summaryrefslogtreecommitdiff
path: root/deps/v8/src/heap/heap-inl.h
blob: 62f07ea322a65409b6a046b734be9b06d470e85d (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
// Copyright 2012 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_HEAP_HEAP_INL_H_
#define V8_HEAP_HEAP_INL_H_

#include <cmath>

// Clients of this interface shouldn't depend on lots of heap internals.
// Do not include anything from src/heap other than src/heap/heap.h and its
// write barrier here!
#include "src/heap/heap-write-barrier.h"
#include "src/heap/heap.h"

#include "src/base/platform/platform.h"
#include "src/counters-inl.h"
#include "src/feedback-vector.h"

// TODO(mstarzinger): There is one more include to remove in order to no longer
// leak heap internals to users of this interface!
#include "src/heap/spaces-inl.h"
#include "src/isolate.h"
#include "src/log.h"
#include "src/msan.h"
#include "src/objects-inl.h"
#include "src/objects/api-callbacks-inl.h"
#include "src/objects/descriptor-array.h"
#include "src/objects/literal-objects.h"
#include "src/objects/scope-info.h"
#include "src/objects/script-inl.h"
#include "src/profiler/heap-profiler.h"
#include "src/string-hasher.h"
#include "src/zone/zone-list-inl.h"

// The following header includes the write barrier essentials that can also be
// used stand-alone without including heap-inl.h.
// TODO(mlippautz): Remove once users of object-macros.h include this file on
// their own.
#include "src/heap/heap-write-barrier-inl.h"

namespace v8 {
namespace internal {

AllocationSpace AllocationResult::RetrySpace() {
  DCHECK(IsRetry());
  return static_cast<AllocationSpace>(Smi::ToInt(object_));
}

HeapObject* AllocationResult::ToObjectChecked() {
  CHECK(!IsRetry());
  return HeapObject::cast(object_);
}

#define ROOT_ACCESSOR(type, name, camel_name) \
  type* Heap::name() { return type::cast(roots_[k##camel_name##RootIndex]); }
MUTABLE_ROOT_LIST(ROOT_ACCESSOR)
#undef ROOT_ACCESSOR

#define DATA_HANDLER_MAP_ACCESSOR(NAME, Name, Size, name)  \
  Map* Heap::name##_map() {                                \
    return Map::cast(roots_[k##Name##Size##MapRootIndex]); \
  }
DATA_HANDLER_LIST(DATA_HANDLER_MAP_ACCESSOR)
#undef DATA_HANDLER_MAP_ACCESSOR

#define ACCESSOR_INFO_ACCESSOR(accessor_name, AccessorName)                \
  AccessorInfo* Heap::accessor_name##_accessor() {                         \
    return AccessorInfo::cast(roots_[k##AccessorName##AccessorRootIndex]); \
  }
ACCESSOR_INFO_LIST(ACCESSOR_INFO_ACCESSOR)
#undef ACCESSOR_INFO_ACCESSOR

#define ROOT_ACCESSOR(type, name, camel_name)                                 \
  void Heap::set_##name(type* value) {                                        \
    /* The deserializer makes use of the fact that these common roots are */  \
    /* never in new space and never on a page that is being compacted.    */  \
    DCHECK(!deserialization_complete() ||                                     \
           RootCanBeWrittenAfterInitialization(k##camel_name##RootIndex));    \
    DCHECK(k##camel_name##RootIndex >= kOldSpaceRoots || !InNewSpace(value)); \
    roots_[k##camel_name##RootIndex] = value;                                 \
  }
ROOT_LIST(ROOT_ACCESSOR)
#undef ROOT_ACCESSOR

PagedSpace* Heap::paged_space(int idx) {
  DCHECK_NE(idx, LO_SPACE);
  DCHECK_NE(idx, NEW_SPACE);
  return static_cast<PagedSpace*>(space_[idx]);
}

Space* Heap::space(int idx) { return space_[idx]; }

Address* Heap::NewSpaceAllocationTopAddress() {
  return new_space_->allocation_top_address();
}

Address* Heap::NewSpaceAllocationLimitAddress() {
  return new_space_->allocation_limit_address();
}

Address* Heap::OldSpaceAllocationTopAddress() {
  return old_space_->allocation_top_address();
}

