summaryrefslogtreecommitdiffstats
path: root/js/src/gc/Heap.h
blob: 2f27702601d09106cfc04ee9a43e160156985610 (plain)
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
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * 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/. */

#ifndef gc_Heap_h
#define gc_Heap_h

#include "mozilla/ArrayUtils.h"
#include "mozilla/Atomics.h"
#include "mozilla/Attributes.h"
#include "mozilla/DebugOnly.h"
#include "mozilla/EnumeratedArray.h"
#include "mozilla/EnumeratedRange.h"
#include "mozilla/PodOperations.h"

#include <stddef.h>
#include <stdint.h>

#include "jsfriendapi.h"
#include "jspubtd.h"
#include "jstypes.h"
#include "jsutil.h"

#include "ds/BitArray.h"
#include "gc/Memory.h"
#include "js/GCAPI.h"
#include "js/HeapAPI.h"
#include "js/RootingAPI.h"
#include "js/TracingAPI.h"
#include "js/TraceKind.h"

struct JSRuntime;

namespace JS {
namespace shadow {
struct Runtime;
} // namespace shadow
} // namespace JS

namespace js {

class AutoLockGC;
class FreeOp;

extern bool
RuntimeFromMainThreadIsHeapMajorCollecting(JS::shadow::Zone* shadowZone);

#ifdef DEBUG

// Barriers can't be triggered during backend Ion compilation, which may run on
// a helper thread.
extern bool
CurrentThreadIsIonCompiling();
#endif

// The return value indicates if anything was unmarked.
extern bool
UnmarkGrayCellRecursively(gc::Cell* cell, JS::TraceKind kind);

extern void
TraceManuallyBarrieredGenericPointerEdge(JSTracer* trc, gc::Cell** thingp, const char* name);

namespace gc {

class Arena;
class ArenaCellSet;
class ArenaList;
class SortedArenaList;
struct Chunk;

/*
 * This flag allows an allocation site to request a specific heap based upon the
 * estimated lifetime or lifetime requirements of objects allocated from that
 * site.
 */
enum InitialHeap {
    DefaultHeap,
    TenuredHeap
};

/* The GC allocation kinds. */
// FIXME: uint8_t would make more sense for the underlying type, but causes
// miscompilations in GCC (fixed in 4.8.5 and 4.9.3). See also bug 1143966.
enum class AllocKind {
    FIRST,
    OBJECT_FIRST = FIRST,
    FUNCTION = FIRST,
    FUNCTION_EXTENDED,
    OBJECT0,
    OBJECT0_BACKGROUND,
    OBJECT2,
    OBJECT2_BACKGROUND,
    OBJECT4,
    OBJECT4_BACKGROUND,
    OBJECT8,
    OBJECT8_BACKGROUND,
    OBJECT12,
    OBJECT12_BACKGROUND,
    OBJECT16,
    OBJECT16_BACKGROUND,
    OBJECT_LIMIT,
    OBJECT_LAST = OBJECT_LIMIT - 1,
    SCRIPT,
    LAZY_SCRIPT,
    SHAPE,
    ACCESSOR_SHAPE,
    BASE_SHAPE,
    OBJECT_GROUP,
    FAT_INLINE_STRING,
    STRING,
    EXTERNAL_STRING,
    FAT_INLINE_ATOM,
    ATOM,
    SYMBOL,
    JITCODE,
    SCOPE,
    LIMIT,
    LAST = LIMIT - 1
};

// Macro to enumerate the different allocation kinds supplying information about
// the trace kind, C++ type and allocation size.
#define FOR_EACH_OBJECT_ALLOCKIND(D) \
 /* AllocKind              TraceKind    TypeName           SizedType */ \
    D(FUNCTION,            Object,      JSObject,          JSFunction) \
    D(FUNCTION_EXTENDED,   Object,      JSObject,          FunctionExtended) \
    D(OBJECT0,             Object,      JSObject,          JSObject_Slots0) \
    D(OBJECT0_BACKGROUND,  Object,      JSObject,          JSObject_Slots0) \
    D(OBJECT2,             Object,      JSObject,          JSObject_Slots2) \
    D(OBJECT2_BACKGROUND,  Object,      JSObject,          JSObject_Slots2) \
    D(OBJECT4,             Object,      JSObject,          JSObject_Slots4) \
    D(OBJECT4_BACKGROUND,  Object,      JSObject,          JSObject_Slots4) \
    D(OBJECT8,             Object,      JSObject,          JSObject_Slots8) \
    D(OBJECT8_BACKGROUND,  Object,      JSObject,          JSObject_Slots8) \
    D(OBJECT12,            Object,      JSObject,          JSObject_Slots12) \
    D(OBJECT12_BACKGROUND, Object,      JSObject,          JSObject_Slots12) \
    D(OBJECT16,            Object,      JSObject,          JSObject_Slots16) \
    D(OBJECT16_BACKGROUND, Object,      JSObject,          JSObject_Slots16)

#define FOR_EACH_NONOBJECT_ALLOCKIND(D) \
 /* AllocKind              TraceKind    TypeName           SizedType */ \
    D(SCRIPT,              Script,      JSScript,          JSScript) \
    D(LAZY_SCRIPT,         LazyScript,  js::LazyScript,    js::LazyScript) \
    D(SHAPE,               Shape,       js::Shape,         js::Shape) \
    D(ACCESSOR_SHAPE,      Shape,       js::AccessorShape, js::AccessorShape) \
    D(BASE_SHAPE,          BaseShape,   js::BaseShape,     js::BaseShape) \
    D(OBJECT_GROUP,        ObjectGroup, js::ObjectGroup,   js::ObjectGroup) \
    D(FAT_INLINE_STRING,   String,      JSFatInlineString, JSFatInlineString) \
    D(STRING,              String,      JSString,          JSString) \
    D(EXTERNAL_STRING,     String,      JSExternalString,  JSExternalString) \
    D(FAT_INLINE_ATOM,     String,      js::FatInlineAtom, js::FatInlineAtom) \
    D(ATOM,                String,      js::NormalAtom,    js::NormalAtom) \
    D(SYMBOL,              Symbol,      JS::Symbol,        JS::Symbol) \
    D(JITCODE,             JitCode,     js::jit::JitCode,  js::jit::JitCode) \
    D(SCOPE,               Scope,       js::Scope,         js::Scope)

