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.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 // 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 HeapWord** _array; // storage for array
256
257 public:
258 ChunkArray() : _index(0), _capacity(0), _array(NULL) {}
259 ChunkArray(HeapWord** a, size_t c):
260 _index(0), _capacity(c), _array(a) {}
261
262 HeapWord** array() { return _array; }
263 void set_array(HeapWord** a) { _array = a; }
264
265 size_t capacity() { return _capacity; }
266 void set_capacity(size_t c) { _capacity = c; }
267
268 size_t end() {
269 assert(_index < capacity(), "_index out of bounds");
270 return _index;
271 } // exclusive
272
273 HeapWord* nth(size_t n) {
274 assert(n < end(), "Out of bounds access");
275 return _array[n];
276 }
277
278 void reset() {
279 _index = 0;
280 }
281
282 void record_sample(HeapWord* p, size_t sz) {
283 // For now we do not do anything with the size
284 if (_index < _capacity) {
285 _array[_index++] = p;
286 }
287 }
288 };
289
290 //
291 // Timing, allocation and promotion statistics for gc scheduling and incremental
292 // mode pacing. Most statistics are exponential averages.
293 //
294 class CMSStats VALUE_OBJ_CLASS_SPEC {
295 private:
296 ConcurrentMarkSweepGeneration* const _cms_gen; // The cms (old) gen.
297
298 // The following are exponential averages with factor alpha:
299 // avg = (100 - alpha) * avg + alpha * cur_sample
300 //
301 // The durations measure: end_time[n] - start_time[n]
302 // The periods measure: start_time[n] - start_time[n-1]
303 //
304 // The cms period and duration include only concurrent collections; time spent
305 // in foreground cms collections due to System.gc() or because of a failure to
306 // keep up are not included.
307 //
308 // There are 3 alphas to "bootstrap" the statistics. The _saved_alpha is the
309 // real value, but is used only after the first period. A value of 100 is
310 // used for the first sample so it gets the entire weight.
311 unsigned int _saved_alpha; // 0-100
312 unsigned int _gc0_alpha;
313 unsigned int _cms_alpha;
314
315 double _gc0_duration;
316 double _gc0_period;
317 size_t _gc0_promoted; // bytes promoted per gc0
318 double _cms_duration;
319 double _cms_duration_pre_sweep; // time from initiation to start of sweep
320 double _cms_duration_per_mb;
321 double _cms_period;
322 size_t _cms_allocated; // bytes of direct allocation per gc0 period
323
324 // Timers.
325 elapsedTimer _cms_timer;
326 TimeStamp _gc0_begin_time;
327 TimeStamp _cms_begin_time;
328 TimeStamp _cms_end_time;
329
330 // Snapshots of the amount used in the CMS generation.
331 size_t _cms_used_at_gc0_begin;
332 size_t _cms_used_at_gc0_end;
333 size_t _cms_used_at_cms_begin;
334
335 // Used to prevent the duty cycle from being reduced in the middle of a cms
336 // cycle.
337 bool _allow_duty_cycle_reduction;
338
339 enum {
340 _GC0_VALID = 0x1,
341 _CMS_VALID = 0x2,
342 _ALL_VALID = _GC0_VALID | _CMS_VALID
343 };
344
345 unsigned int _valid_bits;
346
347 unsigned int _icms_duty_cycle; // icms duty cycle (0-100).
348
349 protected:
350
351 // Return a duty cycle that avoids wild oscillations, by limiting the amount
352 // of change between old_duty_cycle and new_duty_cycle (the latter is treated
353 // as a recommended value).
354 static unsigned int icms_damped_duty_cycle(unsigned int old_duty_cycle,
355 unsigned int new_duty_cycle);
356 unsigned int icms_update_duty_cycle_impl();
357
358 // In support of adjusting of cms trigger ratios based on history
359 // of concurrent mode failure.
360 double cms_free_adjustment_factor(size_t free) const;
361 void adjust_cms_free_adjustment_factor(bool fail, size_t free);
362
363 public:
364 CMSStats(ConcurrentMarkSweepGeneration* cms_gen,
365 unsigned int alpha = CMSExpAvgFactor);
366
367 // Whether or not the statistics contain valid data; higher level statistics
368 // cannot be called until this returns true (they require at least one young
369 // gen and one cms cycle to have completed).
370 bool valid() const;
371
372 // Record statistics.
373 void record_gc0_begin();
374 void record_gc0_end(size_t cms_gen_bytes_used);
375 void record_cms_begin();
376 void record_cms_end();
377
378 // Allow management of the cms timer, which must be stopped/started around
379 // yield points.
380 elapsedTimer& cms_timer() { return _cms_timer; }
381 void start_cms_timer() { _cms_timer.start(); }
382 void stop_cms_timer() { _cms_timer.stop(); }
383
384 // Basic statistics; units are seconds or bytes.
385 double gc0_period() const { return _gc0_period; }
386 double gc0_duration() const { return _gc0_duration; }
387 size_t gc0_promoted() const { return _gc0_promoted; }
388 double cms_period() const { return _cms_period; }
389 double cms_duration() const { return _cms_duration; }
390 double cms_duration_per_mb() const { return _cms_duration_per_mb; }
391 size_t cms_allocated() const { return _cms_allocated; }
392
393 size_t cms_used_at_gc0_end() const { return _cms_used_at_gc0_end;}
394
395 // Seconds since the last background cms cycle began or ended.
396 double cms_time_since_begin() const;
397 double cms_time_since_end() const;
398
399 // Higher level statistics--caller must check that valid() returns true before
400 // calling.
401
402 // Returns bytes promoted per second of wall clock time.
403 double promotion_rate() const;
404
405 // Returns bytes directly allocated per second of wall clock time.
406 double cms_allocation_rate() const;
407
408 // Rate at which space in the cms generation is being consumed (sum of the
409 // above two).
410 double cms_consumption_rate() const;
411
412 // Returns an estimate of the number of seconds until the cms generation will
413 // fill up, assuming no collection work is done.
414 double time_until_cms_gen_full() const;
415
416 // Returns an estimate of the number of seconds remaining until
417 // the cms generation collection should start.
418 double time_until_cms_start() const;
419
420 // End of higher level statistics.
421
422 // Returns the cms incremental mode duty cycle, as a percentage (0-100).
423 unsigned int icms_duty_cycle() const { return _icms_duty_cycle; }
424
425 // Update the duty cycle and return the new value.
426 unsigned int icms_update_duty_cycle();
427
428 // Debugging.
429 void print_on(outputStream* st) const PRODUCT_RETURN;
430 void print() const { print_on(gclog_or_tty); }
431 };
432
433 // A closure related to weak references processing which
434 // we embed in the CMSCollector, since we need to pass
435 // it to the reference processor for secondary filtering
436 // of references based on reachability of referent;
437 // see role of _is_alive_non_header closure in the
438 // ReferenceProcessor class.
439 // For objects in the CMS generation, this closure checks
440 // if the object is "live" (reachable). Used in weak
441 // reference processing.
442 class CMSIsAliveClosure: public BoolObjectClosure {
443 const MemRegion _span;
444 const CMSBitMap* _bit_map;
445
446 friend class CMSCollector;
447 public:
448 CMSIsAliveClosure(MemRegion span,
449 CMSBitMap* bit_map):
450 _span(span),
451 _bit_map(bit_map) {
452 assert(!span.is_empty(), "Empty span could spell trouble");
453 }
454
455 void do_object(oop obj) {
456 assert(false, "not to be invoked");
457 }
458
459 bool do_object_b(oop obj);
460 };
461
462
463 // Implements AbstractRefProcTaskExecutor for CMS.
464 class CMSRefProcTaskExecutor: public AbstractRefProcTaskExecutor {
465 public:
466
467 CMSRefProcTaskExecutor(CMSCollector& collector)
468 : _collector(collector)
469 { }
470
471 // Executes a task using worker threads.
