support
1234 virtual void update_counters();
1235 virtual void update_counters(size_t used);
1236 void initialize_performance_counters();
1237 CollectorCounters* counters() { return collector()->counters(); }
1238
1239 // Support for parallel remark of survivor space
1240 void* get_data_recorder(int thr_num) {
1241 //Delegate to collector
1242 return collector()->get_data_recorder(thr_num);
1243 }
1244
1245 // Printing
1246 const char* name() const;
1247 virtual const char* short_name() const { return "CMS"; }
1248 void print() const;
1249 void printOccupancy(const char* s);
1250 bool must_be_youngest() const { return false; }
1251 bool must_be_oldest() const { return true; }
1252
1253 void compute_new_size();
1254
1255 CollectionTypes debug_collection_type() { return _debug_collection_type; }
1256 void rotate_debug_collection_type();
1257 };
1258
1259 class ASConcurrentMarkSweepGeneration : public ConcurrentMarkSweepGeneration {
1260
1261 // Return the size policy from the heap's collector
1262 // policy casted to CMSAdaptiveSizePolicy*.
1263 CMSAdaptiveSizePolicy* cms_size_policy() const;
1264
1265 // Resize the generation based on the adaptive size
1266 // policy.
1267 void resize(size_t cur_promo, size_t desired_promo);
1268
1269 // Return the GC counters from the collector policy
1270 CMSGCAdaptivePolicyCounters* gc_adaptive_policy_counters();
1271
1272 virtual void shrink_by(size_t bytes);
1273
1274 public:
1275 virtual void compute_new_size();
1276 ASConcurrentMarkSweepGeneration(ReservedSpace rs, size_t initial_byte_size,
1277 int level, CardTableRS* ct,
1278 bool use_adaptive_freelists,
1279 FreeBlockDictionary::DictionaryChoice
1280 dictionaryChoice) :
1281 ConcurrentMarkSweepGeneration(rs, initial_byte_size, level, ct,
1282 use_adaptive_freelists, dictionaryChoice) {}
1283
1284 virtual const char* short_name() const { return "ASCMS"; }
1285 virtual Generation::Name kind() { return Generation::ASConcurrentMarkSweep; }
1286
1287 virtual void update_counters();
1288 virtual void update_counters(size_t used);
1289 };
1290
1291 //
1292 // Closures of various sorts used by CMS to accomplish its work
1293 //
1294
1295 // This closure is used to check that a certain set of oops is empty.
1296 class FalseClosure: public OopClosure {
1297 public:
1298 void do_oop(oop* p) {
1299 guarantee(false, "Should be an empty set");
1300 }
1301 };
1302
1303 // This closure is used to do concurrent marking from the roots
1304 // following the first checkpoint.
1305 class MarkFromRootsClosure: public BitMapClosure {
1306 CMSCollector* _collector;
1307 MemRegion _span;
1308 CMSBitMap* _bitMap;
1309 CMSBitMap* _mut;
1310 CMSMarkStack* _markStack;
1311 CMSMarkStack* _revisitStack;
1312 bool _yield;
1313 int _skipBits;
1314 HeapWord* _finger;
1315 HeapWord* _threshold;
1316 DEBUG_ONLY(bool _verifying;)
1317
1318 public:
1319 MarkFromRootsClosure(CMSCollector* collector, MemRegion span,
1320 CMSBitMap* bitMap,
1321 CMSMarkStack* markStack,
1322 CMSMarkStack* revisitStack,
1323 bool should_yield, bool verifying = false);
1324 void do_bit(size_t offset);
1325 void reset(HeapWord* addr);
1326 inline void do_yield_check();
1327
1328 private:
1329 void scanOopsInOop(HeapWord* ptr);
1330 void do_yield_work();
1331 };
1332
1333 // This closure is used to do concurrent multi-threaded
1334 // marking from the roots following the first checkpoint.
1335 // XXX This should really be a subclass of The serial version
1336 // above, but i have not had the time to refactor things cleanly.