Address* Heap::OldSpaceAllocationLimitAddress() {
  return old_space_->allocation_limit_address();
}

void Heap::UpdateNewSpaceAllocationCounter() {
  new_space_allocation_counter_ = NewSpaceAllocationCounter();
}

size_t Heap::NewSpaceAllocationCounter() {
  return new_space_allocation_counter_ + new_space()->AllocatedSinceLastGC();
}

AllocationResult Heap::AllocateRaw(int size_in_bytes, AllocationSpace space,
                                   AllocationAlignment alignment) {
  DCHECK(AllowHandleAllocation::IsAllowed());
  DCHECK(AllowHeapAllocation::IsAllowed());
  DCHECK(gc_state_ == NOT_IN_GC);
#ifdef V8_ENABLE_ALLOCATION_TIMEOUT
  if (FLAG_random_gc_interval > 0 || FLAG_gc_interval >= 0) {
    if (!always_allocate() && Heap::allocation_timeout_-- <= 0) {
      return AllocationResult::Retry(space);
    }
  }
#endif
#ifdef DEBUG
  isolate_->counters()->objs_since_last_full()->Increment();
  isolate_->counters()->objs_since_last_young()->Increment();
#endif

  bool large_object = size_in_bytes > kMaxRegularHeapObjectSize;
  bool new_large_object = FLAG_young_generation_large_objects &&
                          size_in_bytes > kMaxNewSpaceHeapObjectSize;
  HeapObject* object = nullptr;
  AllocationResult allocation;
  if (NEW_SPACE == space) {
    if (large_object) {
      space = LO_SPACE;
    } else {
      if (new_large_object) {
        allocation = new_lo_space_->AllocateRaw(size_in_bytes);
      } else {
        allocation = new_space_->AllocateRaw(size_in_bytes, alignment);
      }
      if (allocation.To(&object)) {
        OnAllocationEvent(object, size_in_bytes);
      }
      return allocation;
    }
  }

  // Here we only allocate in the old generation.
  if (OLD_SPACE == space) {
    if (large_object) {
      allocation = lo_space_->AllocateRaw(size_in_bytes, NOT_EXECUTABLE);
    } else {
      allocation = old_space_->AllocateRaw(size_in_bytes, alignment);
    }
  } else if (CODE_SPACE == space) {
    if (size_in_bytes <= code_space()->AreaSize()) {
      allocation = code_space_->AllocateRawUnaligned(size_in_bytes);
    } else {
      allocation = lo_space_->AllocateRaw(size_in_bytes, EXECUTABLE);
    }
  } else if (LO_SPACE == space) {
    DCHECK(large_object);
    allocation = lo_space_->AllocateRaw(size_in_bytes, NOT_EXECUTABLE);
  } else if (MAP_SPACE == space) {
    allocation = map_space_->AllocateRawUnaligned(size_in_bytes);
  } else if (RO_SPACE == space) {
#ifdef V8_USE_SNAPSHOT
    DCHECK(isolate_->serializer_enabled());
#endif
    DCHECK(!large_object);
    DCHECK(CanAllocateInReadOnlySpace());
    allocation = read_only_space_->AllocateRaw(size_in_bytes, alignment);
  } else {
    // NEW_SPACE is not allowed here.
    UNREACHABLE();
  }

  if (allocation.To(&object)) {
    if (space == CODE_SPACE) {
      // Unprotect the memory chunk of the object if it was not unprotected
      // already.
      UnprotectAndRegisterMemoryChunk(object);
      ZapCodeObject(object->address(), size_in_bytes);
    }
    OnAllocationEvent(object, size_in_bytes);
  }

  return allocation;
}

void Heap::OnAllocationEvent(HeapObject* object, int size_in_bytes) {
  for (auto& tracker : allocation_trackers_) {
    tracker->AllocationEvent(object->address(), size_in_bytes);
  }

  if (FLAG_verify_predictable) {
    ++allocations_count_;
    // Advance synthetic time by making a time request.
    MonotonicallyIncreasingTimeInMs();