472 virtual void execute(ProcessTask& task);
473 virtual void execute(EnqueueTask& task);
474 private:
475 CMSCollector& _collector;
476 };
477
478
479 class CMSCollector: public CHeapObj {
480 friend class VMStructs;
481 friend class ConcurrentMarkSweepThread;
482 friend class ConcurrentMarkSweepGeneration;
483 friend class CompactibleFreeListSpace;
484 friend class CMSParRemarkTask;
485 friend class CMSConcMarkingTask;
486 friend class CMSRefProcTaskProxy;
487 friend class CMSRefProcTaskExecutor;
488 friend class ScanMarkedObjectsAgainCarefullyClosure; // for sampling eden
489 friend class SurvivorSpacePrecleanClosure; // --- ditto -------
490 friend class PushOrMarkClosure; // to access _restart_addr
491 friend class Par_PushOrMarkClosure; // to access _restart_addr
492 friend class MarkFromRootsClosure; // -- ditto --
493 // ... and for clearing cards
494 friend class Par_MarkFromRootsClosure; // to access _restart_addr
495 // ... and for clearing cards
496 friend class Par_ConcMarkingClosure; // to access _restart_addr etc.
497 friend class MarkFromRootsVerifyClosure; // to access _restart_addr
498 friend class PushAndMarkVerifyClosure; // -- ditto --
499 friend class MarkRefsIntoAndScanClosure; // to access _overflow_list
500 friend class PushAndMarkClosure; // -- ditto --
501 friend class Par_PushAndMarkClosure; // -- ditto --
502 friend class CMSKeepAliveClosure; // -- ditto --
503 friend class CMSDrainMarkingStackClosure; // -- ditto --
504 friend class CMSInnerParMarkAndPushClosure; // -- ditto --
505 NOT_PRODUCT(friend class ScanMarkedObjectsAgainClosure;) // assertion on _overflow_list
506 friend class ReleaseForegroundGC; // to access _foregroundGCShouldWait
507 friend class VM_CMS_Operation;
508 friend class VM_CMS_Initial_Mark;
509 friend class VM_CMS_Final_Remark;
510
511 private:
512 jlong _time_of_last_gc;
513 void update_time_of_last_gc(jlong now) {
514 _time_of_last_gc = now;
515 }
516
517 OopTaskQueueSet* _task_queues;
518
519 // Overflow list of grey objects, threaded through mark-word
520 // Manipulated with CAS in the parallel/multi-threaded case.
521 oop _overflow_list;
522 // The following array-pair keeps track of mark words
523 // displaced for accomodating overflow list above.
524 // This code will likely be revisited under RFE#4922830.
525 GrowableArray<oop>* _preserved_oop_stack;
526 GrowableArray<markOop>* _preserved_mark_stack;
527
528 int* _hash_seed;
529
530 // In support of multi-threaded concurrent phases
531 YieldingFlexibleWorkGang* _conc_workers;
532
533 // Performance Counters
534 CollectorCounters* _gc_counters;
535
536 // Initialization Errors
537 bool _completed_initialization;
538
539 // In support of ExplicitGCInvokesConcurrent
540 static bool _full_gc_requested;
541 unsigned int _collection_count_start;
542
543 // Should we unload classes this concurrent cycle?
544 bool _should_unload_classes;
545 unsigned int _concurrent_cycles_since_last_unload;
546 unsigned int concurrent_cycles_since_last_unload() const {
547 return _concurrent_cycles_since_last_unload;
548 }
549 // Did we (allow) unload classes in the previous concurrent cycle?
550 bool unloaded_classes_last_cycle() const {
551 return concurrent_cycles_since_last_unload() == 0;
552 }
553 // Root scanning options for perm gen
554 int _roots_scanning_options;
555 int roots_scanning_options() const { return _roots_scanning_options; }
556 void add_root_scanning_option(int o) { _roots_scanning_options |= o; }
557 void remove_root_scanning_option(int o) { _roots_scanning_options &= ~o; }
558
559 // Verification support
560 CMSBitMap _verification_mark_bm;
561 void verify_after_remark_work_1();
562 void verify_after_remark_work_2();
563
564 // true if any verification flag is on.
565 bool _verifying;
566 bool verifying() const { return _verifying; }
567 void set_verifying(bool v) { _verifying = v; }
568
569 // Collector policy
570 ConcurrentMarkSweepPolicy* _collector_policy;
571 ConcurrentMarkSweepPolicy* collector_policy() { return _collector_policy; }
572
573 // XXX Move these to CMSStats ??? FIX ME !!!
574 elapsedTimer _inter_sweep_timer; // time between sweeps
575 elapsedTimer _intra_sweep_timer; // time _in_ sweeps
576 // padded decaying average estimates of the above
577 AdaptivePaddedAverage _inter_sweep_estimate;
578 AdaptivePaddedAverage _intra_sweep_estimate;
579
580 protected:
581 ConcurrentMarkSweepGeneration* _cmsGen; // old gen (CMS)
582 ConcurrentMarkSweepGeneration* _permGen; // perm gen
583 MemRegion _span; // span covering above two
584 CardTableRS* _ct; // card table
585
586 // CMS marking support structures
587 CMSBitMap _markBitMap;
588 CMSBitMap _modUnionTable;
589 CMSMarkStack _markStack;
590 CMSMarkStack _revisitStack; // used to keep track of klassKlass objects
591 // to revisit
592 CMSBitMap _perm_gen_verify_bit_map; // Mark bit map for perm gen verification support.
593
594 HeapWord* _restart_addr; // in support of marking stack overflow
595 void lower_restart_addr(HeapWord* low);
596
597 // Counters in support of marking stack / work queue overflow handling:
598 // a non-zero value indicates certain types of overflow events during
599 // the current CMS cycle and could lead to stack resizing efforts at
600 // an opportune future time.
601 size_t _ser_pmc_preclean_ovflw;
602 size_t _ser_pmc_remark_ovflw;
603 size_t _par_pmc_remark_ovflw;
604 size_t _ser_kac_preclean_ovflw;
605 size_t _ser_kac_ovflw;
606 size_t _par_kac_ovflw;
607 NOT_PRODUCT(ssize_t _num_par_pushes;)
608
609 // ("Weak") Reference processing support
610 ReferenceProcessor* _ref_processor;
611 CMSIsAliveClosure _is_alive_closure;
612 // keep this textually after _markBitMap and _span; c'tor dependency
613
614 ConcurrentMarkSweepThread* _cmsThread; // the thread doing the work
615 ModUnionClosure _modUnionClosure;
616 ModUnionClosurePar _modUnionClosurePar;
617
618 // CMS abstract state machine
619 // initial_state: Idling
620 // next_state(Idling) = {Marking}
621 // next_state(Marking) = {Precleaning, Sweeping}
622 // next_state(Precleaning) = {AbortablePreclean, FinalMarking}
623 // next_state(AbortablePreclean) = {FinalMarking}
624 // next_state(FinalMarking) = {Sweeping}
625 // next_state(Sweeping) = {Resizing}
626 // next_state(Resizing) = {Resetting}
627 // next_state(Resetting) = {Idling}
628 // The numeric values below are chosen so that:
629 // . _collectorState <= Idling == post-sweep && pre-mark
630 // . _collectorState in (Idling, Sweeping) == {initial,final}marking ||
631 // precleaning || abortablePrecleanb
632 public:
633 enum CollectorState {
634 Resizing = 0,
635 Resetting = 1,
636 Idling = 2,
637 InitialMarking = 3,
638 Marking = 4,
639 Precleaning = 5,
640 AbortablePreclean = 6,
641 FinalMarking = 7,
642 Sweeping = 8
643 };
644 protected:
645 static CollectorState _collectorState;
646
647 // State related to prologue/epilogue invocation for my generations
648 bool _between_prologue_and_epilogue;
649
650 // Signalling/State related to coordination between fore- and backgroud GC
651 // Note: When the baton has been passed from background GC to foreground GC,
652 // _foregroundGCIsActive is true and _foregroundGCShouldWait is false.
653 static bool _foregroundGCIsActive; // true iff foreground collector is active or
654 // wants to go active
655 static bool _foregroundGCShouldWait; // true iff background GC is active and has not
656 // yet passed the baton to the foreground GC
657
658 // Support for CMSScheduleRemark (abortable preclean)
659 bool _abort_preclean;
660 bool _start_sampling;
661
662 int _numYields;
663 size_t _numDirtyCards;
664 size_t _sweep_count;
665 // number of full gc's since the last concurrent gc.
