-
Notifications
You must be signed in to change notification settings - Fork 54
/
GC.cpp
9065 lines (7599 loc) · 276 KB
/
GC.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/*
* [SMDOC] Garbage Collector
*
* This code implements an incremental mark-and-sweep garbage collector, with
* most sweeping carried out in the background on a parallel thread.
*
* Full vs. zone GC
* ----------------
*
* The collector can collect all zones at once, or a subset. These types of
* collection are referred to as a full GC and a zone GC respectively.
*
* It is possible for an incremental collection that started out as a full GC to
* become a zone GC if new zones are created during the course of the
* collection.
*
* Incremental collection
* ----------------------
*
* For a collection to be carried out incrementally the following conditions
* must be met:
* - the collection must be run by calling js::GCSlice() rather than js::GC()
* - the GC mode must have been set to JSGC_MODE_INCREMENTAL with
* JS_SetGCParameter()
* - no thread may have an AutoKeepAtoms instance on the stack
*
* The last condition is an engine-internal mechanism to ensure that incremental
* collection is not carried out without the correct barriers being implemented.
* For more information see 'Incremental marking' below.
*
* If the collection is not incremental, all foreground activity happens inside
* a single call to GC() or GCSlice(). However the collection is not complete
* until the background sweeping activity has finished.
*
* An incremental collection proceeds as a series of slices, interleaved with
* mutator activity, i.e. running JavaScript code. Slices are limited by a time
* budget. The slice finishes as soon as possible after the requested time has
* passed.
*
* Collector states
* ----------------
*
* The collector proceeds through the following states, the current state being
* held in JSRuntime::gcIncrementalState:
*
* - MarkRoots - marks the stack and other roots
* - Mark - incrementally marks reachable things
* - Sweep - sweeps zones in groups and continues marking unswept zones
* - Finalize - performs background finalization, concurrent with mutator
* - Compact - incrementally compacts by zone
* - Decommit - performs background decommit and chunk removal
*
* The MarkRoots activity always takes place in the first slice. The next two
* states can take place over one or more slices.
*
* In other words an incremental collection proceeds like this:
*
* Slice 1: MarkRoots: Roots pushed onto the mark stack.
* Mark: The mark stack is processed by popping an element,
* marking it, and pushing its children.
*
* ... JS code runs ...
*
* Slice 2: Mark: More mark stack processing.
*
* ... JS code runs ...
*
* Slice n-1: Mark: More mark stack processing.
*
* ... JS code runs ...
*
* Slice n: Mark: Mark stack is completely drained.
* Sweep: Select first group of zones to sweep and sweep them.
*
* ... JS code runs ...
*
* Slice n+1: Sweep: Mark objects in unswept zones that were newly
* identified as alive (see below). Then sweep more zone
* sweep groups.
*
* ... JS code runs ...
*
* Slice n+2: Sweep: Mark objects in unswept zones that were newly
* identified as alive. Then sweep more zones.
*
* ... JS code runs ...
*
* Slice m: Sweep: Sweeping is finished, and background sweeping
* started on the helper thread.
*
* ... JS code runs, remaining sweeping done on background thread ...
*
* When background sweeping finishes the GC is complete.
*
* Incremental marking
* -------------------
*
* Incremental collection requires close collaboration with the mutator (i.e.,
* JS code) to guarantee correctness.
*
* - During an incremental GC, if a memory location (except a root) is written
* to, then the value it previously held must be marked. Write barriers
* ensure this.
*
* - Any object that is allocated during incremental GC must start out marked.
*
* - Roots are marked in the first slice and hence don't need write barriers.
* Roots are things like the C stack and the VM stack.
*
* The problem that write barriers solve is that between slices the mutator can
* change the object graph. We must ensure that it cannot do this in such a way
* that makes us fail to mark a reachable object (marking an unreachable object
* is tolerable).
*
* We use a snapshot-at-the-beginning algorithm to do this. This means that we
* promise to mark at least everything that is reachable at the beginning of
* collection. To implement it we mark the old contents of every non-root memory
* location written to by the mutator while the collection is in progress, using
* write barriers. This is described in gc/Barrier.h.
*
* Incremental sweeping
* --------------------
*
* Sweeping is difficult to do incrementally because object finalizers must be
* run at the start of sweeping, before any mutator code runs. The reason is
* that some objects use their finalizers to remove themselves from caches. If
* mutator code was allowed to run after the start of sweeping, it could observe
* the state of the cache and create a new reference to an object that was just
* about to be destroyed.
*
* Sweeping all finalizable objects in one go would introduce long pauses, so
* instead sweeping broken up into groups of zones. Zones which are not yet
* being swept are still marked, so the issue above does not apply.