    UpdateAllocationsHash(object);
    UpdateAllocationsHash(size_in_bytes);

    if (allocations_count_ % FLAG_dump_allocations_digest_at_alloc == 0) {
      PrintAllocationsHash();
    }
  } else if (FLAG_fuzzer_gc_analysis) {
    ++allocations_count_;
  } else if (FLAG_trace_allocation_stack_interval > 0) {
    ++allocations_count_;
    if (allocations_count_ % FLAG_trace_allocation_stack_interval == 0) {
      isolate()->PrintStack(stdout, Isolate::kPrintStackConcise);
    }
  }
}


void Heap::OnMoveEvent(HeapObject* target, HeapObject* source,
                       int size_in_bytes) {
  HeapProfiler* heap_profiler = isolate_->heap_profiler();
  if (heap_profiler->is_tracking_object_moves()) {
    heap_profiler->ObjectMoveEvent(source->address(), target->address(),
                                   size_in_bytes);
  }
  for (auto& tracker : allocation_trackers_) {
    tracker->MoveEvent(source->address(), target->address(), size_in_bytes);
  }
  if (target->IsSharedFunctionInfo()) {
    LOG_CODE_EVENT(isolate_, SharedFunctionInfoMoveEvent(source->address(),
                                                         target->address()));
  }

  if (FLAG_verify_predictable) {
    ++allocations_count_;
    // Advance synthetic time by making a time request.
    MonotonicallyIncreasingTimeInMs();

    UpdateAllocationsHash(source);
    UpdateAllocationsHash(target);
    UpdateAllocationsHash(size_in_bytes);

    if (allocations_count_ % FLAG_dump_allocations_digest_at_alloc == 0) {
      PrintAllocationsHash();
    }
  } else if (FLAG_fuzzer_gc_analysis) {
    ++allocations_count_;
  }
}

bool Heap::CanAllocateInReadOnlySpace() {
  return !deserialization_complete_ &&
         (isolate()->serializer_enabled() ||
          !isolate()->initialized_from_snapshot());
}

void Heap::UpdateAllocationsHash(HeapObject* object) {
  Address object_address = object->address();
  MemoryChunk* memory_chunk = MemoryChunk::FromAddress(object_address);
  AllocationSpace allocation_space = memory_chunk->owner()->identity();

  STATIC_ASSERT(kSpaceTagSize + kPageSizeBits <= 32);
  uint32_t value =
      static_cast<uint32_t>(object_address - memory_chunk->address()) |
      (static_cast<uint32_t>(allocation_space) << kPageSizeBits);

  UpdateAllocationsHash(value);
}


void Heap::UpdateAllocationsHash(uint32_t value) {
  uint16_t c1 = static_cast<uint16_t>(value);
  uint16_t c2 = static_cast<uint16_t>(value >> 16);
  raw_allocations_hash_ =
      StringHasher::AddCharacterCore(raw_allocations_hash_, c1);
  raw_allocations_hash_ =
      StringHasher::AddCharacterCore(raw_allocations_hash_, c2);
}


void Heap::RegisterExternalString(String* string) {
  DCHECK(string->IsExternalString());
  DCHECK(!string->IsThinString());
  external_string_table_.AddString(string);
}

void Heap::UpdateExternalString(String* string, size_t old_payload,
                                size_t new_payload) {
  DCHECK(string->IsExternalString());
  Page* page = Page::FromHeapObject(string);

  if (old_payload > new_payload)
    page->DecrementExternalBackingStoreBytes(
        ExternalBackingStoreType::kExternalString, old_payload - new_payload);
  else
    page->IncrementExternalBackingStoreBytes(
        ExternalBackingStoreType::kExternalString, new_payload - old_payload);
}

void Heap::FinalizeExternalString(String* string) {
  DCHECK(string->IsExternalString());
  Page* page = Page::FromHeapObject(string);
  ExternalString* ext_string = ExternalString::cast(string);

  page->DecrementExternalBackingStoreBytes(
      ExternalBackingStoreType::kExternalString,
      ext_string->ExternalPayloadSize());

  v8::String::ExternalStringResourceBase** resource_addr =
      reinterpret_cast<v8::String::ExternalStringResourceBase**>(
          reinterpret_cast<byte*>(string) + ExternalString::kResourceOffset -
          kHeapObjectTag);

  // Dispose of the C++ object if it has not already been disposed.
  if (*resource_addr != nullptr) {
    (*resource_addr)->Dispose();
    *resource_addr = nullptr;
  }
}

Address Heap::NewSpaceTop() { return new_space_->top(); }

// static
bool Heap::InNewSpace(Object* object) {
  DCHECK(!HasWeakHeapObjectTag(object));
  return object->IsHeapObject() && InNewSpace(HeapObject::cast(object));
}