666 uint _full_gcs_since_conc_gc;
667
668 // occupancy used for bootstrapping stats
669 double _bootstrap_occupancy;
670
671 // timer
672 elapsedTimer _timer;
673
674 // Timing, allocation and promotion statistics, used for scheduling.
675 CMSStats _stats;
676
677 // Allocation limits installed in the young gen, used only in
678 // CMSIncrementalMode. When an allocation in the young gen would cross one of
679 // these limits, the cms generation is notified and the cms thread is started
680 // or stopped, respectively.
681 HeapWord* _icms_start_limit;
682 HeapWord* _icms_stop_limit;
683
684 enum CMS_op_type {
685 CMS_op_checkpointRootsInitial,
686 CMS_op_checkpointRootsFinal
687 };
688
689 void do_CMS_operation(CMS_op_type op);
690 bool stop_world_and_do(CMS_op_type op);
691
692 OopTaskQueueSet* task_queues() { return _task_queues; }
693 int* hash_seed(int i) { return &_hash_seed[i]; }
694 YieldingFlexibleWorkGang* conc_workers() { return _conc_workers; }
695
696 // Support for parallelizing Eden rescan in CMS remark phase
697 void sample_eden(); // ... sample Eden space top
698
699 private:
700 // Support for parallelizing young gen rescan in CMS remark phase
701 Generation* _young_gen; // the younger gen
702 HeapWord** _top_addr; // ... Top of Eden
703 HeapWord** _end_addr; // ... End of Eden
704 HeapWord** _eden_chunk_array; // ... Eden partitioning array
705 size_t _eden_chunk_index; // ... top (exclusive) of array
706 size_t _eden_chunk_capacity; // ... max entries in array
707
708 // Support for parallelizing survivor space rescan
709 HeapWord** _survivor_chunk_array;
710 size_t _survivor_chunk_index;
711 size_t _survivor_chunk_capacity;
712 size_t* _cursor;
713 ChunkArray* _survivor_plab_array;
714
715 // Support for marking stack overflow handling
716 bool take_from_overflow_list(size_t num, CMSMarkStack* to_stack);
717 bool par_take_from_overflow_list(size_t num, OopTaskQueue* to_work_q);
718 void push_on_overflow_list(oop p);
719 void par_push_on_overflow_list(oop p);
720 // the following is, obviously, not, in general, "MT-stable"
721 bool overflow_list_is_empty() const;
722
723 void preserve_mark_if_necessary(oop p);
724 void par_preserve_mark_if_necessary(oop p);
725 void preserve_mark_work(oop p, markOop m);
726 void restore_preserved_marks_if_any();
727 NOT_PRODUCT(bool no_preserved_marks() const;)
728 // in support of testing overflow code
729 NOT_PRODUCT(int _overflow_counter;)
730 NOT_PRODUCT(bool simulate_overflow();) // sequential
731 NOT_PRODUCT(bool par_simulate_overflow();) // MT version
732
733 // CMS work methods
734 void checkpointRootsInitialWork(bool asynch); // initial checkpoint work
735
736 // a return value of false indicates failure due to stack overflow
737 bool markFromRootsWork(bool asynch); // concurrent marking work
738
739 public: // FIX ME!!! only for testing
740 bool do_marking_st(bool asynch); // single-threaded marking
741 bool do_marking_mt(bool asynch); // multi-threaded marking
742
743 private:
744
745 // concurrent precleaning work
746 size_t preclean_mod_union_table(ConcurrentMarkSweepGeneration* gen,
747 ScanMarkedObjectsAgainCarefullyClosure* cl);
748 size_t preclean_card_table(ConcurrentMarkSweepGeneration* gen,
749 ScanMarkedObjectsAgainCarefullyClosure* cl);
750 // Does precleaning work, returning a quantity indicative of
751 // the amount of "useful work" done.
752 size_t preclean_work(bool clean_refs, bool clean_survivors);
753 void abortable_preclean(); // Preclean while looking for possible abort
754 void initialize_sequential_subtasks_for_young_gen_rescan(int i);
755 // Helper function for above; merge-sorts the per-thread plab samples
756 void merge_survivor_plab_arrays(ContiguousSpace* surv);
757 // Resets (i.e. clears) the per-thread plab sample vectors
758 void reset_survivor_plab_arrays();
759
760 // final (second) checkpoint work
761 void checkpointRootsFinalWork(bool asynch, bool clear_all_soft_refs,
762 bool init_mark_was_synchronous);
763 // work routine for parallel version of remark
764 void do_remark_parallel();
765 // work routine for non-parallel version of remark
766 void do_remark_non_parallel();
767 // reference processing work routine (during second checkpoint)
768 void refProcessingWork(bool asynch, bool clear_all_soft_refs);
769
770 // concurrent sweeping work
771 void sweepWork(ConcurrentMarkSweepGeneration* gen, bool asynch);
772
773 // (concurrent) resetting of support data structures
774 void reset(bool asynch);
775
776 // Clear _expansion_cause fields of constituent generations
777 void clear_expansion_cause();
778
779 // An auxilliary method used to record the ends of
780 // used regions of each generation to limit the extent of sweep
781 void save_sweep_limits();
782
783 // Resize the generations included in the collector.
784 void compute_new_size();
785
786 // A work method used by foreground collection to determine
787 // what type of collection (compacting or not, continuing or fresh)
788 // it should do.
789 void decide_foreground_collection_type(bool clear_all_soft_refs,
790 bool* should_compact, bool* should_start_over);
791
792 // A work method used by the foreground collector to do
793 // a mark-sweep-compact.
794 void do_compaction_work(bool clear_all_soft_refs);
795
796 // A work method used by the foreground collector to do
797 // a mark-sweep, after taking over from a possibly on-going
798 // concurrent mark-sweep collection.
799 void do_mark_sweep_work(bool clear_all_soft_refs,
800 CollectorState first_state, bool should_start_over);
801
802 // If the backgrould GC is active, acquire control from the background
803 // GC and do the collection.
804 void acquire_control_and_collect(bool full, bool clear_all_soft_refs);
805
806 // For synchronizing passing of control from background to foreground
807 // GC. waitForForegroundGC() is called by the background
808 // collector. It if had to wait for a foreground collection,
809 // it returns true and the background collection should assume
810 // that the collection was finished by the foreground
811 // collector.
812 bool waitForForegroundGC();
813
814 // Incremental mode triggering: recompute the icms duty cycle and set the
815 // allocation limits in the young gen.
816 void icms_update_allocation_limits();
817
818 size_t block_size_using_printezis_bits(HeapWord* addr) const;
819 size_t block_size_if_printezis_bits(HeapWord* addr) const;
820 HeapWord* next_card_start_after_block(HeapWord* addr) const;
821
822 void setup_cms_unloading_and_verification_state();
823 public:
824 CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
825 ConcurrentMarkSweepGeneration* permGen,
826 CardTableRS* ct,
827 ConcurrentMarkSweepPolicy* cp);
828 ConcurrentMarkSweepThread* cmsThread() { return _cmsThread; }
829
830 ReferenceProcessor* ref_processor() { return _ref_processor; }
831 void ref_processor_init();
832
833 Mutex* bitMapLock() const { return _markBitMap.lock(); }
834 static CollectorState abstract_state() { return _collectorState; }
835
836 bool should_abort_preclean() const; // Whether preclean should be aborted.
837 size_t get_eden_used() const;
838 size_t get_eden_capacity() const;
839
840 ConcurrentMarkSweepGeneration* cmsGen() { return _cmsGen; }
841
842 // locking checks
843 NOT_PRODUCT(static bool have_cms_token();)
844
845 // XXXPERM bool should_collect(bool full, size_t size, bool tlab);
846 bool shouldConcurrentCollect();
847
848 void collect(bool full,
849 bool clear_all_soft_refs,
850 size_t size,
851 bool tlab);
852 void collect_in_background(bool clear_all_soft_refs);
853 void collect_in_foreground(bool clear_all_soft_refs);
854
855 // In support of ExplicitGCInvokesConcurrent
856 static void request_full_gc(unsigned int full_gc_count);
857 // Should we unload classes in a particular concurrent cycle?
