1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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24
25 #ifndef SHARE_GC_G1_G1CONCURRENTMARK_HPP
26 #define SHARE_GC_G1_G1CONCURRENTMARK_HPP
27
28 #include "gc/g1/g1ConcurrentMarkBitMap.hpp"
29 #include "gc/g1/g1ConcurrentMarkObjArrayProcessor.hpp"
30 #include "gc/g1/g1HeapVerifier.hpp"
31 #include "gc/g1/g1RegionMarkStatsCache.hpp"
32 #include "gc/g1/heapRegionSet.hpp"
33 #include "gc/shared/taskqueue.hpp"
34 #include "memory/allocation.hpp"
35 #include "utilities/compilerWarnings.hpp"
36
37 class ConcurrentGCTimer;
38 class G1ConcurrentMarkThread;
39 class G1CollectedHeap;
40 class G1CMOopClosure;
41 class G1CMTask;
42 class G1ConcurrentMark;
43 class G1OldTracer;
44 class G1RegionToSpaceMapper;
45 class G1SurvivorRegions;
46
47 PRAGMA_DIAG_PUSH
48 // warning C4522: multiple assignment operators specified
49 PRAGMA_DISABLE_MSVC_WARNING(4522)
50
51 // This is a container class for either an oop or a continuation address for
52 // mark stack entries. Both are pushed onto the mark stack.
53 class G1TaskQueueEntry {
54 private:
55 void* _holder;
56
57 static const uintptr_t ArraySliceBit = 1;
58
59 G1TaskQueueEntry(oop obj) : _holder(obj) {
60 assert(_holder != NULL, "Not allowed to set NULL task queue element");
61 }
62 G1TaskQueueEntry(HeapWord* addr) : _holder((void*)((uintptr_t)addr | ArraySliceBit)) { }
63 public:
64 G1TaskQueueEntry(const G1TaskQueueEntry& other) { _holder = other._holder; }
65 G1TaskQueueEntry() : _holder(NULL) { }
66
67 static G1TaskQueueEntry from_slice(HeapWord* what) { return G1TaskQueueEntry(what); }
68 static G1TaskQueueEntry from_oop(oop obj) { return G1TaskQueueEntry(obj); }
69
70 G1TaskQueueEntry& operator=(const G1TaskQueueEntry& t) {
71 _holder = t._holder;
72 return *this;
73 }
74
75 volatile G1TaskQueueEntry& operator=(const volatile G1TaskQueueEntry& t) volatile {
76 _holder = t._holder;
77 return *this;
78 }
79
80 oop obj() const {
81 assert(!is_array_slice(), "Trying to read array slice " PTR_FORMAT " as oop", p2i(_holder));
82 return (oop)_holder;
83 }
84
85 HeapWord* slice() const {
86 assert(is_array_slice(), "Trying to read oop " PTR_FORMAT " as array slice", p2i(_holder));
87 return (HeapWord*)((uintptr_t)_holder & ~ArraySliceBit);
88 }
89
90 bool is_oop() const { return !is_array_slice(); }
91 bool is_array_slice() const { return ((uintptr_t)_holder & ArraySliceBit) != 0; }
92 bool is_null() const { return _holder == NULL; }
93 };
94
95 PRAGMA_DIAG_POP
96
97 typedef GenericTaskQueue<G1TaskQueueEntry, mtGC> G1CMTaskQueue;
98 typedef GenericTaskQueueSet<G1CMTaskQueue, mtGC> G1CMTaskQueueSet;
99
100 // Closure used by CM during concurrent reference discovery
101 // and reference processing (during remarking) to determine
102 // if a particular object is alive. It is primarily used
103 // to determine if referents of discovered reference objects
104 // are alive. An instance is also embedded into the
105 // reference processor as the _is_alive_non_header field
106 class G1CMIsAliveClosure : public BoolObjectClosure {
107 G1CollectedHeap* _g1h;
108 public:
109 G1CMIsAliveClosure(G1CollectedHeap* g1h) : _g1h(g1h) { }
110 bool do_object_b(oop obj);
111 };
112
113 class G1CMSubjectToDiscoveryClosure : public BoolObjectClosure {
114 G1CollectedHeap* _g1h;
115 public:
116 G1CMSubjectToDiscoveryClosure(G1CollectedHeap* g1h) : _g1h(g1h) { }
117 bool do_object_b(oop obj);
118 };
119
120 // Represents the overflow mark stack used by concurrent marking.