1337 // That willbe done for Dolphin.
1338 class Par_MarkFromRootsClosure: public BitMapClosure {
1339 CMSCollector* _collector;
1340 MemRegion _whole_span;
1341 MemRegion _span;
1342 CMSBitMap* _bit_map;
1343 CMSBitMap* _mut;
1344 OopTaskQueue* _work_queue;
1345 CMSMarkStack* _overflow_stack;
1346 CMSMarkStack* _revisit_stack;
1347 bool _yield;
1348 int _skip_bits;
1349 HeapWord* _finger;
1350 HeapWord* _threshold;
1351 CMSConcMarkingTask* _task;
1352 public:
1353 Par_MarkFromRootsClosure(CMSConcMarkingTask* task, CMSCollector* collector,
1354 MemRegion span,
1355 CMSBitMap* bit_map,
1356 OopTaskQueue* work_queue,
1357 CMSMarkStack* overflow_stack,
1358 CMSMarkStack* revisit_stack,
1359 bool should_yield);
1360 void do_bit(size_t offset);
1361 inline void do_yield_check();
1362
1363 private:
1364 void scan_oops_in_oop(HeapWord* ptr);
1365 void do_yield_work();
1366 bool get_work_from_overflow_stack();
1367 };
1368
1369 // The following closures are used to do certain kinds of verification of
1370 // CMS marking.
1371 class PushAndMarkVerifyClosure: public OopClosure {
1372 CMSCollector* _collector;
1373 MemRegion _span;
1374 CMSBitMap* _verification_bm;
1375 CMSBitMap* _cms_bm;
1376 CMSMarkStack* _mark_stack;
1377 public:
1378 PushAndMarkVerifyClosure(CMSCollector* cms_collector,
1379 MemRegion span,
1380 CMSBitMap* verification_bm,
1381 CMSBitMap* cms_bm,
1382 CMSMarkStack* mark_stack);
1383 void do_oop(oop* p);
1384 // Deal with a stack overflow condition
1385 void handle_stack_overflow(HeapWord* lost);
1386 };
1387
1388 class MarkFromRootsVerifyClosure: public BitMapClosure {
1389 CMSCollector* _collector;
1390 MemRegion _span;
1391 CMSBitMap* _verification_bm;
1392 CMSBitMap* _cms_bm;
1393 CMSMarkStack* _mark_stack;
1394 HeapWord* _finger;
1395 PushAndMarkVerifyClosure _pam_verify_closure;
1396 public:
1397 MarkFromRootsVerifyClosure(CMSCollector* collector, MemRegion span,
1398 CMSBitMap* verification_bm,
1399 CMSBitMap* cms_bm,
1400 CMSMarkStack* mark_stack);
1401 void do_bit(size_t offset);
1402 void reset(HeapWord* addr);
1403 };
1404
1405
1406 // This closure is used to check that a certain set of bits is
1407 // "empty" (i.e. the bit vector doesn't have any 1-bits).
1408 class FalseBitMapClosure: public BitMapClosure {
1409 public:
1410 void do_bit(size_t offset) {
1411 guarantee(false, "Should not have a 1 bit");
1412 }
1413 };
1414
1415 // This closure is used during the second checkpointing phase
1416 // to rescan the marked objects on the dirty cards in the mod
1417 // union table and the card table proper. It's invoked via
1418 // MarkFromDirtyCardsClosure below. It uses either
1419 // [Par_]MarkRefsIntoAndScanClosure (Par_ in the parallel case)
1420 // declared in genOopClosures.hpp to accomplish some of its work.
1421 // In the parallel case the bitMap is shared, so access to
1422 // it needs to be suitably synchronized for updates by embedded
1423 // closures that update it; however, this closure itself only
1424 // reads the bit_map and because it is idempotent, is immune to
1425 // reading stale values.