858 bool should_unload_classes() const {
859 return _should_unload_classes;
860 }
861 bool update_should_unload_classes();
862
863 void direct_allocated(HeapWord* start, size_t size);
864
865 // Object is dead if not marked and current phase is sweeping.
866 bool is_dead_obj(oop obj) const;
867
868 // After a promotion (of "start"), do any necessary marking.
869 // If "par", then it's being done by a parallel GC thread.
870 // The last two args indicate if we need precise marking
871 // and if so the size of the object so it can be dirtied
872 // in its entirety.
873 void promoted(bool par, HeapWord* start,
874 bool is_obj_array, size_t obj_size);
875
876 HeapWord* allocation_limit_reached(Space* space, HeapWord* top,
877 size_t word_size);
878
879 void getFreelistLocks() const;
880 void releaseFreelistLocks() const;
881 bool haveFreelistLocks() const;
882
883 // GC prologue and epilogue
884 void gc_prologue(bool full);
885 void gc_epilogue(bool full);
886
887 jlong time_of_last_gc(jlong now) {
888 if (_collectorState <= Idling) {
889 // gc not in progress
890 return _time_of_last_gc;
891 } else {
892 // collection in progress
893 return now;
894 }
895 }
896
897 // Support for parallel remark of survivor space
898 void* get_data_recorder(int thr_num);
899
900 CMSBitMap* markBitMap() { return &_markBitMap; }
901 void directAllocated(HeapWord* start, size_t size);
902
903 // main CMS steps and related support
904 void checkpointRootsInitial(bool asynch);
905 bool markFromRoots(bool asynch); // a return value of false indicates failure
906 // due to stack overflow
907 void preclean();
908 void checkpointRootsFinal(bool asynch, bool clear_all_soft_refs,
909 bool init_mark_was_synchronous);
910 void sweep(bool asynch);
911
912 // Check that the currently executing thread is the expected
913 // one (foreground collector or background collector).
914 static void check_correct_thread_executing() PRODUCT_RETURN;
915 // XXXPERM void print_statistics() PRODUCT_RETURN;
916
917 bool is_cms_reachable(HeapWord* addr);
918
919 // Performance Counter Support
920 CollectorCounters* counters() { return _gc_counters; }
921
922 // timer stuff
923 void startTimer() { assert(!_timer.is_active(), "Error"); _timer.start(); }
924 void stopTimer() { assert( _timer.is_active(), "Error"); _timer.stop(); }
925 void resetTimer() { assert(!_timer.is_active(), "Error"); _timer.reset(); }
926 double timerValue() { assert(!_timer.is_active(), "Error"); return _timer.seconds(); }
927
928 int yields() { return _numYields; }
929 void resetYields() { _numYields = 0; }
930 void incrementYields() { _numYields++; }
931 void resetNumDirtyCards() { _numDirtyCards = 0; }
932 void incrementNumDirtyCards(size_t num) { _numDirtyCards += num; }
933 size_t numDirtyCards() { return _numDirtyCards; }
934
935 static bool foregroundGCShouldWait() { return _foregroundGCShouldWait; }
936 static void set_foregroundGCShouldWait(bool v) { _foregroundGCShouldWait = v; }
937 static bool foregroundGCIsActive() { return _foregroundGCIsActive; }
938 static void set_foregroundGCIsActive(bool v) { _foregroundGCIsActive = v; }
939 size_t sweep_count() const { return _sweep_count; }
940 void increment_sweep_count() { _sweep_count++; }
941
942 // Timers/stats for gc scheduling and incremental mode pacing.
943 CMSStats& stats() { return _stats; }
944
945 // Convenience methods that check whether CMSIncrementalMode is enabled and
946 // forward to the corresponding methods in ConcurrentMarkSweepThread.
947 static void start_icms();
948 static void stop_icms(); // Called at the end of the cms cycle.
949 static void disable_icms(); // Called before a foreground collection.
950 static void enable_icms(); // Called after a foreground collection.
951 void icms_wait(); // Called at yield points.
952
953 // Adaptive size policy
954 CMSAdaptiveSizePolicy* size_policy();
955 CMSGCAdaptivePolicyCounters* gc_adaptive_policy_counters();
956
957 // debugging
958 void verify(bool);
959 bool verify_after_remark();
960 void verify_ok_to_terminate() const PRODUCT_RETURN;
961 void verify_work_stacks_empty() const PRODUCT_RETURN;
962 void verify_overflow_empty() const PRODUCT_RETURN;
963
964 // convenience methods in support of debugging
965 static const size_t skip_header_HeapWords() PRODUCT_RETURN0;
966 HeapWord* block_start(const void* p) const PRODUCT_RETURN0;
967
968 // accessors
969 CMSMarkStack* verification_mark_stack() { return &_markStack; }
970 CMSBitMap* verification_mark_bm() { return &_verification_mark_bm; }
971
972 // Get the bit map with a perm gen "deadness" information.
973 CMSBitMap* perm_gen_verify_bit_map() { return &_perm_gen_verify_bit_map; }
974
975 // Initialization errors
976 bool completed_initialization() { return _completed_initialization; }
977 };
978
979 class CMSExpansionCause : public AllStatic {
980 public:
981 enum Cause {
982 _no_expansion,
983 _satisfy_free_ratio,
984 _satisfy_promotion,
985 _satisfy_allocation,
986 _allocate_par_lab,
987 _allocate_par_spooling_space,
988 _adaptive_size_policy
989 };
990 // Return a string describing the cause of the expansion.
991 static const char* to_string(CMSExpansionCause::Cause cause);
992 };
993
994 class ConcurrentMarkSweepGeneration: public CardGeneration {
995 friend class VMStructs;
996 friend class ConcurrentMarkSweepThread;
997 friend class ConcurrentMarkSweep;
998 friend class CMSCollector;
999 protected:
1000 static CMSCollector* _collector; // the collector that collects us
1001 CompactibleFreeListSpace* _cmsSpace; // underlying space (only one for now)
1002
1003 // Performance Counters
1004 GenerationCounters* _gen_counters;
1005 GSpaceCounters* _space_counters;
1006
1007 // Words directly allocated, used by CMSStats.
1008 size_t _direct_allocated_words;
1009
1010 // Non-product stat counters
1011 NOT_PRODUCT(
1012 int _numObjectsPromoted;
1013 int _numWordsPromoted;
1014 int _numObjectsAllocated;
1015 int _numWordsAllocated;
1016 )
1017
1018 // Used for sizing decisions
1019 bool _incremental_collection_failed;
1020 bool incremental_collection_failed() {
1021 return _incremental_collection_failed;
1022 }
1023 void set_incremental_collection_failed() {
1024 _incremental_collection_failed = true;
1025 }
1026 void clear_incremental_collection_failed() {
1027 _incremental_collection_failed = false;
1028 }
1029
1030 // accessors
1031 void set_expansion_cause(CMSExpansionCause::Cause v) { _expansion_cause = v;}
1032 CMSExpansionCause::Cause expansion_cause() const { return _expansion_cause; }
1033
1034 private:
1035 // For parallel young-gen GC support.
1036 CMSParGCThreadState** _par_gc_thread_states;
1037
1038 // Reason generation was expanded
1039 CMSExpansionCause::Cause _expansion_cause;
1040
1041 // In support of MinChunkSize being larger than min object size
1042 const double _dilatation_factor;
1043
1044 enum CollectionTypes {
1045 Concurrent_collection_type = 0,
1046 MS_foreground_collection_type = 1,
1047 MSC_foreground_collection_type = 2,
1048 Unknown_collection_type = 3
1049 };
1050
1051 CollectionTypes _debug_collection_type;
1052
1053 // Fraction of current occupancy at which to start a CMS collection which
1054 // will collect this generation (at least).
