1 /*
2 * Copyright (c) 2001, 2011, 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
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23 */
24
25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_CONCURRENTMARK_HPP
26 #define SHARE_VM_GC_IMPLEMENTATION_G1_CONCURRENTMARK_HPP
27
28 #include "gc_implementation/g1/heapRegionSets.hpp"
29 #include "utilities/taskqueue.hpp"
30
31 class G1CollectedHeap;
32 class CMTask;
33 typedef GenericTaskQueue<oop> CMTaskQueue;
34 typedef GenericTaskQueueSet<CMTaskQueue> CMTaskQueueSet;
35
36 // Closure used by CM during concurrent reference discovery
37 // and reference processing (during remarking) to determine
38 // if a particular object is alive. It is primarily used
39 // to determine if referents of discovered reference objects
40 // are alive. An instance is also embedded into the
41 // reference processor as the _is_alive_non_header field
42 class G1CMIsAliveClosure: public BoolObjectClosure {
43 G1CollectedHeap* _g1;
44 public:
45 G1CMIsAliveClosure(G1CollectedHeap* g1) :
46 _g1(g1)
47 {}
48
49 void do_object(oop obj) {
50 ShouldNotCallThis();
51 }
52 bool do_object_b(oop obj);
53 };
54
55 // A generic CM bit map. This is essentially a wrapper around the BitMap
56 // class, with one bit per (1<<_shifter) HeapWords.
57
58 class CMBitMapRO VALUE_OBJ_CLASS_SPEC {
59 protected:
60 HeapWord* _bmStartWord; // base address of range covered by map
61 size_t _bmWordSize; // map size (in #HeapWords covered)
62 const int _shifter; // map to char or bit
63 VirtualSpace _virtual_space; // underlying the bit map
64 BitMap _bm; // the bit map itself
65
66 public:
67 // constructor
68 CMBitMapRO(ReservedSpace rs, int shifter);
69
70 enum { do_yield = true };
71
72 // inquiries
73 HeapWord* startWord() const { return _bmStartWord; }
74 size_t sizeInWords() const { return _bmWordSize; }
75 // the following is one past the last word in space
76 HeapWord* endWord() const { return _bmStartWord + _bmWordSize; }
77
78 // read marks
79
80 bool isMarked(HeapWord* addr) const {
81 assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),
82 "outside underlying space?");
83 return _bm.at(heapWordToOffset(addr));
84 }
85
86 // iteration
87 bool iterate(BitMapClosure* cl) { return _bm.iterate(cl); }
88 bool iterate(BitMapClosure* cl, MemRegion mr);
89
90 // Return the address corresponding to the next marked bit at or after
91 // "addr", and before "limit", if "limit" is non-NULL. If there is no
92 // such bit, returns "limit" if that is non-NULL, or else "endWord()".
93 HeapWord* getNextMarkedWordAddress(HeapWord* addr,
94 HeapWord* limit = NULL) const;
95 // Return the address corresponding to the next unmarked bit at or after
96 // "addr", and before "limit", if "limit" is non-NULL. If there is no
97 // such bit, returns "limit" if that is non-NULL, or else "endWord()".
98 HeapWord* getNextUnmarkedWordAddress(HeapWord* addr,
99 HeapWord* limit = NULL) const;
100
101 // conversion utilities
102 // XXX Fix these so that offsets are size_t's...
103 HeapWord* offsetToHeapWord(size_t offset) const {
104 return _bmStartWord + (offset << _shifter);
105 }
106 size_t heapWordToOffset(HeapWord* addr) const {
107 return pointer_delta(addr, _bmStartWord) >> _shifter;
108 }
109 int heapWordDiffToOffsetDiff(size_t diff) const;
110 HeapWord* nextWord(HeapWord* addr) {
111 return offsetToHeapWord(heapWordToOffset(addr) + 1);
112 }
113
114 void mostly_disjoint_range_union(BitMap* from_bitmap,
115 size_t from_start_index,
116 HeapWord* to_start_word,
117 size_t word_num);
118
119 // debugging
120 NOT_PRODUCT(bool covers(ReservedSpace rs) const;)
121 };
122
123 class CMBitMap : public CMBitMapRO {
124
125 public:
126 // constructor
127 CMBitMap(ReservedSpace rs, int shifter) :
128 CMBitMapRO(rs, shifter) {}
129
130 // write marks
131 void mark(HeapWord* addr) {
132 assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),
133 "outside underlying space?");
134 _bm.set_bit(heapWordToOffset(addr));
135 }
136 void clear(HeapWord* addr) {
137 assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),
138 "outside underlying space?");
139 _bm.clear_bit(heapWordToOffset(addr));
140 }
141 bool parMark(HeapWord* addr) {
142 assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),
143 "outside underlying space?");
144 return _bm.par_set_bit(heapWordToOffset(addr));
145 }
146 bool parClear(HeapWord* addr) {
147 assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),
148 "outside underlying space?");
149 return _bm.par_clear_bit(heapWordToOffset(addr));
150 }
151 void markRange(MemRegion mr);
152 void clearAll();
153 void clearRange(MemRegion mr);
154
155 // Starting at the bit corresponding to "addr" (inclusive), find the next
156 // "1" bit, if any. This bit starts some run of consecutive "1"'s; find
157 // the end of this run (stopping at "end_addr"). Return the MemRegion
158 // covering from the start of the region corresponding to the first bit
159 // of the run to the end of the region corresponding to the last bit of
160 // the run. If there is no "1" bit at or after "addr", return an empty
161 // MemRegion.
162 MemRegion getAndClearMarkedRegion(HeapWord* addr, HeapWord* end_addr);
163 };
164
165 // Represents a marking stack used by the CM collector.
166 // Ideally this should be GrowableArray<> just like MSC's marking stack(s).
167 class CMMarkStack VALUE_OBJ_CLASS_SPEC {
168 ConcurrentMark* _cm;
169 oop* _base; // bottom of stack
170 jint _index; // one more than last occupied index
171 jint _capacity; // max #elements
172 jint _oops_do_bound; // Number of elements to include in next iteration.