// static
bool Heap::InNewSpace(MaybeObject* object) {
  HeapObject* heap_object;
  return object->ToStrongOrWeakHeapObject(&heap_object) &&
         InNewSpace(heap_object);
}

// static
bool Heap::InNewSpace(HeapObject* heap_object) {
  // Inlined check from NewSpace::Contains.
  bool result = MemoryChunk::FromHeapObject(heap_object)->InNewSpace();
#ifdef DEBUG
  // If in NEW_SPACE, then check we're either not in the middle of GC or the
  // object is in to-space.
  if (result) {
    // If the object is in NEW_SPACE, then it's not in RO_SPACE so this is safe.
    Heap* heap = Heap::FromWritableHeapObject(heap_object);
    DCHECK(heap->gc_state_ != NOT_IN_GC || InToSpace(heap_object));
  }
#endif
  return result;
}

// static
bool Heap::InFromSpace(Object* object) {
  DCHECK(!HasWeakHeapObjectTag(object));
  return object->IsHeapObject() && InFromSpace(HeapObject::cast(object));
}

// static
bool Heap::InFromSpace(MaybeObject* object) {
  HeapObject* heap_object;
  return object->ToStrongOrWeakHeapObject(&heap_object) &&
         InFromSpace(heap_object);
}

// static
bool Heap::InFromSpace(HeapObject* heap_object) {
  return MemoryChunk::FromHeapObject(heap_object)
      ->IsFlagSet(Page::IN_FROM_SPACE);
}

// static
bool Heap::InToSpace(Object* object) {
  DCHECK(!HasWeakHeapObjectTag(object));
  return object->IsHeapObject() && InToSpace(HeapObject::cast(object));
}

// static
bool Heap::InToSpace(MaybeObject* object) {
  HeapObject* heap_object;
  return object->ToStrongOrWeakHeapObject(&heap_object) &&
         InToSpace(heap_object);
}

// static
bool Heap::InToSpace(HeapObject* heap_object) {
  return MemoryChunk::FromHeapObject(heap_object)->IsFlagSet(Page::IN_TO_SPACE);
}

bool Heap::InOldSpace(Object* object) { return old_space_->Contains(object); }

bool Heap::InReadOnlySpace(Object* object) {
  return read_only_space_->Contains(object);
}

bool Heap::InNewSpaceSlow(Address address) {
  return new_space_->ContainsSlow(address);
}

bool Heap::InOldSpaceSlow(Address address) {
  return old_space_->ContainsSlow(address);
}

// static
Heap* Heap::FromWritableHeapObject(const HeapObject* obj) {
  MemoryChunk* chunk = MemoryChunk::FromHeapObject(obj);
  // RO_SPACE can be shared between heaps, so we can't use RO_SPACE objects to
  // find a heap. The exception is when the ReadOnlySpace is writeable, during
  // bootstrapping, so explicitly allow this case.
  SLOW_DCHECK(chunk->owner()->identity() != RO_SPACE ||
              static_cast<ReadOnlySpace*>(chunk->owner())->writable());
  Heap* heap = chunk->heap();
  SLOW_DCHECK(heap != nullptr);
  return heap;
}

bool Heap::ShouldBePromoted(Address old_address) {
  Page* page = Page::FromAddress(old_address);
  Address age_mark = new_space_->age_mark();
  return page->IsFlagSet(MemoryChunk::NEW_SPACE_BELOW_AGE_MARK) &&
         (!page->ContainsLimit(age_mark) || old_address < age_mark);
}

void Heap::CopyBlock(Address dst, Address src, int byte_size) {
  CopyWords(reinterpret_cast<Object**>(dst), reinterpret_cast<Object**>(src),
            static_cast<size_t>(byte_size / kPointerSize));
}

template <Heap::FindMementoMode mode>
AllocationMemento* Heap::FindAllocationMemento(Map* map, HeapObject* object) {
  Address object_address = object->address();
  Address memento_address = object_address + object->SizeFromMap(map);
  Address last_memento_word_address = memento_address + kPointerSize;
  // If the memento would be on another page, bail out immediately.
  if (!Page::OnSamePage(object_address, last_memento_word_address)) {
    return nullptr;
  }
  HeapObject* candidate = HeapObject::FromAddress(memento_address);
  Map* candidate_map = candidate->map();
  // This fast check may peek at an uninitialized word. However, the slow check
  // below (memento_address == top) ensures that this is safe. Mark the word as
  // initialized to silence MemorySanitizer warnings.
  MSAN_MEMORY_IS_INITIALIZED(&candidate_map, sizeof(candidate_map));
  if (candidate_map != ReadOnlyRoots(this).allocation_memento_map()) {
    return nullptr;
  }

