deps/v8/src/heap/heap.cc - main - githubmirror/node

deps/v8/src/heap/heap.cc
7 929 строк288 KB
Joyee Cheung
build,test: test array index hash collision
24 апр 2026, 19:01
24 апр 2026, 19:01fff9a8a
// 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.

#include "src/heap/heap.h"

#include <algorithm>
#include <atomic>
#include <cinttypes>
#include <iomanip>
#include <memory>
#include <optional>
#include <unordered_map>
#include <unordered_set>

#include "absl/functional/overload.h"
#include "include/v8-callbacks.h"
#include "include/v8-locker.h"
#include "src/api/api-inl.h"
#include "src/base/bits.h"
#include "src/base/flags.h"
#include "src/base/logging.h"
#include "src/base/macros.h"
#include "src/base/numerics/safe_conversions.h"
#include "src/base/once.h"
#include "src/base/platform/memory.h"
#include "src/base/platform/mutex.h"
#include "src/base/platform/time.h"
#include "src/base/utils/random-number-generator.h"
#include "src/builtins/accessors.h"
#include "src/codegen/assembler-inl.h"
#include "src/codegen/compilation-cache.h"
#include "src/common/assert-scope.h"
#include "src/common/globals.h"
#include "src/compiler-dispatcher/optimizing-compile-dispatcher.h"
#include "src/debug/debug.h"
#include "src/deoptimizer/deoptimizer.h"
#include "src/execution/embedder-state.h"
#include "src/execution/isolate-utils-inl.h"
#include "src/execution/microtask-queue.h"
#include "src/execution/v8threads.h"
#include "src/execution/vm-state-inl.h"
#include "src/flags/flags.h"
#include "src/handles/global-handles-inl.h"
#include "src/handles/traced-handles.h"
#include "src/heap/allocation-observer.h"
#include "src/heap/array-buffer-sweeper.h"
#include "src/heap/base-page.h"
#include "src/heap/base/stack.h"
#include "src/heap/base/unsafe-json-emitter.h"
#include "src/heap/base/worklist.h"
#include "src/heap/code-range.h"
#include "src/heap/code-stats.h"
#include "src/heap/collection-barrier.h"
#include "src/heap/combined-heap.h"
#include "src/heap/concurrent-marking.h"
#include "src/heap/conservative-stack-visitor-inl.h"
#include "src/heap/cppgc-js/cpp-heap.h"
#include "src/heap/ephemeron-remembered-set.h"
#include "src/heap/evacuation-verifier-inl.h"
#include "src/heap/finalization-registry-cleanup-task.h"
#include "src/heap/gc-callbacks.h"
#include "src/heap/gc-tracer-inl.h"
#include "src/heap/gc-tracer.h"
#include "src/heap/heap-allocator.h"
#include "src/heap/heap-controller.h"
#include "src/heap/heap-layout-inl.h"
#include "src/heap/heap-layout-tracer.h"
#include "src/heap/heap-utils-inl.h"
#include "src/heap/heap-visitor-inl.h"
#include "src/heap/heap-visitor.h"
#include "src/heap/heap-write-barrier-inl.h"
#include "src/heap/incremental-marking.h"
#include "src/heap/large-spaces.h"
#include "src/heap/local-heap-inl.h"
#include "src/heap/mark-compact-inl.h"
#include "src/heap/mark-compact.h"
#include "src/heap/marking-barrier-inl.h"
#include "src/heap/marking-barrier.h"
#include "src/heap/marking-state-inl.h"
#include "src/heap/marking-state.h"
#include "src/heap/memory-balancer.h"
#include "src/heap/memory-chunk-layout.h"
#include "src/heap/memory-measurement.h"
#include "src/heap/memory-pool.h"
#include "src/heap/memory-reducer.h"
#include "src/heap/minor-gc-job.h"
#include "src/heap/minor-mark-sweep.h"
#include "src/heap/mutable-page-inl.h"
#include "src/heap/new-spaces.h"
#include "src/heap/object-lock.h"
#include "src/heap/object-stats.h"
#include "src/heap/paged-spaces-inl.h"
#include "src/heap/parked-scope.h"
#include "src/heap/pretenuring-handler.h"
#include "src/heap/read-only-heap.h"
#include "src/heap/remembered-set.h"
#include "src/heap/safepoint.h"
#include "src/heap/scavenger.h"
#include "src/heap/stress-scavenge-observer.h"
#include "src/heap/sweeper.h"
#include "src/heap/trusted-range.h"
#include "src/heap/visit-object.h"
#include "src/heap/zapping.h"
#include "src/init/bootstrapper.h"
#include "src/init/v8.h"
#include "src/interpreter/interpreter.h"
#include "src/logging/log.h"
#include "src/logging/runtime-call-stats-scope.h"
#include "src/numbers/conversions.h"
#include "src/objects/allocation-site.h"
#include "src/objects/casting-inl.h"
#include "src/objects/data-handler.h"
#include "src/objects/free-space-inl.h"
#include "src/objects/hash-table-inl.h"
#include "src/objects/hash-table.h"
#include "src/objects/instance-type.h"
#include "src/objects/js-weak-refs-inl.h"
#include "src/objects/maybe-object.h"
#include "src/objects/objects.h"
#include "src/objects/slots-atomic-inl.h"
#include "src/objects/slots-inl.h"
#include "src/objects/slots.h"
#include "src/objects/visitors.h"
#include "src/profiler/heap-profiler.h"
#include "src/regexp/regexp.h"
#include "src/snapshot/embedded/embedded-data.h"
#include "src/snapshot/serializer-deserializer.h"
#include "src/snapshot/snapshot.h"
#include "src/strings/string-hasher.h"
#include "src/strings/string-stream.h"
#include "src/strings/unicode-inl.h"
#include "src/tasks/cancelable-task.h"
#include "src/tracing/trace-event.h"
#include "src/utils/utils-inl.h"
#include "src/utils/utils.h"

#if V8_ENABLE_WEBASSEMBLY
#include "src/wasm/wasm-engine.h"
#endif  // V8_ENABLE_WEBASSEMBLY

// Has to be the last include (doesn't have include guards):
#include "src/objects/object-macros.h"

namespace v8::internal {

class Heap::AllocationTrackerForDebugging final
    : public HeapObjectAllocationTracker {
 public:
  static bool IsNeeded() {
    return v8_flags.verify_predictable || v8_flags.fuzzer_gc_analysis ||
           (v8_flags.trace_allocation_stack_interval > 0);
  }

  explicit AllocationTrackerForDebugging(Heap* heap) : heap_(heap) {
    CHECK(IsNeeded());
    heap_->AddHeapObjectAllocationTracker(this);
  }

  ~AllocationTrackerForDebugging() final {
    heap_->RemoveHeapObjectAllocationTracker(this);
    if (v8_flags.verify_predictable || v8_flags.fuzzer_gc_analysis) {
      PrintAllocationsHash();
    }
  }

  void AllocationEvent(Address addr, int size) final {
    if (v8_flags.verify_predictable) {
      allocations_count_.fetch_add(1, std::memory_order_relaxed);
      // Advance synthetic time by making a time request.
      heap_->MonotonicallyIncreasingTimeInMs();

      UpdateAllocationsHash(HeapObject::FromAddress(addr));
      UpdateAllocationsHash(size);

      if (allocations_count_ % v8_flags.dump_allocations_digest_at_alloc == 0) {
        PrintAllocationsHash();
      }
    } else if (v8_flags.fuzzer_gc_analysis) {
      allocations_count_.fetch_add(1, std::memory_order_relaxed);
    } else if (v8_flags.trace_allocation_stack_interval > 0) {
      allocations_count_.fetch_add(1, std::memory_order_relaxed);
      if (allocations_count_ % v8_flags.trace_allocation_stack_interval == 0) {
        heap_->isolate()->PrintStack(stdout, Isolate::kPrintStackConcise);
      }
    }
  }

  void MoveEvent(Address source, Address target, int size) final {
    if (v8_flags.verify_predictable) {
      allocations_count_.fetch_add(1, std::memory_order_relaxed);
      // Advance synthetic time by making a time request.
      heap_->MonotonicallyIncreasingTimeInMs();

      UpdateAllocationsHash(HeapObject::FromAddress(source));
      UpdateAllocationsHash(HeapObject::FromAddress(target));
      UpdateAllocationsHash(size);

      if (allocations_count_ % v8_flags.dump_allocations_digest_at_alloc == 0) {
        PrintAllocationsHash();
      }
    } else if (v8_flags.fuzzer_gc_analysis) {
      allocations_count_.fetch_add(1, std::memory_order_relaxed);
    }
  }

  void UpdateObjectSizeEvent(Address, int) final {}

 private:
  void UpdateAllocationsHash(Tagged<HeapObject> object) {
    Address object_address = object.address();
    MemoryChunk* memory_chunk = MemoryChunk::FromAddress(object_address);
    AllocationSpace allocation_space =
        SbxCast<MutablePage>(memory_chunk->Metadata())->owner_identity();

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

    UpdateAllocationsHash(value);
  }

  void UpdateAllocationsHash(uint32_t value) {
    const uint16_t c1 = static_cast<uint16_t>(value);
    const uint16_t c2 = static_cast<uint16_t>(value >> 16);
    raw_allocations_hash_.AddCharacter(c1);
    raw_allocations_hash_.AddCharacter(c2);
  }

  void PrintAllocationsHash() {
    uint32_t hash = raw_allocations_hash_.Finalize();
    PrintF("\n### Allocations = %zu, hash = 0x%08x\n",
           allocations_count_.load(std::memory_order_relaxed), hash);
  }

  Heap* const heap_;
  // Count of all allocations performed through C++ bottlenecks. This needs to
  // be atomic as objects are moved in parallel in the GC which counts as
  // allocations.
  std::atomic<size_t> allocations_count_{0};
  // Running hash over allocations performed.
  RunningStringHasher raw_allocations_hash_{0};
};

void Heap::SetConstructStubCreateDeoptPCOffset(int pc_offset) {
  DCHECK_EQ(Smi::zero(), construct_stub_create_deopt_pc_offset());
  set_construct_stub_create_deopt_pc_offset(Smi::FromInt(pc_offset));
}

void Heap::SetConstructStubInvokeDeoptPCOffset(int pc_offset) {
  DCHECK_EQ(Smi::zero(), construct_stub_invoke_deopt_pc_offset());
  set_construct_stub_invoke_deopt_pc_offset(Smi::FromInt(pc_offset));
}

void Heap::SetDeoptPCOffsetAfterAdaptShadowStack(int pc_offset) {
  DCHECK((Smi::zero() == deopt_pc_offset_after_adapt_shadow_stack()) ||
         (pc_offset == deopt_pc_offset_after_adapt_shadow_stack().value()));
  set_deopt_pc_offset_after_adapt_shadow_stack(Smi::FromInt(pc_offset));
}

void Heap::SetInterpreterEntryReturnPCOffset(int pc_offset) {
  DCHECK_EQ(Smi::zero(), interpreter_entry_return_pc_offset());
  set_interpreter_entry_return_pc_offset(Smi::FromInt(pc_offset));
}

void Heap::SetSerializedObjects(Tagged<HeapObject> objects) {
  DCHECK(isolate()->serializer_enabled());
  set_serialized_objects(objects);
}

void Heap::SetSerializedGlobalProxySizes(Tagged<FixedArray> sizes) {
  DCHECK(isolate()->serializer_enabled());
  set_serialized_global_proxy_sizes(sizes);
}

void Heap::SetBasicBlockProfilingData(DirectHandle<ArrayList> list) {
  set_basic_block_profiling_data(*list);
}