#define FOR_EACH_ALLOCKIND(D) \
    FOR_EACH_OBJECT_ALLOCKIND(D) \
    FOR_EACH_NONOBJECT_ALLOCKIND(D)

static_assert(int(AllocKind::FIRST) == 0, "Various places depend on AllocKind starting at 0, "
                                          "please audit them carefully!");
static_assert(int(AllocKind::OBJECT_FIRST) == 0, "Various places depend on AllocKind::OBJECT_FIRST "
                                                 "being 0, please audit them carefully!");

inline bool
IsAllocKind(AllocKind kind)
{
    return kind >= AllocKind::FIRST && kind <= AllocKind::LIMIT;
}

inline bool
IsValidAllocKind(AllocKind kind)
{
    return kind >= AllocKind::FIRST && kind <= AllocKind::LAST;
}

inline bool
IsObjectAllocKind(AllocKind kind)
{
    return kind >= AllocKind::OBJECT_FIRST && kind <= AllocKind::OBJECT_LAST;
}

inline bool
IsShapeAllocKind(AllocKind kind)
{
    return kind == AllocKind::SHAPE || kind == AllocKind::ACCESSOR_SHAPE;
}

// Returns a sequence for use in a range-based for loop,
// to iterate over all alloc kinds.
inline decltype(mozilla::MakeEnumeratedRange(AllocKind::FIRST, AllocKind::LIMIT))
AllAllocKinds()
{
    return mozilla::MakeEnumeratedRange(AllocKind::FIRST, AllocKind::LIMIT);
}

// Returns a sequence for use in a range-based for loop,
// to iterate over all object alloc kinds.
inline decltype(mozilla::MakeEnumeratedRange(AllocKind::OBJECT_FIRST, AllocKind::OBJECT_LIMIT))
ObjectAllocKinds()
{
    return mozilla::MakeEnumeratedRange(AllocKind::OBJECT_FIRST, AllocKind::OBJECT_LIMIT);
}

// Returns a sequence for use in a range-based for loop,
// to iterate over alloc kinds from |first| to |limit|, exclusive.
inline decltype(mozilla::MakeEnumeratedRange(AllocKind::FIRST, AllocKind::LIMIT))
SomeAllocKinds(AllocKind first = AllocKind::FIRST, AllocKind limit = AllocKind::LIMIT)
{
    MOZ_ASSERT(IsAllocKind(first), "|first| is not a valid AllocKind!");
    MOZ_ASSERT(IsAllocKind(limit), "|limit| is not a valid AllocKind!");
    return mozilla::MakeEnumeratedRange(first, limit);
}

// AllAllocKindArray<ValueType> gives an enumerated array of ValueTypes,
// with each index corresponding to a particular alloc kind.
template<typename ValueType> using AllAllocKindArray =
    mozilla::EnumeratedArray<AllocKind, AllocKind::LIMIT, ValueType>;

// ObjectAllocKindArray<ValueType> gives an enumerated array of ValueTypes,
// with each index corresponding to a particular object alloc kind.
template<typename ValueType> using ObjectAllocKindArray =
    mozilla::EnumeratedArray<AllocKind, AllocKind::OBJECT_LIMIT, ValueType>;

static inline JS::TraceKind
MapAllocToTraceKind(AllocKind kind)
{
    static const JS::TraceKind map[] = {
#define EXPAND_ELEMENT(allocKind, traceKind, type, sizedType) \
        JS::TraceKind::traceKind,
FOR_EACH_ALLOCKIND(EXPAND_ELEMENT)
#undef EXPAND_ELEMENT
    };

    static_assert(MOZ_ARRAY_LENGTH(map) == size_t(AllocKind::LIMIT),
                  "AllocKind-to-TraceKind mapping must be in sync");
    return map[size_t(kind)];
}

/*
 * This must be an upper bound, but we do not need the least upper bound, so
 * we just exclude non-background objects.
 */
static const size_t MAX_BACKGROUND_FINALIZE_KINDS =
    size_t(AllocKind::LIMIT) - size_t(AllocKind::OBJECT_LIMIT) / 2;

class TenuredCell;

// A GC cell is the base class for all GC things.
struct Cell
{
  public:
    MOZ_ALWAYS_INLINE bool isTenured() const { return !IsInsideNursery(this); }
    MOZ_ALWAYS_INLINE const TenuredCell& asTenured() const;
    MOZ_ALWAYS_INLINE TenuredCell& asTenured();

    inline JSRuntime* runtimeFromMainThread() const;
    inline JS::shadow::Runtime* shadowRuntimeFromMainThread() const;

    // Note: Unrestricted access to the runtime of a GC thing from an arbitrary
    // thread can easily lead to races. Use this method very carefully.
    inline JSRuntime* runtimeFromAnyThread() const;
    inline JS::shadow::Runtime* shadowRuntimeFromAnyThread() const;

    // May be overridden by GC thing kinds that have a compartment pointer.
    inline JSCompartment* maybeCompartment() const { return nullptr; }

    inline StoreBuffer* storeBuffer() const;

    inline JS::TraceKind getTraceKind() const;

    static MOZ_ALWAYS_INLINE bool needWriteBarrierPre(JS::Zone* zone);

    template <class T>
    inline bool is() const {
        return getTraceKind() == JS::MapTypeToTraceKind<T>::kind;
    }

    template<class T>
    inline T* as() {
        MOZ_ASSERT(this->is<T>());
        return static_cast<T*>(this);
    }

    template <class T>
    inline const T* as() const {
        MOZ_ASSERT(this->is<T>());
        return static_cast<const T*>(this);
    }

#ifdef DEBUG
    inline bool isAligned() const;
    void dump(FILE* fp) const;
    void dump() const;
#endif

  protected:
    inline uintptr_t address() const;
    inline Chunk* chunk() const;
} JS_HAZ_GC_THING;

// A GC TenuredCell gets behaviors that are valid for things in the Tenured
// heap, such as access to the arena and mark bits.
class TenuredCell : public Cell
{
  public:
    // Construct a TenuredCell from a void*, making various sanity assertions.
    static MOZ_ALWAYS_INLINE TenuredCell* fromPointer(void* ptr);
    static MOZ_ALWAYS_INLINE const TenuredCell* fromPointer(const void* ptr);

    // Mark bit management.
    MOZ_ALWAYS_INLINE bool isMarked(uint32_t color = BLACK) const;
    // The return value indicates if the cell went from unmarked to marked.
    MOZ_ALWAYS_INLINE bool markIfUnmarked(uint32_t color = BLACK) const;
    MOZ_ALWAYS_INLINE void unmark(uint32_t color) const;
    MOZ_ALWAYS_INLINE void copyMarkBitsFrom(const TenuredCell* src);

