1 /*
2 * Copyright (c) 2001, 2010, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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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).
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23 */
24
25 // ConcurrentMarkSweepGeneration is in support of a concurrent
26 // mark-sweep old generation in the Detlefs-Printezis--Boehm-Demers-Schenker
27 // style. We assume, for now, that this generation is always the
28 // seniormost generation (modulo the PermGeneration), and for simplicity
29 // in the first implementation, that this generation is a single compactible
30 // space. Neither of these restrictions appears essential, and will be
31 // relaxed in the future when more time is available to implement the
32 // greater generality (and there's a need for it).
33 //
34 // Concurrent mode failures are currently handled by
35 // means of a sliding mark-compact.
36
37 class CMSAdaptiveSizePolicy;
38 class CMSConcMarkingTask;
39 class CMSGCAdaptivePolicyCounters;
40 class ConcurrentMarkSweepGeneration;
41 class ConcurrentMarkSweepPolicy;
42 class ConcurrentMarkSweepThread;
43 class CompactibleFreeListSpace;
44 class FreeChunk;
45 class PromotionInfo;
46 class ScanMarkedObjectsAgainCarefullyClosure;
47
48 // A generic CMS bit map. It's the basis for both the CMS marking bit map
49 // as well as for the mod union table (in each case only a subset of the
50 // methods are used). This is essentially a wrapper around the BitMap class,
51 // with one bit per (1<<_shifter) HeapWords. (i.e. for the marking bit map,
52 // we have _shifter == 0. and for the mod union table we have
53 // shifter == CardTableModRefBS::card_shift - LogHeapWordSize.)
54 // XXX 64-bit issues in BitMap?
55 class CMSBitMap VALUE_OBJ_CLASS_SPEC {
56 friend class VMStructs;
57
58 HeapWord* _bmStartWord; // base address of range covered by map
59 size_t _bmWordSize; // map size (in #HeapWords covered)
60 const int _shifter; // shifts to convert HeapWord to bit position
61 VirtualSpace _virtual_space; // underlying the bit map
62 BitMap _bm; // the bit map itself
63 public:
64 Mutex* const _lock; // mutex protecting _bm;
65
66 public:
67 // constructor
68 CMSBitMap(int shifter, int mutex_rank, const char* mutex_name);
69
70 // allocates the actual storage for the map
71 bool allocate(MemRegion mr);
72 // field getter
73 Mutex* lock() const { return _lock; }
74 // locking verifier convenience function
75 void assert_locked() const PRODUCT_RETURN;
76
77 // inquiries
78 HeapWord* startWord() const { return _bmStartWord; }
79 size_t sizeInWords() const { return _bmWordSize; }
80 size_t sizeInBits() const { return _bm.size(); }
81 // the following is one past the last word in space
82 HeapWord* endWord() const { return _bmStartWord + _bmWordSize; }
83
84 // reading marks
85 bool isMarked(HeapWord* addr) const;
86 bool par_isMarked(HeapWord* addr) const; // do not lock checks
87 bool isUnmarked(HeapWord* addr) const;
88 bool isAllClear() const;
89
90 // writing marks
91 void mark(HeapWord* addr);
92 // For marking by parallel GC threads;
93 // returns true if we did, false if another thread did
94 bool par_mark(HeapWord* addr);
95
96 void mark_range(MemRegion mr);
97 void par_mark_range(MemRegion mr);
98 void mark_large_range(MemRegion mr);
99 void par_mark_large_range(MemRegion mr);
100 void par_clear(HeapWord* addr); // For unmarking by parallel GC threads.
101 void clear_range(MemRegion mr);
102 void par_clear_range(MemRegion mr);
103 void clear_large_range(MemRegion mr);
104 void par_clear_large_range(MemRegion mr);
105 void clear_all();
106 void clear_all_incrementally(); // Not yet implemented!!
107
108 NOT_PRODUCT(
109 // checks the memory region for validity
110 void region_invariant(MemRegion mr);
111 )
112
113 // iteration
114 void iterate(BitMapClosure* cl) {
115 _bm.iterate(cl);
116 }
117 void iterate(BitMapClosure* cl, HeapWord* left, HeapWord* right);
118 void dirty_range_iterate_clear(MemRegionClosure* cl);
119 void dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl);
120
121 // auxiliary support for iteration
122 HeapWord* getNextMarkedWordAddress(HeapWord* addr) const;
123 HeapWord* getNextMarkedWordAddress(HeapWord* start_addr,
124 HeapWord* end_addr) const;
125 HeapWord* getNextUnmarkedWordAddress(HeapWord* addr) const;
126 HeapWord* getNextUnmarkedWordAddress(HeapWord* start_addr,
127 HeapWord* end_addr) const;
128 MemRegion getAndClearMarkedRegion(HeapWord* addr);
129 MemRegion getAndClearMarkedRegion(HeapWord* start_addr,
130 HeapWord* end_addr);
131
132 // conversion utilities
133 HeapWord* offsetToHeapWord(size_t offset) const;
134 size_t heapWordToOffset(HeapWord* addr) const;
135 size_t heapWordDiffToOffsetDiff(size_t diff) const;
136
137 // debugging
138 // is this address range covered by the bit-map?
139 NOT_PRODUCT(
140 bool covers(MemRegion mr) const;
141 bool covers(HeapWord* start, size_t size = 0) const;
142 )
143 void verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) PRODUCT_RETURN;
144 };
145
146 // Represents a marking stack used by the CMS collector.
147 // Ideally this should be GrowableArray<> just like MSC's marking stack(s).
148 class CMSMarkStack: public CHeapObj {
149 //
150 friend class CMSCollector; // to get at expasion stats further below
151 //
152
153 VirtualSpace _virtual_space; // space for the stack
154 oop* _base; // bottom of stack
155 size_t _index; // one more than last occupied index
156 size_t _capacity; // max #elements
157 Mutex _par_lock; // an advisory lock used in case of parallel access
158 NOT_PRODUCT(size_t _max_depth;) // max depth plumbed during run
159
160 protected:
161 size_t _hit_limit; // we hit max stack size limit
162 size_t _failed_double; // we failed expansion before hitting limit
163
164 public:
165 CMSMarkStack():
166 _par_lock(Mutex::event, "CMSMarkStack._par_lock", true),
167 _hit_limit(0),
168 _failed_double(0) {}
169
170 bool allocate(size_t size);
171
172 size_t capacity() const { return _capacity; }
173
174 oop pop() {
175 if (!isEmpty()) {
176 return _base[--_index] ;
177 }
178 return NULL;
179 }
180
181 bool push(oop ptr) {
182 if (isFull()) {
183 return false;
184 } else {
185 _base[_index++] = ptr;
186 NOT_PRODUCT(_max_depth = MAX2(_max_depth, _index));
187 return true;
188 }
189 }
190
191 bool isEmpty() const { return _index == 0; }
192 bool isFull() const {
193 assert(_index <= _capacity, "buffer overflow");
194 return _index == _capacity;
195 }
196
197 size_t length() { return _index; }
198
199 // "Parallel versions" of some of the above
200 oop par_pop() {
201 // lock and pop
202 MutexLockerEx x(&_par_lock, Mutex::_no_safepoint_check_flag);
203 return pop();
204 }
205
206 bool par_push(oop ptr) {
207 // lock and push
208 MutexLockerEx x(&_par_lock, Mutex::_no_safepoint_check_flag);
209 return push(ptr);
210 }
211
212 // Forcibly reset the stack, losing all of its contents.
213 void reset() {
214 _index = 0;
215 }
216
217 // Expand the stack, typically in response to an overflow condition
218 void expand();
219
220 // Compute the least valued stack element.
221 oop least_value(HeapWord* low) {
222 oop least = (oop)low;
223 for (size_t i = 0; i < _index; i++) {
224 least = MIN2(least, _base[i]);
225 }
226 return least;
227 }
228
229 // Exposed here to allow stack expansion in || case
230 Mutex* par_lock() { return &_par_lock; }
231 };
232
233 class CardTableRS;
234 class CMSParGCThreadState;
235
236 class ModUnionClosure: public MemRegionClosure {
237 protected:
238 CMSBitMap* _t;
239 public:
240 ModUnionClosure(CMSBitMap* t): _t(t) { }
241 void do_MemRegion(MemRegion mr);
242 };
243
244 class ModUnionClosurePar: public ModUnionClosure {
245 public:
246 ModUnionClosurePar(CMSBitMap* t): ModUnionClosure(t) { }
247 void do_MemRegion(MemRegion mr);
248 };
249
250 // Survivor Chunk Array in support of parallelization of
251 // Survivor Space rescan.