173 NOT_PRODUCT(jint _max_depth;) // max depth plumbed during run
174
175 bool _overflow;
176 DEBUG_ONLY(bool _drain_in_progress;)
177 DEBUG_ONLY(bool _drain_in_progress_yields;)
178
179 public:
180 CMMarkStack(ConcurrentMark* cm);
181 ~CMMarkStack();
182
183 void allocate(size_t size);
184
185 oop pop() {
186 if (!isEmpty()) {
187 return _base[--_index] ;
188 }
189 return NULL;
190 }
191
192 // If overflow happens, don't do the push, and record the overflow.
193 // *Requires* that "ptr" is already marked.
194 void push(oop ptr) {
195 if (isFull()) {
196 // Record overflow.
197 _overflow = true;
198 return;
199 } else {
200 _base[_index++] = ptr;
201 NOT_PRODUCT(_max_depth = MAX2(_max_depth, _index));
202 }
203 }
204 // Non-block impl. Note: concurrency is allowed only with other
205 // "par_push" operations, not with "pop" or "drain". We would need
206 // parallel versions of them if such concurrency was desired.
207 void par_push(oop ptr);
208
209 // Pushes the first "n" elements of "ptr_arr" on the stack.
210 // Non-block impl. Note: concurrency is allowed only with other
211 // "par_adjoin_arr" or "push" operations, not with "pop" or "drain".
212 void par_adjoin_arr(oop* ptr_arr, int n);
213
214 // Pushes the first "n" elements of "ptr_arr" on the stack.
215 // Locking impl: concurrency is allowed only with
216 // "par_push_arr" and/or "par_pop_arr" operations, which use the same
217 // locking strategy.
218 void par_push_arr(oop* ptr_arr, int n);
219
220 // If returns false, the array was empty. Otherwise, removes up to "max"
221 // elements from the stack, and transfers them to "ptr_arr" in an
222 // unspecified order. The actual number transferred is given in "n" ("n
223 // == 0" is deliberately redundant with the return value.) Locking impl:
224 // concurrency is allowed only with "par_push_arr" and/or "par_pop_arr"
225 // operations, which use the same locking strategy.
226 bool par_pop_arr(oop* ptr_arr, int max, int* n);
227
228 // Drain the mark stack, applying the given closure to all fields of
229 // objects on the stack. (That is, continue until the stack is empty,
230 // even if closure applications add entries to the stack.) The "bm"
231 // argument, if non-null, may be used to verify that only marked objects
232 // are on the mark stack. If "yield_after" is "true", then the
233 // concurrent marker performing the drain offers to yield after
234 // processing each object. If a yield occurs, stops the drain operation
235 // and returns false. Otherwise, returns true.
236 template<class OopClosureClass>
237 bool drain(OopClosureClass* cl, CMBitMap* bm, bool yield_after = false);
238
239 bool isEmpty() { return _index == 0; }
240 bool isFull() { return _index == _capacity; }
241 int maxElems() { return _capacity; }
242
243 bool overflow() { return _overflow; }
244 void clear_overflow() { _overflow = false; }
245
246 int size() { return _index; }
247
248 void setEmpty() { _index = 0; clear_overflow(); }
249
250 // Record the current size; a subsequent "oops_do" will iterate only over
251 // indices valid at the time of this call.
252 void set_oops_do_bound(jint bound = -1) {
253 if (bound == -1) {
254 _oops_do_bound = _index;
255 } else {
256 _oops_do_bound = bound;
257 }
258 }
259 jint oops_do_bound() { return _oops_do_bound; }
260 // iterate over the oops in the mark stack, up to the bound recorded via
261 // the call above.
262 void oops_do(OopClosure* f);
263 };
264
265 class CMRegionStack VALUE_OBJ_CLASS_SPEC {
266 MemRegion* _base;
267 jint _capacity;
268 jint _index;
269 jint _oops_do_bound;
270 bool _overflow;
271 public:
272 CMRegionStack();
273 ~CMRegionStack();
274 void allocate(size_t size);
275
276 // This is lock-free; assumes that it will only be called in parallel
277 // with other "push" operations (no pops).
278 void push_lock_free(MemRegion mr);
279
280 // Lock-free; assumes that it will only be called in parallel
281 // with other "pop" operations (no pushes).
282 MemRegion pop_lock_free();
283
284 #if 0
285 // The routines that manipulate the region stack with a lock are
286 // not currently used. They should be retained, however, as a
287 // diagnostic aid.
288
289 // These two are the implementations that use a lock. They can be
290 // called concurrently with each other but they should not be called
291 // concurrently with the lock-free versions (push() / pop()).
292 void push_with_lock(MemRegion mr);
293 MemRegion pop_with_lock();
294 #endif
295
296 bool isEmpty() { return _index == 0; }
297 bool isFull() { return _index == _capacity; }
298
299 bool overflow() { return _overflow; }
300 void clear_overflow() { _overflow = false; }
301
302 int size() { return _index; }
303
304 // It iterates over the entries in the region stack and it
305 // invalidates (i.e. assigns MemRegion()) the ones that point to
306 // regions in the collection set.
307 bool invalidate_entries_into_cset();
308
309 // This gives an upper bound up to which the iteration in
310 // invalidate_entries_into_cset() will reach. This prevents
311 // newly-added entries to be unnecessarily scanned.