Heap::Heap()
    : isolate_(isolate()),
      memory_pressure_level_(MemoryPressureLevel::kNone),
      safepoint_(std::make_unique<IsolateSafepoint>(this)),
      external_string_table_(this),
      allocation_type_for_in_place_internalizable_strings_(
          v8_flags.shared_string_table ? AllocationType::kSharedOld
                                       : AllocationType::kOld),
      marking_state_(isolate_),
      non_atomic_marking_state_(isolate_),
      pretenuring_handler_(this),
      tracing_track_(perfetto::NamedTrack::FromPointer(
                         "v8::Heap", this, perfetto::ThreadTrack::Current())
                         .disable_sibling_merge()),
      gc_tracing_category_enabled_(TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(
          TRACE_DISABLED_BY_DEFAULT("v8.gc"))) {
#if defined(V8_USE_PERFETTO)
  if (perfetto::Tracing::IsInitialized()) {
    // Because the track may not get any events of its own it must manually emit
    // the track descriptor. This is done conditionally to avoid crashing in
    // unit tests where tracing isn't initialized.
    TrackEvent::SetTrackDescriptor(tracing_track_, tracing_track_.Serialize());
  }
#endif

  max_regular_code_object_size_ = MemoryChunkLayout::MaxRegularCodeObjectSize();

  set_native_contexts_list(Smi::zero());

  // Put a dummy entry in the remembered pages so we can find the list the
  // minidump even if there are no real unmapped pages.
  RememberUnmappedPage(kNullAddress, false);
}

Heap::~Heap() = default;

size_t Heap::MaxReserved() const {
  const size_t kMaxNewLargeObjectSpaceSize = max_semi_space_size_;
  return static_cast<size_t>(
      (v8_flags.minor_ms ? 1 : 2) * max_semi_space_size_ +
      kMaxNewLargeObjectSpaceSize + limits()->max_old_generation_size());
}

// static
size_t Heap::YoungGenerationSizeFromPhysicalMemory(uint64_t physical_memory) {
  // `physical_memory / kPhysicalMemoryToOldGenerationRatio` is not the actual
  // heap size, but achieves desires scaling w.r.t. `physical_memory`.
  const uint64_t target_heap_size =
      physical_memory / kPhysicalMemoryToOldGenerationRatio;
  const size_t capped_heap_size =
      base::saturated_cast<size_t>(target_heap_size);
  return YoungGenerationSizeFromHeapSize(physical_memory, capped_heap_size);
}

// static
size_t Heap::YoungGenerationSizeFromHeapSize(uint64_t physical_memory,
                                             size_t heap_size) {
  // Compute the semi space size and cap it.
  size_t semi_space = heap_size / HeapSizeToSemiSpaceRatio(physical_memory);
  semi_space =
      RoundUp(std::clamp<size_t>(semi_space, 2 * MB,
                                 DefaultMaxSemiSpaceSize(physical_memory)),
              NormalPage::kPageSize);
  return YoungGenerationSizeFromSemiSpaceSize(semi_space);
}

size_t Heap::OldGenerationSizeFromPhysicalMemory(uint64_t physical_memory) {
  // Compute the old generation size and cap it.
  if (v8_flags.new_old_generation_heap_size) {
    uint64_t old_generation = physical_memory /
                              kPhysicalMemoryToOldGenerationRatio *
                              kSystemPointerSize / 4;
    old_generation = std::clamp<uint64_t>(
        old_generation, DefaultMinHeapSize(physical_memory),
        MaxOldGenerationSizeFromPhysicalMemory(physical_memory));
    return RoundUp(old_generation, NormalPage::kPageSize);
  }
  uint64_t old_generation = physical_memory /
                            kPhysicalMemoryToOldGenerationRatio *
                            HeapLimitMultiplier(physical_memory);
  old_generation =
      std::min(old_generation,
               static_cast<uint64_t>(
                   MaxOldGenerationSizeFromPhysicalMemory(physical_memory)));
  old_generation =
      std::max({old_generation,
                static_cast<uint64_t>(DefaultMinHeapSize(physical_memory))});
  old_generation = RoundUp(old_generation, NormalPage::kPageSize);

  return static_cast<size_t>(old_generation);
}

// static
void Heap::GenerationSizesFromHeapSize(uint64_t physical_memory,
                                       size_t heap_size,
                                       size_t* young_generation_size,
                                       size_t* old_generation_size) {
  // Initialize values for the case when the given heap size is too small.
  *young_generation_size =
      RoundUp(YoungGenerationSizeFromHeapSize(physical_memory, heap_size), MB);
  if (*young_generation_size < heap_size) {
    *old_generation_size = heap_size - *young_generation_size;
  } else {
    *young_generation_size = 0;
    *old_generation_size = 0;
  }
}

size_t Heap::MinYoungGenerationSize() {
  return YoungGenerationSizeFromSemiSpaceSize(DefaultMinSemiSpaceSize());
}

size_t Heap::MinOldGenerationSize() {
  size_t paged_space_count =
      LAST_GROWABLE_PAGED_SPACE - FIRST_GROWABLE_PAGED_SPACE + 1;
  return paged_space_count * NormalPage::kPageSize;
}

size_t Heap::MaxOldGenerationSize() {
  return limits()->max_old_generation_size();
}

// static
size_t Heap::AllocatorLimitOnMaxOldGenerationSize(uint64_t physical_memory) {
#ifdef V8_COMPRESS_POINTERS
  if (v8_flags.new_old_generation_heap_size) {
    return kPtrComprCageReservationSize;
  }
  // The young generation is also allocated on the heap.
  return kPtrComprCageReservationSize -
         YoungGenerationSizeFromSemiSpaceSize(
             DefaultMaxSemiSpaceSize(physical_memory));
#else
  return std::numeric_limits<size_t>::max();
#endif
}

// static
size_t Heap::MaxOldGenerationSizeFromPhysicalMemory(uint64_t physical_memory) {
  if (v8_flags.new_old_generation_heap_size) {
#ifdef V8_HOST_ARCH_64_BIT
    return static_cast<uint64_t>(4u) * GB;
#else
    return static_cast<uint64_t>(1u) * GB;
#endif
  }

  size_t max_size = DefaultMaxHeapSize(physical_memory);

  // Increase the heap size from 2GB to 4GB for 64-bit systems with physical
  // memory at least 16GB. The threshold is set to 15GB to accommodate for some
  // memory being reserved by the hardware.
#ifdef V8_HOST_ARCH_64_BIT
  if ((physical_memory / GB) >= 15) {
#if V8_OS_ANDROID
    // As of 2024, Android devices with 16GiB are shipping (for instance the
    // Pixel 9 Pro). However, a large fraction of their memory is not usable,
    // and there is no disk swap, so heaps are still smaller than on desktop for
    // now.
    DCHECK_EQ(max_size / GB, IsHighEndAndroid(physical_memory) ? 2u : 1u);
#else
    DCHECK_EQ(max_size / GB, 2u);
#endif
    max_size *= 2;
  }
#endif  // V8_HOST_ARCH_64_BIT
  return std::min(max_size,
                  AllocatorLimitOnMaxOldGenerationSize(physical_memory));
}

namespace {
int NumberOfSemiSpaces() { return v8_flags.minor_ms ? 1 : 2; }
}  // namespace

size_t Heap::YoungGenerationSizeFromSemiSpaceSize(size_t semi_space_size) {
  return semi_space_size *
         (NumberOfSemiSpaces() + kNewLargeObjectSpaceToSemiSpaceRatio);
}

size_t Heap::SemiSpaceSizeFromYoungGenerationSize(
    size_t young_generation_size) {
  return young_generation_size /
         (NumberOfSemiSpaces() + kNewLargeObjectSpaceToSemiSpaceRatio);
}

size_t Heap::Capacity() {
  if (!HasBeenSetUp()) {
    return 0;
  }
  return NewSpaceCapacity() + OldGenerationCapacity();
}

size_t Heap::OldGenerationCapacity() const {
  if (!HasBeenSetUp()) return 0;
  PagedSpaceIterator spaces(this);
  size_t total = 0;
  for (PagedSpace* space = spaces.Next(); space != nullptr;
       space = spaces.Next()) {
    total += space->Capacity();
  }
  if (shared_lo_space_) {
    total += shared_lo_space_->SizeOfObjects();
  }
  return total + lo_space_->SizeOfObjects() + code_lo_space_->SizeOfObjects() +
         trusted_lo_space_->SizeOfObjects();
}

size_t Heap::CommittedOldGenerationMemory() {
  if (!HasBeenSetUp()) return 0;