252 class ChunkArray: public CHeapObj {
253 size_t _index;
254 size_t _capacity;
255 size_t _overflows;
256 HeapWord** _array; // storage for array
257
258 public:
259 ChunkArray() : _index(0), _capacity(0), _overflows(0), _array(NULL) {}
260 ChunkArray(HeapWord** a, size_t c):
261 _index(0), _capacity(c), _overflows(0), _array(a) {}
262
263 HeapWord** array() { return _array; }
264 void set_array(HeapWord** a) { _array = a; }
265
266 size_t capacity() { return _capacity; }
267 void set_capacity(size_t c) { _capacity = c; }
268
269 size_t end() {
270 assert(_index <= capacity(),
271 err_msg("_index (" SIZE_FORMAT ") > _capacity (" SIZE_FORMAT "): out of bounds",
272 _index, _capacity));
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 if (_overflows > 0 && PrintCMSStatistics > 1) {
284 warning("CMS: ChunkArray[" SIZE_FORMAT "] overflowed " SIZE_FORMAT " times",
285 _capacity, _overflows);
286 }
287 _overflows = 0;
288 }
289
290 void record_sample(HeapWord* p, size_t sz) {
291 // For now we do not do anything with the size
292 if (_index < _capacity) {
293 _array[_index++] = p;
294 } else {
295 ++_overflows;
296 assert(_index == _capacity,
297 err_msg("_index (" SIZE_FORMAT ") > _capacity (" SIZE_FORMAT
298 "): out of bounds at overflow#" SIZE_FORMAT,
299 _index, _capacity, _overflows));
300 }
301 }
302 };
303
304 //
305 // Timing, allocation and promotion statistics for gc scheduling and incremental
306 // mode pacing. Most statistics are exponential averages.
307 //
308 class CMSStats VALUE_OBJ_CLASS_SPEC {
309 private:
310 ConcurrentMarkSweepGeneration* const _cms_gen; // The cms (old) gen.
311
312 // The following are exponential averages with factor alpha:
313 // avg = (100 - alpha) * avg + alpha * cur_sample
314 //
315 // The durations measure: end_time[n] - start_time[n]
316 // The periods measure: start_time[n] - start_time[n-1]
317 //
318 // The cms period and duration include only concurrent collections; time spent
319 // in foreground cms collections due to System.gc() or because of a failure to
320 // keep up are not included.
321 //
322 // There are 3 alphas to "bootstrap" the statistics. The _saved_alpha is the
323 // real value, but is used only after the first period. A value of 100 is
324 // used for the first sample so it gets the entire weight.
325 unsigned int _saved_alpha; // 0-100
326 unsigned int _gc0_alpha;
327 unsigned int _cms_alpha;
328
329 double _gc0_duration;
330 double _gc0_period;
331 size_t _gc0_promoted; // bytes promoted per gc0
332 double _cms_duration;
333 double _cms_duration_pre_sweep; // time from initiation to start of sweep
334 double _cms_duration_per_mb;
335 double _cms_period;
336 size_t _cms_allocated; // bytes of direct allocation per gc0 period
337
338 // Timers.
339 elapsedTimer _cms_timer;
340 TimeStamp _gc0_begin_time;
341 TimeStamp _cms_begin_time;
342 TimeStamp _cms_end_time;
343
344 // Snapshots of the amount used in the CMS generation.
345 size_t _cms_used_at_gc0_begin;
346 size_t _cms_used_at_gc0_end;
347 size_t _cms_used_at_cms_begin;
348
349 // Used to prevent the duty cycle from being reduced in the middle of a cms
350 // cycle.
351 bool _allow_duty_cycle_reduction;
352
353 enum {
354 _GC0_VALID = 0x1,
355 _CMS_VALID = 0x2,
356 _ALL_VALID = _GC0_VALID | _CMS_VALID
357 };
358
359 unsigned int _valid_bits;
360
361 unsigned int _icms_duty_cycle; // icms duty cycle (0-100).
362
363 protected:
364
365 // Return a duty cycle that avoids wild oscillations, by limiting the amount
366 // of change between old_duty_cycle and new_duty_cycle (the latter is treated
367 // as a recommended value).
368 static unsigned int icms_damped_duty_cycle(unsigned int old_duty_cycle,
369 unsigned int new_duty_cycle);
370 unsigned int icms_update_duty_cycle_impl();
371
372 // In support of adjusting of cms trigger ratios based on history
373 // of concurrent mode failure.
374 double cms_free_adjustment_factor(size_t free) const;
375 void adjust_cms_free_adjustment_factor(bool fail, size_t free);
376
377 public:
378 CMSStats(ConcurrentMarkSweepGeneration* cms_gen,
379 unsigned int alpha = CMSExpAvgFactor);
380
381 // Whether or not the statistics contain valid data; higher level statistics
382 // cannot be called until this returns true (they require at least one young
383 // gen and one cms cycle to have completed).
384 bool valid() const;
385
386 // Record statistics.
387 void record_gc0_begin();
388 void record_gc0_end(size_t cms_gen_bytes_used);
389 void record_cms_begin();
390 void record_cms_end();
391
392 // Allow management of the cms timer, which must be stopped/started around
393 // yield points.
394 elapsedTimer& cms_timer() { return _cms_timer; }
395 void start_cms_timer() { _cms_timer.start(); }
396 void stop_cms_timer() { _cms_timer.stop(); }
397
398 // Basic statistics; units are seconds or bytes.
399 double gc0_period() const { return _gc0_period; }
400 double gc0_duration() const { return _gc0_duration; }
401 size_t gc0_promoted() const { return _gc0_promoted; }
402 double cms_period() const { return _cms_period; }
403 double cms_duration() const { return _cms_duration; }
404 double cms_duration_per_mb() const { return _cms_duration_per_mb; }
405 size_t cms_allocated() const { return _cms_allocated; }
406
407 size_t cms_used_at_gc0_end() const { return _cms_used_at_gc0_end;}
408
409 // Seconds since the last background cms cycle began or ended.
410 double cms_time_since_begin() const;
411 double cms_time_since_end() const;
412
413 // Higher level statistics--caller must check that valid() returns true before
414 // calling.
415
416 // Returns bytes promoted per second of wall clock time.
417 double promotion_rate() const;
418
419 // Returns bytes directly allocated per second of wall clock time.
420 double cms_allocation_rate() const;
421
422 // Rate at which space in the cms generation is being consumed (sum of the
423 // above two).
424 double cms_consumption_rate() const;
425
426 // Returns an estimate of the number of seconds until the cms generation will
427 // fill up, assuming no collection work is done.
428 double time_until_cms_gen_full() const;
429
430 // Returns an estimate of the number of seconds remaining until
431 // the cms generation collection should start.
432 double time_until_cms_start() const;
433
434 // End of higher level statistics.
435
436 // Returns the cms incremental mode duty cycle, as a percentage (0-100).
437 unsigned int icms_duty_cycle() const { return _icms_duty_cycle; }
438
439 // Update the duty cycle and return the new value.
440 unsigned int icms_update_duty_cycle();
441
442 // Debugging.
443 void print_on(outputStream* st) const PRODUCT_RETURN;
444 void print() const { print_on(gclog_or_tty); }
445 };
446
447 // A closure related to weak references processing which
448 // we embed in the CMSCollector, since we need to pass
449 // it to the reference processor for secondary filtering
450 // of references based on reachability of referent;
451 // see role of _is_alive_non_header closure in the
452 // ReferenceProcessor class.
453 // For objects in the CMS generation, this closure checks
454 // if the object is "live" (reachable). Used in weak
455 // reference processing.
456 class CMSIsAliveClosure: public BoolObjectClosure {
457 const MemRegion _span;
458 const CMSBitMap* _bit_map;
459
460 friend class CMSCollector;
461 public:
462 CMSIsAliveClosure(MemRegion span,
463 CMSBitMap* bit_map):
464 _span(span),
465 _bit_map(bit_map) {
466 assert(!span.is_empty(), "Empty span could spell trouble");
467 }
468
469 void do_object(oop obj) {
470 assert(false, "not to be invoked");
471 }
472
473 bool do_object_b(oop obj);
474 };
475
476
477 // Implements AbstractRefProcTaskExecutor for CMS.
478 class CMSRefProcTaskExecutor: public AbstractRefProcTaskExecutor {
479 public:
480
481 CMSRefProcTaskExecutor(CMSCollector& collector)
482 : _collector(collector)
483 { }
484
485 // Executes a task using worker threads.
486 virtual void execute(ProcessTask& task);
487 virtual void execute(EnqueueTask& task);
488 private:
489 CMSCollector& _collector;
490 };
491
492
493 class CMSCollector: public CHeapObj {
494 friend class VMStructs;
495 friend class ConcurrentMarkSweepThread;
496 friend class ConcurrentMarkSweepGeneration;
497 friend class CompactibleFreeListSpace;
498 friend class CMSParRemarkTask;
499 friend class CMSConcMarkingTask;
500 friend class CMSRefProcTaskProxy;
501 friend class CMSRefProcTaskExecutor;
502 friend class ScanMarkedObjectsAgainCarefullyClosure; // for sampling eden
503 friend class SurvivorSpacePrecleanClosure; // --- ditto -------
504 friend class PushOrMarkClosure; // to access _restart_addr
505 friend class Par_PushOrMarkClosure; // to access _restart_addr
506 friend class MarkFromRootsClosure; // -- ditto --
507 // ... and for clearing cards
508 friend class Par_MarkFromRootsClosure; // to access _restart_addr
509 // ... and for clearing cards
510 friend class Par_ConcMarkingClosure; // to access _restart_addr etc.