    // Note: this is in TenuredCell because JSObject subclasses are sometimes
    // used tagged.
    static MOZ_ALWAYS_INLINE bool isNullLike(const Cell* thing) { return !thing; }

    // Access to the arena.
    inline Arena* arena() const;
    inline AllocKind getAllocKind() const;
    inline JS::TraceKind getTraceKind() const;
    inline JS::Zone* zone() const;
    inline JS::Zone* zoneFromAnyThread() const;
    inline bool isInsideZone(JS::Zone* zone) const;

    MOZ_ALWAYS_INLINE JS::shadow::Zone* shadowZone() const {
        return JS::shadow::Zone::asShadowZone(zone());
    }
    MOZ_ALWAYS_INLINE JS::shadow::Zone* shadowZoneFromAnyThread() const {
        return JS::shadow::Zone::asShadowZone(zoneFromAnyThread());
    }

    static MOZ_ALWAYS_INLINE void readBarrier(TenuredCell* thing);
    static MOZ_ALWAYS_INLINE void writeBarrierPre(TenuredCell* thing);

    static MOZ_ALWAYS_INLINE void writeBarrierPost(void* cellp, TenuredCell* prior,
                                                   TenuredCell* next);

    // Default implementation for kinds that don't require fixup.
    void fixupAfterMovingGC() {}

#ifdef DEBUG
    inline bool isAligned() const;
#endif
};

/* Cells are aligned to CellShift, so the largest tagged null pointer is: */
const uintptr_t LargestTaggedNullCellPointer = (1 << CellShift) - 1;

constexpr size_t
DivideAndRoundUp(size_t numerator, size_t divisor) {
    return (numerator + divisor - 1) / divisor;
}

const size_t ArenaCellCount = ArenaSize / CellSize;
static_assert(ArenaSize % CellSize == 0, "Arena size must be a multiple of cell size");

/*
 * The mark bitmap has one bit per each GC cell. For multi-cell GC things this
 * wastes space but allows to avoid expensive devisions by thing's size when
 * accessing the bitmap. In addition this allows to use some bits for colored
 * marking during the cycle GC.
 */
const size_t ArenaBitmapBits = ArenaCellCount;
const size_t ArenaBitmapBytes = DivideAndRoundUp(ArenaBitmapBits, 8);
const size_t ArenaBitmapWords = DivideAndRoundUp(ArenaBitmapBits, JS_BITS_PER_WORD);

/*
 * A FreeSpan represents a contiguous sequence of free cells in an Arena. It
 * can take two forms.
 *
 * - In an empty span, |first| and |last| are both zero.
 *
 * - In a non-empty span, |first| is the address of the first free thing in the
 *   span, and |last| is the address of the last free thing in the span.
 *   Furthermore, the memory pointed to by |last| holds a FreeSpan structure
 *   that points to the next span (which may be empty); this works because
 *   sizeof(FreeSpan) is less than the smallest thingSize.
 */
class FreeSpan
{
    friend class Arena;
    friend class ArenaCellIterImpl;

    uint16_t first;
    uint16_t last;

  public:
    // This inits just |first| and |last|; if the span is non-empty it doesn't
    // do anything with the next span stored at |last|.
    void initBounds(uintptr_t firstArg, uintptr_t lastArg, const Arena* arena) {
        checkRange(firstArg, lastArg, arena);
        first = firstArg;
        last = lastArg;
    }

    void initAsEmpty() {
        first = 0;
        last = 0;
    }

    // This sets |first| and |last|, and also sets the next span stored at
    // |last| as empty. (As a result, |firstArg| and |lastArg| cannot represent
    // an empty span.)
    void initFinal(uintptr_t firstArg, uintptr_t lastArg, const Arena* arena) {
        initBounds(firstArg, lastArg, arena);
        FreeSpan* last = nextSpanUnchecked(arena);
        last->initAsEmpty();
        checkSpan(arena);
    }

    bool isEmpty() const {
        return !first;
    }

    Arena* getArenaUnchecked() { return reinterpret_cast<Arena*>(this); }
    inline Arena* getArena();

    static size_t offsetOfFirst() {
        return offsetof(FreeSpan, first);
    }

    static size_t offsetOfLast() {
        return offsetof(FreeSpan, last);
    }

    // Like nextSpan(), but no checking of the following span is done.
    FreeSpan* nextSpanUnchecked(const Arena* arena) const {
        MOZ_ASSERT(arena && !isEmpty());
        return reinterpret_cast<FreeSpan*>(uintptr_t(arena) + last);
    }

    const FreeSpan* nextSpan(const Arena* arena) const {
        checkSpan(arena);
        return nextSpanUnchecked(arena);
    }

    MOZ_ALWAYS_INLINE TenuredCell* allocate(size_t thingSize) {
        // Eschew the usual checks, because this might be the placeholder span.
        // If this is somehow an invalid, non-empty span, checkSpan() will catch it.
        Arena* arena = getArenaUnchecked();
        checkSpan(arena);
        uintptr_t thing = uintptr_t(arena) + first;
        if (first < last) {
            // We have space for at least two more things, so do a simple bump-allocate.
            first += thingSize;
        } else if (MOZ_LIKELY(first)) {
            // The last space points to the next free span (which may be empty).
            const FreeSpan* next = nextSpan(arena);
            first = next->first;
            last = next->last;
        } else {
            return nullptr; // The span is empty.
        }
        checkSpan(arena);
        JS_EXTRA_POISON(reinterpret_cast<void*>(thing), JS_ALLOCATED_TENURED_PATTERN, thingSize);
        MemProfiler::SampleTenured(reinterpret_cast<void*>(thing), thingSize);
        return reinterpret_cast<TenuredCell*>(thing);
    }

    inline void checkSpan(const Arena* arena) const;
    inline void checkRange(uintptr_t first, uintptr_t last, const Arena* arena) const;
};

/*
 * Arenas are the allocation units of the tenured heap in the GC. An arena
 * is 4kiB in size and 4kiB-aligned. It starts with several header fields
 * followed by some bytes of padding. The remainder of the arena is filled
 * with GC things of a particular AllocKind. The padding ensures that the
 * GC thing array ends exactly at the end of the arena:
 *
 * <----------------------------------------------> = ArenaSize bytes
 * +---------------+---------+----+----+-----+----+
 * | header fields | padding | T0 | T1 | ... | Tn |
 * +---------------+---------+----+----+-----+----+
 * <-------------------------> = first thing offset
 */
class Arena
{
    static JS_FRIEND_DATA(const uint32_t) ThingSizes[];
    static JS_FRIEND_DATA(const uint32_t) FirstThingOffsets[];
    static JS_FRIEND_DATA(const uint32_t) ThingsPerArena[];