*
* The order of sweeping is restricted by cross compartment pointers - for
* example say that object |a| from zone A points to object |b| in zone B and
* neither object was marked when we transitioned to the Sweep phase. Imagine we
* sweep B first and then return to the mutator. It's possible that the mutator
* could cause |a| to become alive through a read barrier (perhaps it was a
* shape that was accessed via a shape table). Then we would need to mark |b|,
* which |a| points to, but |b| has already been swept.
*
* So if there is such a pointer then marking of zone B must not finish before
* marking of zone A. Pointers which form a cycle between zones therefore
* restrict those zones to being swept at the same time, and these are found
* using Tarjan's algorithm for finding the strongly connected components of a
* graph.
*
* GC things without finalizers, and things with finalizers that are able to run
* in the background, are swept on the background thread. This accounts for most
* of the sweeping work.
*
* Reset
* -----
*
* During incremental collection it is possible, although unlikely, for
* conditions to change such that incremental collection is no longer safe. In
* this case, the collection is 'reset' by resetIncrementalGC(). If we are in
* the mark state, this just stops marking, but if we have started sweeping
* already, we continue non-incrementally until we have swept the current sweep
* group. Following a reset, a new collection is started.
*
* Compacting GC
* -------------
*
* Compacting GC happens at the end of a major GC as part of the last slice.
* There are three parts:
*
* - Arenas are selected for compaction.
* - The contents of those arenas are moved to new arenas.
* - All references to moved things are updated.
*
* Collecting Atoms
* ----------------
*
* Atoms are collected differently from other GC things. They are contained in
* a special zone and things in other zones may have pointers to them that are
* not recorded in the cross compartment pointer map. Each zone holds a bitmap
* with the atoms it might be keeping alive, and atoms are only collected if
* they are not included in any zone's atom bitmap. See AtomMarking.cpp for how
* this bitmap is managed.
*/
#include "gc/GC-inl.h"
#include "mozilla/ArrayUtils.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/MacroForEach.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/Move.h"
#include "mozilla/Range.h"
#include "mozilla/ScopeExit.h"
#include "mozilla/TimeStamp.h"
#include "mozilla/TypeTraits.h"
#include "mozilla/Unused.h"
#include <ctype.h>
#include <initializer_list>
#include <string.h>
#ifndef XP_WIN
# include <sys/mman.h>
# include <unistd.h>
#endif
#include "jsapi.h"
#include "jsfriendapi.h"
#include "jstypes.h"
#include "jsutil.h"
#include "gc/FindSCCs.h"
#include "gc/FreeOp.h"
#include "gc/GCInternals.h"
#include "gc/GCLock.h"
#include "gc/GCTrace.h"
#include "gc/Memory.h"
#include "gc/Policy.h"
#include "gc/WeakMap.h"
#include "jit/BaselineJIT.h"
#include "jit/IonCode.h"
#include "jit/JitcodeMap.h"
#include "jit/JitRealm.h"
#include "jit/MacroAssembler.h"
#include "js/SliceBudget.h"
#include "proxy/DeadObjectProxy.h"
#include "util/Windows.h"
#include "vm/BigIntType.h"
#include "vm/Debugger.h"
#include "vm/GeckoProfiler.h"
#include "vm/JSAtom.h"
#include "vm/JSContext.h"
#include "vm/JSObject.h"
#include "vm/JSScript.h"
#include "vm/Printer.h"
#include "vm/ProxyObject.h"
#include "vm/Realm.h"
#include "vm/Shape.h"
#include "vm/StringType.h"
#include "vm/SymbolType.h"
#include "vm/Time.h"
#include "vm/TraceLogging.h"
#include "vm/WrapperObject.h"
#include "gc/Heap-inl.h"
#include "gc/Marking-inl.h"
#include "gc/Nursery-inl.h"
#include "gc/PrivateIterators-inl.h"
#include "gc/Zone-inl.h"
#include "vm/GeckoProfiler-inl.h"
#include "vm/JSObject-inl.h"
#include "vm/JSScript-inl.h"
#include "vm/Stack-inl.h"
#include "vm/StringType-inl.h"
using namespace js;
using namespace js::gc;
using mozilla::ArrayLength;
using mozilla::Maybe;
using mozilla::Swap;
using mozilla::TimeDuration;
using mozilla::TimeStamp;
using JS::AutoGCRooter;
/*
* Default settings for tuning the GC. Some of these can be set at runtime,
* This list is not complete, some tuning parameters are not listed here.
*
* If you change the values here, please also consider changing them in
* modules/libpref/init/all.js where they are duplicated for the Firefox
* preferences.