121 //
122 // Stores oops in a huge buffer in virtual memory that is always fully committed.
123 // Resizing may only happen during a STW pause when the stack is empty.
124 //
125 // Memory is allocated on a "chunk" basis, i.e. a set of oops. For this, the mark
126 // stack memory is split into evenly sized chunks of oops. Users can only
127 // add or remove entries on that basis.
128 // Chunks are filled in increasing address order. Not completely filled chunks
129 // have a NULL element as a terminating element.
130 //
131 // Every chunk has a header containing a single pointer element used for memory
132 // management. This wastes some space, but is negligible (< .1% with current sizing).
133 //
134 // Memory management is done using a mix of tracking a high water-mark indicating
135 // that all chunks at a lower address are valid chunks, and a singly linked free
136 // list connecting all empty chunks.
137 class G1CMMarkStack {
138 public:
139 // Number of TaskQueueEntries that can fit in a single chunk.
140 static const size_t EntriesPerChunk = 1024 - 1 /* One reference for the next pointer */;
141 private:
142 struct TaskQueueEntryChunk {
143 TaskQueueEntryChunk* next;
144 G1TaskQueueEntry data[EntriesPerChunk];
145 };
146
147 size_t _max_chunk_capacity; // Maximum number of TaskQueueEntryChunk elements on the stack.
148
149 TaskQueueEntryChunk* _base; // Bottom address of allocated memory area.
150 size_t _chunk_capacity; // Current maximum number of TaskQueueEntryChunk elements.
151
152 char _pad0[DEFAULT_CACHE_LINE_SIZE];
153 TaskQueueEntryChunk* volatile _free_list; // Linked list of free chunks that can be allocated by users.
154 char _pad1[DEFAULT_CACHE_LINE_SIZE - sizeof(TaskQueueEntryChunk*)];
155 TaskQueueEntryChunk* volatile _chunk_list; // List of chunks currently containing data.
156 volatile size_t _chunks_in_chunk_list;
157 char _pad2[DEFAULT_CACHE_LINE_SIZE - sizeof(TaskQueueEntryChunk*) - sizeof(size_t)];
158
159 volatile size_t _hwm; // High water mark within the reserved space.
160 char _pad4[DEFAULT_CACHE_LINE_SIZE - sizeof(size_t)];
161
162 // Allocate a new chunk from the reserved memory, using the high water mark. Returns
163 // NULL if out of memory.
164 TaskQueueEntryChunk* allocate_new_chunk();
165
166 // Atomically add the given chunk to the list.
167 void add_chunk_to_list(TaskQueueEntryChunk* volatile* list, TaskQueueEntryChunk* elem);
168 // Atomically remove and return a chunk from the given list. Returns NULL if the
169 // list is empty.
170 TaskQueueEntryChunk* remove_chunk_from_list(TaskQueueEntryChunk* volatile* list);
171
172 void add_chunk_to_chunk_list(TaskQueueEntryChunk* elem);
173 void add_chunk_to_free_list(TaskQueueEntryChunk* elem);
174
175 TaskQueueEntryChunk* remove_chunk_from_chunk_list();
176 TaskQueueEntryChunk* remove_chunk_from_free_list();
177
178 // Resizes the mark stack to the given new capacity. Releases any previous
179 // memory if successful.
180 bool resize(size_t new_capacity);
181
182 public:
183 G1CMMarkStack();
184 ~G1CMMarkStack();
185
186 // Alignment and minimum capacity of this mark stack in number of oops.
187 static size_t capacity_alignment();
188
189 // Allocate and initialize the mark stack with the given number of oops.
190 bool initialize(size_t initial_capacity, size_t max_capacity);
191
192 // Pushes the given buffer containing at most EntriesPerChunk elements on the mark
193 // stack. If less than EntriesPerChunk elements are to be pushed, the array must
194 // be terminated with a NULL.
195 // Returns whether the buffer contents were successfully pushed to the global mark
196 // stack.
197 bool par_push_chunk(G1TaskQueueEntry* buffer);
198
199 // Pops a chunk from this mark stack, copying them into the given buffer. This
200 // chunk may contain up to EntriesPerChunk elements. If there are less, the last
201 // element in the array is a NULL pointer.
202 bool par_pop_chunk(G1TaskQueueEntry* buffer);
203
204 // Return whether the chunk list is empty. Racy due to unsynchronized access to
205 // _chunk_list.