  // Bail out if the memento is below the age mark, which can happen when
  // mementos survived because a page got moved within new space.
  Page* object_page = Page::FromAddress(object_address);
  if (object_page->IsFlagSet(Page::NEW_SPACE_BELOW_AGE_MARK)) {
    Address age_mark =
        reinterpret_cast<SemiSpace*>(object_page->owner())->age_mark();
    if (!object_page->Contains(age_mark)) {
      return nullptr;
    }
    // Do an exact check in the case where the age mark is on the same page.
    if (object_address < age_mark) {
      return nullptr;
    }
  }

  AllocationMemento* memento_candidate = AllocationMemento::cast(candidate);

  // Depending on what the memento is used for, we might need to perform
  // additional checks.
  Address top;
  switch (mode) {
    case Heap::kForGC:
      return memento_candidate;
    case Heap::kForRuntime:
      if (memento_candidate == nullptr) return nullptr;
      // Either the object is the last object in the new space, or there is
      // another object of at least word size (the header map word) following
      // it, so suffices to compare ptr and top here.
      top = NewSpaceTop();
      DCHECK(memento_address == top ||
             memento_address + HeapObject::kHeaderSize <= top ||
             !Page::OnSamePage(memento_address, top - 1));
      if ((memento_address != top) && memento_candidate->IsValid()) {
        return memento_candidate;
      }
      return nullptr;
    default:
      UNREACHABLE();
  }
  UNREACHABLE();
}

void Heap::UpdateAllocationSite(Map* map, HeapObject* object,
                                PretenuringFeedbackMap* pretenuring_feedback) {
  DCHECK_NE(pretenuring_feedback, &global_pretenuring_feedback_);
  DCHECK(
      InFromSpace(object) ||
      (InToSpace(object) && Page::FromAddress(object->address())
                                ->IsFlagSet(Page::PAGE_NEW_NEW_PROMOTION)) ||
      (!InNewSpace(object) && Page::FromAddress(object->address())
                                  ->IsFlagSet(Page::PAGE_NEW_OLD_PROMOTION)));
  if (!FLAG_allocation_site_pretenuring ||
      !AllocationSite::CanTrack(map->instance_type()))
    return;
  AllocationMemento* memento_candidate =
      FindAllocationMemento<kForGC>(map, object);
  if (memento_candidate == nullptr) return;

  // Entering cached feedback is used in the parallel case. We are not allowed
  // to dereference the allocation site and rather have to postpone all checks
  // till actually merging the data.
  Address key = memento_candidate->GetAllocationSiteUnchecked();
  (*pretenuring_feedback)[reinterpret_cast<AllocationSite*>(key)]++;
}

Isolate* Heap::isolate() {
  return reinterpret_cast<Isolate*>(
      reinterpret_cast<intptr_t>(this) -
      reinterpret_cast<size_t>(reinterpret_cast<Isolate*>(16)->heap()) + 16);
}

void Heap::ExternalStringTable::AddString(String* string) {
  DCHECK(string->IsExternalString());
  DCHECK(!Contains(string));

  if (InNewSpace(string)) {
    new_space_strings_.push_back(string);
  } else {
    old_space_strings_.push_back(string);
  }
}

Oddball* Heap::ToBoolean(bool condition) {
  ReadOnlyRoots roots(this);
  return condition ? roots.true_value() : roots.false_value();
}

uint64_t Heap::HashSeed() {
  uint64_t seed;
  hash_seed()->copy_out(0, reinterpret_cast<byte*>(&seed), kInt64Size);
  DCHECK(FLAG_randomize_hashes || seed == 0);
  return seed;
}

int Heap::NextScriptId() {
  int last_id = last_script_id()->value();
  if (last_id == Smi::kMaxValue) last_id = v8::UnboundScript::kNoScriptId;
  last_id++;
  set_last_script_id(Smi::FromInt(last_id));
  return last_id;
}