1055 double _initiating_occupancy;
1056
1057 protected:
1058 // Shrink generation by specified size (returns false if unable to shrink)
1059 virtual void shrink_by(size_t bytes);
1060
1061 // Update statistics for GC
1062 virtual void update_gc_stats(int level, bool full);
1063
1064 // Maximum available space in the generation (including uncommitted)
1065 // space.
1066 size_t max_available() const;
1067
1068 // getter and initializer for _initiating_occupancy field.
1069 double initiating_occupancy() const { return _initiating_occupancy; }
1070 void init_initiating_occupancy(intx io, intx tr);
1071
1072 public:
1073 ConcurrentMarkSweepGeneration(ReservedSpace rs, size_t initial_byte_size,
1074 int level, CardTableRS* ct,
1075 bool use_adaptive_freelists,
1076 FreeBlockDictionary::DictionaryChoice);
1077
1078 // Accessors
1079 CMSCollector* collector() const { return _collector; }
1080 static void set_collector(CMSCollector* collector) {
1081 assert(_collector == NULL, "already set");
1082 _collector = collector;
1083 }
1084 CompactibleFreeListSpace* cmsSpace() const { return _cmsSpace; }
1085
1086 Mutex* freelistLock() const;
1087
1088 virtual Generation::Name kind() { return Generation::ConcurrentMarkSweep; }
1089
1090 // Adaptive size policy
1091 CMSAdaptiveSizePolicy* size_policy();
1092
1093 bool refs_discovery_is_atomic() const { return false; }
1094 bool refs_discovery_is_mt() const {
1095 // Note: CMS does MT-discovery during the parallel-remark
1096 // phases. Use ReferenceProcessorMTMutator to make refs
1097 // discovery MT-safe during such phases or other parallel
1098 // discovery phases in the future. This may all go away
1099 // if/when we decide that refs discovery is sufficiently
1100 // rare that the cost of the CAS's involved is in the
1101 // noise. That's a measurement that should be done, and
1102 // the code simplified if that turns out to be the case.
1103 return false;
1104 }
1105
1106 // Override
1107 virtual void ref_processor_init();
1108
1109 // Grow generation by specified size (returns false if unable to grow)
1110 bool grow_by(size_t bytes);
1111 // Grow generation to reserved size.
1112 bool grow_to_reserved();
1113
1114 void clear_expansion_cause() { _expansion_cause = CMSExpansionCause::_no_expansion; }
1115
1116 // Space enquiries
1117 size_t capacity() const;
1118 size_t used() const;
1119 size_t free() const;
1120 double occupancy() const { return ((double)used())/((double)capacity()); }
1121 size_t contiguous_available() const;
1122 size_t unsafe_max_alloc_nogc() const;
1123
1124 // over-rides
1125 MemRegion used_region() const;
1126 MemRegion used_region_at_save_marks() const;
1127
1128 // Does a "full" (forced) collection invoked on this generation collect
1129 // all younger generations as well? Note that the second conjunct is a
1130 // hack to allow the collection of the younger gen first if the flag is
1131 // set. This is better than using th policy's should_collect_gen0_first()
1132 // since that causes us to do an extra unnecessary pair of restart-&-stop-world.
1133 virtual bool full_collects_younger_generations() const {
1134 return UseCMSCompactAtFullCollection && !CollectGen0First;
1135 }
1136
1137 void space_iterate(SpaceClosure* blk, bool usedOnly = false);
1138
1139 // Support for compaction
1140 CompactibleSpace* first_compaction_space() const;
1141 // Adjust quantites in the generation affected by
1142 // the compaction.
1143 void reset_after_compaction();
1144
1145 // Allocation support
1146 HeapWord* allocate(size_t size, bool tlab);
1147 HeapWord* have_lock_and_allocate(size_t size, bool tlab);
1148 oop promote(oop obj, size_t obj_size);
1149 HeapWord* par_allocate(size_t size, bool tlab) {
1150 return allocate(size, tlab);
1151 }
1152
1153 // Incremental mode triggering.
1154 HeapWord* allocation_limit_reached(Space* space, HeapWord* top,
1155 size_t word_size);
1156
1157 // Used by CMSStats to track direct allocation. The value is sampled and
1158 // reset after each young gen collection.
1159 size_t direct_allocated_words() const { return _direct_allocated_words; }
1160 void reset_direct_allocated_words() { _direct_allocated_words = 0; }
1161
1162 // Overrides for parallel promotion.
1163 virtual oop par_promote(int thread_num,
1164 oop obj, markOop m, size_t word_sz);
1165 // This one should not be called for CMS.
1166 virtual void par_promote_alloc_undo(int thread_num,
1167 HeapWord* obj, size_t word_sz);
1168 virtual void par_promote_alloc_done(int thread_num);
1169 virtual void par_oop_since_save_marks_iterate_done(int thread_num);
1170
1171 virtual bool promotion_attempt_is_safe(size_t promotion_in_bytes,
1172 bool younger_handles_promotion_failure) const;
1173
1174 // Inform this (non-young) generation that a promotion failure was
1175 // encountered during a collection of a younger generation that
1176 // promotes into this generation.
1177 virtual void promotion_failure_occurred();
1178
1179 bool should_collect(bool full, size_t size, bool tlab);
1180 virtual bool should_concurrent_collect() const;
1181 virtual bool is_too_full() const;
1182 void collect(bool full,
1183 bool clear_all_soft_refs,
1184 size_t size,
1185 bool tlab);
1186
1187 HeapWord* expand_and_allocate(size_t word_size,
1188 bool tlab,
1189 bool parallel = false);
1190
1191 // GC prologue and epilogue
1192 void gc_prologue(bool full);
1193 void gc_prologue_work(bool full, bool registerClosure,
1194 ModUnionClosure* modUnionClosure);
1195 void gc_epilogue(bool full);
1196 void gc_epilogue_work(bool full);
1197
1198 // Time since last GC of this generation
1199 jlong time_of_last_gc(jlong now) {
1200 return collector()->time_of_last_gc(now);
1201 }
1202 void update_time_of_last_gc(jlong now) {
1203 collector()-> update_time_of_last_gc(now);
1204 }
1205
1206 // Allocation failure
1207 void expand(size_t bytes, size_t expand_bytes,
1208 CMSExpansionCause::Cause cause);
1209 virtual bool expand(size_t bytes, size_t expand_bytes);
1210 void shrink(size_t bytes);
1211 HeapWord* expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz);
1212 bool expand_and_ensure_spooling_space(PromotionInfo* promo);
1213
1214 // Iteration support and related enquiries
1215 void save_marks();
1216 bool no_allocs_since_save_marks();
1217 void object_iterate_since_last_GC(ObjectClosure* cl);
1218 void younger_refs_iterate(OopsInGenClosure* cl);
1219
1220 // Iteration support specific to CMS generations
1221 void save_sweep_limit();
1222
1223 // More iteration support
1224 virtual void oop_iterate(MemRegion mr, OopClosure* cl);
1225 virtual void oop_iterate(OopClosure* cl);
1226 virtual void safe_object_iterate(ObjectClosure* cl);
1227 virtual void object_iterate(ObjectClosure* cl);
1228
1229 // Need to declare the full complement of closures, whether we'll
1230 // override them or not, or get message from the compiler:
1231 // oop_since_save_marks_iterate_nv hides virtual function...
1232 #define CMS_SINCE_SAVE_MARKS_DECL(OopClosureType, nv_suffix) \
1233 void oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl);
1234 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DECL)
1235
1236 // Smart allocation XXX -- move to CFLSpace?
1237 void setNearLargestChunk();
1238 bool isNearLargestChunk(HeapWord* addr);
1239
1240 // Get the chunk at the end of the space. Delagates to
1241 // the space.