206 bool is_empty() const { return _chunk_list == NULL; }
207
208 size_t capacity() const { return _chunk_capacity; }
209
210 // Expand the stack, typically in response to an overflow condition
211 void expand();
212
213 // Return the approximate number of oops on this mark stack. Racy due to
214 // unsynchronized access to _chunks_in_chunk_list.
215 size_t size() const { return _chunks_in_chunk_list * EntriesPerChunk; }
216
217 void set_empty();
218
219 // Apply Fn to every oop on the mark stack. The mark stack must not
220 // be modified while iterating.
221 template<typename Fn> void iterate(Fn fn) const PRODUCT_RETURN;
222 };
223
224 // Root Regions are regions that contain objects from nTAMS to top. These are roots
225 // for marking, i.e. their referenced objects must be kept alive to maintain the
226 // SATB invariant.
227 // We could scan and mark them through during the initial-mark pause, but for
228 // pause time reasons we move this work to the concurrent phase.
229 // We need to complete this procedure before the next GC because it might determine
230 // that some of these "root objects" are dead, potentially dropping some required
231 // references.
232 // Root regions comprise of the complete contents of survivor regions, and any
233 // objects copied into old gen during GC.
234 class G1CMRootRegions {
235 HeapRegion** _root_regions;
236 size_t const _max_regions;
237
238 volatile size_t _num_root_regions; // Actual number of root regions.
239
240 volatile size_t _claimed_root_regions; // Number of root regions currently claimed.
241
242 volatile bool _scan_in_progress;
243 volatile bool _should_abort;
244
245 void notify_scan_done();
246
247 public:
248 G1CMRootRegions(uint const max_regions);
249 ~G1CMRootRegions();
250
251 // Reset the data structure to allow addition of new root regions.
252 void reset();
253
254 void add(HeapRegion* hr);
255
256 // Reset the claiming / scanning of the root regions.
257 void prepare_for_scan();
258
259 // Forces get_next() to return NULL so that the iteration aborts early.
260 void abort() { _should_abort = true; }
261
262 // Return true if the CM thread are actively scanning root regions,
263 // false otherwise.
264 bool scan_in_progress() { return _scan_in_progress; }
265
266 // Claim the next root region to scan atomically, or return NULL if
267 // all have been claimed.
268 HeapRegion* claim_next();
269
270 // The number of root regions to scan.
271 uint num_root_regions() const;
272
273 void cancel_scan();
274
275 // Flag that we're done with root region scanning and notify anyone
276 // who's waiting on it. If aborted is false, assume that all regions
277 // have been claimed.
278 void scan_finished();
279
280 // If CM threads are still scanning root regions, wait until they
281 // are done. Return true if we had to wait, false otherwise.
282 bool wait_until_scan_finished();
283 };
284
285 // This class manages data structures and methods for doing liveness analysis in
286 // G1's concurrent cycle.
287 class G1ConcurrentMark : public CHeapObj<mtGC> {
288 friend class G1ConcurrentMarkThread;
289 friend class G1CMRefProcTaskProxy;
290 friend class G1CMRefProcTaskExecutor;
291 friend class G1CMKeepAliveAndDrainClosure;
292 friend class G1CMDrainMarkingStackClosure;
293 friend class G1CMBitMapClosure;
294 friend class G1CMConcurrentMarkingTask;
295 friend class G1CMRemarkTask;
296 friend class G1CMTask;
297
298 G1ConcurrentMarkThread* _cm_thread; // The thread doing the work
299 G1CollectedHeap* _g1h; // The heap
300 bool _completed_initialization; // Set to true when initialization is complete
301
302 // Concurrent marking support structures
303 G1CMBitMap _mark_bitmap_1;
304 G1CMBitMap _mark_bitmap_2;
305 G1CMBitMap* _prev_mark_bitmap; // Completed mark bitmap
306 G1CMBitMap* _next_mark_bitmap; // Under-construction mark bitmap
307
308 // Heap bounds
309 MemRegion const _heap;
310
311 // Root region tracking and claiming
312 G1CMRootRegions _root_regions;
313
314 // For grey objects
315 G1CMMarkStack _global_mark_stack; // Grey objects behind global finger
316 HeapWord* volatile _finger; // The global finger, region aligned,
317 // always pointing to the end of the
318 // last claimed region
319
320 uint _worker_id_offset;
321 uint _max_num_tasks; // Maximum number of marking tasks
322 uint _num_active_tasks; // Number of tasks currently active
323 G1CMTask** _tasks; // Task queue array (max_worker_id length)
324
325 G1CMTaskQueueSet* _task_queues; // Task queue set
326 TaskTerminator _terminator; // For termination
327
328 // Two sync barriers that are used to synchronize tasks when an
329 // overflow occurs. The algorithm is the following. All tasks enter
330 // the first one to ensure that they have all stopped manipulating
331 // the global data structures. After they exit it, they re-initialize
332 // their data structures and task 0 re-initializes the global data
333 // structures. Then, they enter the second sync barrier. This
334 // ensure, that no task starts doing work before all data
335 // structures (local and global) have been re-initialized. When they
336 // exit it, they are free to start working again.