511 friend class MarkFromRootsVerifyClosure; // to access _restart_addr
512 friend class PushAndMarkVerifyClosure; // -- ditto --
513 friend class MarkRefsIntoAndScanClosure; // to access _overflow_list
514 friend class PushAndMarkClosure; // -- ditto --
515 friend class Par_PushAndMarkClosure; // -- ditto --
516 friend class CMSKeepAliveClosure; // -- ditto --
517 friend class CMSDrainMarkingStackClosure; // -- ditto --
518 friend class CMSInnerParMarkAndPushClosure; // -- ditto --
519 NOT_PRODUCT(friend class ScanMarkedObjectsAgainClosure;) // assertion on _overflow_list
520 friend class ReleaseForegroundGC; // to access _foregroundGCShouldWait
521 friend class VM_CMS_Operation;
522 friend class VM_CMS_Initial_Mark;
523 friend class VM_CMS_Final_Remark;
524 friend class TraceCMSMemoryManagerStats;
525
526 private:
527 jlong _time_of_last_gc;
528 void update_time_of_last_gc(jlong now) {
529 _time_of_last_gc = now;
530 }
531
532 OopTaskQueueSet* _task_queues;
533
534 // Overflow list of grey objects, threaded through mark-word
535 // Manipulated with CAS in the parallel/multi-threaded case.
536 oop _overflow_list;
537 // The following array-pair keeps track of mark words
538 // displaced for accomodating overflow list above.
539 // This code will likely be revisited under RFE#4922830.
540 Stack<oop> _preserved_oop_stack;
541 Stack<markOop> _preserved_mark_stack;
542
543 int* _hash_seed;
544
545 // In support of multi-threaded concurrent phases
546 YieldingFlexibleWorkGang* _conc_workers;
547
548 // Performance Counters
549 CollectorCounters* _gc_counters;
550
551 // Initialization Errors
552 bool _completed_initialization;
553
554 // In support of ExplicitGCInvokesConcurrent
555 static bool _full_gc_requested;
556 unsigned int _collection_count_start;
557
558 // Should we unload classes this concurrent cycle?
559 bool _should_unload_classes;
560 unsigned int _concurrent_cycles_since_last_unload;
561 unsigned int concurrent_cycles_since_last_unload() const {
562 return _concurrent_cycles_since_last_unload;
563 }
564 // Did we (allow) unload classes in the previous concurrent cycle?
565 bool unloaded_classes_last_cycle() const {
566 return concurrent_cycles_since_last_unload() == 0;
567 }
568 // Root scanning options for perm gen
569 int _roots_scanning_options;
570 int roots_scanning_options() const { return _roots_scanning_options; }
571 void add_root_scanning_option(int o) { _roots_scanning_options |= o; }
572 void remove_root_scanning_option(int o) { _roots_scanning_options &= ~o; }
573
574 // Verification support
575 CMSBitMap _verification_mark_bm;
576 void verify_after_remark_work_1();
577 void verify_after_remark_work_2();
578
579 // true if any verification flag is on.
580 bool _verifying;
581 bool verifying() const { return _verifying; }
582 void set_verifying(bool v) { _verifying = v; }
583
584 // Collector policy
585 ConcurrentMarkSweepPolicy* _collector_policy;
586 ConcurrentMarkSweepPolicy* collector_policy() { return _collector_policy; }
587
588 // XXX Move these to CMSStats ??? FIX ME !!!
589 elapsedTimer _inter_sweep_timer; // time between sweeps
590 elapsedTimer _intra_sweep_timer; // time _in_ sweeps
591 // padded decaying average estimates of the above
592 AdaptivePaddedAverage _inter_sweep_estimate;
593 AdaptivePaddedAverage _intra_sweep_estimate;
594
595 protected:
596 ConcurrentMarkSweepGeneration* _cmsGen; // old gen (CMS)
597 ConcurrentMarkSweepGeneration* _permGen; // perm gen
598 MemRegion _span; // span covering above two
599 CardTableRS* _ct; // card table
600
601 // CMS marking support structures
602 CMSBitMap _markBitMap;
603 CMSBitMap _modUnionTable;
604 CMSMarkStack _markStack;
605 CMSMarkStack _revisitStack; // used to keep track of klassKlass objects
606 // to revisit
607 CMSBitMap _perm_gen_verify_bit_map; // Mark bit map for perm gen verification support.
608
609 HeapWord* _restart_addr; // in support of marking stack overflow
610 void lower_restart_addr(HeapWord* low);
611
612 // Counters in support of marking stack / work queue overflow handling:
613 // a non-zero value indicates certain types of overflow events during
614 // the current CMS cycle and could lead to stack resizing efforts at
615 // an opportune future time.
616 size_t _ser_pmc_preclean_ovflw;
617 size_t _ser_pmc_remark_ovflw;
618 size_t _par_pmc_remark_ovflw;
619 size_t _ser_kac_preclean_ovflw;
620 size_t _ser_kac_ovflw;
621 size_t _par_kac_ovflw;
622 NOT_PRODUCT(ssize_t _num_par_pushes;)
623
624 // ("Weak") Reference processing support
625 ReferenceProcessor* _ref_processor;
626 CMSIsAliveClosure _is_alive_closure;
627 // keep this textually after _markBitMap and _span; c'tor dependency
628
629 ConcurrentMarkSweepThread* _cmsThread; // the thread doing the work
630 ModUnionClosure _modUnionClosure;
631 ModUnionClosurePar _modUnionClosurePar;
632
633 // CMS abstract state machine
634 // initial_state: Idling
635 // next_state(Idling) = {Marking}
636 // next_state(Marking) = {Precleaning, Sweeping}
637 // next_state(Precleaning) = {AbortablePreclean, FinalMarking}
638 // next_state(AbortablePreclean) = {FinalMarking}
639 // next_state(FinalMarking) = {Sweeping}
640 // next_state(Sweeping) = {Resizing}
641 // next_state(Resizing) = {Resetting}
642 // next_state(Resetting) = {Idling}
643 // The numeric values below are chosen so that:
644 // . _collectorState <= Idling == post-sweep && pre-mark
645 // . _collectorState in (Idling, Sweeping) == {initial,final}marking ||
646 // precleaning || abortablePrecleanb
647 public:
648 enum CollectorState {
649 Resizing = 0,
650 Resetting = 1,
651 Idling = 2,
652 InitialMarking = 3,
653 Marking = 4,
654 Precleaning = 5,
655 AbortablePreclean = 6,
656 FinalMarking = 7,
657 Sweeping = 8
658 };
659 protected:
660 static CollectorState _collectorState;
661
662 // State related to prologue/epilogue invocation for my generations
663 bool _between_prologue_and_epilogue;
664
665 // Signalling/State related to coordination between fore- and backgroud GC
666 // Note: When the baton has been passed from background GC to foreground GC,
667 // _foregroundGCIsActive is true and _foregroundGCShouldWait is false.
668 static bool _foregroundGCIsActive; // true iff foreground collector is active or
669 // wants to go active
670 static bool _foregroundGCShouldWait; // true iff background GC is active and has not
671 // yet passed the baton to the foreground GC
672
673 // Support for CMSScheduleRemark (abortable preclean)
674 bool _abort_preclean;
675 bool _start_sampling;
676
677 int _numYields;
678 size_t _numDirtyCards;
679 size_t _sweep_count;
680 // number of full gc's since the last concurrent gc.
681 uint _full_gcs_since_conc_gc;
682
683 // occupancy used for bootstrapping stats
684 double _bootstrap_occupancy;
685
686 // timer
687 elapsedTimer _timer;
688
689 // Timing, allocation and promotion statistics, used for scheduling.
690 CMSStats _stats;
691
692 // Allocation limits installed in the young gen, used only in
693 // CMSIncrementalMode. When an allocation in the young gen would cross one of
694 // these limits, the cms generation is notified and the cms thread is started
695 // or stopped, respectively.
696 HeapWord* _icms_start_limit;
697 HeapWord* _icms_stop_limit;
698
699 enum CMS_op_type {
700 CMS_op_checkpointRootsInitial,
701 CMS_op_checkpointRootsFinal
702 };
703
704 void do_CMS_operation(CMS_op_type op);
705 bool stop_world_and_do(CMS_op_type op);
706
707 OopTaskQueueSet* task_queues() { return _task_queues; }
708 int* hash_seed(int i) { return &_hash_seed[i]; }
709 YieldingFlexibleWorkGang* conc_workers() { return _conc_workers; }
710
711 // Support for parallelizing Eden rescan in CMS remark phase
712 void sample_eden(); // ... sample Eden space top
713
714 private:
715 // Support for parallelizing young gen rescan in CMS remark phase
716 Generation* _young_gen; // the younger gen
717 HeapWord** _top_addr; // ... Top of Eden
718 HeapWord** _end_addr; // ... End of Eden
719 HeapWord** _eden_chunk_array; // ... Eden partitioning array
720 size_t _eden_chunk_index; // ... top (exclusive) of array
721 size_t _eden_chunk_capacity; // ... max entries in array
722
723 // Support for parallelizing survivor space rescan
724 HeapWord** _survivor_chunk_array;
725 size_t _survivor_chunk_index;
726 size_t _survivor_chunk_capacity;
727 size_t* _cursor;
728 ChunkArray* _survivor_plab_array;
729
730 // Support for marking stack overflow handling
731 bool take_from_overflow_list(size_t num, CMSMarkStack* to_stack);
732 bool par_take_from_overflow_list(size_t num,
733 OopTaskQueue* to_work_q,
734 int no_of_gc_threads);
735 void push_on_overflow_list(oop p);
736 void par_push_on_overflow_list(oop p);
737 // the following is, obviously, not, in general, "MT-stable"
738 bool overflow_list_is_empty() const;
739
740 void preserve_mark_if_necessary(oop p);
741 void par_preserve_mark_if_necessary(oop p);
742 void preserve_mark_work(oop p, markOop m);
743 void restore_preserved_marks_if_any();
744 NOT_PRODUCT(bool no_preserved_marks() const;)
745 // in support of testing overflow code
746 NOT_PRODUCT(int _overflow_counter;)
747 NOT_PRODUCT(bool simulate_overflow();) // sequential
748 NOT_PRODUCT(bool par_simulate_overflow();) // MT version
749
750 // CMS work methods
751 void checkpointRootsInitialWork(bool asynch); // initial checkpoint work
752
753 // a return value of false indicates failure due to stack overflow
754 bool markFromRootsWork(bool asynch); // concurrent marking work
755
756 public: // FIX ME!!! only for testing
757 bool do_marking_st(bool asynch); // single-threaded marking
758 bool do_marking_mt(bool asynch); // multi-threaded marking
759
760 private:
761
762 // concurrent precleaning work
763 size_t preclean_mod_union_table(ConcurrentMarkSweepGeneration* gen,
764 ScanMarkedObjectsAgainCarefullyClosure* cl);
765 size_t preclean_card_table(ConcurrentMarkSweepGeneration* gen,
766 ScanMarkedObjectsAgainCarefullyClosure* cl);
767 // Does precleaning work, returning a quantity indicative of
768 // the amount of "useful work" done.