*/
namespace js {
namespace gc {
namespace TuningDefaults {
/* JSGC_ALLOCATION_THRESHOLD */
static const size_t GCZoneAllocThresholdBase = 30 * 1024 * 1024;
/* JSGC_MAX_MALLOC_BYTES */
static const size_t MaxMallocBytes = 128 * 1024 * 1024;
/* JSGC_ALLOCATION_THRESHOLD_FACTOR */
static const float AllocThresholdFactor = 0.9f;
/* JSGC_ALLOCATION_THRESHOLD_FACTOR_AVOID_INTERRUPT */
static const float AllocThresholdFactorAvoidInterrupt = 0.9f;
/* no parameter */
static const float MallocThresholdGrowFactor = 1.5f;
/* no parameter */
static const float MallocThresholdShrinkFactor = 0.9f;
/* no parameter */
static const size_t MallocThresholdLimit = 1024 * 1024 * 1024;
/* no parameter */
static const size_t ZoneAllocDelayBytes = 1024 * 1024;
/* JSGC_DYNAMIC_HEAP_GROWTH */
static const bool DynamicHeapGrowthEnabled = false;
/* JSGC_HIGH_FREQUENCY_TIME_LIMIT */
static const auto HighFrequencyThreshold = 1; // in seconds
/* JSGC_HIGH_FREQUENCY_LOW_LIMIT */
static const size_t HighFrequencyLowLimitBytes = 100 * 1024 * 1024;
/* JSGC_HIGH_FREQUENCY_HIGH_LIMIT */
static const size_t HighFrequencyHighLimitBytes = 500 * 1024 * 1024;
/* JSGC_HIGH_FREQUENCY_HEAP_GROWTH_MAX */
static const float HighFrequencyHeapGrowthMax = 3.0f;
/* JSGC_HIGH_FREQUENCY_HEAP_GROWTH_MIN */
static const float HighFrequencyHeapGrowthMin = 1.5f;
/* JSGC_LOW_FREQUENCY_HEAP_GROWTH */
static const float LowFrequencyHeapGrowth = 1.5f;
/* JSGC_DYNAMIC_MARK_SLICE */
static const bool DynamicMarkSliceEnabled = false;
/* JSGC_MIN_EMPTY_CHUNK_COUNT */
static const uint32_t MinEmptyChunkCount = 1;
/* JSGC_MAX_EMPTY_CHUNK_COUNT */
static const uint32_t MaxEmptyChunkCount = 30;
/* JSGC_SLICE_TIME_BUDGET */
static const int64_t DefaultTimeBudget = SliceBudget::UnlimitedTimeBudget;
/* JSGC_MODE */
static const JSGCMode Mode = JSGC_MODE_INCREMENTAL;
/* JSGC_COMPACTING_ENABLED */
static const bool CompactingEnabled = true;
/* JSGC_NURSERY_FREE_THRESHOLD_FOR_IDLE_COLLECTION */
static const uint32_t NurseryFreeThresholdForIdleCollection =
Nursery::NurseryChunkUsableSize / 4;
/* JSGC_NURSERY_FREE_THRESHOLD_FOR_IDLE_COLLECTION_PERCENT */
static const float NurseryFreeThresholdForIdleCollectionFraction = 0.25f;
/* JSGC_PRETENURE_THRESHOLD */
static const float PretenureThreshold = 0.6f;
/* JSGC_PRETENURE_GROUP_THRESHOLD */
static const float PretenureGroupThreshold = 3000;
} // namespace TuningDefaults
} // namespace gc
} // namespace js
/*
* We start to incremental collection for a zone when a proportion of its
* threshold is reached. This is configured by the
* JSGC_ALLOCATION_THRESHOLD_FACTOR and
* JSGC_ALLOCATION_THRESHOLD_FACTOR_AVOID_INTERRUPT parameters.
*/
static constexpr float MinAllocationThresholdFactor = 0.9f;
/*
* We may start to collect a zone before its trigger threshold is reached if
* GCRuntime::maybeGC() is called for that zone or we start collecting other
* zones. These eager threshold factors are not configurable.
*/
static constexpr float HighFrequencyEagerAllocTriggerFactor = 0.85f;
static constexpr float LowFrequencyEagerAllocTriggerFactor = 0.9f;
/*
* Don't allow heap growth factors to be set so low that collections could
* reduce the trigger threshold.