1242 FreeChunk* find_chunk_at_end();
1243
1244 // Overriding of unused functionality (sharing not yet supported with CMS)
1245 void pre_adjust_pointers();
1246 void post_compact();
1247
1248 // Debugging
1249 void prepare_for_verify();
1250 void verify(bool allow_dirty);
1251 void print_statistics() PRODUCT_RETURN;
1252
1253 // Performance Counters support
1254 virtual void update_counters();
1255 virtual void update_counters(size_t used);
1256 void initialize_performance_counters();
1257 CollectorCounters* counters() { return collector()->counters(); }
1258
1259 // Support for parallel remark of survivor space
1260 void* get_data_recorder(int thr_num) {
1261 //Delegate to collector
1262 return collector()->get_data_recorder(thr_num);
1263 }
1264
1265 // Printing
1266 const char* name() const;
1267 virtual const char* short_name() const { return "CMS"; }
1268 void print() const;
1269 void printOccupancy(const char* s);
1270 bool must_be_youngest() const { return false; }
1271 bool must_be_oldest() const { return true; }
1272
1273 void compute_new_size();
1274
1275 CollectionTypes debug_collection_type() { return _debug_collection_type; }
1276 void rotate_debug_collection_type();
1277 };
1278
1279 class ASConcurrentMarkSweepGeneration : public ConcurrentMarkSweepGeneration {
1280
1281 // Return the size policy from the heap's collector
1282 // policy casted to CMSAdaptiveSizePolicy*.
1283 CMSAdaptiveSizePolicy* cms_size_policy() const;
1284
1285 // Resize the generation based on the adaptive size
1286 // policy.
1287 void resize(size_t cur_promo, size_t desired_promo);
1288
1289 // Return the GC counters from the collector policy
1290 CMSGCAdaptivePolicyCounters* gc_adaptive_policy_counters();
1291
1292 virtual void shrink_by(size_t bytes);
1293
1294 public:
1295 virtual void compute_new_size();
1296 ASConcurrentMarkSweepGeneration(ReservedSpace rs, size_t initial_byte_size,
1297 int level, CardTableRS* ct,
1298 bool use_adaptive_freelists,
1299 FreeBlockDictionary::DictionaryChoice
1300 dictionaryChoice) :
1301 ConcurrentMarkSweepGeneration(rs, initial_byte_size, level, ct,
1302 use_adaptive_freelists, dictionaryChoice) {}
1303
1304 virtual const char* short_name() const { return "ASCMS"; }
1305 virtual Generation::Name kind() { return Generation::ASConcurrentMarkSweep; }
1306
1307 virtual void update_counters();
1308 virtual void update_counters(size_t used);
1309 };
1310
1311 //
1312 // Closures of various sorts used by CMS to accomplish its work
1313 //
1314
1315 // This closure is used to check that a certain set of oops is empty.
1316 class FalseClosure: public OopClosure {
1317 public:
1318 void do_oop(oop* p) { guarantee(false, "Should be an empty set"); }
1319 void do_oop(narrowOop* p) { guarantee(false, "Should be an empty set"); }
1320 };
1321
1322 // This closure is used to do concurrent marking from the roots
1323 // following the first checkpoint.
1324 class MarkFromRootsClosure: public BitMapClosure {
1325 CMSCollector* _collector;
1326 MemRegion _span;
1327 CMSBitMap* _bitMap;
1328 CMSBitMap* _mut;
1329 CMSMarkStack* _markStack;
1330 CMSMarkStack* _revisitStack;
1331 bool _yield;
1332 int _skipBits;
1333 HeapWord* _finger;
1334 HeapWord* _threshold;
1335 DEBUG_ONLY(bool _verifying;)
1336
1337 public:
1338 MarkFromRootsClosure(CMSCollector* collector, MemRegion span,
1339 CMSBitMap* bitMap,
1340 CMSMarkStack* markStack,
1341 CMSMarkStack* revisitStack,
1342 bool should_yield, bool verifying = false);
1343 bool do_bit(size_t offset);
1344 void reset(HeapWord* addr);
1345 inline void do_yield_check();
1346
1347 private:
1348 void scanOopsInOop(HeapWord* ptr);
1349 void do_yield_work();
1350 };
1351
1352 // This closure is used to do concurrent multi-threaded
1353 // marking from the roots following the first checkpoint.
1354 // XXX This should really be a subclass of The serial version
1355 // above, but i have not had the time to refactor things cleanly.
1356 // That willbe done for Dolphin.
1357 class Par_MarkFromRootsClosure: public BitMapClosure {
1358 CMSCollector* _collector;
1359 MemRegion _whole_span;
1360 MemRegion _span;
1361 CMSBitMap* _bit_map;
1362 CMSBitMap* _mut;
1363 OopTaskQueue* _work_queue;
1364 CMSMarkStack* _overflow_stack;
1365 CMSMarkStack* _revisit_stack;
1366 bool _yield;
1367 int _skip_bits;
1368 HeapWord* _finger;
1369 HeapWord* _threshold;
1370 CMSConcMarkingTask* _task;
1371 public:
1372 Par_MarkFromRootsClosure(CMSConcMarkingTask* task, CMSCollector* collector,
1373 MemRegion span,
1374 CMSBitMap* bit_map,
1375 OopTaskQueue* work_queue,
1376 CMSMarkStack* overflow_stack,
1377 CMSMarkStack* revisit_stack,
1378 bool should_yield);
1379 bool do_bit(size_t offset);
1380 inline void do_yield_check();
1381
1382 private:
1383 void scan_oops_in_oop(HeapWord* ptr);
1384 void do_yield_work();
1385 bool get_work_from_overflow_stack();
1386 };
1387
1388 // The following closures are used to do certain kinds of verification of
1389 // CMS marking.
1390 class PushAndMarkVerifyClosure: public OopClosure {
1391 CMSCollector* _collector;
1392 MemRegion _span;
1393 CMSBitMap* _verification_bm;
1394 CMSBitMap* _cms_bm;
1395 CMSMarkStack* _mark_stack;
1396 protected:
1397 void do_oop(oop p);
1398 template <class T> inline void do_oop_work(T *p) {
1399 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
1400 do_oop(obj);
1401 }
1402 public:
1403 PushAndMarkVerifyClosure(CMSCollector* cms_collector,
1404 MemRegion span,
1405 CMSBitMap* verification_bm,
1406 CMSBitMap* cms_bm,
1407 CMSMarkStack* mark_stack);
1408 void do_oop(oop* p);
1409 void do_oop(narrowOop* p);
1410 // Deal with a stack overflow condition
1411 void handle_stack_overflow(HeapWord* lost);
1412 };
1413
1414 class MarkFromRootsVerifyClosure: public BitMapClosure {
1415 CMSCollector* _collector;
1416 MemRegion _span;
1417 CMSBitMap* _verification_bm;
1418 CMSBitMap* _cms_bm;
1419 CMSMarkStack* _mark_stack;
1420 HeapWord* _finger;
1421 PushAndMarkVerifyClosure _pam_verify_closure;
1422 public:
1423 MarkFromRootsVerifyClosure(CMSCollector* collector, MemRegion span,
1424 CMSBitMap* verification_bm,
1425 CMSBitMap* cms_bm,
1426 CMSMarkStack* mark_stack);
1427 bool do_bit(size_t offset);
1428 void reset(HeapWord* addr);
1429 };
1430
1431
1432 // This closure is used to check that a certain set of bits is
1433 // "empty" (i.e. the bit vector doesn't have any 1-bits).
1434 class FalseBitMapClosure: public BitMapClosure {
1435 public:
1436 bool do_bit(size_t offset) {
1437 guarantee(false, "Should not have a 1 bit");
1438 return true;
1439 }
1440 };
1441
1442 // This closure is used during the second checkpointing phase
1443 // to rescan the marked objects on the dirty cards in the mod
1444 // union table and the card table proper. It's invoked via
1445 // MarkFromDirtyCardsClosure below. It uses either
1446 // [Par_]MarkRefsIntoAndScanClosure (Par_ in the parallel case)
1447 // declared in genOopClosures.hpp to accomplish some of its work.
1448 // In the parallel case the bitMap is shared, so access to
1449 // it needs to be suitably synchronized for updates by embedded
1450 // closures that update it; however, this closure itself only
1451 // reads the bit_map and because it is idempotent, is immune to
1452 // reading stale values.