  PagedSpaceIterator spaces(this);
  size_t total = 0;
  for (PagedSpace* space = spaces.Next(); space != nullptr;
       space = spaces.Next()) {
    total += space->CommittedMemory();
  }
  if (shared_lo_space_) {
    total += shared_lo_space_->Size();
  }
  return total + lo_space_->Size() + code_lo_space_->Size() +
         trusted_lo_space_->Size();
}

size_t Heap::CommittedMemory() {
  if (!HasBeenSetUp()) return 0;

  size_t new_space_committed = new_space_ ? new_space_->CommittedMemory() : 0;
  size_t new_lo_space_committed = new_lo_space_ ? new_lo_space_->Size() : 0;

  return new_space_committed + new_lo_space_committed +
         CommittedOldGenerationMemory();
}

size_t Heap::CommittedPhysicalMemory() {
  if (!HasBeenSetUp()) return 0;

  size_t total = 0;
  for (SpaceIterator it(this); it.HasNext();) {
    total += it.Next()->CommittedPhysicalMemory();
  }

  return total;
}

size_t Heap::CommittedMemoryExecutable() {
  if (!HasBeenSetUp()) return 0;

  return static_cast<size_t>(memory_allocator()->SizeExecutable());
}

void Heap::UpdateMaximumCommitted() {
  if (!HasBeenSetUp()) return;

  const size_t current_committed_memory = CommittedMemory();
  if (current_committed_memory > maximum_committed_) {
    maximum_committed_ = current_committed_memory;
  }
}

size_t Heap::Available() {
  if (!HasBeenSetUp()) return 0;

  size_t total = 0;

  for (SpaceIterator it(this); it.HasNext();) {
    total += it.Next()->Available();
  }

  total += memory_allocator()->Available();
  return total;
}

bool Heap::CanExpandOldGeneration(size_t size) const {
  if (force_oom_ || force_gc_on_next_allocation_) return false;
  if (OldGenerationCapacity() + size > limits()->max_old_generation_size()) {
    return false;
  }
  // Stay below `MaxReserved()` such that it is more likely that committing the
  // second semi space at the beginning of a GC succeeds.
  return memory_allocator()->Size() + size <= MaxReserved();
}

bool Heap::IsOldGenerationExpansionAllowed(
    size_t size, const base::MutexGuard& expansion_mutex_witness) const {
  return OldGenerationCapacity() + size <= limits()->max_old_generation_size();
}

bool Heap::CanPromoteYoungAndExpandOldGeneration(size_t size) const {
  if (v8_flags.sticky_mark_bits) {
    DCHECK_NULL(new_space());
    size_t new_space_capacity =
        sticky_space()->Capacity() - sticky_space()->young_objects_size();
    size_t new_lo_space_capacity = new_lo_space_ ? new_lo_space_->Size() : 0;
    return CanExpandOldGeneration(size + new_space_capacity +
                                  new_lo_space_capacity);
  }
  if (!new_space()) {
    DCHECK_NULL(new_lo_space());
    return CanExpandOldGeneration(size);
  }
  size_t new_space_capacity =
      new_space()->Capacity() + new_lo_space()->Size() +
      (v8_flags.minor_ms ? 0
                         : semi_space_new_space()->QuarantinedPageCount() *
                               NormalPage::kPageSize);

  // Over-estimate the new space size using capacity to allow some slack.
  return CanExpandOldGeneration(size + new_space_capacity);
}

bool Heap::HasBeenSetUp() const {
  // We will always have an old space when the heap is set up.
  return old_space_ != nullptr;
}

bool Heap::ShouldUseBackgroundThreads() const {
  return !v8_flags.single_threaded_gc_in_background ||
         !isolate()->EfficiencyModeEnabled();
}

bool Heap::ShouldUseIncrementalMarking() const {
  if (v8_flags.single_threaded_gc_in_background &&
      isolate()->EfficiencyModeEnabled()) {
    return v8_flags.incremental_marking_for_gc_in_background;
  } else {
    return true;
  }
}

bool Heap::ShouldOptimizeForBattery() const {
  return v8_flags.optimize_gc_for_battery ||
         isolate()->BatterySaverModeEnabled();
}

GarbageCollector Heap::SelectGarbageCollector(AllocationSpace space,
                                              GarbageCollectionReason gc_reason,
                                              const char** reason) const {
  if (gc_reason == GarbageCollectionReason::kFinalizeMinorMSForMajorGC) {
    DCHECK_NE(static_cast<bool>(new_space()),
              v8_flags.sticky_mark_bits.value());
    DCHECK(!ShouldReduceMemory());
    *reason = "MinorMS finalization for starting major GC";
    return GarbageCollector::MINOR_MARK_SWEEPER;
  }

  if (gc_reason == GarbageCollectionReason::kFinalizeConcurrentMinorMS) {
    DCHECK_NE(static_cast<bool>(new_space()),
              v8_flags.sticky_mark_bits.value());
    DCHECK(!ShouldReduceMemory());
    *reason = "Concurrent MinorMS needs finalization";
    return GarbageCollector::MINOR_MARK_SWEEPER;
  }
  // Is global GC requested?
  if (space != NEW_SPACE && space != NEW_LO_SPACE) {
    isolate_->counters()->gc_compactor_caused_by_request()->Increment();
    *reason = "GC in old space requested";
    return GarbageCollector::MARK_COMPACTOR;
  }

  DCHECK_IMPLIES(ShouldStressCompaction(), v8_flags.gc_global);
  if (v8_flags.gc_global || !use_new_space()) {
    *reason = "GC in old space forced by flags";
    return GarbageCollector::MARK_COMPACTOR;
  }

  if (incremental_marking()->IsMajorMarking()) {
    *reason = "Incremental marking forced finalization";
    return GarbageCollector::MARK_COMPACTOR;
  }

  if (!CanPromoteYoungAndExpandOldGeneration(0)) {
    isolate_->counters()
        ->gc_compactor_caused_by_oldspace_exhaustion()
        ->Increment();
    *reason = "scavenge might not succeed";
    return GarbageCollector::MARK_COMPACTOR;
  }

  DCHECK(!v8_flags.single_generation);
  DCHECK(!v8_flags.gc_global);
  // Default
  *reason = nullptr;
  return YoungGenerationCollector();
}

void Heap::SetGCState(HeapState state) {
  gc_state_.store(state, std::memory_order_relaxed);
}

bool Heap::IsGCWithMainThreadStack() const {
  return embedder_stack_state_ == StackState::kMayContainHeapPointers;
}

bool Heap::IsGCWithStack() const {
  return IsGCWithMainThreadStack() || stack().HasBackgroundStacks();
}

bool Heap::CanShortcutStringsDuringGC(GarbageCollector collector) const {
  if (!v8_flags.shortcut_strings_with_stack && IsGCWithStack()) return false;

  switch (collector) {
    case GarbageCollector::MINOR_MARK_SWEEPER:
      if (!v8_flags.minor_ms_shortcut_strings) return false;

      DCHECK(!incremental_marking()->IsMajorMarking());

      // Minor MS cannot short cut strings during concurrent marking.
      if (incremental_marking()->IsMinorMarking()) return false;

      // Minor MS uses static roots to check for strings to shortcut.
      if (!V8_STATIC_ROOTS_BOOL) return false;

      break;
    case GarbageCollector::SCAVENGER:
      // Scavenger cannot short cut strings during incremental marking.
      DCHECK(!incremental_marking()->IsMajorMarking());

      if (isolate()->has_shared_space() &&
          !isolate()->is_shared_space_isolate() &&
          isolate()
              ->shared_space_isolate()
              ->heap()
              ->incremental_marking()
              ->IsMarking()) {
        DCHECK(isolate()
                   ->shared_space_isolate()
                   ->heap()
                   ->incremental_marking()
                   ->IsMajorMarking());
        return false;
      }
      break;
    default:
      UNREACHABLE();
  }

  return true;
}

void Heap::PrintShortHeapStatistics() {
  if (!v8_flags.trace_gc_verbose) return;
  PrintIsolate(isolate_,
               "Memory allocator,           used: %6zu KB"
               ", available:  %7zu KB\n",
               memory_allocator()->Size() / KB,
               memory_allocator()->Available() / KB);
  PrintIsolate(isolate_,
               "Read-only space,            used: %6zu KB"
               ", available:  %7zu KB"
               ", committed: %6zu KB\n",
               read_only_space_->Size() / KB, size_t{0},
               read_only_space_->CommittedMemory() / KB);
  PrintIsolate(isolate_,
               "New space,                  used: %6zu KB"
               ", available:%c %7zu KB"
               ", committed: %6zu KB\n",
               NewSpaceSize() / KB,
               (v8_flags.minor_ms && minor_sweeping_in_progress()) ? '*' : ' ',
               new_space_->Available() / KB,
               new_space_->CommittedMemory() / KB);
  PrintIsolate(isolate_,
               "New large object space,     used: %6zu KB"
               ", available:  %7zu KB"
               ", committed: %6zu KB\n",
               new_lo_space_->SizeOfObjects() / KB,
               new_lo_space_->Available() / KB,
               new_lo_space_->CommittedMemory() / KB);
  PrintIsolate(isolate_,
               "Old space,                  used: %6zu KB"
               ", available:%c %7zu KB"
               ", committed: %6zu KB\n",
               old_space_->SizeOfObjects() / KB,
               major_sweeping_in_progress() ? '*' : ' ',
               old_space_->Available() / KB,
               old_space_->CommittedMemory() / KB);
  PrintIsolate(isolate_,
               "Code space,                 used: %6zu KB"
               ", available:%c %7zu KB"
               ", committed: %6zu KB\n",
               code_space_->SizeOfObjects() / KB,
               major_sweeping_in_progress() ? '*' : ' ',
               code_space_->Available() / KB,
               code_space_->CommittedMemory() / KB);
  PrintIsolate(isolate_,
               "Large object space,         used: %6zu KB"
               ", available:  %7zu KB"
               ", committed: %6zu KB\n",
               lo_space_->SizeOfObjects() / KB, lo_space_->Available() / KB,
               lo_space_->CommittedMemory() / KB);
  PrintIsolate(isolate_,
               "Code large object space,    used: %6zu KB"
               ", available:  %7zu KB"
               ", committed: %6zu KB\n",
               code_lo_space_->SizeOfObjects() / KB,
               code_lo_space_->Available() / KB,
               code_lo_space_->CommittedMemory() / KB);
  PrintIsolate(isolate_,
               "Trusted space,              used: %6zu KB"
               ", available:%c %7zu KB"
               ", committed: %6zu KB\n",
               trusted_space_->SizeOfObjects() / KB,
               major_sweeping_in_progress() ? '*' : ' ',
               trusted_space_->Available() / KB,
               trusted_space_->CommittedMemory() / KB);
  PrintIsolate(isolate_,
               "Trusted large object space, used: %6zu KB"
               ", available:  %7zu KB"
               ", committed: %6zu KB\n",
               trusted_lo_space_->SizeOfObjects() / KB,
               trusted_lo_space_->Available() / KB,
               trusted_lo_space_->CommittedMemory() / KB);
  ReadOnlySpace* const ro_space = read_only_space_;
  PrintIsolate(isolate_,
               "All spaces,                 used: %6zu KB"
               ", available:%c %7zu KB"
               ", committed: %6zu KB\n",
               (this->SizeOfObjects() + ro_space->Size()) / KB,
               sweeping_in_progress() ? '*' : ' ', (this->Available()) / KB,
               (this->CommittedMemory() + ro_space->CommittedMemory()) / KB);
  const size_t chunks = memory_allocator()->GetPooledChunksCount();
  PrintIsolate(isolate_, "Pool buffering %4zu chunk(s) of committed: %7zu KB\n",
               chunks, (chunks * NormalPage::kPageSize) / KB);
  PrintIsolate(isolate_,
               "External memory reported:                  %7" PRId64 " KB\n",
               external_memory() / KB);
  PrintIsolate(isolate_,
               "Backing store memory:                      %7" PRIu64 " KB\n",
               backing_store_bytes() / KB);
  PrintIsolate(isolate_, "External memory global:                    %7zu KB\n",
               external_memory_callback_() / KB);
  PrintIsolate(isolate_,
               "Total time spent in GC:                    %7.1f ms\n",
               total_gc_time_ms_.InMillisecondsF());
  if (sweeping_in_progress()) {
    PrintIsolate(isolate_,
                 "(*) Sweeping is still in progress, making available sizes "
                 "inaccurate.\n");
  }
}

void Heap::PrintFreeListsStats() {
  DCHECK(v8_flags.trace_gc_freelists);

  if (v8_flags.trace_gc_freelists_verbose) {
    PrintIsolate(isolate_,
                 "Freelists statistics per Page: "
                 "[category: length || total free bytes]\n");
  }

  std::vector<int> categories_lengths(
      old_space()->free_list()->number_of_categories(), 0);
  std::vector<size_t> categories_sums(
      old_space()->free_list()->number_of_categories(), 0);
  unsigned int pageCnt = 0;