    /*
     * The first span of free things in the arena. Most of these spans are
     * stored as offsets in free regions of the data array, and most operations
     * on FreeSpans take an Arena pointer for safety. However, the FreeSpans
     * used for allocation are stored here, at the start of an Arena, and use
     * their own address to grab the next span within the same Arena.
     */
    FreeSpan firstFreeSpan;

  public:
    /*
     * The zone that this Arena is contained within, when allocated. The offset
     * of this field must match the ArenaZoneOffset stored in js/HeapAPI.h,
     * as is statically asserted below.
     */
    JS::Zone* zone;

    /*
     * Arena::next has two purposes: when unallocated, it points to the next
     * available Arena. When allocated, it points to the next Arena in the same
     * zone and with the same alloc kind.
     */
    Arena* next;

  private:
    /*
     * One of the AllocKind constants or AllocKind::LIMIT when the arena does
     * not contain any GC things and is on the list of empty arenas in the GC
     * chunk.
     *
     * We use 8 bits for the alloc kind so the compiler can use byte-level
     * memory instructions to access it.
     */
    size_t allocKind : 8;

  public:
    /*
     * When collecting we sometimes need to keep an auxillary list of arenas,
     * for which we use the following fields. This happens for several reasons:
     *
     * When recursive marking uses too much stack, the marking is delayed and
     * the corresponding arenas are put into a stack. To distinguish the bottom
     * of the stack from the arenas not present in the stack we use the
     * markOverflow flag to tag arenas on the stack.
     *
     * Delayed marking is also used for arenas that we allocate into during an
     * incremental GC. In this case, we intend to mark all the objects in the
     * arena, and it's faster to do this marking in bulk.
     *
     * When sweeping we keep track of which arenas have been allocated since
     * the end of the mark phase. This allows us to tell whether a pointer to
     * an unmarked object is yet to be finalized or has already been
     * reallocated. We set the allocatedDuringIncremental flag for this and
     * clear it at the end of the sweep phase.
     *
     * To minimize the size of the header fields we record the next linkage as
     * address() >> ArenaShift and pack it with the allocKind and the flags.
     */
    size_t hasDelayedMarking : 1;
    size_t allocatedDuringIncremental : 1;
    size_t markOverflow : 1;
    size_t auxNextLink : JS_BITS_PER_WORD - 8 - 1 - 1 - 1;
    static_assert(ArenaShift >= 8 + 1 + 1 + 1,
                  "Arena::auxNextLink packing assumes that ArenaShift has "
                  "enough bits to cover allocKind and hasDelayedMarking.");

    /*
     * If non-null, points to an ArenaCellSet that represents the set of cells
     * in this arena that are in the nursery's store buffer.
     */
    ArenaCellSet* bufferedCells;

    /*
     * The size of data should be |ArenaSize - offsetof(data)|, but the offset
     * is not yet known to the compiler, so we do it by hand. |firstFreeSpan|
     * takes up 8 bytes on 64-bit due to alignment requirements; the rest are
     * obvious. This constant is stored in js/HeapAPI.h.
     */
    uint8_t data[ArenaSize - ArenaHeaderSize];

    void init(JS::Zone* zoneArg, AllocKind kind);

    // Sets |firstFreeSpan| to the Arena's entire valid range, and
    // also sets the next span stored at |firstFreeSpan.last| as empty.
    void setAsFullyUnused() {
        AllocKind kind = getAllocKind();
        firstFreeSpan.first = firstThingOffset(kind);
        firstFreeSpan.last = lastThingOffset(kind);
        FreeSpan* last = firstFreeSpan.nextSpanUnchecked(this);
        last->initAsEmpty();
    }

    void setAsNotAllocated() {
        firstFreeSpan.initAsEmpty();
        zone = nullptr;
        allocKind = size_t(AllocKind::LIMIT);
        hasDelayedMarking = 0;
        allocatedDuringIncremental = 0;
        markOverflow = 0;
        auxNextLink = 0;
        bufferedCells = nullptr;
    }

    uintptr_t address() const {
        checkAddress();
        return uintptr_t(this);
    }

    inline void checkAddress() const;

    inline Chunk* chunk() const;

    bool allocated() const {
        MOZ_ASSERT(IsAllocKind(AllocKind(allocKind)));
        return IsValidAllocKind(AllocKind(allocKind));
    }

    AllocKind getAllocKind() const {
        MOZ_ASSERT(allocated());
        return AllocKind(allocKind);
    }

    FreeSpan* getFirstFreeSpan() { return &firstFreeSpan; }

    static size_t thingSize(AllocKind kind) { return ThingSizes[size_t(kind)]; }
    static size_t thingsPerArena(AllocKind kind) { return ThingsPerArena[size_t(kind)]; }
    static size_t thingsSpan(AllocKind kind) { return thingsPerArena(kind) * thingSize(kind); }

    static size_t firstThingOffset(AllocKind kind) { return FirstThingOffsets[size_t(kind)]; }
    static size_t lastThingOffset(AllocKind kind) { return ArenaSize - thingSize(kind); }

    size_t getThingSize() const { return thingSize(getAllocKind()); }
    size_t getThingsPerArena() const { return thingsPerArena(getAllocKind()); }
    size_t getThingsSpan() const { return getThingsPerArena() * getThingSize(); }

    uintptr_t thingsStart() const { return address() + firstThingOffset(getAllocKind()); }
    uintptr_t thingsEnd() const { return address() + ArenaSize; }

    bool isEmpty() const {
        // Arena is empty if its first span covers the whole arena.
        firstFreeSpan.checkSpan(this);
        AllocKind kind = getAllocKind();
        return firstFreeSpan.first == firstThingOffset(kind) &&
               firstFreeSpan.last == lastThingOffset(kind);
    }

    bool hasFreeThings() const { return !firstFreeSpan.isEmpty(); }

    size_t numFreeThings(size_t thingSize) const {
        firstFreeSpan.checkSpan(this);
        size_t numFree = 0;
        const FreeSpan* span = &firstFreeSpan;
        for (; !span->isEmpty(); span = span->nextSpan(this))
            numFree += (span->last - span->first) / thingSize + 1;
        return numFree;
    }

    size_t countFreeCells() { return numFreeThings(getThingSize()); }
    size_t countUsedCells() { return getThingsPerArena() - countFreeCells(); }

    bool inFreeList(uintptr_t thing) {
        uintptr_t base = address();
        const FreeSpan* span = &firstFreeSpan;
        for (; !span->isEmpty(); span = span->nextSpan(this)) {
            /* If the thing comes before the current span, it's not free. */
            if (thing < base + span->first)
                return false;