1453 class ScanMarkedObjectsAgainClosure: public UpwardsObjectClosure {
1454 #ifdef ASSERT
1455 CMSCollector* _collector;
1456 MemRegion _span;
1457 union {
1458 CMSMarkStack* _mark_stack;
1459 OopTaskQueue* _work_queue;
1460 };
1461 #endif // ASSERT
1462 bool _parallel;
1463 CMSBitMap* _bit_map;
1464 union {
1465 MarkRefsIntoAndScanClosure* _scan_closure;
1466 Par_MarkRefsIntoAndScanClosure* _par_scan_closure;
1467 };
1468
1469 public:
1470 ScanMarkedObjectsAgainClosure(CMSCollector* collector,
1471 MemRegion span,
1472 ReferenceProcessor* rp,
1473 CMSBitMap* bit_map,
1474 CMSMarkStack* mark_stack,
1475 CMSMarkStack* revisit_stack,
1476 MarkRefsIntoAndScanClosure* cl):
1477 #ifdef ASSERT
1478 _collector(collector),
1479 _span(span),
1480 _mark_stack(mark_stack),
1481 #endif // ASSERT
1482 _parallel(false),
1483 _bit_map(bit_map),
1484 _scan_closure(cl) { }
1485
1486 ScanMarkedObjectsAgainClosure(CMSCollector* collector,
1487 MemRegion span,
1488 ReferenceProcessor* rp,
1489 CMSBitMap* bit_map,
1490 OopTaskQueue* work_queue,
1491 CMSMarkStack* revisit_stack,
1492 Par_MarkRefsIntoAndScanClosure* cl):
1493 #ifdef ASSERT
1494 _collector(collector),
1495 _span(span),
1496 _work_queue(work_queue),
1497 #endif // ASSERT
1498 _parallel(true),
1499 _bit_map(bit_map),
1500 _par_scan_closure(cl) { }
1501
1502 void do_object(oop obj) {
1503 guarantee(false, "Call do_object_b(oop, MemRegion) instead");
1504 }
1505 bool do_object_b(oop obj) {
1506 guarantee(false, "Call do_object_b(oop, MemRegion) form instead");
1507 return false;
1508 }
1509 bool do_object_bm(oop p, MemRegion mr);
1510 };
1511
1512 // This closure is used during the second checkpointing phase
1513 // to rescan the marked objects on the dirty cards in the mod
1514 // union table and the card table proper. It invokes
1515 // ScanMarkedObjectsAgainClosure above to accomplish much of its work.
1516 // In the parallel case, the bit map is shared and requires
1517 // synchronized access.
1518 class MarkFromDirtyCardsClosure: public MemRegionClosure {
1519 CompactibleFreeListSpace* _space;
1520 ScanMarkedObjectsAgainClosure _scan_cl;
1521 size_t _num_dirty_cards;
1522
1523 public:
1524 MarkFromDirtyCardsClosure(CMSCollector* collector,
1525 MemRegion span,
1526 CompactibleFreeListSpace* space,
1527 CMSBitMap* bit_map,
1528 CMSMarkStack* mark_stack,
1529 CMSMarkStack* revisit_stack,
1530 MarkRefsIntoAndScanClosure* cl):
1531 _space(space),
1532 _num_dirty_cards(0),
1533 _scan_cl(collector, span, collector->ref_processor(), bit_map,
1534 mark_stack, revisit_stack, cl) { }
1535
1536 MarkFromDirtyCardsClosure(CMSCollector* collector,
1537 MemRegion span,
1538 CompactibleFreeListSpace* space,
1539 CMSBitMap* bit_map,
1540 OopTaskQueue* work_queue,
1541 CMSMarkStack* revisit_stack,
1542 Par_MarkRefsIntoAndScanClosure* cl):
1543 _space(space),
1544 _num_dirty_cards(0),
1545 _scan_cl(collector, span, collector->ref_processor(), bit_map,
1546 work_queue, revisit_stack, cl) { }
1547
1548 void do_MemRegion(MemRegion mr);
1549 void set_space(CompactibleFreeListSpace* space) { _space = space; }
1550 size_t num_dirty_cards() { return _num_dirty_cards; }
1551 };
1552
1553 // This closure is used in the non-product build to check
1554 // that there are no MemRegions with a certain property.
1555 class FalseMemRegionClosure: public MemRegionClosure {
1556 void do_MemRegion(MemRegion mr) {
1557 guarantee(!mr.is_empty(), "Shouldn't be empty");
1558 guarantee(false, "Should never be here");
1559 }
1560 };
1561
1562 // This closure is used during the precleaning phase
1563 // to "carefully" rescan marked objects on dirty cards.
1564 // It uses MarkRefsIntoAndScanClosure declared in genOopClosures.hpp
1565 // to accomplish some of its work.
1566 class ScanMarkedObjectsAgainCarefullyClosure: public ObjectClosureCareful {
1567 CMSCollector* _collector;
1568 MemRegion _span;
1569 bool _yield;
1570 Mutex* _freelistLock;
1571 CMSBitMap* _bitMap;
1572 CMSMarkStack* _markStack;
1573 MarkRefsIntoAndScanClosure* _scanningClosure;
1574
1575 public:
1576 ScanMarkedObjectsAgainCarefullyClosure(CMSCollector* collector,
1577 MemRegion span,
1578 CMSBitMap* bitMap,
1579 CMSMarkStack* markStack,
1580 CMSMarkStack* revisitStack,
1581 MarkRefsIntoAndScanClosure* cl,
1582 bool should_yield):
1583 _collector(collector),
1584 _span(span),
1585 _yield(should_yield),
1586 _bitMap(bitMap),
1587 _markStack(markStack),
1588 _scanningClosure(cl) {
1589 }
1590
1591 void do_object(oop p) {
1592 guarantee(false, "call do_object_careful instead");
1593 }
1594
1595 size_t do_object_careful(oop p) {
1596 guarantee(false, "Unexpected caller");
1597 return 0;
1598 }
1599
1600 size_t do_object_careful_m(oop p, MemRegion mr);
1601
1602 void setFreelistLock(Mutex* m) {
1603 _freelistLock = m;
1604 _scanningClosure->set_freelistLock(m);
1605 }
1606
1607 private:
1608 inline bool do_yield_check();
1609
1610 void do_yield_work();
1611 };
1612
1613 class SurvivorSpacePrecleanClosure: public ObjectClosureCareful {
1614 CMSCollector* _collector;
1615 MemRegion _span;
1616 bool _yield;
1617 CMSBitMap* _bit_map;
1618 CMSMarkStack* _mark_stack;
1619 PushAndMarkClosure* _scanning_closure;
1620 unsigned int _before_count;
1621
1622 public:
1623 SurvivorSpacePrecleanClosure(CMSCollector* collector,
1624 MemRegion span,
1625 CMSBitMap* bit_map,
1626 CMSMarkStack* mark_stack,
1627 PushAndMarkClosure* cl,
1628 unsigned int before_count,
1629 bool should_yield):
1630 _collector(collector),
1631 _span(span),
1632 _yield(should_yield),
1633 _bit_map(bit_map),
1634 _mark_stack(mark_stack),
1635 _scanning_closure(cl),
1636 _before_count(before_count)
1637 { }
1638
1639 void do_object(oop p) {
1640 guarantee(false, "call do_object_careful instead");
1641 }
1642
1643 size_t do_object_careful(oop p);
1644
1645 size_t do_object_careful_m(oop p, MemRegion mr) {
1646 guarantee(false, "Unexpected caller");
1647 return 0;
1648 }
1649
1650 private:
1651 inline void do_yield_check();
1652 void do_yield_work();
1653 };
1654
1655 // This closure is used to accomplish the sweeping work
1656 // after the second checkpoint but before the concurrent reset
1657 // phase.
1658 //
1659 // Terminology
1660 // left hand chunk (LHC) - block of one or more chunks currently being
1661 // coalesced. The LHC is available for coalescing with a new chunk.
1662 // right hand chunk (RHC) - block that is currently being swept that is
1663 // free or garbage that can be coalesced with the LHC.
1664 // _inFreeRange is true if there is currently a LHC
1665 // _lastFreeRangeCoalesced is true if the LHC consists of more than one chunk.