312 void set_oops_do_bound() {
313 _oops_do_bound = _index;
314 }
315
316 void setEmpty() { _index = 0; clear_overflow(); }
317 };
318
319 class ForceOverflowSettings VALUE_OBJ_CLASS_SPEC {
320 private:
321 #ifndef PRODUCT
322 uintx _num_remaining;
323 bool _force;
324 #endif // !defined(PRODUCT)
325
326 public:
327 void init() PRODUCT_RETURN;
328 void update() PRODUCT_RETURN;
329 bool should_force() PRODUCT_RETURN_( return false; );
330 };
331
332 // this will enable a variety of different statistics per GC task
333 #define _MARKING_STATS_ 0
334 // this will enable the higher verbose levels
335 #define _MARKING_VERBOSE_ 0
336
337 #if _MARKING_STATS_
338 #define statsOnly(statement) \
339 do { \
340 statement ; \
341 } while (0)
342 #else // _MARKING_STATS_
343 #define statsOnly(statement) \
344 do { \
345 } while (0)
346 #endif // _MARKING_STATS_
347
348 typedef enum {
349 no_verbose = 0, // verbose turned off
350 stats_verbose, // only prints stats at the end of marking
351 low_verbose, // low verbose, mostly per region and per major event
352 medium_verbose, // a bit more detailed than low
353 high_verbose // per object verbose
354 } CMVerboseLevel;
355
356
357 class ConcurrentMarkThread;
358
359 class ConcurrentMark: public CHeapObj {
360 friend class ConcurrentMarkThread;
361 friend class CMTask;
362 friend class CMBitMapClosure;
363 friend class CSMarkOopClosure;
364 friend class CMGlobalObjectClosure;
365 friend class CMRemarkTask;
366 friend class CMConcurrentMarkingTask;
367 friend class G1ParNoteEndTask;
368 friend class CalcLiveObjectsClosure;
369 friend class G1CMRefProcTaskProxy;
370 friend class G1CMRefProcTaskExecutor;
371 friend class G1CMParKeepAliveAndDrainClosure;
372 friend class G1CMParDrainMarkingStackClosure;
373
374 protected:
375 ConcurrentMarkThread* _cmThread; // the thread doing the work
376 G1CollectedHeap* _g1h; // the heap.
377 size_t _parallel_marking_threads; // the number of marking
378 // threads we'll use
379 double _sleep_factor; // how much we have to sleep, with
380 // respect to the work we just did, to
381 // meet the marking overhead goal
382 double _marking_task_overhead; // marking target overhead for
383 // a single task
384
385 // same as the two above, but for the cleanup task
386 double _cleanup_sleep_factor;
387 double _cleanup_task_overhead;
388
389 FreeRegionList _cleanup_list;
390
391 // CMS marking support structures
392 CMBitMap _markBitMap1;
393 CMBitMap _markBitMap2;
394 CMBitMapRO* _prevMarkBitMap; // completed mark bitmap
395 CMBitMap* _nextMarkBitMap; // under-construction mark bitmap
396 bool _at_least_one_mark_complete;
397
398 BitMap _region_bm;
399 BitMap _card_bm;
400
401 // Heap bounds
402 HeapWord* _heap_start;
403 HeapWord* _heap_end;
404
405 // For gray objects
406 CMMarkStack _markStack; // Grey objects behind global finger.
407 CMRegionStack _regionStack; // Grey regions behind global finger.
408 HeapWord* volatile _finger; // the global finger, region aligned,
409 // always points to the end of the
410 // last claimed region
411
412 // marking tasks
413 size_t _max_task_num; // maximum task number
414 size_t _active_tasks; // task num currently active
415 CMTask** _tasks; // task queue array (max_task_num len)
416 CMTaskQueueSet* _task_queues; // task queue set
417 ParallelTaskTerminator _terminator; // for termination
418
419 // Two sync barriers that are used to synchronise tasks when an
420 // overflow occurs. The algorithm is the following. All tasks enter
421 // the first one to ensure that they have all stopped manipulating
422 // the global data structures. After they exit it, they re-initialise
423 // their data structures and task 0 re-initialises the global data
424 // structures. Then, they enter the second sync barrier. This
425 // ensure, that no task starts doing work before all data
426 // structures (local and global) have been re-initialised. When they
427 // exit it, they are free to start working again.
428 WorkGangBarrierSync _first_overflow_barrier_sync;
429 WorkGangBarrierSync _second_overflow_barrier_sync;
430
431 // this is set by any task, when an overflow on the global data
432 // structures is detected.
433 volatile bool _has_overflown;
434 // true: marking is concurrent, false: we're in remark
435 volatile bool _concurrent;
436 // set at the end of a Full GC so that marking aborts
437 volatile bool _has_aborted;
438
439 // used when remark aborts due to an overflow to indicate that
440 // another concurrent marking phase should start
441 volatile bool _restart_for_overflow;
442
443 // This is true from the very start of concurrent marking until the
444 // point when all the tasks complete their work. It is really used
445 // to determine the points between the end of concurrent marking and
446 // time of remark.
447 volatile bool _concurrent_marking_in_progress;
448
449 // verbose level
450 CMVerboseLevel _verbose_level;
451
452 // These two fields are used to implement the optimisation that
453 // avoids pushing objects on the global/region stack if there are
454 // no collection set regions above the lowest finger.
455
456 // This is the lowest finger (among the global and local fingers),
457 // which is calculated before a new collection set is chosen.
458 HeapWord* _min_finger;
459 // If this flag is true, objects/regions that are marked below the
460 // finger should be pushed on the stack(s). If this is flag is
461 // false, it is safe not to push them on the stack(s).
462 bool _should_gray_objects;
463
464 // All of these times are in ms.
465 NumberSeq _init_times;
466 NumberSeq _remark_times;
467 NumberSeq _remark_mark_times;
468 NumberSeq _remark_weak_ref_times;
469 NumberSeq _cleanup_times;
470 double _total_counting_time;
471 double _total_rs_scrub_time;
472
473 double* _accum_task_vtime; // accumulated task vtime
474
475 WorkGang* _parallel_workers;
476
477 ForceOverflowSettings _force_overflow_conc;
478 ForceOverflowSettings _force_overflow_stw;
479
480 void weakRefsWork(bool clear_all_soft_refs);
481
482 void swapMarkBitMaps();
483
484 // It resets the global marking data structures, as well as the
485 // task local ones; should be called during initial mark.
486 void reset();
487 // It resets all the marking data structures.
488 void clear_marking_state(bool clear_overflow = true);
489
490 // It should be called to indicate which phase we're in (concurrent
491 // mark or remark) and how many threads are currently active.
492 void set_phase(size_t active_tasks, bool concurrent);
493 // We do this after we're done with marking so that the marking data
494 // structures are initialised to a sensible and predictable state.