769 size_t preclean_work(bool clean_refs, bool clean_survivors);
770 void abortable_preclean(); // Preclean while looking for possible abort
771 void initialize_sequential_subtasks_for_young_gen_rescan(int i);
772 // Helper function for above; merge-sorts the per-thread plab samples
773 void merge_survivor_plab_arrays(ContiguousSpace* surv, int no_of_gc_threads);
774 // Resets (i.e. clears) the per-thread plab sample vectors
775 void reset_survivor_plab_arrays();
776
777 // final (second) checkpoint work
778 void checkpointRootsFinalWork(bool asynch, bool clear_all_soft_refs,
779 bool init_mark_was_synchronous);
780 // work routine for parallel version of remark
781 void do_remark_parallel();
782 // work routine for non-parallel version of remark
783 void do_remark_non_parallel();
784 // reference processing work routine (during second checkpoint)
785 void refProcessingWork(bool asynch, bool clear_all_soft_refs);
786
787 // concurrent sweeping work
788 void sweepWork(ConcurrentMarkSweepGeneration* gen, bool asynch);
789
790 // (concurrent) resetting of support data structures
791 void reset(bool asynch);
792
793 // Clear _expansion_cause fields of constituent generations
794 void clear_expansion_cause();
795
796 // An auxilliary method used to record the ends of
797 // used regions of each generation to limit the extent of sweep
798 void save_sweep_limits();
799
800 // Resize the generations included in the collector.
801 void compute_new_size();
802
803 // A work method used by foreground collection to determine
804 // what type of collection (compacting or not, continuing or fresh)
805 // it should do.
806 void decide_foreground_collection_type(bool clear_all_soft_refs,
807 bool* should_compact, bool* should_start_over);
808
809 // A work method used by the foreground collector to do
810 // a mark-sweep-compact.
811 void do_compaction_work(bool clear_all_soft_refs);
812
813 // A work method used by the foreground collector to do
814 // a mark-sweep, after taking over from a possibly on-going
815 // concurrent mark-sweep collection.
816 void do_mark_sweep_work(bool clear_all_soft_refs,
817 CollectorState first_state, bool should_start_over);
818
819 // If the backgrould GC is active, acquire control from the background
820 // GC and do the collection.
821 void acquire_control_and_collect(bool full, bool clear_all_soft_refs);
822
823 // For synchronizing passing of control from background to foreground
824 // GC. waitForForegroundGC() is called by the background
825 // collector. It if had to wait for a foreground collection,
826 // it returns true and the background collection should assume
827 // that the collection was finished by the foreground
828 // collector.
829 bool waitForForegroundGC();
830
831 // Incremental mode triggering: recompute the icms duty cycle and set the
832 // allocation limits in the young gen.
833 void icms_update_allocation_limits();
834
835 size_t block_size_using_printezis_bits(HeapWord* addr) const;
836 size_t block_size_if_printezis_bits(HeapWord* addr) const;
837 HeapWord* next_card_start_after_block(HeapWord* addr) const;
838
839 void setup_cms_unloading_and_verification_state();
840 public:
841 CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
842 ConcurrentMarkSweepGeneration* permGen,
843 CardTableRS* ct,
844 ConcurrentMarkSweepPolicy* cp);
845 ConcurrentMarkSweepThread* cmsThread() { return _cmsThread; }
846
847 ReferenceProcessor* ref_processor() { return _ref_processor; }
848 void ref_processor_init();
849
850 Mutex* bitMapLock() const { return _markBitMap.lock(); }
851 static CollectorState abstract_state() { return _collectorState; }
852
853 bool should_abort_preclean() const; // Whether preclean should be aborted.
854 size_t get_eden_used() const;
855 size_t get_eden_capacity() const;
856
857 ConcurrentMarkSweepGeneration* cmsGen() { return _cmsGen; }
858
859 // locking checks
860 NOT_PRODUCT(static bool have_cms_token();)
861
862 // XXXPERM bool should_collect(bool full, size_t size, bool tlab);
863 bool shouldConcurrentCollect();
864
865 void collect(bool full,
866 bool clear_all_soft_refs,
867 size_t size,
868 bool tlab);
869 void collect_in_background(bool clear_all_soft_refs);
870 void collect_in_foreground(bool clear_all_soft_refs);
871
872 // In support of ExplicitGCInvokesConcurrent
873 static void request_full_gc(unsigned int full_gc_count);
874 // Should we unload classes in a particular concurrent cycle?
875 bool should_unload_classes() const {
876 return _should_unload_classes;
877 }
878 bool update_should_unload_classes();
879
880 void direct_allocated(HeapWord* start, size_t size);
881
882 // Object is dead if not marked and current phase is sweeping.
883 bool is_dead_obj(oop obj) const;
884
885 // After a promotion (of "start"), do any necessary marking.
886 // If "par", then it's being done by a parallel GC thread.
887 // The last two args indicate if we need precise marking
888 // and if so the size of the object so it can be dirtied
889 // in its entirety.
890 void promoted(bool par, HeapWord* start,
891 bool is_obj_array, size_t obj_size);
892
893 HeapWord* allocation_limit_reached(Space* space, HeapWord* top,
894 size_t word_size);
895
896 void getFreelistLocks() const;
897 void releaseFreelistLocks() const;
898 bool haveFreelistLocks() const;
899
900 // GC prologue and epilogue
901 void gc_prologue(bool full);
902 void gc_epilogue(bool full);
903
904 jlong time_of_last_gc(jlong now) {
905 if (_collectorState <= Idling) {
906 // gc not in progress
907 return _time_of_last_gc;
908 } else {
909 // collection in progress
910 return now;
911 }
912 }
913
914 // Support for parallel remark of survivor space
915 void* get_data_recorder(int thr_num);
916
917 CMSBitMap* markBitMap() { return &_markBitMap; }
918 void directAllocated(HeapWord* start, size_t size);
919
920 // main CMS steps and related support
921 void checkpointRootsInitial(bool asynch);
922 bool markFromRoots(bool asynch); // a return value of false indicates failure
923 // due to stack overflow
924 void preclean();
925 void checkpointRootsFinal(bool asynch, bool clear_all_soft_refs,
926 bool init_mark_was_synchronous);
927 void sweep(bool asynch);
928
929 // Check that the currently executing thread is the expected
930 // one (foreground collector or background collector).
931 static void check_correct_thread_executing() PRODUCT_RETURN;
932 // XXXPERM void print_statistics() PRODUCT_RETURN;
933
934 bool is_cms_reachable(HeapWord* addr);
935
936 // Performance Counter Support
937 CollectorCounters* counters() { return _gc_counters; }
938
939 // timer stuff
940 void startTimer() { assert(!_timer.is_active(), "Error"); _timer.start(); }
941 void stopTimer() { assert( _timer.is_active(), "Error"); _timer.stop(); }
942 void resetTimer() { assert(!_timer.is_active(), "Error"); _timer.reset(); }
943 double timerValue() { assert(!_timer.is_active(), "Error"); return _timer.seconds(); }
944
945 int yields() { return _numYields; }
946 void resetYields() { _numYields = 0; }
947 void incrementYields() { _numYields++; }
948 void resetNumDirtyCards() { _numDirtyCards = 0; }
949 void incrementNumDirtyCards(size_t num) { _numDirtyCards += num; }
950 size_t numDirtyCards() { return _numDirtyCards; }
951
952 static bool foregroundGCShouldWait() { return _foregroundGCShouldWait; }
953 static void set_foregroundGCShouldWait(bool v) { _foregroundGCShouldWait = v; }
954 static bool foregroundGCIsActive() { return _foregroundGCIsActive; }
955 static void set_foregroundGCIsActive(bool v) { _foregroundGCIsActive = v; }
956 size_t sweep_count() const { return _sweep_count; }
957 void increment_sweep_count() { _sweep_count++; }
958
959 // Timers/stats for gc scheduling and incremental mode pacing.