337 WorkGangBarrierSync _first_overflow_barrier_sync;
338 WorkGangBarrierSync _second_overflow_barrier_sync;
339
340 // This is set by any task, when an overflow on the global data
341 // structures is detected
342 volatile bool _has_overflown;
343 // True: marking is concurrent, false: we're in remark
344 volatile bool _concurrent;
345 // Set at the end of a Full GC so that marking aborts
346 volatile bool _has_aborted;
347
348 // Used when remark aborts due to an overflow to indicate that
349 // another concurrent marking phase should start
350 volatile bool _restart_for_overflow;
351
352 ConcurrentGCTimer* _gc_timer_cm;
353
354 G1OldTracer* _gc_tracer_cm;
355
356 // Timing statistics. All of them are in ms
357 NumberSeq _init_times;
358 NumberSeq _remark_times;
359 NumberSeq _remark_mark_times;
360 NumberSeq _remark_weak_ref_times;
361 NumberSeq _cleanup_times;
362 double _total_cleanup_time;
363
364 double* _accum_task_vtime; // Accumulated task vtime
365
366 WorkGang* _concurrent_workers;
367 uint _num_concurrent_workers; // The number of marking worker threads we're using
368 uint _max_concurrent_workers; // Maximum number of marking worker threads
369
370 void verify_during_pause(G1HeapVerifier::G1VerifyType type, VerifyOption vo, const char* caller);
371
372 void finalize_marking();
373
374 void weak_refs_work_parallel_part(BoolObjectClosure* is_alive, bool purged_classes);
375 void weak_refs_work(bool clear_all_soft_refs);
376
377 void report_object_count(bool mark_completed);
378
379 void swap_mark_bitmaps();
380
381 void reclaim_empty_regions();
382
383 // After reclaiming empty regions, update heap sizes.
384 void compute_new_sizes();
385
386 // Clear statistics gathered during the concurrent cycle for the given region after
387 // it has been reclaimed.
388 void clear_statistics(HeapRegion* r);
389
390 // Resets the global marking data structures, as well as the
391 // task local ones; should be called during initial mark.
392 void reset();
393
394 // Resets all the marking data structures. Called when we have to restart
395 // marking or when marking completes (via set_non_marking_state below).
396 void reset_marking_for_restart();
397
398 // We do this after we're done with marking so that the marking data
399 // structures are initialized to a sensible and predictable state.
400 void reset_at_marking_complete();
401
402 // Called to indicate how many threads are currently active.
403 void set_concurrency(uint active_tasks);
404
405 // Should be called to indicate which phase we're in (concurrent
406 // mark or remark) and how many threads are currently active.
407 void set_concurrency_and_phase(uint active_tasks, bool concurrent);
408
409 // Prints all gathered CM-related statistics
410 void print_stats();
411
412 HeapWord* finger() { return _finger; }
413 bool concurrent() { return _concurrent; }
414 uint active_tasks() { return _num_active_tasks; }
415 ParallelTaskTerminator* terminator() const { return _terminator.terminator(); }
416
417 // Claims the next available region to be scanned by a marking
418 // task/thread. It might return NULL if the next region is empty or
419 // we have run out of regions. In the latter case, out_of_regions()
420 // determines whether we've really run out of regions or the task
421 // should call claim_region() again. This might seem a bit
422 // awkward. Originally, the code was written so that claim_region()
423 // either successfully returned with a non-empty region or there
424 // were no more regions to be claimed. The problem with this was
425 // that, in certain circumstances, it iterated over large chunks of
426 // the heap finding only empty regions and, while it was working, it
427 // was preventing the calling task to call its regular clock
428 // method. So, this way, each task will spend very little time in
429 // claim_region() and is allowed to call the regular clock method
430 // frequently.