1426 class ScanMarkedObjectsAgainClosure: public UpwardsObjectClosure {
1427 #ifdef ASSERT
1428 CMSCollector* _collector;
1429 MemRegion _span;
1430 union {
1431 CMSMarkStack* _mark_stack;
1432 OopTaskQueue* _work_queue;
1433 };
1434 #endif // ASSERT
1435 bool _parallel;
1436 CMSBitMap* _bit_map;
1437 union {
1438 MarkRefsIntoAndScanClosure* _scan_closure;
1439 Par_MarkRefsIntoAndScanClosure* _par_scan_closure;
1440 };
1441
1442 public:
1443 ScanMarkedObjectsAgainClosure(CMSCollector* collector,
1444 MemRegion span,
1445 ReferenceProcessor* rp,
1446 CMSBitMap* bit_map,
1447 CMSMarkStack* mark_stack,
1448 CMSMarkStack* revisit_stack,
1449 MarkRefsIntoAndScanClosure* cl):
1450 #ifdef ASSERT
1451 _collector(collector),
1452 _span(span),
1453 _mark_stack(mark_stack),
1454 #endif // ASSERT
1455 _parallel(false),
1456 _bit_map(bit_map),
1457 _scan_closure(cl) { }
1458
1459 ScanMarkedObjectsAgainClosure(CMSCollector* collector,
1460 MemRegion span,
1461 ReferenceProcessor* rp,
1462 CMSBitMap* bit_map,
1463 OopTaskQueue* work_queue,
1464 CMSMarkStack* revisit_stack,
1465 Par_MarkRefsIntoAndScanClosure* cl):
1466 #ifdef ASSERT
1467 _collector(collector),
1468 _span(span),
1469 _work_queue(work_queue),
1470 #endif // ASSERT
1471 _parallel(true),
1472 _bit_map(bit_map),
1473 _par_scan_closure(cl) { }
1474
1475 void do_object(oop obj) {
1476 guarantee(false, "Call do_object_b(oop, MemRegion) instead");
1477 }
1478 bool do_object_b(oop obj) {
1479 guarantee(false, "Call do_object_b(oop, MemRegion) form instead");
1480 return false;
1481 }
1482 bool do_object_bm(oop p, MemRegion mr);
1483 };
1484
1485 // This closure is used during the second checkpointing phase
1486 // to rescan the marked objects on the dirty cards in the mod
1487 // union table and the card table proper. It invokes
1488 // ScanMarkedObjectsAgainClosure above to accomplish much of its work.
1489 // In the parallel case, the bit map is shared and requires
1490 // synchronized access.
1491 class MarkFromDirtyCardsClosure: public MemRegionClosure {
1492 CompactibleFreeListSpace* _space;
1493 ScanMarkedObjectsAgainClosure _scan_cl;
1494 size_t _num_dirty_cards;
1495
1496 public:
1497 MarkFromDirtyCardsClosure(CMSCollector* collector,
1498 MemRegion span,
1499 CompactibleFreeListSpace* space,
1500 CMSBitMap* bit_map,
1501 CMSMarkStack* mark_stack,
1502 CMSMarkStack* revisit_stack,
1503 MarkRefsIntoAndScanClosure* cl):
1504 _space(space),
1505 _num_dirty_cards(0),
1506 _scan_cl(collector, span, collector->ref_processor(), bit_map,
1507 mark_stack, revisit_stack, cl) { }
1508
1509 MarkFromDirtyCardsClosure(CMSCollector* collector,
1510 MemRegion span,
1511 CompactibleFreeListSpace* space,
1512 CMSBitMap* bit_map,
1513 OopTaskQueue* work_queue,
1514 CMSMarkStack* revisit_stack,
1515 Par_MarkRefsIntoAndScanClosure* cl):
1516 _space(space),
1517 _num_dirty_cards(0),
1518 _scan_cl(collector, span, collector->ref_processor(), bit_map,
1519 work_queue, revisit_stack, cl) { }
1520
1521 void do_MemRegion(MemRegion mr);
1522 void set_space(CompactibleFreeListSpace* space) { _space = space; }
1523 size_t num_dirty_cards() { return _num_dirty_cards; }
1524 };
1525
1526 // This closure is used in the non-product build to check
1527 // that there are no MemRegions with a certain property.