  // This loops computes freelists lengths and sum.
  // If v8_flags.trace_gc_freelists_verbose is enabled, it also prints
  // the stats of each FreeListCategory of each Page.
  for (NormalPage* page : *old_space()) {
    std::ostringstream out_str;

    if (v8_flags.trace_gc_freelists_verbose) {
      out_str << "Page " << std::setw(4) << pageCnt;
    }

    for (int cat = kFirstCategory;
         cat <= old_space()->free_list()->last_category(); cat++) {
      FreeListCategory* free_list =
          page->free_list_category(static_cast<FreeListCategoryType>(cat));
      int length = free_list->FreeListLength();
      size_t sum = free_list->SumFreeList();

      if (v8_flags.trace_gc_freelists_verbose) {
        out_str << "[" << cat << ": " << std::setw(4) << length << " || "
                << std::setw(6) << sum << " ]"
                << (cat == old_space()->free_list()->last_category() ? "\n"
                                                                     : ", ");
      }
      categories_lengths[cat] += length;
      categories_sums[cat] += sum;
    }

    if (v8_flags.trace_gc_freelists_verbose) {
      PrintIsolate(isolate_, "%s", out_str.str().c_str());
    }

    pageCnt++;
  }

  // Print statistics about old_space (pages, free/wasted/used memory...).
  PrintIsolate(
      isolate_,
      "%d pages. Free space: %.1f MB (waste: %.2f). "
      "Usage: %.1f/%.1f (MB) -> %.2f%%.\n",
      pageCnt, static_cast<double>(old_space_->Available()) / MB,
      static_cast<double>(old_space_->Waste()) / MB,
      static_cast<double>(old_space_->Size()) / MB,
      static_cast<double>(old_space_->Capacity()) / MB,
      static_cast<double>(old_space_->Size()) / old_space_->Capacity() * 100);

  // Print global statistics of each FreeListCategory (length & sum).
  PrintIsolate(isolate_,
               "FreeLists global statistics: "
               "[category: length || total free KB]\n");
  std::ostringstream out_str;
  for (int cat = kFirstCategory;
       cat <= old_space()->free_list()->last_category(); cat++) {
    out_str << "[" << cat << ": " << categories_lengths[cat] << " || "
            << std::fixed << std::setprecision(2)
            << static_cast<double>(categories_sums[cat]) / KB << " KB]"
            << (cat == old_space()->free_list()->last_category() ? "\n" : ", ");
  }
  PrintIsolate(isolate_, "%s", out_str.str().c_str());
}

void Heap::DumpJSONHeapStatistics(std::stringstream& stream) {
  HeapStatistics stats;
  reinterpret_cast<v8::Isolate*>(isolate())->GetHeapStatistics(&stats);

// clang-format off
#define DICT(s) "{" << s << "}"
#define LIST(s) "[" << s << "]"
#define QUOTE(s) "\"" << s << "\""
#define MEMBER(s) QUOTE(s) << ":"

  auto SpaceStatistics = [this](int space_index) {
    HeapSpaceStatistics space_stats;
    reinterpret_cast<v8::Isolate*>(isolate())->GetHeapSpaceStatistics(
        &space_stats, space_index);
    std::stringstream stream;
    stream << DICT(
      MEMBER("name")
        << QUOTE(ToString(
              static_cast<AllocationSpace>(space_index)))
        << ","
      MEMBER("size") << space_stats.space_size() << ","
      MEMBER("used_size") << space_stats.space_used_size() << ","
      MEMBER("available_size") << space_stats.space_available_size() << ","
      MEMBER("physical_size") << space_stats.physical_space_size());
    return stream.str();
  };

  stream << DICT(
    MEMBER("isolate") << QUOTE(reinterpret_cast<void*>(isolate())) << ","
    MEMBER("id") << gc_count() << ","
    MEMBER("time_ms") << isolate()->time_millis_since_init() << ","
    MEMBER("total_heap_size") << stats.total_heap_size() << ","
    MEMBER("total_heap_size_executable")
      << stats.total_heap_size_executable() << ","
    MEMBER("total_physical_size") << stats.total_physical_size() << ","
    MEMBER("total_available_size") << stats.total_available_size() << ","
    MEMBER("used_heap_size") << stats.used_heap_size() << ","
    MEMBER("heap_size_limit") << stats.heap_size_limit() << ","
    MEMBER("malloced_memory") << stats.malloced_memory() << ","
    MEMBER("external_memory") << stats.external_memory() << ","
    MEMBER("peak_malloced_memory") << stats.peak_malloced_memory() << ","
    MEMBER("spaces") << LIST(
      SpaceStatistics(RO_SPACE)      << "," <<
      SpaceStatistics(NEW_SPACE)     << "," <<
      SpaceStatistics(OLD_SPACE)     << "," <<
      SpaceStatistics(CODE_SPACE)    << "," <<
      SpaceStatistics(LO_SPACE)      << "," <<
      SpaceStatistics(CODE_LO_SPACE) << "," <<
      SpaceStatistics(NEW_LO_SPACE)  << "," <<
      SpaceStatistics(TRUSTED_SPACE) << "," <<
      SpaceStatistics(TRUSTED_LO_SPACE)));

#undef DICT
#undef LIST
#undef QUOTE
#undef MEMBER
  // clang-format on
}

void Heap::ReportStatisticsAfterGC() {
  if (deferred_counters_.empty()) return;
  // Move the contents into a new SmallVector first, in case
  // {Isolate::CountUsage} puts the counters into {deferred_counters_} again.
  decltype(deferred_counters_) to_report = std::move(deferred_counters_);
  DCHECK(deferred_counters_.empty());
  isolate()->CountUsage(base::VectorOf(to_report));
}

void Heap::AddHeapObjectAllocationTracker(
    HeapObjectAllocationTracker* tracker) {
  if (allocation_trackers_.empty() && v8_flags.inline_new) {
    DisableInlineAllocation();
  }
  allocation_trackers_.push_back(tracker);
  if (allocation_trackers_.size() == 1) {
    isolate_->UpdateLogObjectRelocation();
  }
}

void Heap::RemoveHeapObjectAllocationTracker(
    HeapObjectAllocationTracker* tracker) {
  std::erase(allocation_trackers_, tracker);
  if (allocation_trackers_.empty()) {
    isolate_->UpdateLogObjectRelocation();
  }
  if (allocation_trackers_.empty() && v8_flags.inline_new) {
    EnableInlineAllocation();
  }
}

void Heap::IncrementDeferredCounts(
    base::Vector<const v8::Isolate::UseCounterFeature> features) {
  deferred_counters_.insert(deferred_counters_.end(), features.begin(),
                            features.end());
}

void Heap::GarbageCollectionPrologue(
    GarbageCollectionReason gc_reason,
    const v8::GCCallbackFlags gc_callback_flags) {
  TRACE_GC(tracer(), GCTracer::Scope::HEAP_PROLOGUE);

  is_current_gc_forced_ = gc_callback_flags & v8::kGCCallbackFlagForced ||
                          current_gc_flags_ & GCFlag::kForced ||
                          force_gc_on_next_allocation_;
  is_current_gc_for_heap_profiler_ =
      gc_reason == GarbageCollectionReason::kHeapProfiler;
  if (force_gc_on_next_allocation_) force_gc_on_next_allocation_ = false;

#ifdef V8_ENABLE_ALLOCATION_TIMEOUT
  heap_allocator_->UpdateAllocationTimeout();
#endif  // V8_ENABLE_ALLOCATION_TIMEOUT

  if (minor_gc_job()) {
    DCHECK(use_new_space());
    minor_gc_job()->CancelTaskIfScheduled();
  }

  // Reset GC statistics.
  promoted_objects_size_ = 0;
  previous_new_space_surviving_object_size_ = new_space_surviving_object_size_;
  new_space_surviving_object_size_ = 0;
  nodes_died_in_new_space_ = 0;
  nodes_copied_in_new_space_ = 0;
  nodes_promoted_ = 0;

  UpdateMaximumCommitted();

#ifdef DEBUG
  DCHECK(!AllowGarbageCollection::IsAllowed());
  DCHECK_EQ(gc_state(), NOT_IN_GC);

  if (v8_flags.gc_verbose) Print();
#endif  // DEBUG
}

void Heap::GarbageCollectionPrologueInSafepoint(GarbageCollector collector) {
  TRACE_GC(tracer(), GCTracer::Scope::HEAP_PROLOGUE_SAFEPOINT);
  gc_count_ = GCEpoch(gc_count_.value() + 1);
  new_space_allocation_counter_ = NewSpaceAllocationCounter();
  // We provide a fallback for the case when the page pool timeout is disabled.
  // This is to prevent unbounded growth of the pool for the non-default
  // configuration.
  if (V8_UNLIKELY(v8_flags.memory_pool_timeout == 0) &&
      collector == GarbageCollector::MARK_COMPACTOR) {
    if (auto* memory_pool = isolate_->isolate_group()->memory_pool()) {
      memory_pool->ReleaseImmediately(isolate_);
    }
  }
}

size_t Heap::NewSpaceAllocationCounter() const {
  size_t counter = new_space_allocation_counter_;
  if (new_space_) {
    DCHECK(!allocator()->new_space_allocator()->IsLabValid());
    counter += new_space()->AllocatedSinceLastGC();
  }
  return counter;
}

size_t Heap::SizeOfObjects() {
  size_t total = 0;

  for (SpaceIterator it(this); it.HasNext();) {
    total += it.Next()->SizeOfObjects();
  }
  return total;
}

size_t Heap::TotalGlobalHandlesSize() {
  return isolate_->global_handles()->TotalSize() +
         isolate_->traced_handles()->total_size_bytes();
}

size_t Heap::UsedGlobalHandlesSize() {
  return isolate_->global_handles()->UsedSize() +
         isolate_->traced_handles()->used_size_bytes();
}

void Heap::AddAllocationObserversToAllSpaces(
    AllocationObserver* observer, AllocationObserver* new_space_observer) {
  DCHECK(observer && new_space_observer);
  FreeMainThreadLinearAllocationAreas();
  allocator()->AddAllocationObserver(observer, new_space_observer);
}

void Heap::RemoveAllocationObserversFromAllSpaces(
    AllocationObserver* observer, AllocationObserver* new_space_observer) {
  DCHECK(observer && new_space_observer);
  allocator()->RemoveAllocationObserver(observer, new_space_observer);
}

void Heap::PublishMainThreadPendingAllocations() {
  allocator()->PublishPendingAllocations();
}

void Heap::DeoptMarkedAllocationSites() {
  // TODO(hpayer): If iterating over the allocation sites list becomes a
  // performance issue, use a cache data structure in heap instead.