960 CMSStats& stats() { return _stats; }
961
962 // Convenience methods that check whether CMSIncrementalMode is enabled and
963 // forward to the corresponding methods in ConcurrentMarkSweepThread.
964 static void start_icms();
965 static void stop_icms(); // Called at the end of the cms cycle.
966 static void disable_icms(); // Called before a foreground collection.
967 static void enable_icms(); // Called after a foreground collection.
968 void icms_wait(); // Called at yield points.
969
970 // Adaptive size policy
971 CMSAdaptiveSizePolicy* size_policy();
972 CMSGCAdaptivePolicyCounters* gc_adaptive_policy_counters();
973
974 // debugging
975 void verify(bool);
976 bool verify_after_remark();
977 void verify_ok_to_terminate() const PRODUCT_RETURN;
978 void verify_work_stacks_empty() const PRODUCT_RETURN;
979 void verify_overflow_empty() const PRODUCT_RETURN;
980
981 // convenience methods in support of debugging
982 static const size_t skip_header_HeapWords() PRODUCT_RETURN0;
983 HeapWord* block_start(const void* p) const PRODUCT_RETURN0;
984
985 // accessors
986 CMSMarkStack* verification_mark_stack() { return &_markStack; }
987 CMSBitMap* verification_mark_bm() { return &_verification_mark_bm; }
988
989 // Get the bit map with a perm gen "deadness" information.
990 CMSBitMap* perm_gen_verify_bit_map() { return &_perm_gen_verify_bit_map; }
991
992 // Initialization errors
993 bool completed_initialization() { return _completed_initialization; }
994 };
995
996 class CMSExpansionCause : public AllStatic {
997 public:
998 enum Cause {
999 _no_expansion,
1000 _satisfy_free_ratio,
1001 _satisfy_promotion,
1002 _satisfy_allocation,
1003 _allocate_par_lab,
1004 _allocate_par_spooling_space,
1005 _adaptive_size_policy
1006 };
1007 // Return a string describing the cause of the expansion.
1008 static const char* to_string(CMSExpansionCause::Cause cause);
1009 };
1010
1011 class ConcurrentMarkSweepGeneration: public CardGeneration {
1012 friend class VMStructs;
1013 friend class ConcurrentMarkSweepThread;
1014 friend class ConcurrentMarkSweep;
1015 friend class CMSCollector;
1016 protected:
1017 static CMSCollector* _collector; // the collector that collects us
1018 CompactibleFreeListSpace* _cmsSpace; // underlying space (only one for now)
1019
1020 // Performance Counters
1021 GenerationCounters* _gen_counters;
1022 GSpaceCounters* _space_counters;
1023
1024 // Words directly allocated, used by CMSStats.
1025 size_t _direct_allocated_words;
1026
1027 // Non-product stat counters
1028 NOT_PRODUCT(
1029 size_t _numObjectsPromoted;
1030 size_t _numWordsPromoted;
1031 size_t _numObjectsAllocated;
1032 size_t _numWordsAllocated;
1033 )
1034
1035 // Used for sizing decisions
1036 bool _incremental_collection_failed;
1037 bool incremental_collection_failed() {
1038 return _incremental_collection_failed;
1039 }
1040 void set_incremental_collection_failed() {
1041 _incremental_collection_failed = true;
1042 }
1043 void clear_incremental_collection_failed() {
1044 _incremental_collection_failed = false;
1045 }
1046
1047 // accessors
1048 void set_expansion_cause(CMSExpansionCause::Cause v) { _expansion_cause = v;}
1049 CMSExpansionCause::Cause expansion_cause() const { return _expansion_cause; }
1050
1051 private:
1052 // For parallel young-gen GC support.
1053 CMSParGCThreadState** _par_gc_thread_states;
1054
1055 // Reason generation was expanded
1056 CMSExpansionCause::Cause _expansion_cause;
1057
1058 // In support of MinChunkSize being larger than min object size
1059 const double _dilatation_factor;
1060
1061 enum CollectionTypes {
1062 Concurrent_collection_type = 0,
1063 MS_foreground_collection_type = 1,
1064 MSC_foreground_collection_type = 2,
1065 Unknown_collection_type = 3
1066 };
1067
1068 CollectionTypes _debug_collection_type;
1069
1070 // Fraction of current occupancy at which to start a CMS collection which
1071 // will collect this generation (at least).
1072 double _initiating_occupancy;
1073
1074 protected:
1075 // Shrink generation by specified size (returns false if unable to shrink)
1076 virtual void shrink_by(size_t bytes);
1077
1078 // Update statistics for GC
1079 virtual void update_gc_stats(int level, bool full);
1080
1081 // Maximum available space in the generation (including uncommitted)
1082 // space.
1083 size_t max_available() const;
1084
1085 // getter and initializer for _initiating_occupancy field.
1086 double initiating_occupancy() const { return _initiating_occupancy; }
1087 void init_initiating_occupancy(intx io, intx tr);
1088
1089 public:
1090 ConcurrentMarkSweepGeneration(ReservedSpace rs, size_t initial_byte_size,
1091 int level, CardTableRS* ct,
1092 bool use_adaptive_freelists,
1093 FreeBlockDictionary::DictionaryChoice);
1094
1095 // Accessors
1096 CMSCollector* collector() const { return _collector; }
1097 static void set_collector(CMSCollector* collector) {
1098 assert(_collector == NULL, "already set");
1099 _collector = collector;
1100 }
1101 CompactibleFreeListSpace* cmsSpace() const { return _cmsSpace; }
1102
1103 Mutex* freelistLock() const;
1104
1105 virtual Generation::Name kind() { return Generation::ConcurrentMarkSweep; }
1106
1107 // Adaptive size policy
1108 CMSAdaptiveSizePolicy* size_policy();
1109
1110 bool refs_discovery_is_atomic() const { return false; }
1111 bool refs_discovery_is_mt() const {
1112 // Note: CMS does MT-discovery during the parallel-remark
1113 // phases. Use ReferenceProcessorMTMutator to make refs
1114 // discovery MT-safe during such phases or other parallel
1115 // discovery phases in the future. This may all go away
1116 // if/when we decide that refs discovery is sufficiently
1117 // rare that the cost of the CAS's involved is in the
1118 // noise. That's a measurement that should be done, and
1119 // the code simplified if that turns out to be the case.
1120 return false;
1121 }
1122
1123 // Override
1124 virtual void ref_processor_init();
1125
1126 // Grow generation by specified size (returns false if unable to grow)
1127 bool grow_by(size_t bytes);
1128 // Grow generation to reserved size.
1129 bool grow_to_reserved();
1130
1131 void clear_expansion_cause() { _expansion_cause = CMSExpansionCause::_no_expansion; }
1132
1133 // Space enquiries
1134 size_t capacity() const;
1135 size_t used() const;
1136 size_t free() const;
1137 double occupancy() const { return ((double)used())/((double)capacity()); }
1138 size_t contiguous_available() const;
1139 size_t unsafe_max_alloc_nogc() const;
1140
1141 // over-rides
1142 MemRegion used_region() const;
1143 MemRegion used_region_at_save_marks() const;
1144
1145 // Does a "full" (forced) collection invoked on this generation collect
1146 // all younger generations as well? Note that the second conjunct is a
1147 // hack to allow the collection of the younger gen first if the flag is
1148 // set. This is better than using th policy's should_collect_gen0_first()
1149 // since that causes us to do an extra unnecessary pair of restart-&-stop-world.
1150 virtual bool full_collects_younger_generations() const {
1151 return UseCMSCompactAtFullCollection && !CollectGen0First;
1152 }
1153
1154 void space_iterate(SpaceClosure* blk, bool usedOnly = false);
1155
1156 // Support for compaction
1157 CompactibleSpace* first_compaction_space() const;
1158 // Adjust quantites in the generation affected by
1159 // the compaction.
1160 void reset_after_compaction();
1161
1162 // Allocation support
1163 HeapWord* allocate(size_t size, bool tlab);
1164 HeapWord* have_lock_and_allocate(size_t size, bool tlab);
1165 oop promote(oop obj, size_t obj_size);
1166 HeapWord* par_allocate(size_t size, bool tlab) {
1167 return allocate(size, tlab);
1168 }
1169
1170 // Incremental mode triggering.
1171 HeapWord* allocation_limit_reached(Space* space, HeapWord* top,
1172 size_t word_size);
1173
1174 // Used by CMSStats to track direct allocation. The value is sampled and
1175 // reset after each young gen collection.
1176 size_t direct_allocated_words() const { return _direct_allocated_words; }
1177 void reset_direct_allocated_words() { _direct_allocated_words = 0; }
1178
1179 // Overrides for parallel promotion.
1180 virtual oop par_promote(int thread_num,
1181 oop obj, markOop m, size_t word_sz);
1182 // This one should not be called for CMS.