*/
static constexpr float MinHighFrequencyHeapGrowthFactor =
1.0f /
Min(HighFrequencyEagerAllocTriggerFactor, MinAllocationThresholdFactor);
static constexpr float MinLowFrequencyHeapGrowthFactor =
1.0f /
Min(LowFrequencyEagerAllocTriggerFactor, MinAllocationThresholdFactor);
/* Increase the IGC marking slice time if we are in highFrequencyGC mode. */
static constexpr int IGC_MARK_SLICE_MULTIPLIER = 2;
const AllocKind gc::slotsToThingKind[] = {
// clang-format off
/* 0 */ AllocKind::OBJECT0, AllocKind::OBJECT2, AllocKind::OBJECT2, AllocKind::OBJECT4,
/* 4 */ AllocKind::OBJECT4, AllocKind::OBJECT8, AllocKind::OBJECT8, AllocKind::OBJECT8,
/* 8 */ AllocKind::OBJECT8, AllocKind::OBJECT12, AllocKind::OBJECT12, AllocKind::OBJECT12,
/* 12 */ AllocKind::OBJECT12, AllocKind::OBJECT16, AllocKind::OBJECT16, AllocKind::OBJECT16,
/* 16 */ AllocKind::OBJECT16
// clang-format on
};
// Check that reserved bits of a Cell are compatible with our typical allocators
// since most derived classes will store a pointer in the first word.
static_assert(js::detail::LIFO_ALLOC_ALIGN > JS_BITMASK(Cell::ReservedBits),
"Cell::ReservedBits should support LifoAlloc");
static_assert(CellAlignBytes > JS_BITMASK(Cell::ReservedBits),
"Cell::ReservedBits should support gc::Cell");
static_assert(
sizeof(uintptr_t) > JS_BITMASK(Cell::ReservedBits),
"Cell::ReservedBits should support small malloc / aligned globals");
static_assert(js::jit::CodeAlignment > JS_BITMASK(Cell::ReservedBits),
"Cell::ReservedBits should support JIT code");
static_assert(mozilla::ArrayLength(slotsToThingKind) ==
SLOTS_TO_THING_KIND_LIMIT,
"We have defined a slot count for each kind.");
#define CHECK_THING_SIZE(allocKind, traceKind, type, sizedType, bgFinal, \
nursery, compact) \
static_assert(sizeof(sizedType) >= SortedArenaList::MinThingSize, \
#sizedType " is smaller than SortedArenaList::MinThingSize!"); \
static_assert(sizeof(sizedType) >= sizeof(FreeSpan), \
#sizedType " is smaller than FreeSpan"); \
static_assert(sizeof(sizedType) % CellAlignBytes == 0, \
"Size of " #sizedType " is not a multiple of CellAlignBytes"); \
static_assert(sizeof(sizedType) >= MinCellSize, \
"Size of " #sizedType " is smaller than the minimum size");
FOR_EACH_ALLOCKIND(CHECK_THING_SIZE);
#undef CHECK_THING_SIZE
const uint32_t Arena::ThingSizes[] = {
#define EXPAND_THING_SIZE(allocKind, traceKind, type, sizedType, bgFinal, \
nursery, compact) \
sizeof(sizedType),
FOR_EACH_ALLOCKIND(EXPAND_THING_SIZE)
#undef EXPAND_THING_SIZE
};
FreeSpan FreeLists::emptySentinel;
#undef CHECK_THING_SIZE_INNER
#undef CHECK_THING_SIZE
#define OFFSET(type) \
uint32_t(ArenaHeaderSize + (ArenaSize - ArenaHeaderSize) % sizeof(type))
const uint32_t Arena::FirstThingOffsets[] = {
#define EXPAND_FIRST_THING_OFFSET(allocKind, traceKind, type, sizedType, \
bgFinal, nursery, compact) \
OFFSET(sizedType),
FOR_EACH_ALLOCKIND(EXPAND_FIRST_THING_OFFSET)
#undef EXPAND_FIRST_THING_OFFSET
};
#undef OFFSET
#define COUNT(type) uint32_t((ArenaSize - ArenaHeaderSize) / sizeof(type))
const uint32_t Arena::ThingsPerArena[] = {
#define EXPAND_THINGS_PER_ARENA(allocKind, traceKind, type, sizedType, \
bgFinal, nursery, compact) \
COUNT(sizedType),
FOR_EACH_ALLOCKIND(EXPAND_THINGS_PER_ARENA)
#undef EXPAND_THINGS_PER_ARENA
};
#undef COUNT
struct js::gc::FinalizePhase {
gcstats::PhaseKind statsPhase;
AllocKinds kinds;
};
/*
* Finalization order for objects swept incrementally on the main thread.
*/
static constexpr FinalizePhase ForegroundObjectFinalizePhase = {
gcstats::PhaseKind::SWEEP_OBJECT,
{AllocKind::OBJECT0, AllocKind::OBJECT2, AllocKind::OBJECT4,
AllocKind::OBJECT8, AllocKind::OBJECT12, AllocKind::OBJECT16}};
/*
* Finalization order for GC things swept incrementally on the main thread.
*/
static constexpr FinalizePhase ForegroundNonObjectFinalizePhase = {
gcstats::PhaseKind::SWEEP_SCRIPT, {AllocKind::SCRIPT, AllocKind::JITCODE}};
/*
* Finalization order for GC things swept on the background thread.