495 void set_non_marking_state();
496
497 // prints all gathered CM-related statistics
498 void print_stats();
499
500 bool cleanup_list_is_empty() {
501 return _cleanup_list.is_empty();
502 }
503
504 // accessor methods
505 size_t parallel_marking_threads() { return _parallel_marking_threads; }
506 double sleep_factor() { return _sleep_factor; }
507 double marking_task_overhead() { return _marking_task_overhead;}
508 double cleanup_sleep_factor() { return _cleanup_sleep_factor; }
509 double cleanup_task_overhead() { return _cleanup_task_overhead;}
510
511 HeapWord* finger() { return _finger; }
512 bool concurrent() { return _concurrent; }
513 size_t active_tasks() { return _active_tasks; }
514 ParallelTaskTerminator* terminator() { return &_terminator; }
515
516 // It claims the next available region to be scanned by a marking
517 // task. It might return NULL if the next region is empty or we have
518 // run out of regions. In the latter case, out_of_regions()
519 // determines whether we've really run out of regions or the task
520 // should call claim_region() again. This might seem a bit
521 // awkward. Originally, the code was written so that claim_region()
522 // either successfully returned with a non-empty region or there
523 // were no more regions to be claimed. The problem with this was
524 // that, in certain circumstances, it iterated over large chunks of
525 // the heap finding only empty regions and, while it was working, it
526 // was preventing the calling task to call its regular clock
527 // method. So, this way, each task will spend very little time in
528 // claim_region() and is allowed to call the regular clock method
529 // frequently.
530 HeapRegion* claim_region(int task);
531
532 // It determines whether we've run out of regions to scan.
533 bool out_of_regions() { return _finger == _heap_end; }
534
535 // Returns the task with the given id
536 CMTask* task(int id) {
537 assert(0 <= id && id < (int) _active_tasks,
538 "task id not within active bounds");
539 return _tasks[id];
540 }
541
542 // Returns the task queue with the given id
543 CMTaskQueue* task_queue(int id) {
544 assert(0 <= id && id < (int) _active_tasks,
545 "task queue id not within active bounds");
546 return (CMTaskQueue*) _task_queues->queue(id);
547 }
548
549 // Returns the task queue set
550 CMTaskQueueSet* task_queues() { return _task_queues; }
551
552 // Access / manipulation of the overflow flag which is set to
553 // indicate that the global stack or region stack has overflown
554 bool has_overflown() { return _has_overflown; }
555 void set_has_overflown() { _has_overflown = true; }
556 void clear_has_overflown() { _has_overflown = false; }
557
558 bool has_aborted() { return _has_aborted; }
559 bool restart_for_overflow() { return _restart_for_overflow; }
560
561 // Methods to enter the two overflow sync barriers
562 void enter_first_sync_barrier(int task_num);
563 void enter_second_sync_barrier(int task_num);
564
565 ForceOverflowSettings* force_overflow_conc() {
566 return &_force_overflow_conc;
567 }
568
569 ForceOverflowSettings* force_overflow_stw() {
570 return &_force_overflow_stw;
571 }
572
573 ForceOverflowSettings* force_overflow() {
574 if (concurrent()) {
575 return force_overflow_conc();
576 } else {
577 return force_overflow_stw();
578 }
579 }
580
581 // Live Data Counting data structures...
582 // These data structures are initialized at the start of
583 // marking. They are written to while marking is active.
584 // They are aggregated during remark; the aggregated values
585 // are then used to populate the _region_bm, _card_bm, and
586 // the total live bytes, which are then subsequently updated
587 // during cleanup.
588
589 // An array of bitmaps (one bit map per task). Each bitmap
590 // is used to record the cards spanned by the live objects
591 // marked by that task/worker.
592 BitMap* _count_card_bitmaps;
593
594 // Used to record the number of marked live bytes
595 // (for each region, by worker thread).
596 size_t** _count_marked_bytes;
597
598 public:
599 // Manipulation of the global mark stack.
600 // Notice that the first mark_stack_push is CAS-based, whereas the
601 // two below are Mutex-based. This is OK since the first one is only
602 // called during evacuation pauses and doesn't compete with the
603 // other two (which are called by the marking tasks during
604 // concurrent marking or remark).
605 bool mark_stack_push(oop p) {
606 _markStack.par_push(p);
607 if (_markStack.overflow()) {
608 set_has_overflown();
609 return false;
610 }
611 return true;
612 }
613 bool mark_stack_push(oop* arr, int n) {
614 _markStack.par_push_arr(arr, n);
615 if (_markStack.overflow()) {
616 set_has_overflown();
617 return false;
618 }
619 return true;
620 }
621 void mark_stack_pop(oop* arr, int max, int* n) {
622 _markStack.par_pop_arr(arr, max, n);
623 }
624 size_t mark_stack_size() { return _markStack.size(); }
625 size_t partial_mark_stack_size_target() { return _markStack.maxElems()/3; }
626 bool mark_stack_overflow() { return _markStack.overflow(); }
627 bool mark_stack_empty() { return _markStack.isEmpty(); }
628
629 // (Lock-free) Manipulation of the region stack
630 bool region_stack_push_lock_free(MemRegion mr) {
631 // Currently we only call the lock-free version during evacuation
632 // pauses.
633 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
634
635 _regionStack.push_lock_free(mr);
636 if (_regionStack.overflow()) {
637 set_has_overflown();
638 return false;
639 }
640 return true;
641 }
642
643 // Lock-free version of region-stack pop. Should only be
644 // called in tandem with other lock-free pops.
645 MemRegion region_stack_pop_lock_free() {
646 return _regionStack.pop_lock_free();
647 }
648
649 #if 0
650 // The routines that manipulate the region stack with a lock are
651 // not currently used. They should be retained, however, as a
652 // diagnostic aid.
653
654 bool region_stack_push_with_lock(MemRegion mr) {
655 // Currently we only call the lock-based version during either
656 // concurrent marking or remark.
657 assert(!SafepointSynchronize::is_at_safepoint() || !concurrent(),
658 "if we are at a safepoint it should be the remark safepoint");
659
660 _regionStack.push_with_lock(mr);
661 if (_regionStack.overflow()) {
662 set_has_overflown();
663 return false;
664 }
665 return true;
666 }
667
668 MemRegion region_stack_pop_with_lock() {
669 // Currently we only call the lock-based version during either
670 // concurrent marking or remark.
671 assert(!SafepointSynchronize::is_at_safepoint() || !concurrent(),
672 "if we are at a safepoint it should be the remark safepoint");
673
674 return _regionStack.pop_with_lock();
675 }
676 #endif
677
678 int region_stack_size() { return _regionStack.size(); }
679 bool region_stack_overflow() { return _regionStack.overflow(); }
680 bool region_stack_empty() { return _regionStack.isEmpty(); }
681
682 // Iterate over any regions that were aborted while draining the
683 // region stack (any such regions are saved in the corresponding
684 // CMTask) and invalidate (i.e. assign to the empty MemRegion())
685 // any regions that point into the collection set.