1183 virtual void par_promote_alloc_undo(int thread_num,
1184 HeapWord* obj, size_t word_sz);
1185 virtual void par_promote_alloc_done(int thread_num);
1186 virtual void par_oop_since_save_marks_iterate_done(int thread_num);
1187
1188 virtual bool promotion_attempt_is_safe(size_t promotion_in_bytes,
1189 bool younger_handles_promotion_failure) const;
1190
1191 // Inform this (non-young) generation that a promotion failure was
1192 // encountered during a collection of a younger generation that
1193 // promotes into this generation.
1194 virtual void promotion_failure_occurred();
1195
1196 bool should_collect(bool full, size_t size, bool tlab);
1197 virtual bool should_concurrent_collect() const;
1198 virtual bool is_too_full() const;
1199 void collect(bool full,
1200 bool clear_all_soft_refs,
1201 size_t size,
1202 bool tlab);
1203
1204 HeapWord* expand_and_allocate(size_t word_size,
1205 bool tlab,
1206 bool parallel = false);
1207
1208 // GC prologue and epilogue
1209 void gc_prologue(bool full);
1210 void gc_prologue_work(bool full, bool registerClosure,
1211 ModUnionClosure* modUnionClosure);
1212 void gc_epilogue(bool full);
1213 void gc_epilogue_work(bool full);
1214
1215 // Time since last GC of this generation
1216 jlong time_of_last_gc(jlong now) {
1217 return collector()->time_of_last_gc(now);
1218 }
1219 void update_time_of_last_gc(jlong now) {
1220 collector()-> update_time_of_last_gc(now);
1221 }
1222
1223 // Allocation failure
1224 void expand(size_t bytes, size_t expand_bytes,
1225 CMSExpansionCause::Cause cause);
1226 virtual bool expand(size_t bytes, size_t expand_bytes);
1227 void shrink(size_t bytes);
1228 HeapWord* expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz);
1229 bool expand_and_ensure_spooling_space(PromotionInfo* promo);
1230
1231 // Iteration support and related enquiries
1232 void save_marks();
1233 bool no_allocs_since_save_marks();
1234 void object_iterate_since_last_GC(ObjectClosure* cl);
1235 void younger_refs_iterate(OopsInGenClosure* cl);
1236
1237 // Iteration support specific to CMS generations
1238 void save_sweep_limit();
1239
1240 // More iteration support
1241 virtual void oop_iterate(MemRegion mr, OopClosure* cl);
1242 virtual void oop_iterate(OopClosure* cl);
1243 virtual void safe_object_iterate(ObjectClosure* cl);
1244 virtual void object_iterate(ObjectClosure* cl);
1245
1246 // Need to declare the full complement of closures, whether we'll
1247 // override them or not, or get message from the compiler:
1248 // oop_since_save_marks_iterate_nv hides virtual function...
1249 #define CMS_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \
1250 void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl);
1251 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DECL)
1252
1253 // Smart allocation XXX -- move to CFLSpace?
1254 void setNearLargestChunk();
1255 bool isNearLargestChunk(HeapWord* addr);
1256
1257 // Get the chunk at the end of the space. Delagates to
1258 // the space.
1259 FreeChunk* find_chunk_at_end();
1260
1261 // Overriding of unused functionality (sharing not yet supported with CMS)
1262 void pre_adjust_pointers();
1263 void post_compact();
1264
1265 // Debugging
1266 void prepare_for_verify();
1267 void verify(bool allow_dirty);
1268 void print_statistics() PRODUCT_RETURN;
1269
1270 // Performance Counters support
1271 virtual void update_counters();
1272 virtual void update_counters(size_t used);
1273 void initialize_performance_counters();
1274 CollectorCounters* counters() { return collector()->counters(); }
1275
1276 // Support for parallel remark of survivor space
1277 void* get_data_recorder(int thr_num) {
1278 //Delegate to collector
1279 return collector()->get_data_recorder(thr_num);
1280 }
1281
1282 // Printing
1283 const char* name() const;
1284 virtual const char* short_name() const { return "CMS"; }
1285 void print() const;
1286 void printOccupancy(const char* s);
1287 bool must_be_youngest() const { return false; }
1288 bool must_be_oldest() const { return true; }
1289
1290 void compute_new_size();
1291
1292 CollectionTypes debug_collection_type() { return _debug_collection_type; }
1293 void rotate_debug_collection_type();
1294 };
1295
1296 class ASConcurrentMarkSweepGeneration : public ConcurrentMarkSweepGeneration {
1297
1298 // Return the size policy from the heap's collector
1299 // policy casted to CMSAdaptiveSizePolicy*.
1300 CMSAdaptiveSizePolicy* cms_size_policy() const;
1301
1302 // Resize the generation based on the adaptive size
1303 // policy.
1304 void resize(size_t cur_promo, size_t desired_promo);
1305
1306 // Return the GC counters from the collector policy
1307 CMSGCAdaptivePolicyCounters* gc_adaptive_policy_counters();
1308
1309 virtual void shrink_by(size_t bytes);
1310
1311 public:
1312 virtual void compute_new_size();
1313 ASConcurrentMarkSweepGeneration(ReservedSpace rs, size_t initial_byte_size,
1314 int level, CardTableRS* ct,
1315 bool use_adaptive_freelists,
1316 FreeBlockDictionary::DictionaryChoice
1317 dictionaryChoice) :
1318 ConcurrentMarkSweepGeneration(rs, initial_byte_size, level, ct,
1319 use_adaptive_freelists, dictionaryChoice) {}
1320
1321 virtual const char* short_name() const { return "ASCMS"; }
1322 virtual Generation::Name kind() { return Generation::ASConcurrentMarkSweep; }
1323
1324 virtual void update_counters();
1325 virtual void update_counters(size_t used);
1326 };
1327
1328 //
1329 // Closures of various sorts used by CMS to accomplish its work
1330 //
1331
1332 // This closure is used to check that a certain set of oops is empty.
1333 class FalseClosure: public OopClosure {
1334 public:
1335 void do_oop(oop* p) { guarantee(false, "Should be an empty set"); }
1336 void do_oop(narrowOop* p) { guarantee(false, "Should be an empty set"); }
1337 };
1338
1339 // This closure is used to do concurrent marking from the roots
1340 // following the first checkpoint.
1341 class MarkFromRootsClosure: public BitMapClosure {
1342 CMSCollector* _collector;
1343 MemRegion _span;
1344 CMSBitMap* _bitMap;
1345 CMSBitMap* _mut;
1346 CMSMarkStack* _markStack;
1347 CMSMarkStack* _revisitStack;
1348 bool _yield;
1349 int _skipBits;
1350 HeapWord* _finger;
1351 HeapWord* _threshold;
1352 DEBUG_ONLY(bool _verifying;)
1353
1354 public:
1355 MarkFromRootsClosure(CMSCollector* collector, MemRegion span,
1356 CMSBitMap* bitMap,
1357 CMSMarkStack* markStack,
1358 CMSMarkStack* revisitStack,
1359 bool should_yield, bool verifying = false);
1360 bool do_bit(size_t offset);
1361 void reset(HeapWord* addr);
1362 inline void do_yield_check();
1363
1364 private:
1365 void scanOopsInOop(HeapWord* ptr);
1366 void do_yield_work();
1367 };
1368
1369 // This closure is used to do concurrent multi-threaded
1370 // marking from the roots following the first checkpoint.
1371 // XXX This should really be a subclass of The serial version
1372 // above, but i have not had the time to refactor things cleanly.
1373 // That willbe done for Dolphin.
1374 class Par_MarkFromRootsClosure: public BitMapClosure {
1375 CMSCollector* _collector;
1376 MemRegion _whole_span;
1377 MemRegion _span;
1378 CMSBitMap* _bit_map;
1379 CMSBitMap* _mut;
1380 OopTaskQueue* _work_queue;
1381 CMSMarkStack* _overflow_stack;
1382 CMSMarkStack* _revisit_stack;
1383 bool _yield;
1384 int _skip_bits;
1385 HeapWord* _finger;
1386 HeapWord* _threshold;
1387 CMSConcMarkingTask* _task;
1388 public:
1389 Par_MarkFromRootsClosure(CMSConcMarkingTask* task, CMSCollector* collector,
1390 MemRegion span,
1391 CMSBitMap* bit_map,
1392 OopTaskQueue* work_queue,
1393 CMSMarkStack* overflow_stack,
1394 CMSMarkStack* revisit_stack,
1395 bool should_yield);
1396 bool do_bit(size_t offset);
1397 inline void do_yield_check();
1398
1399 private:
1400 void scan_oops_in_oop(HeapWord* ptr);
1401 void do_yield_work();
1402 bool get_work_from_overflow_stack();
1403 };
1404
1405 // The following closures are used to do certain kinds of verification of
1406 // CMS marking.