*/
static constexpr FinalizePhase BackgroundFinalizePhases[] = {
{gcstats::PhaseKind::SWEEP_SCRIPT, {AllocKind::LAZY_SCRIPT}},
{gcstats::PhaseKind::SWEEP_OBJECT,
{AllocKind::FUNCTION, AllocKind::FUNCTION_EXTENDED,
AllocKind::OBJECT0_BACKGROUND, AllocKind::OBJECT2_BACKGROUND,
AllocKind::OBJECT4_BACKGROUND, AllocKind::OBJECT8_BACKGROUND,
AllocKind::OBJECT12_BACKGROUND, AllocKind::OBJECT16_BACKGROUND}},
{gcstats::PhaseKind::SWEEP_SCOPE,
{
AllocKind::SCOPE,
}},
{gcstats::PhaseKind::SWEEP_REGEXP_SHARED,
{
AllocKind::REGEXP_SHARED,
}},
{gcstats::PhaseKind::SWEEP_STRING,
{AllocKind::FAT_INLINE_STRING, AllocKind::STRING,
AllocKind::EXTERNAL_STRING, AllocKind::FAT_INLINE_ATOM, AllocKind::ATOM,
AllocKind::SYMBOL, AllocKind::BIGINT}},
{gcstats::PhaseKind::SWEEP_SHAPE,
{AllocKind::SHAPE, AllocKind::ACCESSOR_SHAPE, AllocKind::BASE_SHAPE,
AllocKind::OBJECT_GROUP}}};
template <>
JSObject* ArenaCellIterImpl::get<JSObject>() const {
MOZ_ASSERT(!done());
return reinterpret_cast<JSObject*>(getCell());
}
void Arena::unmarkAll() {
uintptr_t* word = chunk()->bitmap.arenaBits(this);
memset(word, 0, ArenaBitmapWords * sizeof(uintptr_t));
}
void Arena::unmarkPreMarkedFreeCells() {
for (ArenaFreeCellIter iter(this); !iter.done(); iter.next()) {
TenuredCell* cell = iter.getCell();
MOZ_ASSERT(cell->isMarkedBlack());
cell->unmark();
}
}
#ifdef DEBUG
void Arena::checkNoMarkedFreeCells() {
for (ArenaFreeCellIter iter(this); !iter.done(); iter.next()) {
MOZ_ASSERT(!iter.getCell()->isMarkedAny());
}
}
#endif
/* static */
void Arena::staticAsserts() {
static_assert(size_t(AllocKind::LIMIT) <= 255,
"We must be able to fit the allockind into uint8_t.");
static_assert(mozilla::ArrayLength(ThingSizes) == size_t(AllocKind::LIMIT),
"We haven't defined all thing sizes.");
static_assert(
mozilla::ArrayLength(FirstThingOffsets) == size_t(AllocKind::LIMIT),
"We haven't defined all offsets.");
static_assert(
mozilla::ArrayLength(ThingsPerArena) == size_t(AllocKind::LIMIT),
"We haven't defined all counts.");
}
template <typename T>
inline size_t Arena::finalize(FreeOp* fop, AllocKind thingKind,
size_t thingSize) {
/* Enforce requirements on size of T. */
MOZ_ASSERT(thingSize % CellAlignBytes == 0);
MOZ_ASSERT(thingSize >= MinCellSize);
MOZ_ASSERT(thingSize <= 255);
MOZ_ASSERT(allocated());
MOZ_ASSERT(thingKind == getAllocKind());
MOZ_ASSERT(thingSize == getThingSize());
MOZ_ASSERT(!onDelayedMarkingList_);
uint_fast16_t firstThing = firstThingOffset(thingKind);
uint_fast16_t firstThingOrSuccessorOfLastMarkedThing = firstThing;
uint_fast16_t lastThing = ArenaSize - thingSize;
FreeSpan newListHead;
FreeSpan* newListTail = &newListHead;
size_t nmarked = 0;
for (ArenaCellIterUnderFinalize i(this); !i.done(); i.next()) {
T* t = i.get<T>();
if (t->asTenured().isMarkedAny()) {
uint_fast16_t thing = uintptr_t(t) & ArenaMask;
if (thing != firstThingOrSuccessorOfLastMarkedThing) {
// We just finished passing over one or more free things,
// so record a new FreeSpan.
newListTail->initBounds(firstThingOrSuccessorOfLastMarkedThing,
thing - thingSize, this);
newListTail = newListTail->nextSpanUnchecked(this);
}
firstThingOrSuccessorOfLastMarkedThing = thing + thingSize;
nmarked++;
} else {
t->finalize(fop);
AlwaysPoison(t, JS_SWEPT_TENURED_PATTERN, thingSize,
MemCheckKind::MakeUndefined);
gcTracer.traceTenuredFinalize(t);
}
}
if (nmarked == 0) {
// Do nothing. The caller will update the arena appropriately.