686 bool invalidate_aborted_regions_in_cset();
687
688 // Returns true if there are any aborted memory regions.
689 bool has_aborted_regions();
690
691 bool concurrent_marking_in_progress() {
692 return _concurrent_marking_in_progress;
693 }
694 void set_concurrent_marking_in_progress() {
695 _concurrent_marking_in_progress = true;
696 }
697 void clear_concurrent_marking_in_progress() {
698 _concurrent_marking_in_progress = false;
699 }
700
701 void update_accum_task_vtime(int i, double vtime) {
702 _accum_task_vtime[i] += vtime;
703 }
704
705 double all_task_accum_vtime() {
706 double ret = 0.0;
707 for (int i = 0; i < (int)_max_task_num; ++i)
708 ret += _accum_task_vtime[i];
709 return ret;
710 }
711
712 // Attempts to steal an object from the task queues of other tasks
713 bool try_stealing(int task_num, int* hash_seed, oop& obj) {
714 return _task_queues->steal(task_num, hash_seed, obj);
715 }
716
717 // It grays an object by first marking it. Then, if it's behind the
718 // global finger, it also pushes it on the global stack.
719 void deal_with_reference(oop obj);
720
721 ConcurrentMark(ReservedSpace rs, int max_regions);
722 ~ConcurrentMark();
723 ConcurrentMarkThread* cmThread() { return _cmThread; }
724
725 CMBitMapRO* prevMarkBitMap() const { return _prevMarkBitMap; }
726 CMBitMap* nextMarkBitMap() const { return _nextMarkBitMap; }
727
728 // The following three are interaction between CM and
729 // G1CollectedHeap
730
731 // This notifies CM that a root during initial-mark needs to be
732 // grayed and it's MT-safe. Currently, we just mark it. But, in the
733 // future, we can experiment with pushing it on the stack and we can
734 // do this without changing G1CollectedHeap.
735 void grayRoot(oop p, int worker_i);
736
737 // It's used during evacuation pauses to gray a region, if
738 // necessary, and it's MT-safe. It assumes that the caller has
739 // marked any objects on that region. If _should_gray_objects is
740 // true and we're still doing concurrent marking, the region is
741 // pushed on the region stack, if it is located below the global
742 // finger, otherwise we do nothing.
743 void grayRegionIfNecessary(MemRegion mr);
744
745 // It's used during evacuation pauses to mark and, if necessary,
746 // gray a single object and it's MT-safe. It assumes the caller did
747 // not mark the object. If _should_gray_objects is true and we're
748 // still doing concurrent marking, the objects is pushed on the
749 // global stack, if it is located below the global finger, otherwise
750 // we do nothing.
751 void markAndGrayObjectIfNecessary(oop p, int worker_i);
752
753 // It iterates over the heap and for each object it comes across it
754 // will dump the contents of its reference fields, as well as
755 // liveness information for the object and its referents. The dump
756 // will be written to a file with the following name:
757 // G1PrintReachableBaseFile + "." + str.
758 // vo decides whether the prev (vo == UsePrevMarking), the next
759 // (vo == UseNextMarking) marking information, or the mark word
760 // (vo == UseMarkWord) will be used to determine the liveness of
761 // each object / referent.
762 // If all is true, all objects in the heap will be dumped, otherwise
763 // only the live ones. In the dump the following symbols / breviations
764 // are used:
765 // M : an explicitly live object (its bitmap bit is set)
766 // > : an implicitly live object (over tams)
767 // O : an object outside the G1 heap (typically: in the perm gen)
768 // NOT : a reference field whose referent is not live
769 // AND MARKED : indicates that an object is both explicitly and
770 // implicitly live (it should be one or the other, not both)
771 void print_reachable(const char* str,
772 VerifyOption vo, bool all) PRODUCT_RETURN;
773
774 // Clear the next marking bitmap (will be called concurrently).
775 void clearNextBitmap();
776
777 // These two do the work that needs to be done before and after the
778 // initial root checkpoint. Since this checkpoint can be done at two
779 // different points (i.e. an explicit pause or piggy-backed on a
780 // young collection), then it's nice to be able to easily share the
781 // pre/post code. It might be the case that we can put everything in
782 // the post method. TP
783 void checkpointRootsInitialPre();
784 void checkpointRootsInitialPost();
785
786 // Do concurrent phase of marking, to a tentative transitive closure.
787 void markFromRoots();
788
789 // Process all unprocessed SATB buffers. It is called at the
790 // beginning of an evacuation pause.
791 void drainAllSATBBuffers();
792
793 void checkpointRootsFinal(bool clear_all_soft_refs);
794 void checkpointRootsFinalWork();
795 void cleanup();
796 void completeCleanup();
797
798 // Mark in the previous bitmap. NB: this is usually read-only, so use
799 // this carefully!
800 void markPrev(oop p);
801
802 // Clears the mark in the next bitmap for the given object.
803 void clear(oop p);
804
805 // Clears marks for all objects in the given range, for both prev and
806 // next bitmaps. NB: the previous bitmap is usually read-only, so use
807 // this carefully!
808 void clearRangeBothMaps(MemRegion mr);
809
810 // Record the current top of the mark and region stacks; a
811 // subsequent oops_do() on the mark stack and
812 // invalidate_entries_into_cset() on the region stack will iterate
813 // only over indices valid at the time of this call.
814 void set_oops_do_bound() {
815 _markStack.set_oops_do_bound();
816 _regionStack.set_oops_do_bound();
817 }
818 // Iterate over the oops in the mark stack and all local queues. It
819 // also calls invalidate_entries_into_cset() on the region stack.
820 void oops_do(OopClosure* f);
821 // It is called at the end of an evacuation pause during marking so
822 // that CM is notified of where the new end of the heap is. It
823 // doesn't do anything if concurrent_marking_in_progress() is false,
824 // unless the force parameter is true.
825 void update_g1_committed(bool force = false);
826
827 void complete_marking_in_collection_set();
828
829 // It indicates that a new collection set is being chosen.