int Heap::NextDebuggingId() {
  int last_id = last_debugging_id()->value();
  if (last_id == DebugInfo::DebuggingIdBits::kMax) {
    last_id = DebugInfo::kNoDebuggingId;
  }
  last_id++;
  set_last_debugging_id(Smi::FromInt(last_id));
  return last_id;
}

int Heap::GetNextTemplateSerialNumber() {
  int next_serial_number = next_template_serial_number()->value() + 1;
  set_next_template_serial_number(Smi::FromInt(next_serial_number));
  return next_serial_number;
}

int Heap::MaxNumberToStringCacheSize() const {
  // Compute the size of the number string cache based on the max newspace size.
  // The number string cache has a minimum size based on twice the initial cache
  // size to ensure that it is bigger after being made 'full size'.
  size_t number_string_cache_size = max_semi_space_size_ / 512;
  number_string_cache_size =
      Max(static_cast<size_t>(kInitialNumberStringCacheSize * 2),
          Min<size_t>(0x4000u, number_string_cache_size));
  // There is a string and a number per entry so the length is twice the number
  // of entries.
  return static_cast<int>(number_string_cache_size * 2);
}
AlwaysAllocateScope::AlwaysAllocateScope(Isolate* isolate)
    : heap_(isolate->heap()) {
  heap_->always_allocate_scope_count_++;
}

AlwaysAllocateScope::~AlwaysAllocateScope() {
  heap_->always_allocate_scope_count_--;
}

CodeSpaceMemoryModificationScope::CodeSpaceMemoryModificationScope(Heap* heap)
    : heap_(heap) {
  if (heap_->write_protect_code_memory()) {
    heap_->increment_code_space_memory_modification_scope_depth();
    heap_->code_space()->SetReadAndWritable();
    LargePage* page = heap_->lo_space()->first_page();
    while (page != nullptr) {
      if (page->IsFlagSet(MemoryChunk::IS_EXECUTABLE)) {
        CHECK(heap_->memory_allocator()->IsMemoryChunkExecutable(page));
        page->SetReadAndWritable();
      }
      page = page->next_page();
    }
  }
}

CodeSpaceMemoryModificationScope::~CodeSpaceMemoryModificationScope() {
  if (heap_->write_protect_code_memory()) {
    heap_->decrement_code_space_memory_modification_scope_depth();
    heap_->code_space()->SetReadAndExecutable();
    LargePage* page = heap_->lo_space()->first_page();
    while (page != nullptr) {
      if (page->IsFlagSet(MemoryChunk::IS_EXECUTABLE)) {
        CHECK(heap_->memory_allocator()->IsMemoryChunkExecutable(page));
        page->SetReadAndExecutable();
      }
      page = page->next_page();
    }
  }
}

CodePageCollectionMemoryModificationScope::
    CodePageCollectionMemoryModificationScope(Heap* heap)
    : heap_(heap) {
  if (heap_->write_protect_code_memory() &&
      !heap_->code_space_memory_modification_scope_depth()) {
    heap_->EnableUnprotectedMemoryChunksRegistry();
  }
}

CodePageCollectionMemoryModificationScope::
    ~CodePageCollectionMemoryModificationScope() {
  if (heap_->write_protect_code_memory() &&
      !heap_->code_space_memory_modification_scope_depth()) {
    heap_->ProtectUnprotectedMemoryChunks();
    heap_->DisableUnprotectedMemoryChunksRegistry();
  }
}

CodePageMemoryModificationScope::CodePageMemoryModificationScope(
    MemoryChunk* chunk)
    : chunk_(chunk),
      scope_active_(chunk_->heap()->write_protect_code_memory() &&
                    chunk_->IsFlagSet(MemoryChunk::IS_EXECUTABLE)) {
  if (scope_active_) {
    DCHECK(chunk_->owner()->identity() == CODE_SPACE ||
           (chunk_->owner()->identity() == LO_SPACE &&
            chunk_->IsFlagSet(MemoryChunk::IS_EXECUTABLE)));
    chunk_->SetReadAndWritable();
  }
}

CodePageMemoryModificationScope::~CodePageMemoryModificationScope() {
  if (scope_active_) {
    chunk_->SetReadAndExecutable();
  }
}

}  // namespace internal
}  // namespace v8

#endif  // V8_HEAP_HEAP_INL_H_