1528 class FalseMemRegionClosure: public MemRegionClosure {
1529 void do_MemRegion(MemRegion mr) {
1530 guarantee(!mr.is_empty(), "Shouldn't be empty");
1531 guarantee(false, "Should never be here");
1532 }
1533 };
1534
1535 // This closure is used during the precleaning phase
1536 // to "carefully" rescan marked objects on dirty cards.
1537 // It uses MarkRefsIntoAndScanClosure declared in genOopClosures.hpp
1538 // to accomplish some of its work.
1539 class ScanMarkedObjectsAgainCarefullyClosure: public ObjectClosureCareful {
1540 CMSCollector* _collector;
1541 MemRegion _span;
1542 bool _yield;
1543 Mutex* _freelistLock;
1544 CMSBitMap* _bitMap;
1545 CMSMarkStack* _markStack;
1546 MarkRefsIntoAndScanClosure* _scanningClosure;
1547
1548 public:
1549 ScanMarkedObjectsAgainCarefullyClosure(CMSCollector* collector,
1550 MemRegion span,
1551 CMSBitMap* bitMap,
1552 CMSMarkStack* markStack,
1553 CMSMarkStack* revisitStack,
1554 MarkRefsIntoAndScanClosure* cl,
1555 bool should_yield):
1556 _collector(collector),
1557 _span(span),
1558 _yield(should_yield),
1559 _bitMap(bitMap),
1560 _markStack(markStack),
1561 _scanningClosure(cl) {
1562 }
1563
1564 void do_object(oop p) {
1565 guarantee(false, "call do_object_careful instead");
1566 }
1567
1568 size_t do_object_careful(oop p) {
1569 guarantee(false, "Unexpected caller");
1570 return 0;
1571 }
1572
1573 size_t do_object_careful_m(oop p, MemRegion mr);
1574
1575 void setFreelistLock(Mutex* m) {
1576 _freelistLock = m;
1577 _scanningClosure->set_freelistLock(m);
1578 }
1579
1580 private:
1581 inline bool do_yield_check();
1582
1583 void do_yield_work();
1584 };
1585
1586 class SurvivorSpacePrecleanClosure: public ObjectClosureCareful {
1587 CMSCollector* _collector;
1588 MemRegion _span;
1589 bool _yield;
1590 CMSBitMap* _bit_map;
1591 CMSMarkStack* _mark_stack;
1592 PushAndMarkClosure* _scanning_closure;
1593 unsigned int _before_count;
1594
1595 public:
1596 SurvivorSpacePrecleanClosure(CMSCollector* collector,
1597 MemRegion span,
1598 CMSBitMap* bit_map,
1599 CMSMarkStack* mark_stack,
1600 PushAndMarkClosure* cl,
1601 unsigned int before_count,
1602 bool should_yield):
1603 _collector(collector),
1604 _span(span),
1605 _yield(should_yield),
1606 _bit_map(bit_map),
1607 _mark_stack(mark_stack),
1608 _scanning_closure(cl),
1609 _before_count(before_count)
1610 { }
1611
1612 void do_object(oop p) {
1613 guarantee(false, "call do_object_careful instead");
1614 }
1615
1616 size_t do_object_careful(oop p);
1617
1618 size_t do_object_careful_m(oop p, MemRegion mr) {
1619 guarantee(false, "Unexpected caller");
1620 return 0;
1621 }
1622
1623 private:
1624 inline void do_yield_check();
1625 void do_yield_work();
1626 };
1627
1628 // This closure is used to accomplish the sweeping work
1629 // after the second checkpoint but before the concurrent reset
1630 // phase.
1631 //
1632 // Terminology
1633 // left hand chunk (LHC) - block of one or more chunks currently being
1634 // coalesced. The LHC is available for coalescing with a new chunk.
1635 // right hand chunk (RHC) - block that is currently being swept that is
1636 // free or garbage that can be coalesced with the LHC.