431 HeapRegion* claim_region(uint worker_id);
432
433 // Determines whether we've run out of regions to scan. Note that
434 // the finger can point past the heap end in case the heap was expanded
435 // to satisfy an allocation without doing a GC. This is fine, because all
436 // objects in those regions will be considered live anyway because of
437 // SATB guarantees (i.e. their TAMS will be equal to bottom).
438 bool out_of_regions() { return _finger >= _heap.end(); }
439
440 // Returns the task with the given id
441 G1CMTask* task(uint id) {
442 // During initial mark we use the parallel gc threads to do some work, so
443 // we can only compare against _max_num_tasks.
444 assert(id < _max_num_tasks, "Task id %u not within bounds up to %u", id, _max_num_tasks);
445 return _tasks[id];
446 }
447
448 // Access / manipulation of the overflow flag which is set to
449 // indicate that the global stack has overflown
450 bool has_overflown() { return _has_overflown; }
451 void set_has_overflown() { _has_overflown = true; }
452 void clear_has_overflown() { _has_overflown = false; }
453 bool restart_for_overflow() { return _restart_for_overflow; }
454
455 // Methods to enter the two overflow sync barriers
456 void enter_first_sync_barrier(uint worker_id);
457 void enter_second_sync_barrier(uint worker_id);
458
459 // Clear the given bitmap in parallel using the given WorkGang. If may_yield is
460 // true, periodically insert checks to see if this method should exit prematurely.
461 void clear_bitmap(G1CMBitMap* bitmap, WorkGang* workers, bool may_yield);
462
463 // Region statistics gathered during marking.
464 G1RegionMarkStats* _region_mark_stats;
465 // Top pointer for each region at the start of the rebuild remembered set process
466 // for regions which remembered sets need to be rebuilt. A NULL for a given region
467 // means that this region does not be scanned during the rebuilding remembered
468 // set phase at all.
469 HeapWord* volatile* _top_at_rebuild_starts;
470 public:
471 void add_to_liveness(uint worker_id, oop const obj, size_t size);
472 // Liveness of the given region as determined by concurrent marking, i.e. the amount of
473 // live words between bottom and nTAMS.
474 size_t liveness(uint region) const { return _region_mark_stats[region]._live_words; }
475
476 // Sets the internal top_at_region_start for the given region to current top of the region.
477 inline void update_top_at_rebuild_start(HeapRegion* r);
478 // TARS for the given region during remembered set rebuilding.
479 inline HeapWord* top_at_rebuild_start(uint region) const;
480
481 // Clear statistics gathered during the concurrent cycle for the given region after
482 // it has been reclaimed.
483 void clear_statistics_in_region(uint region_idx);
484 // Notification for eagerly reclaimed regions to clean up.
485 void humongous_object_eagerly_reclaimed(HeapRegion* r);
486 // Manipulation of the global mark stack.
487 // The push and pop operations are used by tasks for transfers
488 // between task-local queues and the global mark stack.
489 bool mark_stack_push(G1TaskQueueEntry* arr) {
490 if (!_global_mark_stack.par_push_chunk(arr)) {
491 set_has_overflown();
492 return false;
493 }
494 return true;
495 }
496 bool mark_stack_pop(G1TaskQueueEntry* arr) {
497 return _global_mark_stack.par_pop_chunk(arr);
498 }
499 size_t mark_stack_size() const { return _global_mark_stack.size(); }
500 size_t partial_mark_stack_size_target() const { return _global_mark_stack.capacity() / 3; }
501 bool mark_stack_empty() const { return _global_mark_stack.is_empty(); }
502
503 G1CMRootRegions* root_regions() { return &_root_regions; }
504
505 void concurrent_cycle_start();
506 // Abandon current marking iteration due to a Full GC.
507 void concurrent_cycle_abort();
508 void concurrent_cycle_end();
509
510 void update_accum_task_vtime(int i, double vtime) {
511 _accum_task_vtime[i] += vtime;
512 }
513
514 double all_task_accum_vtime() {
515 double ret = 0.0;
516 for (uint i = 0; i < _max_num_tasks; ++i)
517 ret += _accum_task_vtime[i];
518 return ret;
519 }
520
521 // Attempts to steal an object from the task queues of other tasks
522 bool try_stealing(uint worker_id, G1TaskQueueEntry& task_entry);
523
524 G1ConcurrentMark(G1CollectedHeap* g1h,
525 G1RegionToSpaceMapper* prev_bitmap_storage,
526 G1RegionToSpaceMapper* next_bitmap_storage);
527 ~G1ConcurrentMark();
528
529 G1ConcurrentMarkThread* cm_thread() { return _cm_thread; }
530
531 const G1CMBitMap* const prev_mark_bitmap() const { return _prev_mark_bitmap; }
532 G1CMBitMap* next_mark_bitmap() const { return _next_mark_bitmap; }
533
534 // Calculates the number of concurrent GC threads to be used in the marking phase.