1407 class PushAndMarkVerifyClosure: public OopClosure {
1408 CMSCollector* _collector;
1409 MemRegion _span;
1410 CMSBitMap* _verification_bm;
1411 CMSBitMap* _cms_bm;
1412 CMSMarkStack* _mark_stack;
1413 protected:
1414 void do_oop(oop p);
1415 template <class T> inline void do_oop_work(T *p) {
1416 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
1417 do_oop(obj);
1418 }
1419 public:
1420 PushAndMarkVerifyClosure(CMSCollector* cms_collector,
1421 MemRegion span,
1422 CMSBitMap* verification_bm,
1423 CMSBitMap* cms_bm,
1424 CMSMarkStack* mark_stack);
1425 void do_oop(oop* p);
1426 void do_oop(narrowOop* p);
1427 // Deal with a stack overflow condition
1428 void handle_stack_overflow(HeapWord* lost);
1429 };
1430
1431 class MarkFromRootsVerifyClosure: public BitMapClosure {
1432 CMSCollector* _collector;
1433 MemRegion _span;
1434 CMSBitMap* _verification_bm;
1435 CMSBitMap* _cms_bm;
1436 CMSMarkStack* _mark_stack;
1437 HeapWord* _finger;
1438 PushAndMarkVerifyClosure _pam_verify_closure;
1439 public:
1440 MarkFromRootsVerifyClosure(CMSCollector* collector, MemRegion span,
1441 CMSBitMap* verification_bm,
1442 CMSBitMap* cms_bm,
1443 CMSMarkStack* mark_stack);
1444 bool do_bit(size_t offset);
1445 void reset(HeapWord* addr);
1446 };
1447
1448
1449 // This closure is used to check that a certain set of bits is
1450 // "empty" (i.e. the bit vector doesn't have any 1-bits).
1451 class FalseBitMapClosure: public BitMapClosure {
1452 public:
1453 bool do_bit(size_t offset) {
1454 guarantee(false, "Should not have a 1 bit");
1455 return true;
1456 }
1457 };
1458
1459 // This closure is used during the second checkpointing phase
1460 // to rescan the marked objects on the dirty cards in the mod
1461 // union table and the card table proper. It's invoked via
1462 // MarkFromDirtyCardsClosure below. It uses either
1463 // [Par_]MarkRefsIntoAndScanClosure (Par_ in the parallel case)
1464 // declared in genOopClosures.hpp to accomplish some of its work.
1465 // In the parallel case the bitMap is shared, so access to
1466 // it needs to be suitably synchronized for updates by embedded
1467 // closures that update it; however, this closure itself only
1468 // reads the bit_map and because it is idempotent, is immune to
1469 // reading stale values.
1470 class ScanMarkedObjectsAgainClosure: public UpwardsObjectClosure {
1471 #ifdef ASSERT
1472 CMSCollector* _collector;
1473 MemRegion _span;
1474 union {
1475 CMSMarkStack* _mark_stack;
1476 OopTaskQueue* _work_queue;
1477 };
1478 #endif // ASSERT
1479 bool _parallel;
1480 CMSBitMap* _bit_map;
1481 union {
1482 MarkRefsIntoAndScanClosure* _scan_closure;
1483 Par_MarkRefsIntoAndScanClosure* _par_scan_closure;
1484 };
1485
1486 public:
1487 ScanMarkedObjectsAgainClosure(CMSCollector* collector,
1488 MemRegion span,
1489 ReferenceProcessor* rp,
1490 CMSBitMap* bit_map,
1491 CMSMarkStack* mark_stack,
1492 CMSMarkStack* revisit_stack,
1493 MarkRefsIntoAndScanClosure* cl):
1494 #ifdef ASSERT
1495 _collector(collector),
1496 _span(span),
1497 _mark_stack(mark_stack),
1498 #endif // ASSERT
1499 _parallel(false),
1500 _bit_map(bit_map),
1501 _scan_closure(cl) { }
1502
1503 ScanMarkedObjectsAgainClosure(CMSCollector* collector,
1504 MemRegion span,
1505 ReferenceProcessor* rp,
1506 CMSBitMap* bit_map,
1507 OopTaskQueue* work_queue,
1508 CMSMarkStack* revisit_stack,
1509 Par_MarkRefsIntoAndScanClosure* cl):
1510 #ifdef ASSERT
1511 _collector(collector),
1512 _span(span),
1513 _work_queue(work_queue),
1514 #endif // ASSERT
1515 _parallel(true),
1516 _bit_map(bit_map),
1517 _par_scan_closure(cl) { }
1518
1519 void do_object(oop obj) {
1520 guarantee(false, "Call do_object_b(oop, MemRegion) instead");
1521 }
1522 bool do_object_b(oop obj) {
1523 guarantee(false, "Call do_object_b(oop, MemRegion) form instead");
1524 return false;
1525 }
1526 bool do_object_bm(oop p, MemRegion mr);
1527 };
1528
1529 // This closure is used during the second checkpointing phase
1530 // to rescan the marked objects on the dirty cards in the mod
1531 // union table and the card table proper. It invokes
1532 // ScanMarkedObjectsAgainClosure above to accomplish much of its work.
1533 // In the parallel case, the bit map is shared and requires
1534 // synchronized access.
1535 class MarkFromDirtyCardsClosure: public MemRegionClosure {
1536 CompactibleFreeListSpace* _space;
1537 ScanMarkedObjectsAgainClosure _scan_cl;
1538 size_t _num_dirty_cards;
1539
1540 public:
1541 MarkFromDirtyCardsClosure(CMSCollector* collector,
1542 MemRegion span,
1543 CompactibleFreeListSpace* space,
1544 CMSBitMap* bit_map,
1545 CMSMarkStack* mark_stack,
1546 CMSMarkStack* revisit_stack,
1547 MarkRefsIntoAndScanClosure* cl):
1548 _space(space),
1549 _num_dirty_cards(0),
1550 _scan_cl(collector, span, collector->ref_processor(), bit_map,
1551 mark_stack, revisit_stack, cl) { }
1552
1553 MarkFromDirtyCardsClosure(CMSCollector* collector,
1554 MemRegion span,
1555 CompactibleFreeListSpace* space,
1556 CMSBitMap* bit_map,
1557 OopTaskQueue* work_queue,
1558 CMSMarkStack* revisit_stack,
1559 Par_MarkRefsIntoAndScanClosure* cl):
1560 _space(space),
1561 _num_dirty_cards(0),
1562 _scan_cl(collector, span, collector->ref_processor(), bit_map,
1563 work_queue, revisit_stack, cl) { }
1564
1565 void do_MemRegion(MemRegion mr);
1566 void set_space(CompactibleFreeListSpace* space) { _space = space; }
1567 size_t num_dirty_cards() { return _num_dirty_cards; }
1568 };
1569
1570 // This closure is used in the non-product build to check
1571 // that there are no MemRegions with a certain property.
1572 class FalseMemRegionClosure: public MemRegionClosure {
1573 void do_MemRegion(MemRegion mr) {
1574 guarantee(!mr.is_empty(), "Shouldn't be empty");
1575 guarantee(false, "Should never be here");
1576 }
1577 };
1578
1579 // This closure is used during the precleaning phase
1580 // to "carefully" rescan marked objects on dirty cards.
1581 // It uses MarkRefsIntoAndScanClosure declared in genOopClosures.hpp
1582 // to accomplish some of its work.
1583 class ScanMarkedObjectsAgainCarefullyClosure: public ObjectClosureCareful {
1584 CMSCollector* _collector;
1585 MemRegion _span;
1586 bool _yield;
1587 Mutex* _freelistLock;
1588 CMSBitMap* _bitMap;
1589 CMSMarkStack* _markStack;
1590 MarkRefsIntoAndScanClosure* _scanningClosure;
1591
1592 public:
1593 ScanMarkedObjectsAgainCarefullyClosure(CMSCollector* collector,
1594 MemRegion span,
1595 CMSBitMap* bitMap,
1596 CMSMarkStack* markStack,
1597 CMSMarkStack* revisitStack,
1598 MarkRefsIntoAndScanClosure* cl,
1599 bool should_yield):
1600 _collector(collector),
1601 _span(span),
1602 _yield(should_yield),
1603 _bitMap(bitMap),
1604 _markStack(markStack),
1605 _scanningClosure(cl) {
1606 }
1607
1608 void do_object(oop p) {
1609 guarantee(false, "call do_object_careful instead");
1610 }
1611
1612 size_t do_object_careful(oop p) {
1613 guarantee(false, "Unexpected caller");
1614 return 0;
1615 }
1616
1617 size_t do_object_careful_m(oop p, MemRegion mr);
1618
1619 void setFreelistLock(Mutex* m) {
1620 _freelistLock = m;
1621 _scanningClosure->set_freelistLock(m);
1622 }
1623
1624 private:
1625 inline bool do_yield_check();
1626
1627 void do_yield_work();
1628 };
1629
1630 class SurvivorSpacePrecleanClosure: public ObjectClosureCareful {
1631 CMSCollector* _collector;
1632 MemRegion _span;
1633 bool _yield;
1634 CMSBitMap* _bit_map;
1635 CMSMarkStack* _mark_stack;
1636 PushAndMarkClosure* _scanning_closure;
1637 unsigned int _before_count;
1638
1639 public:
1640 SurvivorSpacePrecleanClosure(CMSCollector* collector,
1641 MemRegion span,
1642 CMSBitMap* bit_map,
1643 CMSMarkStack* mark_stack,
1644 PushAndMarkClosure* cl,
1645 unsigned int before_count,
1646 bool should_yield):
1647 _collector(collector),
1648 _span(span),
1649 _yield(should_yield),
1650 _bit_map(bit_map),
1651 _mark_stack(mark_stack),
1652 _scanning_closure(cl),
1653 _before_count(before_count)
1654 { }
1655
1656 void do_object(oop p) {
1657 guarantee(false, "call do_object_careful instead");
1658 }
1659
1660 size_t do_object_careful(oop p);
1661
1662 size_t do_object_careful_m(oop p, MemRegion mr) {
1663 guarantee(false, "Unexpected caller");
1664 return 0;
1665 }
1666
1667 private:
1668 inline void do_yield_check();
1669 void do_yield_work();
1670 };
1671
1672 // This closure is used to accomplish the sweeping work
1673 // after the second checkpoint but before the concurrent reset
1674 // phase.