            /* If we find it before the end of the span, it's free. */
            if (thing <= base + span->last)
                return true;
        }
        return false;
    }

    static bool isAligned(uintptr_t thing, size_t thingSize) {
        /* Things ends at the arena end. */
        uintptr_t tailOffset = ArenaSize - (thing & ArenaMask);
        return tailOffset % thingSize == 0;
    }

    Arena* getNextDelayedMarking() const {
        MOZ_ASSERT(hasDelayedMarking);
        return reinterpret_cast<Arena*>(auxNextLink << ArenaShift);
    }

    void setNextDelayedMarking(Arena* arena) {
        MOZ_ASSERT(!(uintptr_t(arena) & ArenaMask));
        MOZ_ASSERT(!auxNextLink && !hasDelayedMarking);
        hasDelayedMarking = 1;
        if (arena)
            auxNextLink = arena->address() >> ArenaShift;
    }

    void unsetDelayedMarking() {
        MOZ_ASSERT(hasDelayedMarking);
        hasDelayedMarking = 0;
        auxNextLink = 0;
    }

    Arena* getNextAllocDuringSweep() const {
        MOZ_ASSERT(allocatedDuringIncremental);
        return reinterpret_cast<Arena*>(auxNextLink << ArenaShift);
    }

    void setNextAllocDuringSweep(Arena* arena) {
        MOZ_ASSERT(!(uintptr_t(arena) & ArenaMask));
        MOZ_ASSERT(!auxNextLink && !allocatedDuringIncremental);
        allocatedDuringIncremental = 1;
        if (arena)
            auxNextLink = arena->address() >> ArenaShift;
    }

    void unsetAllocDuringSweep() {
        MOZ_ASSERT(allocatedDuringIncremental);
        allocatedDuringIncremental = 0;
        auxNextLink = 0;
    }

    template <typename T>
    size_t finalize(FreeOp* fop, AllocKind thingKind, size_t thingSize);

    static void staticAsserts();

    void unmarkAll();

    static size_t offsetOfBufferedCells() {
        return offsetof(Arena, bufferedCells);
    }
};

static_assert(ArenaZoneOffset == offsetof(Arena, zone),
              "The hardcoded API zone offset must match the actual offset.");

static_assert(sizeof(Arena) == ArenaSize,
              "ArenaSize must match the actual size of the Arena structure.");

static_assert(offsetof(Arena, data) == ArenaHeaderSize,
              "ArenaHeaderSize must match the actual size of the header fields.");

inline Arena*
FreeSpan::getArena()
{
    Arena* arena = getArenaUnchecked();
    arena->checkAddress();
    return arena;
}

inline void
FreeSpan::checkSpan(const Arena* arena) const
{
#ifdef DEBUG
    if (!first) {
        MOZ_ASSERT(!first && !last);
        return;
    }

    arena->checkAddress();
    checkRange(first, last, arena);

    // If there's a following span, it must have a higher address,
    // and the gap must be at least 2 * thingSize.
    const FreeSpan* next = nextSpanUnchecked(arena);
    if (next->first) {
        checkRange(next->first, next->last, arena);
        size_t thingSize = arena->getThingSize();
        MOZ_ASSERT(last + 2 * thingSize <= next->first);
    }
#endif
}

inline void
FreeSpan::checkRange(uintptr_t first, uintptr_t last, const Arena* arena) const
{
#ifdef DEBUG
    MOZ_ASSERT(arena);
    MOZ_ASSERT(first <= last);
    AllocKind thingKind = arena->getAllocKind();
    MOZ_ASSERT(first >= Arena::firstThingOffset(thingKind));
    MOZ_ASSERT(last <= Arena::lastThingOffset(thingKind));
    MOZ_ASSERT((last - first) % Arena::thingSize(thingKind) == 0);
#endif
}

/*
 * The tail of the chunk info is shared between all chunks in the system, both
 * nursery and tenured. This structure is locatable from any GC pointer by
 * aligning to 1MiB.
 */
struct ChunkTrailer
{
    /* Construct a Nursery ChunkTrailer. */
    ChunkTrailer(JSRuntime* rt, StoreBuffer* sb)
      : location(ChunkLocation::Nursery), storeBuffer(sb), runtime(rt)
    {}

    /* Construct a Tenured heap ChunkTrailer. */
    explicit ChunkTrailer(JSRuntime* rt)
      : location(ChunkLocation::TenuredHeap), storeBuffer(nullptr), runtime(rt)
    {}

  public:
    /* The index the chunk in the nursery, or LocationTenuredHeap. */
    ChunkLocation   location;
    uint32_t        padding;

    /* The store buffer for writes to things in this chunk or nullptr. */
    StoreBuffer*    storeBuffer;

    /* This provides quick access to the runtime from absolutely anywhere. */
    JSRuntime*      runtime;
};

static_assert(sizeof(ChunkTrailer) == ChunkTrailerSize,
              "ChunkTrailer size must match the API defined size.");

/* The chunk header (located at the end of the chunk to preserve arena alignment). */
struct ChunkInfo
{
    void init() {
        next = prev = nullptr;
    }

  private:
    friend class ChunkPool;
    Chunk*          next;
    Chunk*          prev;

  public:
    /* Free arenas are linked together with arena.next. */
    Arena*          freeArenasHead;

#if JS_BITS_PER_WORD == 32
    /*
     * Calculating sizes and offsets is simpler if sizeof(ChunkInfo) is
     * architecture-independent.
     */
    char            padding[24];
#endif

    /*
     * Decommitted arenas are tracked by a bitmap in the chunk header. We use
     * this offset to start our search iteration close to a decommitted arena
     * that we can allocate.
     */
    uint32_t        lastDecommittedArenaOffset;

    /* Number of free arenas, either committed or decommitted. */
    uint32_t        numArenasFree;

    /* Number of free, committed arenas. */
    uint32_t        numArenasFreeCommitted;
};