535 uint calc_active_marking_workers();
536
537 // Moves all per-task cached data into global state.
538 void flush_all_task_caches();
539 // Prepare internal data structures for the next mark cycle. This includes clearing
540 // the next mark bitmap and some internal data structures. This method is intended
541 // to be called concurrently to the mutator. It will yield to safepoint requests.
542 void cleanup_for_next_mark();
543
544 // Clear the previous marking bitmap during safepoint.
545 void clear_prev_bitmap(WorkGang* workers);
546
547 // These two methods do the work that needs to be done at the start and end of the
548 // initial mark pause.
549 void pre_initial_mark();
550 void post_initial_mark();
551
552 // Scan all the root regions and mark everything reachable from
553 // them.
554 void scan_root_regions();
555
556 // Scan a single root region from nTAMS to top and mark everything reachable from it.
557 void scan_root_region(HeapRegion* hr, uint worker_id);
558
559 // Do concurrent phase of marking, to a tentative transitive closure.
560 void mark_from_roots();
561
562 // Do concurrent preclean work.
563 void preclean();
564
565 void remark();
566
567 void cleanup();
568 // Mark in the previous bitmap. Caution: the prev bitmap is usually read-only, so use
569 // this carefully.
570 inline void mark_in_prev_bitmap(oop p);
571
572 // Clears marks for all objects in the given range, for the prev or
573 // next bitmaps. Caution: the previous bitmap is usually
574 // read-only, so use this carefully!
575 void clear_range_in_prev_bitmap(MemRegion mr);
576
577 inline bool is_marked_in_prev_bitmap(oop p) const;
578
579 // Verify that there are no collection set oops on the stacks (taskqueues /
580 // global mark stack) and fingers (global / per-task).
581 // If marking is not in progress, it's a no-op.
582 void verify_no_collection_set_oops_in_stacks() PRODUCT_RETURN;
583
584 inline bool do_yield_check();
585
586 bool has_aborted() { return _has_aborted; }
587
588 void print_summary_info();
589
590 void print_worker_threads_on(outputStream* st) const;
591 void threads_do(ThreadClosure* tc) const;
592
593 void print_on_error(outputStream* st) const;
594
595 // Mark the given object on the next bitmap if it is below nTAMS.
596 inline bool mark_in_next_bitmap(uint worker_id, HeapRegion* const hr, oop const obj);
597 inline bool mark_in_next_bitmap(uint worker_id, oop const obj);
598
599 inline bool is_marked_in_next_bitmap(oop p) const;
600
601 // Returns true if initialization was successfully completed.
602 bool completed_initialization() const {
603 return _completed_initialization;
604 }
605
606 ConcurrentGCTimer* gc_timer_cm() const { return _gc_timer_cm; }
607 G1OldTracer* gc_tracer_cm() const { return _gc_tracer_cm; }
608
609 private:
610 // Rebuilds the remembered sets for chosen regions in parallel and concurrently to the application.
611 void rebuild_rem_set_concurrently();
612 };
613
614 // A class representing a marking task.
615 class G1CMTask : public TerminatorTerminator {
616 private:
617 enum PrivateConstants {
618 // The regular clock call is called once the scanned words reaches
619 // this limit
620 words_scanned_period = 12*1024,
621 // The regular clock call is called once the number of visited
622 // references reaches this limit
623 refs_reached_period = 1024,
624 // Initial value for the hash seed, used in the work stealing code
625 init_hash_seed = 17
626 };
627
628 // Number of entries in the per-task stats entry. This seems enough to have a very
629 // low cache miss rate.