MOZ_ASSERT(newListTail == &newListHead);
DebugOnlyPoison(data, JS_SWEPT_TENURED_PATTERN, sizeof(data),
MemCheckKind::MakeUndefined);
return nmarked;
}
MOZ_ASSERT(firstThingOrSuccessorOfLastMarkedThing != firstThing);
uint_fast16_t lastMarkedThing =
firstThingOrSuccessorOfLastMarkedThing - thingSize;
if (lastThing == lastMarkedThing) {
// If the last thing was marked, we will have already set the bounds of
// the final span, and we just need to terminate the list.
newListTail->initAsEmpty();
} else {
// Otherwise, end the list with a span that covers the final stretch of free
// things.
newListTail->initFinal(firstThingOrSuccessorOfLastMarkedThing, lastThing,
this);
}
firstFreeSpan = newListHead;
#ifdef DEBUG
size_t nfree = numFreeThings(thingSize);
MOZ_ASSERT(nfree + nmarked == thingsPerArena(thingKind));
#endif
return nmarked;
}
// Finalize arenas from src list, releasing empty arenas if keepArenas wasn't
// specified and inserting the others into the appropriate destination size
// bins.
template <typename T>
static inline bool FinalizeTypedArenas(FreeOp* fop, Arena** src,
SortedArenaList& dest,
AllocKind thingKind, SliceBudget& budget,
ArenaLists::KeepArenasEnum keepArenas) {
// When operating in the foreground, take the lock at the top.
Maybe<AutoLockGC> maybeLock;
if (fop->onMainThread()) {
maybeLock.emplace(fop->runtime());
}
// During background sweeping free arenas are released later on in
// sweepBackgroundThings().
MOZ_ASSERT_IF(!fop->onMainThread(), keepArenas == ArenaLists::KEEP_ARENAS);
size_t thingSize = Arena::thingSize(thingKind);
size_t thingsPerArena = Arena::thingsPerArena(thingKind);
while (Arena* arena = *src) {
*src = arena->next;
size_t nmarked = arena->finalize<T>(fop, thingKind, thingSize);
size_t nfree = thingsPerArena - nmarked;
if (nmarked) {
dest.insertAt(arena, nfree);
} else if (keepArenas == ArenaLists::KEEP_ARENAS) {
arena->chunk()->recycleArena(arena, dest, thingsPerArena);
} else {
fop->runtime()->gc.releaseArena(arena, maybeLock.ref());
}
budget.step(thingsPerArena);
if (budget.isOverBudget()) {
return false;
}
}
return true;
}
/*
* Finalize the list of areans.
*/
static bool FinalizeArenas(FreeOp* fop, Arena** src, SortedArenaList& dest,
AllocKind thingKind, SliceBudget& budget,
ArenaLists::KeepArenasEnum keepArenas) {
switch (thingKind) {
#define EXPAND_CASE(allocKind, traceKind, type, sizedType, bgFinal, nursery, \
compact) \
case AllocKind::allocKind: \
return FinalizeTypedArenas<type>(fop, src, dest, thingKind, budget, \
keepArenas);
FOR_EACH_ALLOCKIND(EXPAND_CASE)
#undef EXPAND_CASE
default:
MOZ_CRASH("Invalid alloc kind");
}
}
Chunk* ChunkPool::pop() {
MOZ_ASSERT(bool(head_) == bool(count_));
if (!count_) {
return nullptr;
}
return remove(head_);
}
void ChunkPool::push(Chunk* chunk) {
MOZ_ASSERT(!chunk->info.next);
MOZ_ASSERT(!chunk->info.prev);
chunk->info.next = head_;
if (head_) {
head_->info.prev = chunk;
}
head_ = chunk;
++count_;
}
Chunk* ChunkPool::remove(Chunk* chunk) {
MOZ_ASSERT(count_ > 0);
MOZ_ASSERT(contains(chunk));
if (head_ == chunk) {
head_ = chunk->info.next;
}
if (chunk->info.prev) {
chunk->info.prev->info.next = chunk->info.next;
}
if (chunk->info.next) {
chunk->info.next->info.prev = chunk->info.prev;
}
chunk->info.next = chunk->info.prev = nullptr;
--count_;
return chunk;
}
#ifdef DEBUG
bool ChunkPool::contains(Chunk* chunk) const {
verify();
for (Chunk* cursor = head_; cursor; cursor = cursor->info.next) {
if (cursor == chunk) {
return true;
}
}
return false;
}
bool ChunkPool::verify() const {
MOZ_ASSERT(bool(head_) == bool(count_));
uint32_t count = 0;
for (Chunk* cursor = head_; cursor; cursor = cursor->info.next, ++count) {
MOZ_ASSERT_IF(cursor->info.prev, cursor->info.prev->info.next == cursor);
MOZ_ASSERT_IF(cursor->info.next, cursor->info.next->info.prev == cursor);
}
MOZ_ASSERT(count_ == count);
return true;
}
#endif
void ChunkPool::Iter::next() {
MOZ_ASSERT(!done());
current_ = current_->info.next;
}