1666 // _freeRangeInFreeLists is true if the LHC is in the free lists.
1667 // _freeFinger is the address of the current LHC
1668 class SweepClosure: public BlkClosureCareful {
1669 CMSCollector* _collector; // collector doing the work
1670 ConcurrentMarkSweepGeneration* _g; // Generation being swept
1671 CompactibleFreeListSpace* _sp; // Space being swept
1672 HeapWord* _limit;
1673 Mutex* _freelistLock; // Free list lock (in space)
1674 CMSBitMap* _bitMap; // Marking bit map (in
1675 // generation)
1676 bool _inFreeRange; // Indicates if we are in the
1677 // midst of a free run
1678 bool _freeRangeInFreeLists;
1679 // Often, we have just found
1680 // a free chunk and started
1681 // a new free range; we do not
1682 // eagerly remove this chunk from
1683 // the free lists unless there is
1684 // a possibility of coalescing.
1685 // When true, this flag indicates
1686 // that the _freeFinger below
1687 // points to a potentially free chunk
1688 // that may still be in the free lists
1689 bool _lastFreeRangeCoalesced;
1690 // free range contains chunks
1691 // coalesced
1692 bool _yield;
1693 // Whether sweeping should be
1694 // done with yields. For instance
1695 // when done by the foreground
1696 // collector we shouldn't yield.
1697 HeapWord* _freeFinger; // When _inFreeRange is set, the
1698 // pointer to the "left hand
1699 // chunk"
1700 size_t _freeRangeSize;
1701 // When _inFreeRange is set, this
1702 // indicates the accumulated size
1703 // of the "left hand chunk"
1704 NOT_PRODUCT(
1705 size_t _numObjectsFreed;
1706 size_t _numWordsFreed;
1707 size_t _numObjectsLive;
1708 size_t _numWordsLive;
1709 size_t _numObjectsAlreadyFree;
1710 size_t _numWordsAlreadyFree;
1711 FreeChunk* _last_fc;
1712 )
1713 private:
1714 // Code that is common to a free chunk or garbage when
1715 // encountered during sweeping.
1716 void doPostIsFreeOrGarbageChunk(FreeChunk *fc,
1717 size_t chunkSize);
1718 // Process a free chunk during sweeping.
1719 void doAlreadyFreeChunk(FreeChunk *fc);
1720 // Process a garbage chunk during sweeping.
1721 size_t doGarbageChunk(FreeChunk *fc);
1722 // Process a live chunk during sweeping.
1723 size_t doLiveChunk(FreeChunk* fc);
1724
1725 // Accessors.
1726 HeapWord* freeFinger() const { return _freeFinger; }
1727 void set_freeFinger(HeapWord* v) { _freeFinger = v; }
1728 size_t freeRangeSize() const { return _freeRangeSize; }
1729 void set_freeRangeSize(size_t v) { _freeRangeSize = v; }
1730 bool inFreeRange() const { return _inFreeRange; }
1731 void set_inFreeRange(bool v) { _inFreeRange = v; }
1732 bool lastFreeRangeCoalesced() const { return _lastFreeRangeCoalesced; }
1733 void set_lastFreeRangeCoalesced(bool v) { _lastFreeRangeCoalesced = v; }
1734 bool freeRangeInFreeLists() const { return _freeRangeInFreeLists; }
1735 void set_freeRangeInFreeLists(bool v) { _freeRangeInFreeLists = v; }
1736
1737 // Initialize a free range.
1738 void initialize_free_range(HeapWord* freeFinger, bool freeRangeInFreeLists);
1739 // Return this chunk to the free lists.
1740 void flushCurFreeChunk(HeapWord* chunk, size_t size);
1741
1742 // Check if we should yield and do so when necessary.
1743 inline void do_yield_check(HeapWord* addr);
1744
1745 // Yield
1746 void do_yield_work(HeapWord* addr);
1747
1748 // Debugging/Printing
1749 void record_free_block_coalesced(FreeChunk* fc) const PRODUCT_RETURN;
1750
1751 public:
1752 SweepClosure(CMSCollector* collector, ConcurrentMarkSweepGeneration* g,
1753 CMSBitMap* bitMap, bool should_yield);
1754 ~SweepClosure();
1755
1756 size_t do_blk_careful(HeapWord* addr);
1757 };
1758
1759 // Closures related to weak references processing
1760
1761 // During CMS' weak reference processing, this is a
1762 // work-routine/closure used to complete transitive
1763 // marking of objects as live after a certain point
1764 // in which an initial set has been completely accumulated.
1765 // This closure is currently used both during the final
1766 // remark stop-world phase, as well as during the concurrent
1767 // precleaning of the discovered reference lists.
1768 class CMSDrainMarkingStackClosure: public VoidClosure {
1769 CMSCollector* _collector;
1770 MemRegion _span;
1771 CMSMarkStack* _mark_stack;
1772 CMSBitMap* _bit_map;
1773 CMSKeepAliveClosure* _keep_alive;
1774 bool _concurrent_precleaning;
1775 public:
1776 CMSDrainMarkingStackClosure(CMSCollector* collector, MemRegion span,
1777 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
1778 CMSKeepAliveClosure* keep_alive,
1779 bool cpc):
1780 _collector(collector),
1781 _span(span),
1782 _bit_map(bit_map),
1783 _mark_stack(mark_stack),
1784 _keep_alive(keep_alive),
1785 _concurrent_precleaning(cpc) {
1786 assert(_concurrent_precleaning == _keep_alive->concurrent_precleaning(),
1787 "Mismatch");
1788 }
1789
1790 void do_void();
1791 };
1792
1793 // A parallel version of CMSDrainMarkingStackClosure above.
1794 class CMSParDrainMarkingStackClosure: public VoidClosure {
1795 CMSCollector* _collector;
1796 MemRegion _span;
1797 OopTaskQueue* _work_queue;
1798 CMSBitMap* _bit_map;
1799 CMSInnerParMarkAndPushClosure _mark_and_push;
1800
1801 public:
1802 CMSParDrainMarkingStackClosure(CMSCollector* collector,
1803 MemRegion span, CMSBitMap* bit_map,
1804 CMSMarkStack* revisit_stack,
1805 OopTaskQueue* work_queue):
1806 _collector(collector),
1807 _span(span),
1808 _bit_map(bit_map),
1809 _work_queue(work_queue),
1810 _mark_and_push(collector, span, bit_map, revisit_stack, work_queue) { }
1811
1812 public:
1813 void trim_queue(uint max);
1814 void do_void();
1815 };
1816
1817 // Allow yielding or short-circuiting of reference list
1818 // prelceaning work.
1819 class CMSPrecleanRefsYieldClosure: public YieldClosure {
1820 CMSCollector* _collector;
1821 void do_yield_work();
1822 public:
1823 CMSPrecleanRefsYieldClosure(CMSCollector* collector):
1824 _collector(collector) {}
1825 virtual bool should_return();
1826 };
1827
1828
1829 // Convenience class that locks free list locks for given CMS collector
1830 class FreelistLocker: public StackObj {
1831 private:
1832 CMSCollector* _collector;
1833 public:
1834 FreelistLocker(CMSCollector* collector):
1835 _collector(collector) {
1836 _collector->getFreelistLocks();
1837 }
1838
1839 ~FreelistLocker() {
1840 _collector->releaseFreelistLocks();
1841 }
1842 };
1843
1844 // Mark all dead objects in a given space.
1845 class MarkDeadObjectsClosure: public BlkClosure {
1846 const CMSCollector* _collector;
1847 const CompactibleFreeListSpace* _sp;
1848 CMSBitMap* _live_bit_map;
1849 CMSBitMap* _dead_bit_map;
1850 public:
1851 MarkDeadObjectsClosure(const CMSCollector* collector,
1852 const CompactibleFreeListSpace* sp,
1853 CMSBitMap *live_bit_map,
1854 CMSBitMap *dead_bit_map) :
1855 _collector(collector),
1856 _sp(sp),
1857 _live_bit_map(live_bit_map),
1858 _dead_bit_map(dead_bit_map) {}
1859 size_t do_blk(HeapWord* addr);
1860 };