630 static const uint RegionMarkStatsCacheSize = 1024;
631
632 G1CMObjArrayProcessor _objArray_processor;
633
634 uint _worker_id;
635 G1CollectedHeap* _g1h;
636 G1ConcurrentMark* _cm;
637 G1CMBitMap* _next_mark_bitmap;
638 // the task queue of this task
639 G1CMTaskQueue* _task_queue;
640
641 G1RegionMarkStatsCache _mark_stats_cache;
642 // Number of calls to this task
643 uint _calls;
644
645 // When the virtual timer reaches this time, the marking step should exit
646 double _time_target_ms;
647 // Start time of the current marking step
648 double _start_time_ms;
649
650 // Oop closure used for iterations over oops
651 G1CMOopClosure* _cm_oop_closure;
652
653 // Region this task is scanning, NULL if we're not scanning any
654 HeapRegion* _curr_region;
655 // Local finger of this task, NULL if we're not scanning a region
656 HeapWord* _finger;
657 // Limit of the region this task is scanning, NULL if we're not scanning one
658 HeapWord* _region_limit;
659
660 // Number of words this task has scanned
661 size_t _words_scanned;
662 // When _words_scanned reaches this limit, the regular clock is
663 // called. Notice that this might be decreased under certain
664 // circumstances (i.e. when we believe that we did an expensive
665 // operation).
666 size_t _words_scanned_limit;
667 // Initial value of _words_scanned_limit (i.e. what it was
668 // before it was decreased).
669 size_t _real_words_scanned_limit;
670
671 // Number of references this task has visited
672 size_t _refs_reached;
673 // When _refs_reached reaches this limit, the regular clock is
674 // called. Notice this this might be decreased under certain
675 // circumstances (i.e. when we believe that we did an expensive
676 // operation).
677 size_t _refs_reached_limit;
678 // Initial value of _refs_reached_limit (i.e. what it was before
679 // it was decreased).
680 size_t _real_refs_reached_limit;
681
682 // If true, then the task has aborted for some reason
683 bool _has_aborted;
684 // Set when the task aborts because it has met its time quota
685 bool _has_timed_out;
686 // True when we're draining SATB buffers; this avoids the task
687 // aborting due to SATB buffers being available (as we're already
688 // dealing with them)
689 bool _draining_satb_buffers;
690
691 // Number sequence of past step times
692 NumberSeq _step_times_ms;
693 // Elapsed time of this task
694 double _elapsed_time_ms;
695 // Termination time of this task
696 double _termination_time_ms;
697 // When this task got into the termination protocol
698 double _termination_start_time_ms;
699
700 TruncatedSeq _marking_step_diffs_ms;
701
702 // Updates the local fields after this task has claimed
703 // a new region to scan
704 void setup_for_region(HeapRegion* hr);
705 // Makes the limit of the region up-to-date
706 void update_region_limit();
707
708 // Called when either the words scanned or the refs visited limit
709 // has been reached
710 void reached_limit();
711 // Recalculates the words scanned and refs visited limits
712 void recalculate_limits();
713 // Decreases the words scanned and refs visited limits when we reach
714 // an expensive operation
715 void decrease_limits();
716 // Checks whether the words scanned or refs visited reached their
717 // respective limit and calls reached_limit() if they have
718 void check_limits() {
719 if (_words_scanned >= _words_scanned_limit ||
720 _refs_reached >= _refs_reached_limit) {
721 reached_limit();
722 }
723 }
724 // Supposed to be called regularly during a marking step as
725 // it checks a bunch of conditions that might cause the marking step
726 // to abort
727 // Return true if the marking step should continue. Otherwise, return false to abort
728 bool regular_clock_call();
729
730 // Set abort flag if regular_clock_call() check fails
731 inline void abort_marking_if_regular_check_fail();
732
733 // Test whether obj might have already been passed over by the
734 // mark bitmap scan, and so needs to be pushed onto the mark stack.
735 bool is_below_finger(oop obj, HeapWord* global_finger) const;
736
737 template<bool scan> void process_grey_task_entry(G1TaskQueueEntry task_entry);
738 public:
739 // Apply the closure on the given area of the objArray. Return the number of words
740 // scanned.
741 inline size_t scan_objArray(objArrayOop obj, MemRegion mr);
742 // Resets the task; should be called right at the beginning of a marking phase.
743 void reset(G1CMBitMap* next_mark_bitmap);
744 // Clears all the fields that correspond to a claimed region.
745 void clear_region_fields();
746
747 // The main method of this class which performs a marking step
748 // trying not to exceed the given duration. However, it might exit
749 // prematurely, according to some conditions (i.e. SATB buffers are
750 // available for processing).
751 void do_marking_step(double target_ms,
752 bool do_termination,
753 bool is_serial);
754
755 // These two calls start and stop the timer
756 void record_start_time() {
757 _elapsed_time_ms = os::elapsedTime() * 1000.0;
758 }
759 void record_end_time() {
760 _elapsed_time_ms = os::elapsedTime() * 1000.0 - _elapsed_time_ms;
761 }
762
763 // Returns the worker ID associated with this task.