ChunkPool GCRuntime::expireEmptyChunkPool(const AutoLockGC& lock) {
MOZ_ASSERT(emptyChunks(lock).verify());
MOZ_ASSERT(tunables.minEmptyChunkCount(lock) <=
tunables.maxEmptyChunkCount());
ChunkPool expired;
while (emptyChunks(lock).count() > tunables.minEmptyChunkCount(lock)) {
Chunk* chunk = emptyChunks(lock).pop();
prepareToFreeChunk(chunk->info);
expired.push(chunk);
}
MOZ_ASSERT(expired.verify());
MOZ_ASSERT(emptyChunks(lock).verify());
MOZ_ASSERT(emptyChunks(lock).count() <= tunables.maxEmptyChunkCount());
MOZ_ASSERT(emptyChunks(lock).count() <= tunables.minEmptyChunkCount(lock));
return expired;
}
static void FreeChunkPool(ChunkPool& pool) {
for (ChunkPool::Iter iter(pool); !iter.done();) {
Chunk* chunk = iter.get();
iter.next();
pool.remove(chunk);
MOZ_ASSERT(!chunk->info.numArenasFreeCommitted);
UnmapPages(static_cast<void*>(chunk), ChunkSize);
}
MOZ_ASSERT(pool.count() == 0);
}
void GCRuntime::freeEmptyChunks(const AutoLockGC& lock) {
FreeChunkPool(emptyChunks(lock));
}
inline void GCRuntime::prepareToFreeChunk(ChunkInfo& info) {
MOZ_ASSERT(numArenasFreeCommitted >= info.numArenasFreeCommitted);
numArenasFreeCommitted -= info.numArenasFreeCommitted;
stats().count(gcstats::COUNT_DESTROY_CHUNK);
#ifdef DEBUG
/*
* Let FreeChunkPool detect a missing prepareToFreeChunk call before it
* frees chunk.
*/
info.numArenasFreeCommitted = 0;
#endif
}
inline void GCRuntime::updateOnArenaFree() { ++numArenasFreeCommitted; }
void Chunk::addArenaToFreeList(JSRuntime* rt, Arena* arena) {
MOZ_ASSERT(!arena->allocated());
arena->next = info.freeArenasHead;
info.freeArenasHead = arena;
++info.numArenasFreeCommitted;
++info.numArenasFree;
rt->gc.updateOnArenaFree();
}
void Chunk::addArenaToDecommittedList(const Arena* arena) {
++info.numArenasFree;
decommittedArenas.set(Chunk::arenaIndex(arena->address()));
}
void Chunk::recycleArena(Arena* arena, SortedArenaList& dest,
size_t thingsPerArena) {
arena->setAsFullyUnused();
dest.insertAt(arena, thingsPerArena);
}
void Chunk::releaseArena(JSRuntime* rt, Arena* arena, const AutoLockGC& lock) {
MOZ_ASSERT(arena->allocated());
MOZ_ASSERT(!arena->onDelayedMarkingList());
arena->release(lock);
addArenaToFreeList(rt, arena);
updateChunkListAfterFree(rt, lock);
}
bool Chunk::decommitOneFreeArena(JSRuntime* rt, AutoLockGC& lock) {
MOZ_ASSERT(info.numArenasFreeCommitted > 0);
Arena* arena = fetchNextFreeArena(rt);
updateChunkListAfterAlloc(rt, lock);
bool ok;
{
AutoUnlockGC unlock(lock);
ok = MarkPagesUnused(arena, ArenaSize);
}
if (ok) {
addArenaToDecommittedList(arena);
} else {
addArenaToFreeList(rt, arena);
}
updateChunkListAfterFree(rt, lock);
return ok;
}
void Chunk::decommitAllArenasWithoutUnlocking(const AutoLockGC& lock) {
for (size_t i = 0; i < ArenasPerChunk; ++i) {
if (decommittedArenas.get(i) || arenas[i].allocated()) {
continue;
}
if (MarkPagesUnused(&arenas[i], ArenaSize)) {
info.numArenasFreeCommitted--;
decommittedArenas.set(i);
}
}
}
void Chunk::updateChunkListAfterAlloc(JSRuntime* rt, const AutoLockGC& lock) {
if (MOZ_UNLIKELY(!hasAvailableArenas())) {
rt->gc.availableChunks(lock).remove(this);
rt->gc.fullChunks(lock).push(this);
}
}
void Chunk::updateChunkListAfterFree(JSRuntime* rt, const AutoLockGC& lock) {
if (info.numArenasFree == 1) {
rt->gc.fullChunks(lock).remove(this);
rt->gc.availableChunks(lock).push(this);
} else if (!unused()) {
MOZ_ASSERT(rt->gc.availableChunks(lock).contains(this));
} else {
MOZ_ASSERT(unused());
rt->gc.availableChunks(lock).remove(this);
decommitAllArenas();
MOZ_ASSERT(info.numArenasFreeCommitted == 0);
rt->gc.recycleChunk(this, lock);
}
}
void GCRuntime::releaseArena(Arena* arena, const AutoLockGC& lock) {
arena->zone->zoneSize.removeGCArena();
arena->chunk()->releaseArena(rt, arena, lock);
}
GCRuntime::GCRuntime(JSRuntime* rt)
: rt(rt),
systemZone(nullptr),
atomsZone(nullptr),
stats_(rt),
marker(rt),
heapSize(nullptr),
rootsHash(256),
nextCellUniqueId_(LargestTaggedNullCellPointer +
1), // Ensure disjoint from null tagged pointers.