  ForeachAllocationSite(
      allocation_sites_list(), [this](Tagged<AllocationSite> site) {
        if (site->deopt_dependent_code()) {
          DependentCode::MarkCodeForDeoptimization(
              isolate_, site,
              DependentCode::kAllocationSiteTenuringChangedGroup);
          site->set_deopt_dependent_code(false);
        }
      });

  Deoptimizer::DeoptimizeMarkedCode(isolate_);
}

static GCType GetGCTypeFromGarbageCollector(GarbageCollector collector) {
  switch (collector) {
    case GarbageCollector::MARK_COMPACTOR:
      return kGCTypeMarkSweepCompact;
    case GarbageCollector::SCAVENGER:
      return kGCTypeScavenge;
    case GarbageCollector::MINOR_MARK_SWEEPER:
      return kGCTypeMinorMarkSweep;
    default:
      UNREACHABLE();
  }
}

void Heap::GarbageCollectionEpilogueInSafepoint(GarbageCollector collector) {
  TRACE_GC(tracer(), GCTracer::Scope::HEAP_EPILOGUE_SAFEPOINT);

  // Invoke GCEpilogueCallbacks for all involved LocalHeaps.
  {
    // Allows handle derefs for all threads/isolates from this thread.
    AllowHandleUsageOnAllThreads allow_all_handle_derefs;
    safepoint()->IterateLocalHeaps([](LocalHeap* local_heap) {
      local_heap->InvokeGCEpilogueCallbacksInSafepoint(
          GCCallbacksInSafepoint::GCType::kLocal);
    });

    if (collector == GarbageCollector::MARK_COMPACTOR &&
        isolate()->is_shared_space_isolate()) {
      isolate()->global_safepoint()->IterateClientIsolates([](Isolate* client) {
        client->heap()->safepoint()->IterateLocalHeaps(
            [](LocalHeap* local_heap) {
              local_heap->InvokeGCEpilogueCallbacksInSafepoint(
                  GCCallbacksInSafepoint::GCType::kShared);
            });
      });
    }
  }

  // Invoke global GCRootsProviders for all involved Heap.
  {
    GCType gc_type = GetGCTypeFromGarbageCollector(collector);
    for (GCRootsProvider* provider : global_gc_roots_providers_) {
      provider->GCEpilogueInSafepoint(gc_type);
    }

    if (collector == GarbageCollector::MARK_COMPACTOR &&
        isolate()->is_shared_space_isolate()) {
      isolate()->global_safepoint()->IterateClientIsolates(
          [gc_type](Isolate* client) {
            for (GCRootsProvider* provider :
                 client->heap()->global_gc_roots_providers_) {
              provider->GCEpilogueInSafepoint(gc_type);
            }
          });
    }
  }

#define UPDATE_COUNTERS_FOR_SPACE(space)                \
  isolate_->counters()->space##_bytes_available()->Set( \
      static_cast<int>(space()->Available()));          \
  isolate_->counters()->space##_bytes_committed()->Set( \
      static_cast<int>(space()->CommittedMemory()));    \
  isolate_->counters()->space##_bytes_used()->Set(      \
      static_cast<int>(space()->SizeOfObjects()));
#define UPDATE_FRAGMENTATION_FOR_SPACE(space)                          \
  if (space()->CommittedMemory() > 0) {                                \
    isolate_->counters()->external_fragmentation_##space()->AddSample( \
        static_cast<int>(100 - (space()->SizeOfObjects() * 100.0) /    \
                                   space()->CommittedMemory()));       \
  }
#define UPDATE_COUNTERS_AND_FRAGMENTATION_FOR_SPACE(space) \
  UPDATE_COUNTERS_FOR_SPACE(space)                         \
  UPDATE_FRAGMENTATION_FOR_SPACE(space)

  if (new_space()) {
    UPDATE_COUNTERS_FOR_SPACE(new_space)
  }

  UPDATE_COUNTERS_AND_FRAGMENTATION_FOR_SPACE(old_space)
  UPDATE_COUNTERS_AND_FRAGMENTATION_FOR_SPACE(code_space)

  UPDATE_COUNTERS_AND_FRAGMENTATION_FOR_SPACE(lo_space)
#undef UPDATE_COUNTERS_FOR_SPACE
#undef UPDATE_FRAGMENTATION_FOR_SPACE
#undef UPDATE_COUNTERS_AND_FRAGMENTATION_FOR_SPACE

#ifdef DEBUG
  if (v8_flags.print_global_handles) isolate_->global_handles()->Print();
  if (v8_flags.print_handles) PrintHandles();
  if (v8_flags.check_handle_count) CheckHandleCount();
#endif

  // Young generation GCs only run with  memory reducing flags during
  // interleaved GCs.
  DCHECK_IMPLIES(IsYoungGenerationCollector(collector), !ShouldReduceMemory());
  if (collector == GarbageCollector::MARK_COMPACTOR) {
    memory_pressure_level_.store(MemoryPressureLevel::kNone,
                                 std::memory_order_relaxed);

    if (v8_flags.stress_marking > 0) {
      stress_marking_percentage_ = NextStressMarkingLimit();
    }
    // Discard memory if the GC was requested to reduce memory.
    if (ShouldReduceMemory()) {
      memory_allocator_->ReleasePooledChunksImmediately();
#if V8_ENABLE_WEBASSEMBLY
      isolate_->stack_pool().ReleaseFinishedStacks();
#endif
    }
  }

  // Remove CollectionRequested flag from main thread state, as the collection
  // was just performed.
  safepoint()->AssertActive();
  LocalHeap::ThreadState old_state =
      main_thread_local_heap()->state_.ClearCollectionRequested();

  CHECK(old_state.IsRunning());

  // Resume all threads waiting for the GC.
  collection_barrier_->ResumeThreadsAwaitingCollection(RequestedGCKind::kMajor);
}

void Heap::GarbageCollectionEpilogue(GarbageCollector collector) {
  TRACE_GC(tracer(), GCTracer::Scope::HEAP_EPILOGUE);
  AllowGarbageCollection for_the_rest_of_the_epilogue;

  UpdateMaximumCommitted();

  isolate_->counters()->alive_after_last_gc()->Set(
      static_cast<int>(SizeOfObjects()));

  if (CommittedMemory() > 0) {
    isolate_->counters()->external_fragmentation_total()->AddSample(
        static_cast<int>(100 - (SizeOfObjects() * 100.0) / CommittedMemory()));

    isolate_->counters()->heap_sample_total_committed()->AddSample(
        static_cast<int>(CommittedMemory() / KB));
    isolate_->counters()->heap_sample_total_used()->AddSample(
        static_cast<int>(SizeOfObjects() / KB));
    isolate_->counters()->heap_sample_code_space_committed()->AddSample(
        static_cast<int>(code_space()->CommittedMemory() / KB));

    isolate_->counters()->heap_sample_maximum_committed()->AddSample(
        static_cast<int>(MaximumCommittedMemory() / KB));
  }

#ifdef DEBUG
  ReportStatisticsAfterGC();
  if (v8_flags.code_stats) ReportCodeStatistics("After GC");
#endif  // DEBUG

  last_gc_time_ = MonotonicallyIncreasingTimeInMs();
}

GCCallbacksScope::GCCallbacksScope(Heap* heap) : heap_(heap) {
  heap_->gc_callbacks_depth_++;
}

GCCallbacksScope::~GCCallbacksScope() { heap_->gc_callbacks_depth_--; }

bool GCCallbacksScope::CheckReenter() const {
  return heap_->gc_callbacks_depth_ == 1;
}

void Heap::HandleGCRequest() {
  if (IsStressingScavenge() && stress_scavenge_observer_->HasRequestedGC()) {
    CollectGarbage(NEW_SPACE, GarbageCollectionReason::kTesting);
    stress_scavenge_observer_->RequestedGCDone();
  } else if (HighMemoryPressure()) {
    CheckMemoryPressure();
  } else if (CollectionRequested()) {
    PerformRequestedGC(main_thread_local_heap_);
  } else if (incremental_marking()->MajorCollectionRequested()) {
    CollectAllGarbage(current_gc_flags_,
                      GarbageCollectionReason::kFinalizeMarkingViaStackGuard,
                      current_gc_callback_flags_);
  } else if (minor_mark_sweep_collector()->gc_finalization_requsted()) {
    CollectGarbage(NEW_SPACE,
                   GarbageCollectionReason::kFinalizeConcurrentMinorMS);
  }
}

namespace {
size_t MinorMSConcurrentMarkingTrigger(Heap* heap) {
  size_t young_capacity = 0;
  if (v8_flags.sticky_mark_bits) {
    // TODO(333906585): Adjust parameters.
    young_capacity = heap->sticky_space()->Capacity() -
                     heap->sticky_space()->old_objects_size();
  } else {
    young_capacity = heap->new_space()->TotalCapacity();
  }
  return young_capacity * v8_flags.minor_ms_concurrent_marking_trigger / 100;
}
}  // namespace

void Heap::StartMinorMSConcurrentMarkingIfNeeded() {
  if (incremental_marking()->IsMarking()) return;
  if (v8_flags.concurrent_minor_ms_marking && !IsTearingDown() &&
      incremental_marking()->CanAndShouldBeStarted() &&
      V8_LIKELY(!v8_flags.gc_global)) {
    size_t usable_capacity = 0;
    size_t new_space_size = 0;
    if (v8_flags.sticky_mark_bits) {
      // TODO(333906585): Adjust parameters.
      usable_capacity =
          sticky_space()->Capacity() - sticky_space()->old_objects_size();
      new_space_size = sticky_space()->young_objects_size();
    } else {
      usable_capacity = paged_new_space()->paged_space()->UsableCapacity();
      new_space_size = new_space()->Size();
    }
    if ((usable_capacity >=
         v8_flags.minor_ms_min_new_space_capacity_for_concurrent_marking_mb *
             MB) &&
        (new_space_size >= MinorMSConcurrentMarkingTrigger(this)) &&
        ShouldUseBackgroundThreads()) {
      StartIncrementalMarking(GCFlag::kNoFlags, GarbageCollectionReason::kTask,
                              kNoGCCallbackFlags,
                              GarbageCollector::MINOR_MARK_SWEEPER);
      // Schedule a task for finalizing the GC if needed.
      minor_gc_job()->TryScheduleTask();
    }
  }
}

void Heap::CollectAllGarbage(GCFlags gc_flags,
                             GarbageCollectionReason gc_reason,
                             const v8::GCCallbackFlags gc_callback_flags,
                             PerformHeapLimitCheck check_heap_limit_reached) {
  current_gc_flags_ = gc_flags;
  CollectGarbage(OLD_SPACE, gc_reason, gc_callback_flags,
                 check_heap_limit_reached);
  DCHECK_EQ(GCFlags(GCFlag::kNoFlags), current_gc_flags_);
}

namespace {

// Frees caches when under memory pressure. The method assumes that callsites
// are close to crashing and will very aggressively free memory.
void FreeCachesOnMemoryPressure(Isolate* isolate) {
  isolate->AbortConcurrentOptimization(BlockingBehavior::kDontBlock);
  isolate->ClearSerializerData();
  isolate->compilation_cache()->Clear();