830 void newCSet();
831
832 // It registers a collection set heap region with CM. This is used
833 // to determine whether any heap regions are located above the finger.
834 void registerCSetRegion(HeapRegion* hr);
835
836 // Resets the region fields of any active CMTask whose region fields
837 // are in the collection set (i.e. the region currently claimed by
838 // the CMTask will be evacuated and may be used, subsequently, as
839 // an alloc region). When this happens the region fields in the CMTask
840 // are stale and, hence, should be cleared causing the worker thread
841 // to claim a new region.
842 void reset_active_task_region_fields_in_cset();
843
844 // Registers the maximum region-end associated with a set of
845 // regions with CM. Again this is used to determine whether any
846 // heap regions are located above the finger.
847 void register_collection_set_finger(HeapWord* max_finger) {
848 // max_finger is the highest heap region end of the regions currently
849 // contained in the collection set. If this value is larger than
850 // _min_finger then we need to gray objects.
851 // This routine is like registerCSetRegion but for an entire
852 // collection of regions.
853 if (max_finger > _min_finger) {
854 _should_gray_objects = true;
855 }
856 }
857
858 // Returns "true" if at least one mark has been completed.
859 bool at_least_one_mark_complete() { return _at_least_one_mark_complete; }
860
861 bool isMarked(oop p) const {
862 assert(p != NULL && p->is_oop(), "expected an oop");
863 HeapWord* addr = (HeapWord*)p;
864 assert(addr >= _nextMarkBitMap->startWord() ||
865 addr < _nextMarkBitMap->endWord(), "in a region");
866
867 return _nextMarkBitMap->isMarked(addr);
868 }
869
870 inline bool not_yet_marked(oop p) const;
871
872 // XXX Debug code
873 bool containing_card_is_marked(void* p);
874 bool containing_cards_are_marked(void* start, void* last);
875
876 bool isPrevMarked(oop p) const {
877 assert(p != NULL && p->is_oop(), "expected an oop");
878 HeapWord* addr = (HeapWord*)p;
879 assert(addr >= _prevMarkBitMap->startWord() ||
880 addr < _prevMarkBitMap->endWord(), "in a region");
881
882 return _prevMarkBitMap->isMarked(addr);
883 }
884
885 inline bool do_yield_check(int worker_i = 0);
886 inline bool should_yield();
887
888 // Called to abort the marking cycle after a Full GC takes palce.
889 void abort();
890
891 // This prints the global/local fingers. It is used for debugging.
892 NOT_PRODUCT(void print_finger();)
893
894 void print_summary_info();
895
896 void print_worker_threads_on(outputStream* st) const;
897
898 // The following indicate whether a given verbose level has been
899 // set. Notice that anything above stats is conditional to
900 // _MARKING_VERBOSE_ having been set to 1
901 bool verbose_stats() {
902 return _verbose_level >= stats_verbose;
903 }
904 bool verbose_low() {
905 return _MARKING_VERBOSE_ && _verbose_level >= low_verbose;
906 }
907 bool verbose_medium() {
908 return _MARKING_VERBOSE_ && _verbose_level >= medium_verbose;
909 }
910 bool verbose_high() {
911 return _MARKING_VERBOSE_ && _verbose_level >= high_verbose;
912 }
913
914 // Counting data structure accessors
915
916 // Returns the card bitmap for a given task or worker id.
917 BitMap& count_card_bitmap_for(int worker_i) {
918 assert(0 <= worker_i && worker_i < _max_task_num, "oob");
919 assert(_count_card_bitmaps != NULL, "uninitialized");
920 BitMap& task_card_bm = _count_card_bitmaps[worker_i];
921 assert(task_card_bm.size() == _card_bm.size(), "size mismatch");
922 return task_card_bm;
923 }
924
925 // Returns the array containing the marked bytes for each region,
926 // for the given worker or task id.
927 size_t* count_marked_bytes_for(int worker_i) {
928 assert(0 <= worker_i && worker_i < _max_task_num, "oob");
929 assert(_count_marked_bytes != NULL, "uninitialized");
930 size_t* marked_bytes_array = _count_marked_bytes[worker_i];
931 assert(marked_bytes_array != NULL, "uninitialized");
932 return marked_bytes_array;
933 }
934
935 // Add the given region's size to the # marked bytes for
936 // the given worker and region. Set the bits in the
937 // worker's/task's card bitmap that are associated
938 // with the range of cards spanned by the region.
939 // Note the memory region could be just one object.
940 void add_to_count_data_for(MemRegion mr, int worker_i);
941
942 // As above, but for a single object
943 void add_to_count_data_for(oop obj, int worker_i);
944
945 // As above but when we have already been given the heap
946 // region.
947 void add_to_count_data_for(MemRegion mr, HeapRegion* hr, int worker_i);
948
949 // As above, but for a single object
950 void add_to_count_data_for(oop obj, HeapRegion* hr, int worker_i);
951
952 // Updates the counting data with liveness info recorded for a
953 // region (typically a GCLab).
954 void add_to_count_data_for_region(MemRegion lab_mr,
955 BitMap* lab_card_bm,
956 intptr_t lab_bottom_card_num,
957 size_t lab_marked_bytes,
958 int worker_i);
959
960 // Clears the count data for the given region from _all_ of
961 // the per-task counting data structures.
962 void clear_count_data_for_heap_region(HeapRegion* hr);
963
964 protected:
965 // Clear all the per-task bitmaps and arrays used to store the
966 // counting data.
967 void clear_all_count_data();
968
969 // Aggregates the counting data for each worker/task
970 // that was constructed while marking. Also sets
971 // the amount of marked bytes for each region and
972 // the top at concurrent mark count.
973 void aggregate_all_count_data();
974
975 // Verification routine
976 void verify_count_data();
977 };
978
979 // A class representing a marking task.