/*
 * Calculating ArenasPerChunk:
 *
 * In order to figure out how many Arenas will fit in a chunk, we need to know
 * how much extra space is available after we allocate the header data. This
 * is a problem because the header size depends on the number of arenas in the
 * chunk. The two dependent fields are bitmap and decommittedArenas.
 *
 * For the mark bitmap, we know that each arena will use a fixed number of full
 * bytes: ArenaBitmapBytes. The full size of the header data is this number
 * multiplied by the eventual number of arenas we have in the header. We,
 * conceptually, distribute this header data among the individual arenas and do
 * not include it in the header. This way we do not have to worry about its
 * variable size: it gets attached to the variable number we are computing.
 *
 * For the decommitted arena bitmap, we only have 1 bit per arena, so this
 * technique will not work. Instead, we observe that we do not have enough
 * header info to fill 8 full arenas: it is currently 4 on 64bit, less on
 * 32bit. Thus, with current numbers, we need 64 bytes for decommittedArenas.
 * This will not become 63 bytes unless we double the data required in the
 * header. Therefore, we just compute the number of bytes required to track
 * every possible arena and do not worry about slop bits, since there are too
 * few to usefully allocate.
 *
 * To actually compute the number of arenas we can allocate in a chunk, we
 * divide the amount of available space less the header info (not including
 * the mark bitmap which is distributed into the arena size) by the size of
 * the arena (with the mark bitmap bytes it uses).
 */
const size_t BytesPerArenaWithHeader = ArenaSize + ArenaBitmapBytes;
const size_t ChunkDecommitBitmapBytes = ChunkSize / ArenaSize / JS_BITS_PER_BYTE;
const size_t ChunkBytesAvailable = ChunkSize - sizeof(ChunkTrailer) - sizeof(ChunkInfo) - ChunkDecommitBitmapBytes;
const size_t ArenasPerChunk = ChunkBytesAvailable / BytesPerArenaWithHeader;

#ifdef JS_GC_SMALL_CHUNK_SIZE
static_assert(ArenasPerChunk == 62, "Do not accidentally change our heap's density.");
#else
static_assert(ArenasPerChunk == 252, "Do not accidentally change our heap's density.");
#endif

/* A chunk bitmap contains enough mark bits for all the cells in a chunk. */
struct ChunkBitmap
{
    volatile uintptr_t bitmap[ArenaBitmapWords * ArenasPerChunk];

  public:
    ChunkBitmap() { }

    MOZ_ALWAYS_INLINE void getMarkWordAndMask(const Cell* cell, uint32_t color,
                                              uintptr_t** wordp, uintptr_t* maskp)
    {
        detail::GetGCThingMarkWordAndMask(uintptr_t(cell), color, wordp, maskp);
    }

    MOZ_ALWAYS_INLINE MOZ_TSAN_BLACKLIST bool isMarked(const Cell* cell, uint32_t color) {
        uintptr_t* word, mask;
        getMarkWordAndMask(cell, color, &word, &mask);
        return *word & mask;
    }

    // The return value indicates if the cell went from unmarked to marked.
    MOZ_ALWAYS_INLINE bool markIfUnmarked(const Cell* cell, uint32_t color) {
        uintptr_t* word, mask;
        getMarkWordAndMask(cell, BLACK, &word, &mask);
        if (*word & mask)
            return false;
        *word |= mask;
        if (color != BLACK) {
            /*
             * We use getMarkWordAndMask to recalculate both mask and word as
             * doing just mask << color may overflow the mask.
             */
            getMarkWordAndMask(cell, color, &word, &mask);
            if (*word & mask)
                return false;
            *word |= mask;
        }
        return true;
    }

    MOZ_ALWAYS_INLINE void unmark(const Cell* cell, uint32_t color) {
        uintptr_t* word, mask;
        getMarkWordAndMask(cell, color, &word, &mask);
        *word &= ~mask;
    }

    MOZ_ALWAYS_INLINE void copyMarkBit(Cell* dst, const TenuredCell* src, uint32_t color) {
        uintptr_t* word, mask;
        getMarkWordAndMask(dst, color, &word, &mask);
        *word = (*word & ~mask) | (src->isMarked(color) ? mask : 0);
    }

    void clear() {
        memset((void*)bitmap, 0, sizeof(bitmap));
    }

    uintptr_t* arenaBits(Arena* arena) {
        static_assert(ArenaBitmapBits == ArenaBitmapWords * JS_BITS_PER_WORD,
                      "We assume that the part of the bitmap corresponding to the arena "
                      "has the exact number of words so we do not need to deal with a word "
                      "that covers bits from two arenas.");

        uintptr_t* word, unused;
        getMarkWordAndMask(reinterpret_cast<Cell*>(arena->address()), BLACK, &word, &unused);
        return word;
    }
};

static_assert(ArenaBitmapBytes * ArenasPerChunk == sizeof(ChunkBitmap),
              "Ensure our ChunkBitmap actually covers all arenas.");
static_assert(js::gc::ChunkMarkBitmapBits == ArenaBitmapBits * ArenasPerChunk,
              "Ensure that the mark bitmap has the right number of bits.");

typedef BitArray<ArenasPerChunk> PerArenaBitmap;

const size_t ChunkPadSize = ChunkSize
                            - (sizeof(Arena) * ArenasPerChunk)
                            - sizeof(ChunkBitmap)
                            - sizeof(PerArenaBitmap)
                            - sizeof(ChunkInfo)
                            - sizeof(ChunkTrailer);
static_assert(ChunkPadSize < BytesPerArenaWithHeader,
              "If the chunk padding is larger than an arena, we should have one more arena.");

/*
 * Chunks contain arenas and associated data structures (mark bitmap, delayed
 * marking state).
 */
struct Chunk
{
    Arena           arenas[ArenasPerChunk];

    /* Pad to full size to ensure cache alignment of ChunkInfo. */
    uint8_t         padding[ChunkPadSize];