1637 // _inFreeRange is true if there is currently a LHC
1638 // _lastFreeRangeCoalesced is true if the LHC consists of more than one chunk.
1639 // _freeRangeInFreeLists is true if the LHC is in the free lists.
1640 // _freeFinger is the address of the current LHC
1641 class SweepClosure: public BlkClosureCareful {
1642 CMSCollector* _collector; // collector doing the work
1643 ConcurrentMarkSweepGeneration* _g; // Generation being swept
1644 CompactibleFreeListSpace* _sp; // Space being swept
1645 HeapWord* _limit;
1646 Mutex* _freelistLock; // Free list lock (in space)
1647 CMSBitMap* _bitMap; // Marking bit map (in
1648 // generation)
1649 bool _inFreeRange; // Indicates if we are in the
1650 // midst of a free run
1651 bool _freeRangeInFreeLists;
1652 // Often, we have just found
1653 // a free chunk and started
1654 // a new free range; we do not
1655 // eagerly remove this chunk from
1656 // the free lists unless there is
1657 // a possibility of coalescing.
1658 // When true, this flag indicates
1659 // that the _freeFinger below
1660 // points to a potentially free chunk
1661 // that may still be in the free lists
1662 bool _lastFreeRangeCoalesced;
1663 // free range contains chunks
1664 // coalesced
1665 bool _yield;
1666 // Whether sweeping should be
1667 // done with yields. For instance
1668 // when done by the foreground
1669 // collector we shouldn't yield.
1670 HeapWord* _freeFinger; // When _inFreeRange is set, the
1671 // pointer to the "left hand
1672 // chunk"
1673 size_t _freeRangeSize;
1674 // When _inFreeRange is set, this
1675 // indicates the accumulated size
1676 // of the "left hand chunk"
1677 NOT_PRODUCT(
1678 size_t _numObjectsFreed;
1679 size_t _numWordsFreed;
1680 size_t _numObjectsLive;
1681 size_t _numWordsLive;
1682 size_t _numObjectsAlreadyFree;
1683 size_t _numWordsAlreadyFree;
1684 FreeChunk* _last_fc;
1685 )
1686 private:
1687 // Code that is common to a free chunk or garbage when
1688 // encountered during sweeping.
1689 void doPostIsFreeOrGarbageChunk(FreeChunk *fc,
1690 size_t chunkSize);
1691 // Process a free chunk during sweeping.
1692 void doAlreadyFreeChunk(FreeChunk *fc);
1693 // Process a garbage chunk during sweeping.
1694 size_t doGarbageChunk(FreeChunk *fc);
1695 // Process a live chunk during sweeping.
1696 size_t doLiveChunk(FreeChunk* fc);
1697
1698 // Accessors.
1699 HeapWord* freeFinger() const { return _freeFinger; }
1700 void set_freeFinger(HeapWord* v) { _freeFinger = v; }
1701 size_t freeRangeSize() const { return _freeRangeSize; }
1702 void set_freeRangeSize(size_t v) { _freeRangeSize = v; }
1703 bool inFreeRange() const { return _inFreeRange; }
1704 void set_inFreeRange(bool v) { _inFreeRange = v; }
1705 bool lastFreeRangeCoalesced() const { return _lastFreeRangeCoalesced; }
1706 void set_lastFreeRangeCoalesced(bool v) { _lastFreeRangeCoalesced = v; }
1707 bool freeRangeInFreeLists() const { return _freeRangeInFreeLists; }
1708 void set_freeRangeInFreeLists(bool v) { _freeRangeInFreeLists = v; }
1709
1710 // Initialize a free range.
1711 void initialize_free_range(HeapWord* freeFinger, bool freeRangeInFreeLists);
1712 // Return this chunk to the free lists.
1713 void flushCurFreeChunk(HeapWord* chunk, size_t size);
1714
1715 // Check if we should yield and do so when necessary.