  // TODO(ishell): consider trimming number to string caches to initial size.

  if (auto* memory_pool = IsolateGroup::current()->memory_pool()) {
    if (v8_flags.memory_pool_release_before_memory_pressure_gcs) {
      memory_pool->ReleaseImmediately(isolate);
    }
  }
}

}  // anonymous namespace

void Heap::CollectAllAvailableGarbage(GarbageCollectionReason gc_reason) {
  // Min and max number of attempts for GC. The method will continue with more
  // GCs until the root set is stable.
  static constexpr int kMaxNumberOfAttempts = 7;
  static constexpr int kMinNumberOfAttempts = 2;

  // Stop background threads from running/allocating until all individual GCs
  // triggered by this function are done.
  SafepointScope safepoint_scope(isolate(),
                                 kGlobalSafepointForSharedSpaceIsolate);

  collection_barrier_->StopTimeToCollectionTimer(RequestedGCKind::kLastResort);

  // Returns the number of roots. We assume stack layout is stable but global
  // roots could change between GCs due to finalizers and weak callbacks.
  const auto num_roots = [this]() {
    size_t js_roots = 0;
    js_roots += isolate()->global_handles()->handles_count();
    js_roots += isolate()->eternal_handles()->handles_count();
    size_t cpp_roots = 0;
    if (auto* cpp_heap = CppHeap::From(cpp_heap_)) {
      cpp_roots += cpp_heap->GetStrongPersistentRegion().NodesInUse();
      cpp_roots +=
          cpp_heap->GetStrongCrossThreadPersistentRegion().NodesInUse();
    }
    return js_roots + cpp_roots;
  };

  if (gc_reason == GarbageCollectionReason::kLastResort) {
    InvokeNearHeapLimitCallback();
  }
  RCS_SCOPE(isolate(), RuntimeCallCounterId::kGC_Custom_AllAvailableGarbage);

  FreeCachesOnMemoryPressure(isolate());

  GCFlags gc_flags = GCFlag::kReduceMemoryFootprint;
  GCCallbackFlags gc_callback_flags =
      GCCallbackFlags::kGCCallbackFlagCollectAllAvailableGarbage;

  if (gc_reason == GarbageCollectionReason::kLastResort ||
      gc_reason == GarbageCollectionReason::kExternalMemoryPressure) {
    gc_flags |= GCFlag::kLastResort;
    gc_callback_flags = static_cast<GCCallbackFlags>(
        gc_callback_flags | GCCallbackFlags::kGCCallbackFlagLastResort);
  }

  if (gc_reason == GarbageCollectionReason::kLowMemoryNotification) {
    gc_flags |= GCFlag::kForced;
  }

  const auto perform_heap_limit_check = v8_flags.late_heap_limit_check
                                            ? PerformHeapLimitCheck::kNo
                                            : PerformHeapLimitCheck::kYes;
  const auto perform_ineffective_mc_check =
      v8_flags.ineffective_gcs_forces_last_resort
          ? PerformIneffectiveMarkCompactCheck::kNo
          : PerformIneffectiveMarkCompactCheck::kYes;
  for (int attempt = 0; attempt < kMaxNumberOfAttempts; attempt++) {
    const size_t roots_before = num_roots();
    current_gc_flags_ = gc_flags;
    CollectGarbage(OLD_SPACE, gc_reason, gc_callback_flags,
                   perform_heap_limit_check, perform_ineffective_mc_check);
    DCHECK_EQ(GCFlags(GCFlag::kNoFlags), current_gc_flags_);

    // As long as we are at or above the heap limit, we need another GC to
    // survive CheckHeapLimitReached() after the loop.
    if (ReachedHeapLimit()) {
      continue;
    }

    if ((roots_before == num_roots()) &&
        ((attempt + 1) >= kMinNumberOfAttempts)) {
      break;
    }
  }

  CheckHeapLimitReached();
  if (v8_flags.ineffective_gcs_forces_last_resort) {
    CheckIneffectiveMarkCompact(
        OldGenerationConsumedBytes(), GlobalConsumedBytes(),
        tracer()->AverageMarkCompactMutatorUtilization());
  }

  FlushLiftoffCode(gc_reason);
  CompleteArrayBufferSweeping();

  if (gc_reason == GarbageCollectionReason::kLastResort &&
      v8_flags.heap_snapshot_on_oom) {
    heap_profiler()->WriteSnapshotToDiskAfterGC();
  }

  collection_barrier_->ResumeThreadsAwaitingCollection(
      RequestedGCKind::kLastResort);
}

void Heap::PreciseCollectAllGarbage(GCFlags gc_flags,
                                    GarbageCollectionReason gc_reason,
                                    const GCCallbackFlags gc_callback_flags) {
  FinalizeIncrementalMarkingAtomicallyIfRunning(gc_reason);
  CollectAllGarbage(gc_flags, gc_reason, gc_callback_flags);
}

void Heap::HandleExternalMemoryInterrupt() {
  const GCCallbackFlags kGCCallbackFlagsForExternalMemory =
      static_cast<GCCallbackFlags>(
          kGCCallbackFlagSynchronousPhantomCallbackProcessing |
          kGCCallbackFlagCollectAllExternalMemory);
  uint64_t current = external_memory();
  if (current > external_memory_hard_limit()) {
    TRACE_EVENT2("devtools.timeline,v8", "V8.ExternalMemoryPressure",
                 "external_memory_mb", static_cast<int>((current) / MB),
                 "external_memory_hard_limit_mb",
                 static_cast<int>((external_memory_hard_limit()) / MB));
    CollectAllGarbage(
        GCFlag::kReduceMemoryFootprint,
        GarbageCollectionReason::kExternalMemoryPressure,
        static_cast<GCCallbackFlags>(kGCCallbackFlagCollectAllAvailableGarbage |
                                     kGCCallbackFlagsForExternalMemory));
    return;
  }
  if (v8_flags.external_memory_accounted_in_global_limit) {
    // Under `external_memory_accounted_in_global_limit`, external interrupt
    // only triggers a check to allocation limits.
    limits()->UpdateExternalMemoryLimitForInterrupt(current);
    StartIncrementalMarkingIfAllocationLimitIsReached(
        main_thread_local_heap(), GCFlagsForIncrementalMarking(),
        kGCCallbackFlagsForExternalMemory);
    return;
  }
  uint64_t soft_limit = external_memory_soft_limit();
  if (current <= soft_limit) {
    return;
  }
  TRACE_EVENT2("devtools.timeline,v8", "V8.ExternalMemoryPressure",
               "external_memory_mb", static_cast<int>((current) / MB),
               "external_memory_soft_limit_mb",
               static_cast<int>((soft_limit) / MB));
  if (incremental_marking()->IsStopped()) {
    if (incremental_marking()->CanAndShouldBeStarted()) {
      StartIncrementalMarking(GCFlagsForIncrementalMarking(),
                              GarbageCollectionReason::kExternalMemoryPressure,
                              kGCCallbackFlagsForExternalMemory);
    } else {
      CollectAllGarbage(i::GCFlag::kNoFlags,
                        GarbageCollectionReason::kExternalMemoryPressure,
                        kGCCallbackFlagsForExternalMemory);
    }
  } else {
    // Incremental marking is turned on and has already been started.
    current_gc_callback_flags_ = static_cast<GCCallbackFlags>(
        current_gc_callback_flags_ | kGCCallbackFlagsForExternalMemory);
    incremental_marking()->AdvanceAndFinalizeIfNecessary();
  }
}

uint64_t Heap::external_memory_hard_limit() {
  return limits()->external_memory_low_since_last_gc() +
         limits()->max_old_generation_size() / 2;
}

uint64_t Heap::external_memory_limit_for_interrupt() {
  return limits()->external_memory_limit_for_interrupt();
}

uint64_t Heap::external_memory_soft_limit() {
  return limits()->external_memory_low_since_last_gc() +
         kExternalAllocationSoftLimit;
}

Heap::DevToolsTraceEventScope::DevToolsTraceEventScope(Heap* heap,
                                                       const char* event_name,
                                                       const char* event_type)
    : heap_(heap), event_name_(event_name) {
  TRACE_EVENT_BEGIN2("devtools.timeline,v8", event_name_, "usedHeapSizeBefore",
                     heap_->SizeOfObjects(), "type", event_type);
}

Heap::DevToolsTraceEventScope::~DevToolsTraceEventScope() {
  TRACE_EVENT_END1("devtools.timeline,v8", event_name_, "usedHeapSizeAfter",
                   heap_->SizeOfObjects());
}

namespace {

template <typename Callback>
void InvokeExternalCallbacks(Isolate* isolate, Callback callback) {
  DCHECK(!AllowJavascriptExecution::IsAllowed(isolate));
  AllowGarbageCollection allow_gc;
  // Temporary override any embedder stack state as callbacks may create
  // their own state on the stack and recursively trigger GC.
  EmbedderStackStateScope embedder_scope(
      isolate->heap(), EmbedderStackStateOrigin::kExplicitInvocation,
      StackState::kMayContainHeapPointers);
  VMState<EXTERNAL> callback_state(isolate);

  callback();
}

}  // anonymous namespace

void Heap::CollectGarbage(
    AllocationSpace space, GarbageCollectionReason gc_reason,
    const v8::GCCallbackFlags gc_callback_flags,
    PerformHeapLimitCheck perform_heap_limit_check,
    PerformIneffectiveMarkCompactCheck check_ineffective_mark_compact) {
  CHECK(isolate_->IsOnCentralStack());
  // Any handles that are created during GC (eg during API callbacks)
  // should be in a fresh handle scope that is torn down before the GC
  // terminates. We don't really want new handles to appear during GC,
  // but some APIs require it - they should at least be short lived.
  SealHandleScope scope(isolate_);
  DCHECK_EQ(Isolate::TryGetCurrent(), isolate_);
  DCHECK_EQ(resize_new_space_mode_, ResizeNewSpaceMode::kNone);

  if (V8_UNLIKELY(!deserialization_complete_)) {
    // During isolate initialization heap always grows. GC is only requested
    // if a new page allocation fails. In such a case we should crash with
    // an out-of-memory instead of performing GC because the prologue/epilogue
    // callbacks may see objects that are not yet deserialized.
    CHECK(always_allocate());
    FatalProcessOutOfMemory("GC during deserialization");
  }

  // CollectGarbage consists of three parts:
  // 1. The prologue part which may execute callbacks. These callbacks may
  // allocate and trigger another garbage collection.
  // 2. The main garbage collection phase.
  // 3. The epilogue part which may execute callbacks. These callbacks may
  // allocate and trigger another garbage collection

  // Part 1: Invoke all callbacks which should happen before the actual garbage
  // collection is triggered. Note that these callbacks may trigger another
  // garbage collection since they may allocate.