980 class CMTask : public TerminatorTerminator {
981 private:
982 enum PrivateConstants {
983 // the regular clock call is called once the scanned words reaches
984 // this limit
985 words_scanned_period = 12*1024,
986 // the regular clock call is called once the number of visited
987 // references reaches this limit
988 refs_reached_period = 384,
989 // initial value for the hash seed, used in the work stealing code
990 init_hash_seed = 17,
991 // how many entries will be transferred between global stack and
992 // local queues
993 global_stack_transfer_size = 16
994 };
995
996 int _task_id;
997 G1CollectedHeap* _g1h;
998 ConcurrentMark* _cm;
999 CMBitMap* _nextMarkBitMap;
1000 // the task queue of this task
1001 CMTaskQueue* _task_queue;
1002 private:
1003 // the task queue set---needed for stealing
1004 CMTaskQueueSet* _task_queues;
1005 // indicates whether the task has been claimed---this is only for
1006 // debugging purposes
1007 bool _claimed;
1008
1009 // number of calls to this task
1010 int _calls;
1011
1012 // when the virtual timer reaches this time, the marking step should
1013 // exit
1014 double _time_target_ms;
1015 // the start time of the current marking step
1016 double _start_time_ms;
1017
1018 // the oop closure used for iterations over oops
1019 G1CMOopClosure* _cm_oop_closure;
1020
1021 // the region this task is scanning, NULL if we're not scanning any
1022 HeapRegion* _curr_region;
1023 // the local finger of this task, NULL if we're not scanning a region
1024 HeapWord* _finger;
1025 // limit of the region this task is scanning, NULL if we're not scanning one
1026 HeapWord* _region_limit;
1027
1028 // This is used only when we scan regions popped from the region
1029 // stack. It records what the last object on such a region we
1030 // scanned was. It is used to ensure that, if we abort region
1031 // iteration, we do not rescan the first part of the region. This
1032 // should be NULL when we're not scanning a region from the region
1033 // stack.
1034 HeapWord* _region_finger;
1035
1036 // If we abort while scanning a region we record the remaining
1037 // unscanned portion and check this field when marking restarts.
1038 // This avoids having to push on the region stack while other
1039 // marking threads may still be popping regions.
1040 // If we were to push the unscanned portion directly to the
1041 // region stack then we would need to using locking versions
1042 // of the push and pop operations.
1043 MemRegion _aborted_region;
1044
1045 // the number of words this task has scanned
1046 size_t _words_scanned;
1047 // When _words_scanned reaches this limit, the regular clock is
1048 // called. Notice that this might be decreased under certain
1049 // circumstances (i.e. when we believe that we did an expensive
1050 // operation).
1051 size_t _words_scanned_limit;
1052 // the initial value of _words_scanned_limit (i.e. what it was
1053 // before it was decreased).
1054 size_t _real_words_scanned_limit;
1055
1056 // the number of references this task has visited
1057 size_t _refs_reached;
1058 // When _refs_reached reaches this limit, the regular clock is
1059 // called. Notice this this might be decreased under certain
1060 // circumstances (i.e. when we believe that we did an expensive
1061 // operation).
1062 size_t _refs_reached_limit;
1063 // the initial value of _refs_reached_limit (i.e. what it was before
1064 // it was decreased).
1065 size_t _real_refs_reached_limit;
1066
1067 // used by the work stealing stuff
1068 int _hash_seed;
1069 // if this is true, then the task has aborted for some reason
1070 bool _has_aborted;
1071 // set when the task aborts because it has met its time quota
1072 bool _has_timed_out;
1073 // true when we're draining SATB buffers; this avoids the task
1074 // aborting due to SATB buffers being available (as we're already
1075 // dealing with them)
1076 bool _draining_satb_buffers;
1077
1078 // number sequence of past step times
1079 NumberSeq _step_times_ms;
1080 // elapsed time of this task
1081 double _elapsed_time_ms;
1082 // termination time of this task
1083 double _termination_time_ms;
1084 // when this task got into the termination protocol
1085 double _termination_start_time_ms;
1086
1087 // true when the task is during a concurrent phase, false when it is
1088 // in the remark phase (so, in the latter case, we do not have to
1089 // check all the things that we have to check during the concurrent
1090 // phase, i.e. SATB buffer availability...)
1091 bool _concurrent;
1092
1093 TruncatedSeq _marking_step_diffs_ms;
1094
1095 // LOTS of statistics related with this task
1096 #if _MARKING_STATS_
1097 NumberSeq _all_clock_intervals_ms;
1098 double _interval_start_time_ms;
1099
1100 int _aborted;
1101 int _aborted_overflow;
1102 int _aborted_cm_aborted;
1103 int _aborted_yield;
1104 int _aborted_timed_out;
1105 int _aborted_satb;
1106 int _aborted_termination;
1107
1108 int _steal_attempts;
1109 int _steals;
1110
1111 int _clock_due_to_marking;
1112 int _clock_due_to_scanning;
1113
1114 int _local_pushes;
1115 int _local_pops;
1116 int _local_max_size;
1117 int _objs_scanned;
1118
1119 int _global_pushes;
1120 int _global_pops;
1121 int _global_max_size;
1122
1123 int _global_transfers_to;
1124 int _global_transfers_from;
1125
1126 int _region_stack_pops;
1127
1128 int _regions_claimed;
1129 int _objs_found_on_bitmap;
1130
1131 int _satb_buffers_processed;
1132 #endif // _MARKING_STATS_
1133
1134 // it updates the local fields after this task has claimed
1135 // a new region to scan
1136 void setup_for_region(HeapRegion* hr);
1137 // it brings up-to-date the limit of the region
1138 void update_region_limit();
1139
1140 // called when either the words scanned or the refs visited limit
1141 // has been reached
1142 void reached_limit();
1143 // recalculates the words scanned and refs visited limits
1144 void recalculate_limits();
1145 // decreases the words scanned and refs visited limits when we reach
1146 // an expensive operation
1147 void decrease_limits();
1148 // it checks whether the words scanned or refs visited reached their
1149 // respective limit and calls reached_limit() if they have
1150 void check_limits() {
1151 if (_words_scanned >= _words_scanned_limit ||
1152 _refs_reached >= _refs_reached_limit) {
1153 reached_limit();
1154 }
1155 }
1156 // this is supposed to be called regularly during a marking step as
1157 // it checks a bunch of conditions that might cause the marking step
1158 // to abort
1159 void regular_clock_call();
1160 bool concurrent() { return _concurrent; }
1161
1162 public:
1163 // It resets the task; it should be called right at the beginning of
1164 // a marking phase.