    ChunkBitmap     bitmap;
    PerArenaBitmap  decommittedArenas;
    ChunkInfo       info;
    ChunkTrailer    trailer;

    static Chunk* fromAddress(uintptr_t addr) {
        addr &= ~ChunkMask;
        return reinterpret_cast<Chunk*>(addr);
    }

    static bool withinValidRange(uintptr_t addr) {
        uintptr_t offset = addr & ChunkMask;
        return Chunk::fromAddress(addr)->isNurseryChunk()
               ? offset < ChunkSize - sizeof(ChunkTrailer)
               : offset < ArenasPerChunk * ArenaSize;
    }

    static size_t arenaIndex(uintptr_t addr) {
        MOZ_ASSERT(!Chunk::fromAddress(addr)->isNurseryChunk());
        MOZ_ASSERT(withinValidRange(addr));
        return (addr & ChunkMask) >> ArenaShift;
    }

    uintptr_t address() const {
        uintptr_t addr = reinterpret_cast<uintptr_t>(this);
        MOZ_ASSERT(!(addr & ChunkMask));
        return addr;
    }

    bool unused() const {
        return info.numArenasFree == ArenasPerChunk;
    }

    bool hasAvailableArenas() const {
        return info.numArenasFree != 0;
    }

    bool isNurseryChunk() const {
        return trailer.storeBuffer;
    }

    Arena* allocateArena(JSRuntime* rt, JS::Zone* zone, AllocKind kind, const AutoLockGC& lock);

    void releaseArena(JSRuntime* rt, Arena* arena, const AutoLockGC& lock);
    void recycleArena(Arena* arena, SortedArenaList& dest, size_t thingsPerArena);

    MOZ_MUST_USE bool decommitOneFreeArena(JSRuntime* rt, AutoLockGC& lock);
    void decommitAllArenasWithoutUnlocking(const AutoLockGC& lock);

    static Chunk* allocate(JSRuntime* rt);
    void init(JSRuntime* rt);

  private:
    void decommitAllArenas(JSRuntime* rt);

    /* Search for a decommitted arena to allocate. */
    unsigned findDecommittedArenaOffset();
    Arena* fetchNextDecommittedArena();

    void addArenaToFreeList(JSRuntime* rt, Arena* arena);
    void addArenaToDecommittedList(JSRuntime* rt, const Arena* arena);

    void updateChunkListAfterAlloc(JSRuntime* rt, const AutoLockGC& lock);
    void updateChunkListAfterFree(JSRuntime* rt, const AutoLockGC& lock);

  public:
    /* Unlink and return the freeArenasHead. */
    Arena* fetchNextFreeArena(JSRuntime* rt);
};

static_assert(sizeof(Chunk) == ChunkSize,
              "Ensure the hardcoded chunk size definition actually matches the struct.");
static_assert(js::gc::ChunkMarkBitmapOffset == offsetof(Chunk, bitmap),
              "The hardcoded API bitmap offset must match the actual offset.");
static_assert(js::gc::ChunkRuntimeOffset == offsetof(Chunk, trailer) +
                                            offsetof(ChunkTrailer, runtime),
              "The hardcoded API runtime offset must match the actual offset.");
static_assert(js::gc::ChunkLocationOffset == offsetof(Chunk, trailer) +
                                             offsetof(ChunkTrailer, location),
              "The hardcoded API location offset must match the actual offset.");

/*
 * Tracks the used sizes for owned heap data and automatically maintains the
 * memory usage relationship between GCRuntime and Zones.
 */
class HeapUsage
{
    /*
     * A heap usage that contains our parent's heap usage, or null if this is
     * the top-level usage container.
     */
    HeapUsage* parent_;

    /*
     * The approximate number of bytes in use on the GC heap, to the nearest
     * ArenaSize. This does not include any malloc data. It also does not
     * include not-actively-used addresses that are still reserved at the OS
     * level for GC usage. It is atomic because it is updated by both the main
     * and GC helper threads.
     */
    mozilla::Atomic<size_t, mozilla::ReleaseAcquire> gcBytes_;

  public:
    explicit HeapUsage(HeapUsage* parent)
      : parent_(parent),
        gcBytes_(0)
    {}

    size_t gcBytes() const { return gcBytes_; }

    void addGCArena() {
        gcBytes_ += ArenaSize;
        if (parent_)
            parent_->addGCArena();
    }
    void removeGCArena() {
        MOZ_ASSERT(gcBytes_ >= ArenaSize);
        gcBytes_ -= ArenaSize;
        if (parent_)
            parent_->removeGCArena();
    }

    /* Pair to adoptArenas. Adopts the attendant usage statistics. */
    void adopt(HeapUsage& other) {
        gcBytes_ += other.gcBytes_;
        other.gcBytes_ = 0;
    }
};

inline void
Arena::checkAddress() const
{
    mozilla::DebugOnly<uintptr_t> addr = uintptr_t(this);
    MOZ_ASSERT(addr);
    MOZ_ASSERT(!(addr & ArenaMask));
    MOZ_ASSERT(Chunk::withinValidRange(addr));
}

inline Chunk*
Arena::chunk() const
{
    return Chunk::fromAddress(address());
}

static void
AssertValidColor(const TenuredCell* thing, uint32_t color)
{
#ifdef DEBUG
    Arena* arena = thing->arena();
    MOZ_ASSERT(color < arena->getThingSize() / CellSize);
#endif
}

MOZ_ALWAYS_INLINE const TenuredCell&
Cell::asTenured() const
{
    MOZ_ASSERT(isTenured());
    return *static_cast<const TenuredCell*>(this);
}

MOZ_ALWAYS_INLINE TenuredCell&
Cell::asTenured()
{
    MOZ_ASSERT(isTenured());
    return *static_cast<TenuredCell*>(this);
}

inline JSRuntime*
Cell::runtimeFromMainThread() const
{
    JSRuntime* rt = chunk()->trailer.runtime;
    MOZ_ASSERT(CurrentThreadCanAccessRuntime(rt));
    return rt;
}

inline JS::shadow::Runtime*
Cell::shadowRuntimeFromMainThread() const
{
    return reinterpret_cast<JS::shadow::Runtime*>(runtimeFromMainThread());
}

inline JSRuntime*
Cell::runtimeFromAnyThread() const
{
    return chunk()->trailer.runtime;
}

inline JS::shadow::Runtime*
Cell::shadowRuntimeFromAnyThread() const
{
    return reinterpret_cast<JS::shadow::Runtime*>(runtimeFromAnyThread());
}

inline uintptr_t
Cell::address() const
{
    uintptr_t addr = uintptr_t(this);
    MOZ_ASSERT(addr % CellSize == 0);
    MOZ_ASSERT(Chunk::withinValidRange(addr));
    return addr;
}