  // JS execution is not allowed in any of the callbacks.
  DisallowJavascriptExecution no_js(isolate());

  // Some custom flushing (currently: FlushBytecodeFromSFI) can create
  // fresh TrustedPointerTableEntries during GC. These must not be affected
  // by an active TrustedPointerPublishingScope, so disable any such scope.
  DisableTrustedPointerPublishingScope no_trusted_pointer_tracking(isolate());

  DCHECK(AllowGarbageCollection::IsAllowed());

  const char* collector_reason = nullptr;
  const GarbageCollector collector =
      SelectGarbageCollector(space, gc_reason, &collector_reason);
  current_or_last_garbage_collector_ = collector;
  DCHECK_IMPLIES(v8_flags.minor_ms && IsYoungGenerationCollector(collector),
                 !ShouldReduceMemory());

  if (collector == GarbageCollector::MARK_COMPACTOR &&
      incremental_marking()->IsMinorMarking()) {
    const GCFlags gc_flags = current_gc_flags_;
    // Minor GCs should not be memory reducing.
    current_gc_flags_ &= ~GCFlag::kReduceMemoryFootprint;
    CollectGarbage(NEW_SPACE,
                   GarbageCollectionReason::kFinalizeMinorMSForMajorGC);
    current_gc_flags_ = gc_flags;
  }

  const GCType gc_type = GetGCTypeFromGarbageCollector(collector);

  // Prologue callbacks. These callbacks may trigger GC themselves and thus
  // cannot be related exactly to garbage collection cycles.
  //
  // GCTracer scopes are managed by callees.
  InvokeExternalCallbacks(isolate(), [this, gc_callback_flags, gc_type]() {
    // Ensure that all pending phantom callbacks are invoked.
    isolate()->global_handles()->InvokeSecondPassPhantomCallbacks();

    // Prologue callbacks registered with Heap.
    CallGCPrologueCallbacks(gc_type, gc_callback_flags,
                            GCTracer::Scope::HEAP_EXTERNAL_PROLOGUE);
  });

  // The main garbage collection phase.
  //
  // We need a stack marker at the top of all entry points to allow
  // deterministic passes over the stack. E.g., a verifier that should only
  // find a subset of references of the marker.
  //
  // TODO(chromium:1056170): Consider adding a component that keeps track
  // of relevant GC stack regions where interesting pointers can be found.
  stack().SetMarkerIfNeededAndCallback([this, collector, gc_reason,
                                        collector_reason, gc_callback_flags]() {
    DisallowGarbageCollection no_gc_during_gc;

    size_t committed_memory_before =
        collector == GarbageCollector::MARK_COMPACTOR
            ? CommittedOldGenerationMemory()
            : 0;

    tracer()->StartObservablePause(base::TimeTicks::Now());
    VMState<GC> state(isolate());
    DevToolsTraceEventScope devtools_trace_event_scope(
        this, IsYoungGenerationCollector(collector) ? "MinorGC" : "MajorGC",
        ToString(gc_reason));

    GarbageCollectionPrologue(gc_reason, gc_callback_flags);
    {
      GCTracer::RecordGCPhasesInfo record_gc_phases_info(this, collector,
                                                         gc_reason);
      std::optional<TimedHistogramScope> histogram_timer_scope;
      std::optional<OptionalTimedHistogramScope> histogram_timer_priority_scope;
      TRACE_EVENT0("v8", record_gc_phases_info.trace_event_name());
      if (record_gc_phases_info.type_timer()) {
        histogram_timer_scope.emplace(record_gc_phases_info.type_timer(),
                                      isolate_);
      }
      if (record_gc_phases_info.type_priority_timer()) {
        histogram_timer_priority_scope.emplace(
            record_gc_phases_info.type_priority_timer(), isolate_,
            OptionalTimedHistogramScopeMode::TAKE_TIME);
      }

      PerformGarbageCollection(collector, gc_reason, collector_reason);

      // Clear flags describing the current GC now that the current GC is
      // complete. Do this before GarbageCollectionEpilogue() since that could
      // trigger another unforced GC.
      is_current_gc_forced_ = false;
      is_current_gc_for_heap_profiler_ = false;

      if (collector == GarbageCollector::MARK_COMPACTOR ||
          collector == GarbageCollector::SCAVENGER) {
        tracer()->RecordGCPhasesHistograms(record_gc_phases_info.mode());
      }
      if ((collector == GarbageCollector::MARK_COMPACTOR ||
           collector == GarbageCollector::MINOR_MARK_SWEEPER) &&
          cpp_heap()) {
        CppHeap::From(cpp_heap())->FinishAtomicSweepingIfRunning();
      }
    }

    GarbageCollectionEpilogue(collector);
    if (collector == GarbageCollector::MARK_COMPACTOR &&
        v8_flags.track_detached_contexts) {
      isolate()->CheckDetachedContextsAfterGC();
    }

    if (collector == GarbageCollector::MARK_COMPACTOR) {
      if (memory_reducer_ != nullptr) {
        memory_reducer_->NotifyMarkCompact(committed_memory_before);
      }
      if (OldGenerationSizeOfObjects() <
          initial_max_old_generation_size_threshold_) {
        limits()->MaybeResetMaximumSizes(physical_memory());
      }
    }

    tracer()->StopAtomicPause();
    tracer()->StopObservablePause(collector, base::TimeTicks::Now());
    // Young generation cycles finish atomically. It is important that
    // StopObservablePause, and StopCycle are called in this
    // order; the latter may replace the current event with that of an
    // interrupted full cycle.
    if (IsYoungGenerationCollector(collector)) {
      tracer()->StopYoungCycleIfFinished();
    } else {
      tracer()->StopFullCycleIfFinished();
    }
    RecomputeLimits(collector);
  });

  if (IsLoadingInitialized() && !IsLoading()) {
    NotifyLoadingEnded(LeaveHeapState::kReachedTimeout);
  }

  if (IsInputHandlingInitialized() && !IsInputHandling()) {
    NotifyInputHandlingEnded(LeaveHeapState::kReachedTimeout);
  }

  // Epilogue callbacks. These callbacks may trigger GC themselves and thus
  // cannot be related exactly to garbage collection cycles.
  //
  // GCTracer scopes are managed by callees.
  InvokeExternalCallbacks(isolate(), [this, gc_callback_flags, gc_type]() {
    // Epilogue callbacks registered with Heap.
    CallGCEpilogueCallbacks(gc_type, gc_callback_flags,
                            GCTracer::Scope::HEAP_EXTERNAL_EPILOGUE);

    isolate()->global_handles()->PostGarbageCollectionProcessing(
        gc_callback_flags);
  });

  if (collector == GarbageCollector::MARK_COMPACTOR) {
    if ((gc_callback_flags &
         (kGCCallbackFlagForced | kGCCallbackFlagCollectAllAvailableGarbage))) {
      isolate()->CountUsage(v8::Isolate::kForcedGC);
    }
    if (v8_flags.heap_snapshot_on_gc >= 0) [[unlikely]] {
      const size_t gc_counter_filter =
          static_cast<size_t>(v8_flags.heap_snapshot_on_gc);
      if (gc_counter_filter == 0 || gc_counter_filter == ms_count_) {
        heap_profiler()->WriteSnapshotToDiskAfterGC();
      }
    }
  } else {
    // Start incremental marking for the next cycle. We do this only for
    // minor GCs to avoid a loop where mark-compact causes another mark-compact.
    StartIncrementalMarkingIfAllocationLimitIsReached(
        main_thread_local_heap(), GCFlagsForIncrementalMarking(),
        kGCCallbackScheduleIdleGarbageCollection);
    if (v8_flags.minor_ms &&
        (gc_reason != GarbageCollectionReason::kFinalizeMinorMSForMajorGC)) {
      StartMinorMSConcurrentMarkingIfNeeded();
    }
  }

  if (perform_heap_limit_check == PerformHeapLimitCheck::kYes) {
    CheckHeapLimitReached();
  }

  if (collector == GarbageCollector::MARK_COMPACTOR) {
    if (check_ineffective_mark_compact ==
        PerformIneffectiveMarkCompactCheck::kYes) {
      CheckIneffectiveMarkCompact(
          OldGenerationConsumedBytes(), GlobalConsumedBytes(),
          tracer()->AverageMarkCompactMutatorUtilization());
    }
    current_gc_flags_ = GCFlag::kNoFlags;
  }
}

bool Heap::ReachedHeapLimit() { return !CanExpandOldGeneration(0); }

bool Heap::HasConsecutiveIneffectiveMarkCompact() const {
  return consecutive_ineffective_mark_compacts_.load(
             std::memory_order_relaxed) > 0;
}

void Heap::CheckHeapLimitReached() {
  if (ReachedHeapLimit()) {
    InvokeNearHeapLimitCallback();
    if (ReachedHeapLimit()) {
      if (v8_flags.heap_snapshot_on_oom) {
        heap_profiler()->WriteSnapshotToDiskAfterGC();
      }
      FatalProcessOutOfMemory("Reached heap limit");
    }
  }
}

class TaskOnContextDispose final : public CancelableTask {
 public:
  static void TryPostJob(Heap* heap, size_t id, GCEpoch gc_count) {
    const auto task_runner =
        heap->GetForegroundTaskRunner(TaskPriority::kUserVisible);
    const bool non_nestable_tasks_enabled =
        task_runner->NonNestableTasksEnabled();
    auto task = std::make_unique<TaskOnContextDispose>(
        heap->isolate(),
        non_nestable_tasks_enabled ? StackState::kNoHeapPointers
                                   : StackState::kMayContainHeapPointers,
        id, gc_count);

    if (non_nestable_tasks_enabled) {
      task_runner->PostNonNestableTask(std::move(task));
    } else {
      task_runner->PostTask(std::move(task));
    }
  }