1716 inline void do_yield_check(HeapWord* addr);
1717
1718 // Yield
1719 void do_yield_work(HeapWord* addr);
1720
1721 // Debugging/Printing
1722 void record_free_block_coalesced(FreeChunk* fc) const PRODUCT_RETURN;
1723
1724 public:
1725 SweepClosure(CMSCollector* collector, ConcurrentMarkSweepGeneration* g,
1726 CMSBitMap* bitMap, bool should_yield);
1727 ~SweepClosure();
1728
1729 size_t do_blk_careful(HeapWord* addr);
1730 };
1731
1732 // Closures related to weak references processing
1733
1734 // During CMS' weak reference processing, this is a
1735 // work-routine/closure used to complete transitive
1736 // marking of objects as live after a certain point
1737 // in which an initial set has been completely accumulated.
1738 class CMSDrainMarkingStackClosure: public VoidClosure {
1739 CMSCollector* _collector;
1740 MemRegion _span;
1741 CMSMarkStack* _mark_stack;
1742 CMSBitMap* _bit_map;
1743 CMSKeepAliveClosure* _keep_alive;
1744 public:
1745 CMSDrainMarkingStackClosure(CMSCollector* collector, MemRegion span,
1746 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
1747 CMSKeepAliveClosure* keep_alive):
1748 _collector(collector),
1749 _span(span),
1750 _bit_map(bit_map),
1751 _mark_stack(mark_stack),
1752 _keep_alive(keep_alive) { }
1753
1754 void do_void();
1755 };
1756
1757 // A parallel version of CMSDrainMarkingStackClosure above.
1758 class CMSParDrainMarkingStackClosure: public VoidClosure {
1759 CMSCollector* _collector;
1760 MemRegion _span;
1761 OopTaskQueue* _work_queue;
1762 CMSBitMap* _bit_map;
1763 CMSInnerParMarkAndPushClosure _mark_and_push;
1764
1765 public:
1766 CMSParDrainMarkingStackClosure(CMSCollector* collector,
1767 MemRegion span, CMSBitMap* bit_map,
1768 OopTaskQueue* work_queue):
1769 _collector(collector),
1770 _span(span),
1771 _bit_map(bit_map),
1772 _work_queue(work_queue),
1773 _mark_and_push(collector, span, bit_map, work_queue) { }
1774
1775 public:
1776 void trim_queue(uint max);
1777 void do_void();
1778 };
1779
1780 // Allow yielding or short-circuiting of reference list
1781 // prelceaning work.
1782 class CMSPrecleanRefsYieldClosure: public YieldClosure {
1783 CMSCollector* _collector;
1784 void do_yield_work();
1785 public:
1786 CMSPrecleanRefsYieldClosure(CMSCollector* collector):
1787 _collector(collector) {}
1788 virtual bool should_return();
1789 };
1790
1791
1792 // Convenience class that locks free list locks for given CMS collector
1793 class FreelistLocker: public StackObj {
1794 private:
1795 CMSCollector* _collector;
1796 public:
1797 FreelistLocker(CMSCollector* collector):
1798 _collector(collector) {
1799 _collector->getFreelistLocks();
1800 }
1801
1802 ~FreelistLocker() {
1803 _collector->releaseFreelistLocks();
1804 }
1805 };
1806
1807 // Mark all dead objects in a given space.
1808 class MarkDeadObjectsClosure: public BlkClosure {
1809 const CMSCollector* _collector;
1810 const CompactibleFreeListSpace* _sp;
1811 CMSBitMap* _live_bit_map;
1812 CMSBitMap* _dead_bit_map;
1813 public:
1814 MarkDeadObjectsClosure(const CMSCollector* collector,
1815 const CompactibleFreeListSpace* sp,
1816 CMSBitMap *live_bit_map,
1817 CMSBitMap *dead_bit_map) :
1818 _collector(collector),
1819 _sp(sp),
1820 _live_bit_map(live_bit_map),
1821 _dead_bit_map(dead_bit_map) {}
1822 size_t do_blk(HeapWord* addr);
1823 };