764 uint worker_id() { return _worker_id; }
765
766 // From TerminatorTerminator. It determines whether this task should
767 // exit the termination protocol after it's entered it.
768 virtual bool should_exit_termination();
769
770 // Resets the local region fields after a task has finished scanning a
771 // region; or when they have become stale as a result of the region
772 // being evacuated.
773 void giveup_current_region();
774
775 HeapWord* finger() { return _finger; }
776
777 bool has_aborted() { return _has_aborted; }
778 void set_has_aborted() { _has_aborted = true; }
779 void clear_has_aborted() { _has_aborted = false; }
780
781 void set_cm_oop_closure(G1CMOopClosure* cm_oop_closure);
782
783 // Increment the number of references this task has visited.
784 void increment_refs_reached() { ++_refs_reached; }
785
786 // Grey the object by marking it. If not already marked, push it on
787 // the local queue if below the finger. obj is required to be below its region's NTAMS.
788 // Returns whether there has been a mark to the bitmap.
789 inline bool make_reference_grey(oop obj);
790
791 // Grey the object (by calling make_grey_reference) if required,
792 // e.g. obj is below its containing region's NTAMS.
793 // Precondition: obj is a valid heap object.
794 // Returns true if the reference caused a mark to be set in the next bitmap.
795 template <class T>
796 inline bool deal_with_reference(T* p);
797
798 // Scans an object and visits its children.
799 inline void scan_task_entry(G1TaskQueueEntry task_entry);
800
801 // Pushes an object on the local queue.
802 inline void push(G1TaskQueueEntry task_entry);
803
804 // Move entries to the global stack.
805 void move_entries_to_global_stack();
806 // Move entries from the global stack, return true if we were successful to do so.
807 bool get_entries_from_global_stack();
808
809 // Pops and scans objects from the local queue. If partially is
810 // true, then it stops when the queue size is of a given limit. If
811 // partially is false, then it stops when the queue is empty.
812 void drain_local_queue(bool partially);
813 // Moves entries from the global stack to the local queue and
814 // drains the local queue. If partially is true, then it stops when
815 // both the global stack and the local queue reach a given size. If
816 // partially if false, it tries to empty them totally.
817 void drain_global_stack(bool partially);
818 // Keeps picking SATB buffers and processing them until no SATB
819 // buffers are available.
820 void drain_satb_buffers();
821
822 // Moves the local finger to a new location
823 inline void move_finger_to(HeapWord* new_finger) {
824 assert(new_finger >= _finger && new_finger < _region_limit, "invariant");
825 _finger = new_finger;
826 }
827
828 G1CMTask(uint worker_id,
829 G1ConcurrentMark *cm,
830 G1CMTaskQueue* task_queue,
831 G1RegionMarkStats* mark_stats,
832 uint max_regions);
833
834 inline void update_liveness(oop const obj, size_t const obj_size);
835
836 // Clear (without flushing) the mark cache entry for the given region.
837 void clear_mark_stats_cache(uint region_idx);
838 // Evict the whole statistics cache into the global statistics. Returns the
839 // number of cache hits and misses so far.
840 Pair<size_t, size_t> flush_mark_stats_cache();
841 // Prints statistics associated with this task
842 void print_stats();
843 };
844
845 // Class that's used to to print out per-region liveness
846 // information. It's currently used at the end of marking and also
847 // after we sort the old regions at the end of the cleanup operation.
848 class G1PrintRegionLivenessInfoClosure : public HeapRegionClosure {
849 // Accumulators for these values.
850 size_t _total_used_bytes;
851 size_t _total_capacity_bytes;
852 size_t _total_prev_live_bytes;
853 size_t _total_next_live_bytes;
854
855 // Accumulator for the remembered set size
856 size_t _total_remset_bytes;
857
858 // Accumulator for strong code roots memory size
859 size_t _total_strong_code_roots_bytes;
860
861 static double bytes_to_mb(size_t val) {
862 return (double) val / (double) M;
863 }
864
865 public:
866 // The header and footer are printed in the constructor and
867 // destructor respectively.
868 G1PrintRegionLivenessInfoClosure(const char* phase_name);
869 virtual bool do_heap_region(HeapRegion* r);
870 ~G1PrintRegionLivenessInfoClosure();
871 };
872
873 #endif // SHARE_GC_G1_G1CONCURRENTMARK_HPP