1675 //
1676 // Terminology
1677 // left hand chunk (LHC) - block of one or more chunks currently being
1678 // coalesced. The LHC is available for coalescing with a new chunk.
1679 // right hand chunk (RHC) - block that is currently being swept that is
1680 // free or garbage that can be coalesced with the LHC.
1681 // _inFreeRange is true if there is currently a LHC
1682 // _lastFreeRangeCoalesced is true if the LHC consists of more than one chunk.
1683 // _freeRangeInFreeLists is true if the LHC is in the free lists.
1684 // _freeFinger is the address of the current LHC
1685 class SweepClosure: public BlkClosureCareful {
1686 CMSCollector* _collector; // collector doing the work
1687 ConcurrentMarkSweepGeneration* _g; // Generation being swept
1688 CompactibleFreeListSpace* _sp; // Space being swept
1689 HeapWord* _limit;
1690 Mutex* _freelistLock; // Free list lock (in space)
1691 CMSBitMap* _bitMap; // Marking bit map (in
1692 // generation)
1693 bool _inFreeRange; // Indicates if we are in the
1694 // midst of a free run
1695 bool _freeRangeInFreeLists;
1696 // Often, we have just found
1697 // a free chunk and started
1698 // a new free range; we do not
1699 // eagerly remove this chunk from
1700 // the free lists unless there is
1701 // a possibility of coalescing.
1702 // When true, this flag indicates
1703 // that the _freeFinger below
1704 // points to a potentially free chunk
1705 // that may still be in the free lists
1706 bool _lastFreeRangeCoalesced;
1707 // free range contains chunks
1708 // coalesced
1709 bool _yield;
1710 // Whether sweeping should be
1711 // done with yields. For instance
1712 // when done by the foreground
1713 // collector we shouldn't yield.
1714 HeapWord* _freeFinger; // When _inFreeRange is set, the
1715 // pointer to the "left hand
1716 // chunk"
1717 size_t _freeRangeSize;
1718 // When _inFreeRange is set, this
1719 // indicates the accumulated size
1720 // of the "left hand chunk"
1721 NOT_PRODUCT(
1722 size_t _numObjectsFreed;
1723 size_t _numWordsFreed;
1724 size_t _numObjectsLive;
1725 size_t _numWordsLive;
1726 size_t _numObjectsAlreadyFree;
1727 size_t _numWordsAlreadyFree;
1728 FreeChunk* _last_fc;
1729 )
1730 private:
1731 // Code that is common to a free chunk or garbage when
1732 // encountered during sweeping.
1733 void doPostIsFreeOrGarbageChunk(FreeChunk *fc,
1734 size_t chunkSize);
1735 // Process a free chunk during sweeping.
1736 void doAlreadyFreeChunk(FreeChunk *fc);
1737 // Process a garbage chunk during sweeping.
1738 size_t doGarbageChunk(FreeChunk *fc);
1739 // Process a live chunk during sweeping.
1740 size_t doLiveChunk(FreeChunk* fc);
1741
1742 // Accessors.
1743 HeapWord* freeFinger() const { return _freeFinger; }
1744 void set_freeFinger(HeapWord* v) { _freeFinger = v; }
1745 size_t freeRangeSize() const { return _freeRangeSize; }
1746 void set_freeRangeSize(size_t v) { _freeRangeSize = v; }
1747 bool inFreeRange() const { return _inFreeRange; }
1748 void set_inFreeRange(bool v) { _inFreeRange = v; }
1749 bool lastFreeRangeCoalesced() const { return _lastFreeRangeCoalesced; }
1750 void set_lastFreeRangeCoalesced(bool v) { _lastFreeRangeCoalesced = v; }
1751 bool freeRangeInFreeLists() const { return _freeRangeInFreeLists; }
1752 void set_freeRangeInFreeLists(bool v) { _freeRangeInFreeLists = v; }
1753
1754 // Initialize a free range.
1755 void initialize_free_range(HeapWord* freeFinger, bool freeRangeInFreeLists);
1756 // Return this chunk to the free lists.
1757 void flushCurFreeChunk(HeapWord* chunk, size_t size);
1758
1759 // Check if we should yield and do so when necessary.
1760 inline void do_yield_check(HeapWord* addr);
1761
1762 // Yield
1763 void do_yield_work(HeapWord* addr);
1764
1765 // Debugging/Printing
1766 void record_free_block_coalesced(FreeChunk* fc) const PRODUCT_RETURN;
1767
1768 public:
1769 SweepClosure(CMSCollector* collector, ConcurrentMarkSweepGeneration* g,
1770 CMSBitMap* bitMap, bool should_yield);
1771 ~SweepClosure();
1772
1773 size_t do_blk_careful(HeapWord* addr);
1774 };
1775
1776 // Closures related to weak references processing
1777
1778 // During CMS' weak reference processing, this is a
1779 // work-routine/closure used to complete transitive
1780 // marking of objects as live after a certain point
1781 // in which an initial set has been completely accumulated.
1782 // This closure is currently used both during the final
1783 // remark stop-world phase, as well as during the concurrent
1784 // precleaning of the discovered reference lists.
1785 class CMSDrainMarkingStackClosure: public VoidClosure {
1786 CMSCollector* _collector;
1787 MemRegion _span;
1788 CMSMarkStack* _mark_stack;
1789 CMSBitMap* _bit_map;
1790 CMSKeepAliveClosure* _keep_alive;
1791 bool _concurrent_precleaning;
1792 public:
1793 CMSDrainMarkingStackClosure(CMSCollector* collector, MemRegion span,
1794 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
1795 CMSKeepAliveClosure* keep_alive,
1796 bool cpc):
1797 _collector(collector),
1798 _span(span),
1799 _bit_map(bit_map),
1800 _mark_stack(mark_stack),
1801 _keep_alive(keep_alive),
1802 _concurrent_precleaning(cpc) {
1803 assert(_concurrent_precleaning == _keep_alive->concurrent_precleaning(),
1804 "Mismatch");
1805 }
1806
1807 void do_void();
1808 };
1809
1810 // A parallel version of CMSDrainMarkingStackClosure above.
1811 class CMSParDrainMarkingStackClosure: public VoidClosure {
1812 CMSCollector* _collector;
1813 MemRegion _span;
1814 OopTaskQueue* _work_queue;
1815 CMSBitMap* _bit_map;
1816 CMSInnerParMarkAndPushClosure _mark_and_push;
1817
1818 public:
1819 CMSParDrainMarkingStackClosure(CMSCollector* collector,
1820 MemRegion span, CMSBitMap* bit_map,
1821 CMSMarkStack* revisit_stack,
1822 OopTaskQueue* work_queue):
1823 _collector(collector),
1824 _span(span),
1825 _bit_map(bit_map),
1826 _work_queue(work_queue),
1827 _mark_and_push(collector, span, bit_map, revisit_stack, work_queue) { }
1828
1829 public:
1830 void trim_queue(uint max);
1831 void do_void();
1832 };
1833
1834 // Allow yielding or short-circuiting of reference list
1835 // prelceaning work.
1836 class CMSPrecleanRefsYieldClosure: public YieldClosure {
1837 CMSCollector* _collector;
1838 void do_yield_work();
1839 public:
1840 CMSPrecleanRefsYieldClosure(CMSCollector* collector):
1841 _collector(collector) {}
1842 virtual bool should_return();
1843 };
1844
1845
1846 // Convenience class that locks free list locks for given CMS collector
1847 class FreelistLocker: public StackObj {
1848 private:
1849 CMSCollector* _collector;
1850 public:
1851 FreelistLocker(CMSCollector* collector):
1852 _collector(collector) {
1853 _collector->getFreelistLocks();
1854 }
1855
1856 ~FreelistLocker() {
1857 _collector->releaseFreelistLocks();
1858 }
1859 };
1860
1861 // Mark all dead objects in a given space.
1862 class MarkDeadObjectsClosure: public BlkClosure {
1863 const CMSCollector* _collector;
1864 const CompactibleFreeListSpace* _sp;
1865 CMSBitMap* _live_bit_map;
1866 CMSBitMap* _dead_bit_map;
1867 public:
1868 MarkDeadObjectsClosure(const CMSCollector* collector,
1869 const CompactibleFreeListSpace* sp,
1870 CMSBitMap *live_bit_map,
1871 CMSBitMap *dead_bit_map) :
1872 _collector(collector),
1873 _sp(sp),
1874 _live_bit_map(live_bit_map),
1875 _dead_bit_map(dead_bit_map) {}
1876 size_t do_blk(HeapWord* addr);
1877 };
1878
1879 class TraceCMSMemoryManagerStats : public TraceMemoryManagerStats {
1880
1881 public:
1882 TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase);
1883 TraceCMSMemoryManagerStats();
1884 };
1885