numArenasFreeCommitted(0),
verifyPreData(nullptr),
chunkAllocationSinceLastGC(false),
lastGCTime(ReallyNow()),
mode(TuningDefaults::Mode),
numActiveZoneIters(0),
cleanUpEverything(false),
grayBufferState(GCRuntime::GrayBufferState::Unused),
grayBitsValid(false),
majorGCTriggerReason(JS::GCReason::NO_REASON),
fullGCForAtomsRequested_(false),
minorGCNumber(0),
majorGCNumber(0),
number(0),
isFull(false),
incrementalState(gc::State::NotActive),
initialState(gc::State::NotActive),
#ifdef JS_GC_ZEAL
useZeal(false),
#endif
lastMarkSlice(false),
safeToYield(true),
sweepOnBackgroundThread(false),
lifoBlocksToFree((size_t)JSContext::TEMP_LIFO_ALLOC_PRIMARY_CHUNK_SIZE),
lifoBlocksToFreeAfterMinorGC(
(size_t)JSContext::TEMP_LIFO_ALLOC_PRIMARY_CHUNK_SIZE),
sweepGroupIndex(0),
sweepGroups(nullptr),
currentSweepGroup(nullptr),
sweepZone(nullptr),
hasMarkedGrayRoots(false),
abortSweepAfterCurrentGroup(false),
startedCompacting(false),
relocatedArenasToRelease(nullptr),
#ifdef JS_GC_ZEAL
markingValidator(nullptr),
#endif
defaultTimeBudget_(TuningDefaults::DefaultTimeBudget),
incrementalAllowed(true),
compactingEnabled(TuningDefaults::CompactingEnabled),
rootsRemoved(false),
#ifdef JS_GC_ZEAL
zealModeBits(0),
zealFrequency(0),
nextScheduled(0),
deterministicOnly(false),
incrementalLimit(0),
#endif
fullCompartmentChecks(false),
gcCallbackDepth(0),
alwaysPreserveCode(false),
#ifdef DEBUG
arenasEmptyAtShutdown(true),
#endif
lock(mutexid::GCLock),
allocTask(rt, emptyChunks_.ref()),
sweepTask(rt),
freeTask(rt),
decommitTask(rt),
nursery_(rt),
storeBuffer_(rt, nursery()) {
setGCMode(JSGC_MODE_GLOBAL);
}
#ifdef JS_GC_ZEAL
void GCRuntime::getZealBits(uint32_t* zealBits, uint32_t* frequency,
uint32_t* scheduled) {
*zealBits = zealModeBits;
*frequency = zealFrequency;
*scheduled = nextScheduled;
}
const char gc::ZealModeHelpText[] =
" Specifies how zealous the garbage collector should be. Some of these "
"modes can\n"
" be set simultaneously, by passing multiple level options, e.g. \"2;4\" "
"will activate\n"
" both modes 2 and 4. Modes can be specified by name or number.\n"
" \n"
" Values:\n"
" 0: (None) Normal amount of collection (resets all modes)\n"
" 1: (RootsChange) Collect when roots are added or removed\n"
" 2: (Alloc) Collect when every N allocations (default: 100)\n"
" 4: (VerifierPre) Verify pre write barriers between instructions\n"
" 7: (GenerationalGC) Collect the nursery every N nursery allocations\n"
" 8: (YieldBeforeMarking) Incremental GC in two slices that yields "
"between\n"
" the root marking and marking phases\n"
" 9: (YieldBeforeSweeping) Incremental GC in two slices that yields "
"between\n"
" the marking and sweeping phases\n"
" 10: (IncrementalMultipleSlices) Incremental GC in many slices\n"
" 11: (IncrementalMarkingValidator) Verify incremental marking\n"