Chunk*
Cell::chunk() const
{
    uintptr_t addr = uintptr_t(this);
    MOZ_ASSERT(addr % CellSize == 0);
    addr &= ~ChunkMask;
    return reinterpret_cast<Chunk*>(addr);
}

inline StoreBuffer*
Cell::storeBuffer() const
{
    return chunk()->trailer.storeBuffer;
}

inline JS::TraceKind
Cell::getTraceKind() const
{
    return isTenured() ? asTenured().getTraceKind() : JS::TraceKind::Object;
}

inline bool
InFreeList(Arena* arena, void* thing)
{
    uintptr_t addr = reinterpret_cast<uintptr_t>(thing);
    MOZ_ASSERT(Arena::isAligned(addr, arena->getThingSize()));
    return arena->inFreeList(addr);
}

/* static */ MOZ_ALWAYS_INLINE bool
Cell::needWriteBarrierPre(JS::Zone* zone) {
    return JS::shadow::Zone::asShadowZone(zone)->needsIncrementalBarrier();
}

/* static */ MOZ_ALWAYS_INLINE TenuredCell*
TenuredCell::fromPointer(void* ptr)
{
    MOZ_ASSERT(static_cast<TenuredCell*>(ptr)->isTenured());
    return static_cast<TenuredCell*>(ptr);
}

/* static */ MOZ_ALWAYS_INLINE const TenuredCell*
TenuredCell::fromPointer(const void* ptr)
{
    MOZ_ASSERT(static_cast<const TenuredCell*>(ptr)->isTenured());
    return static_cast<const TenuredCell*>(ptr);
}

bool
TenuredCell::isMarked(uint32_t color /* = BLACK */) const
{
    MOZ_ASSERT(arena()->allocated());
    AssertValidColor(this, color);
    return chunk()->bitmap.isMarked(this, color);
}

bool
TenuredCell::markIfUnmarked(uint32_t color /* = BLACK */) const
{
    AssertValidColor(this, color);
    return chunk()->bitmap.markIfUnmarked(this, color);
}

void
TenuredCell::unmark(uint32_t color) const
{
    MOZ_ASSERT(color != BLACK);
    AssertValidColor(this, color);
    chunk()->bitmap.unmark(this, color);
}

void
TenuredCell::copyMarkBitsFrom(const TenuredCell* src)
{
    ChunkBitmap& bitmap = chunk()->bitmap;
    bitmap.copyMarkBit(this, src, BLACK);
    bitmap.copyMarkBit(this, src, GRAY);
}

inline Arena*
TenuredCell::arena() const
{
    MOZ_ASSERT(isTenured());
    uintptr_t addr = address();
    addr &= ~ArenaMask;
    return reinterpret_cast<Arena*>(addr);
}

AllocKind
TenuredCell::getAllocKind() const
{
    return arena()->getAllocKind();
}

JS::TraceKind
TenuredCell::getTraceKind() const
{
    return MapAllocToTraceKind(getAllocKind());
}

JS::Zone*
TenuredCell::zone() const
{
    JS::Zone* zone = arena()->zone;
    MOZ_ASSERT(CurrentThreadCanAccessZone(zone));
    return zone;
}

JS::Zone*
TenuredCell::zoneFromAnyThread() const
{
    return arena()->zone;
}

bool
TenuredCell::isInsideZone(JS::Zone* zone) const
{
    return zone == arena()->zone;
}

/* static */ MOZ_ALWAYS_INLINE void
TenuredCell::readBarrier(TenuredCell* thing)
{
    MOZ_ASSERT(!CurrentThreadIsIonCompiling());
    MOZ_ASSERT(!isNullLike(thing));

    // It would be good if barriers were never triggered during collection, but
    // at the moment this can happen e.g. when rekeying tables containing
    // read-barriered GC things after a moving GC.
    //
    // TODO: Fix this and assert we're not collecting if we're on the main
    // thread.

    JS::shadow::Zone* shadowZone = thing->shadowZoneFromAnyThread();
    if (shadowZone->needsIncrementalBarrier()) {
        // Barriers are only enabled on the main thread and are disabled while collecting.
        MOZ_ASSERT(!RuntimeFromMainThreadIsHeapMajorCollecting(shadowZone));
        Cell* tmp = thing;
        TraceManuallyBarrieredGenericPointerEdge(shadowZone->barrierTracer(), &tmp, "read barrier");
        MOZ_ASSERT(tmp == thing);
    }

    if (thing->isMarked(GRAY)) {
        // There shouldn't be anything marked grey unless we're on the main thread.
        MOZ_ASSERT(CurrentThreadCanAccessRuntime(thing->runtimeFromAnyThread()));
        if (!RuntimeFromMainThreadIsHeapMajorCollecting(shadowZone))
            UnmarkGrayCellRecursively(thing, thing->getTraceKind());
    }
}

void
AssertSafeToSkipBarrier(TenuredCell* thing);

/* static */ MOZ_ALWAYS_INLINE void
TenuredCell::writeBarrierPre(TenuredCell* thing)
{
    MOZ_ASSERT(!CurrentThreadIsIonCompiling());
    MOZ_ASSERT_IF(thing, !isNullLike(thing));
    if (!thing)
        return;

    JS::shadow::Zone* shadowZone = thing->shadowZoneFromAnyThread();
    if (shadowZone->needsIncrementalBarrier()) {
        MOZ_ASSERT(!RuntimeFromMainThreadIsHeapMajorCollecting(shadowZone));
        Cell* tmp = thing;
        TraceManuallyBarrieredGenericPointerEdge(shadowZone->barrierTracer(), &tmp, "pre barrier");
        MOZ_ASSERT(tmp == thing);
    }
}

static MOZ_ALWAYS_INLINE void
AssertValidToSkipBarrier(TenuredCell* thing)
{
    MOZ_ASSERT(!IsInsideNursery(thing));
    MOZ_ASSERT_IF(thing, MapAllocToTraceKind(thing->getAllocKind()) != JS::TraceKind::Object);
}

/* static */ MOZ_ALWAYS_INLINE void
TenuredCell::writeBarrierPost(void* cellp, TenuredCell* prior, TenuredCell* next)
{
    AssertValidToSkipBarrier(next);
}

#ifdef DEBUG
bool
Cell::isAligned() const
{
    if (!isTenured())
        return true;
    return asTenured().isAligned();
}

bool
TenuredCell::isAligned() const
{
    return Arena::isAligned(address(), arena()->getThingSize());
}
#endif

static const int32_t ChunkLocationOffsetFromLastByte =
    int32_t(gc::ChunkLocationOffset) - int32_t(gc::ChunkMask);

} /* namespace gc */
} /* namespace js */

#endif /* gc_Heap_h */