1165 void reset(CMBitMap* _nextMarkBitMap);
1166 // it clears all the fields that correspond to a claimed region.
1167 void clear_region_fields();
1168
1169 void set_concurrent(bool concurrent) { _concurrent = concurrent; }
1170
1171 // The main method of this class which performs a marking step
1172 // trying not to exceed the given duration. However, it might exit
1173 // prematurely, according to some conditions (i.e. SATB buffers are
1174 // available for processing).
1175 void do_marking_step(double target_ms, bool do_stealing, bool do_termination);
1176
1177 // These two calls start and stop the timer
1178 void record_start_time() {
1179 _elapsed_time_ms = os::elapsedTime() * 1000.0;
1180 }
1181 void record_end_time() {
1182 _elapsed_time_ms = os::elapsedTime() * 1000.0 - _elapsed_time_ms;
1183 }
1184
1185 // returns the task ID
1186 int task_id() { return _task_id; }
1187
1188 // From TerminatorTerminator. It determines whether this task should
1189 // exit the termination protocol after it's entered it.
1190 virtual bool should_exit_termination();
1191
1192 // Resets the local region fields after a task has finished scanning a
1193 // region; or when they have become stale as a result of the region
1194 // being evacuated.
1195 void giveup_current_region();
1196
1197 HeapWord* finger() { return _finger; }
1198
1199 bool has_aborted() { return _has_aborted; }
1200 void set_has_aborted() { _has_aborted = true; }
1201 void clear_has_aborted() { _has_aborted = false; }
1202 bool has_timed_out() { return _has_timed_out; }
1203 bool claimed() { return _claimed; }
1204
1205 // Support routines for the partially scanned region that may be
1206 // recorded as a result of aborting while draining the CMRegionStack
1207 MemRegion aborted_region() { return _aborted_region; }
1208 void set_aborted_region(MemRegion mr)
1209 { _aborted_region = mr; }
1210
1211 // Clears any recorded partially scanned region
1212 void clear_aborted_region() { set_aborted_region(MemRegion()); }
1213
1214 void set_cm_oop_closure(G1CMOopClosure* cm_oop_closure);
1215
1216 // It grays the object by marking it and, if necessary, pushing it
1217 // on the local queue
1218 inline void deal_with_reference(oop obj);
1219
1220 // It scans an object and visits its children.
1221 void scan_object(oop obj);
1222
1223 // It pushes an object on the local queue.
1224 inline void push(oop obj);
1225
1226 // These two move entries to/from the global stack.
1227 void move_entries_to_global_stack();
1228 void get_entries_from_global_stack();
1229
1230 // It pops and scans objects from the local queue. If partially is
1231 // true, then it stops when the queue size is of a given limit. If
1232 // partially is false, then it stops when the queue is empty.
1233 void drain_local_queue(bool partially);
1234 // It moves entries from the global stack to the local queue and
1235 // drains the local queue. If partially is true, then it stops when
1236 // both the global stack and the local queue reach a given size. If
1237 // partially if false, it tries to empty them totally.
1238 void drain_global_stack(bool partially);
1239 // It keeps picking SATB buffers and processing them until no SATB
1240 // buffers are available.
1241 void drain_satb_buffers();
1242 // It keeps popping regions from the region stack and processing
1243 // them until the region stack is empty.
1244 void drain_region_stack(BitMapClosure* closure);
1245
1246 // moves the local finger to a new location
1247 inline void move_finger_to(HeapWord* new_finger) {
1248 assert(new_finger >= _finger && new_finger < _region_limit, "invariant");
1249 _finger = new_finger;
1250 }
1251
1252 // moves the region finger to a new location
1253 inline void move_region_finger_to(HeapWord* new_finger) {
1254 assert(new_finger < _cm->finger(), "invariant");
1255 _region_finger = new_finger;
1256 }
1257
1258 CMTask(int task_num, ConcurrentMark *cm,
1259 CMTaskQueue* task_queue, CMTaskQueueSet* task_queues);
1260
1261 // it prints statistics associated with this task
1262 void print_stats();
1263
1264 #if _MARKING_STATS_
1265 void increase_objs_found_on_bitmap() { ++_objs_found_on_bitmap; }
1266 #endif // _MARKING_STATS_
1267 };
1268
1269 // Class that's used to to print out per-region liveness
1270 // information. It's currently used at the end of marking and also
1271 // after we sort the old regions at the end of the cleanup operation.
1272 class G1PrintRegionLivenessInfoClosure: public HeapRegionClosure {
1273 private:
1274 outputStream* _out;
1275
1276 // Accumulators for these values.
1277 size_t _total_used_bytes;
1278 size_t _total_capacity_bytes;
1279 size_t _total_prev_live_bytes;
1280 size_t _total_next_live_bytes;
1281
1282 // These are set up when we come across a "stars humongous" region
1283 // (as this is where most of this information is stored, not in the
1284 // subsequent "continues humongous" regions). After that, for every
1285 // region in a given humongous region series we deduce the right
1286 // values for it by simply subtracting the appropriate amount from
1287 // these fields. All these values should reach 0 after we've visited
1288 // the last region in the series.
1289 size_t _hum_used_bytes;
1290 size_t _hum_capacity_bytes;
1291 size_t _hum_prev_live_bytes;
1292 size_t _hum_next_live_bytes;
1293
1294 static double perc(size_t val, size_t total) {
1295 if (total == 0) {
1296 return 0.0;
1297 } else {
1298 return 100.0 * ((double) val / (double) total);
1299 }
1300 }
1301
1302 static double bytes_to_mb(size_t val) {
1303 return (double) val / (double) M;
1304 }
1305
1306 // See the .cpp file.
1307 size_t get_hum_bytes(size_t* hum_bytes);
1308 void get_hum_bytes(size_t* used_bytes, size_t* capacity_bytes,
1309 size_t* prev_live_bytes, size_t* next_live_bytes);
1310
1311 public:
1312 // The header and footer are printed in the constructor and
1313 // destructor respectively.
1314 G1PrintRegionLivenessInfoClosure(outputStream* out, const char* phase_name);
1315 virtual bool doHeapRegion(HeapRegion* r);
1316 ~G1PrintRegionLivenessInfoClosure();
1317 };
1318
1319 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_CONCURRENTMARK_HPP