  TaskOnContextDispose(Isolate* isolate, StackState stack_state, size_t id,
                       GCEpoch gc_count)
      : CancelableTask(isolate),
        isolate_(isolate),
        stack_state_(stack_state),
        id_(id),
        gc_count_(gc_count) {}

  void RunInternal() override {
    // If the GC epoch doesn't match anymore, a GC was already triggered since
    // NotifyContextDisposed(). In this case we just bail out.
    const bool is_same_epoch = isolate_->heap()->gc_count() == gc_count_;

    TRACE_EVENT(TRACE_DISABLED_BY_DEFAULT("v8.gc"), "V8.GCContextDisposedTask",
                "id", id_, "is_same_epoch", is_same_epoch);
    USE(id_);

    if (is_same_epoch) {
      TryRunMinorGC();
    } else if (V8_UNLIKELY(v8_flags.trace_context_disposal)) {
      isolate_->PrintWithTimestamp(
          "[context-disposal task] epochs do not match, not starting any "
          "action.");
    }
  }

 private:
  void TryRunMinorGC() {
    // We bail out for a young gen below 1MB to avoid executing GC
    // when the mutator is not actually active.
    static constexpr size_t kMinYounGenSize = 1 * MB;
    // Use a small limit here to not postpone other work too much. We only
    // trigger the GC when the estimated GC time is below this limit.
    static constexpr base::TimeDelta kIdleLimit =
        base::TimeDelta::FromMilliseconds(5);
    static_assert(kIdleLimit <= kMaxSynchronuousGCOperation);

    // Do not trigger Minor GC if marking is running. This would finalize it.
    if (isolate_->heap()->incremental_marking()->IsMarking()) [[unlikely]] {
      if (V8_UNLIKELY(v8_flags.trace_context_disposal)) {
        isolate_->PrintWithTimestamp(
            "[context-disposal task] marking already running\n");
      }
      return;
    }

    auto* heap = isolate_->heap();
    const std::optional<double> young_gen_gc_speed =
        heap->tracer()->YoungGenerationSpeedInBytesPerMillisecond(
            YoungGenerationSpeedMode::kUpToAndIncludingAtomicPause);
    if (!young_gen_gc_speed) {
      return;
    }
    const size_t young_gen_bytes = heap->YoungGenerationSizeOfObjects();
    const base::TimeDelta young_gen_estimate =
        base::TimeDelta::FromMillisecondsD(young_gen_bytes /
                                           *young_gen_gc_speed);
    const bool run_young_gen_gc =
        young_gen_estimate < kIdleLimit && young_gen_bytes > kMinYounGenSize;
    if (V8_UNLIKELY(v8_flags.trace_context_disposal)) {
      isolate_->PrintWithTimestamp(
          "[context-disposal task] young generation size: %zuKB (min: "
          "%zuKB), GC speed: %fKB/ms, estimated time: %fms%s\n",
          young_gen_bytes / KB, kMinYounGenSize / KB, *young_gen_gc_speed / KB,
          young_gen_estimate.InMillisecondsF(),
          run_young_gen_gc ? ", performing young gen GC"
                           : ", not starting young gen GC");
    }
    if (run_young_gen_gc) {
      EmbedderStackStateScope scope(
          heap, EmbedderStackStateOrigin::kImplicitThroughTask, stack_state_);

      heap->CollectGarbage(NEW_SPACE,
                           GarbageCollectionReason::kIdleContextDisposal);
    }
  }

  Isolate* const isolate_;
  StackState const stack_state_;
  const size_t id_;
  const GCEpoch gc_count_;
  const base::TimeTicks creation_time_ = base::TimeTicks::Now();
};

int Heap::NotifyContextDisposed(bool has_dependent_context) {
  if (!has_dependent_context) {
    tracer()->ResetSurvivalEvents();
    if (!initial_size_overwritten_) {
      DCHECK_IMPLIES(initial_size_overwritten_, !configured_);
      limits()->ResetAllocationLimit();
    } else if (preconfigured_old_generation_size_) {
      EnsureMinimumRemainingAllocationLimit(
          limits()->initial_old_generation_size());
      // Reset using_initial_limit() to prevent the sweeper from overwriting
      // this limit right after this operation.
      limits()->set_using_initial_limit(true);
    }
    if (memory_reducer_) {
      memory_reducer_->NotifyPossibleGarbage();
    }
  } else if (v8_flags.idle_gc_on_context_disposal &&
             !v8_flags.single_generation) {
    DCHECK_NOT_NULL(new_space());
    const size_t id = notify_context_disposed_counter_++;
    TRACE_EVENT(TRACE_DISABLED_BY_DEFAULT("v8.gc"),
                "V8.GCNotifyContextDisposed", "id", id);
    TaskOnContextDispose::TryPostJob(this, id, gc_count());
  }
  if (!isolate()->context().is_null()) {
    RemoveDirtyFinalizationRegistriesOnContext(isolate()->raw_native_context());
    isolate()->raw_native_context()->set_retained_maps(
        ReadOnlyRoots(this).empty_weak_array_list());
  }

  return ++contexts_disposed_;
}

void Heap::StartIncrementalMarking(GCFlags gc_flags,
                                   GarbageCollectionReason gc_reason,
                                   GCCallbackFlags gc_callback_flags,
                                   GarbageCollector collector,
                                   const char* reason) {
  DCHECK(incremental_marking()->IsStopped());
  DCHECK_EQ(isolate(), Isolate::TryGetCurrent());

  if (gc_callbacks_depth_ > 0) {
    // Do not start incremental marking while invoking GC callbacks.
    // Heap::CollectGarbage already decided which GC is going to be
    // invoked. In case it chose a young-gen GC, starting an incremental
    // full GC during callbacks would break the separate GC phases
    // guarantee.
    return;
  }

  TRACE_EVENT(
      "v8",
      perfetto::StaticString(IsYoungGenerationCollector(collector)
                                 ? "V8.GCMinorIncrementalMarkingStart"
                                 : "V8.GCIncrementalMarkingStart"),
      "value", [this, reason, gc_reason](perfetto::TracedValue ctx) {
        auto dict = std::move(ctx).WriteDictionary();
        // Do not emit an epoch on purpose here because finishing sweeping and
        // starting the next marking cycle (which are both within this scope)
        // have different epochs.
        dict.Add("gc_reason", ToString(gc_reason));
        dict.Add("reason", reason);
        dict.Add("old_gen_allocation_limit",
                 limits()->old_generation_allocation_limit());
        dict.Add("old_gen_consumed_bytes", OldGenerationConsumedBytes());
        dict.Add("old_gen_allocation_limit_consumed_bytes",
                 OldGenerationAllocationLimitConsumedBytes());
        dict.Add("old_gen_space_available", OldGenerationSpaceAvailable());
        dict.Add("global_allocation_limit",
                 limits()->global_allocation_limit());
        dict.Add("global_consumed_bytes", GlobalConsumedBytes());
        dict.Add("global_space_available", GlobalSpaceAvailable());
      });

  if (IsYoungGenerationCollector(collector)) {
    CompleteSweepingYoung(CompleteSweepingReason::kStartMinorMarking);
  } else {
    // Sweeping needs to be completed such that markbits are all cleared before
    // starting marking again.
    CompleteSweepingFull(CompleteSweepingReason::kStartMajorMarking);
  }

  std::optional<SafepointScope> safepoint_scope;

  {
    AllowGarbageCollection allow_shared_gc;
    safepoint_scope.emplace(isolate(), kGlobalSafepointForSharedSpaceIsolate);
  }

#ifdef DEBUG
  VerifyCountersAfterSweeping();
#endif

  std::vector<Isolate*> paused_clients =
      PauseConcurrentThreadsInClients(collector);

  // Now that sweeping is completed, we can start the next full GC cycle.
  tracer()->StartCycle(collector, gc_reason, nullptr,
                       GCTracer::MarkingType::kIncremental);

  current_gc_flags_ = gc_flags;
  current_gc_callback_flags_ = gc_callback_flags;

  incremental_marking()->Start(collector, gc_reason, reason);

  if (collector == GarbageCollector::MARK_COMPACTOR) {
    // During loading we might overshoot the limit by a large amount. Ensure
    // allocation limits are at least at or above current sizes to not finalize
    // incremental marking prematurely.
    EnsureMinimumRemainingAllocationLimit(0);
  }

  if (isolate()->is_shared_space_isolate()) {
    for (Isolate* client : paused_clients) {
      client->heap()->concurrent_marking()->Resume();
    }
  } else {
    DCHECK(paused_clients.empty());
  }
}

void Heap::CompleteArrayBufferSweeping() {
  if (array_buffer_sweeper()->sweeping_in_progress()) {
    GCTracer::Scope::ScopeId scope_id;

    switch (tracer()->GetCurrentCollector()) {
      case GarbageCollector::MINOR_MARK_SWEEPER:
        scope_id = GCTracer::Scope::MINOR_MS_COMPLETE_SWEEP_ARRAY_BUFFERS;
        break;
      case GarbageCollector::SCAVENGER:
        scope_id = GCTracer::Scope::SCAVENGER_COMPLETE_SWEEP_ARRAY_BUFFERS;
        break;
      case GarbageCollector::MARK_COMPACTOR:
        scope_id = GCTracer::Scope::MC_COMPLETE_SWEEP_ARRAY_BUFFERS;
    }

    TRACE_GC_EPOCH_WITH_FLOW(tracer(), scope_id, ThreadKind::kMain,
                             array_buffer_sweeper()->GetTraceIdForFlowEvent(),
                             TRACE_EVENT_FLAG_FLOW_IN);
    array_buffer_sweeper()->EnsureFinished();
  }
}

void Heap::CompleteSweepingFull(CompleteSweepingReason reason) {
  EnsureSweepingCompleted(SweepingForcedFinalizationMode::kUnifiedHeap, reason);

  DCHECK(!sweeping_in_progress());
  DCHECK_IMPLIES(cpp_heap(),
                 !CppHeap::From(cpp_heap())->sweeper().IsSweepingInProgress());
  DCHECK(!tracer()->IsSweepingInProgress());
}

void Heap::StartIncrementalMarkingOnInterrupt() {
  StartIncrementalMarkingIfAllocationLimitIsReached(
      main_thread_local_heap(), GCFlagsForIncrementalMarking(),
      kGCCallbackScheduleIdleGarbageCollection);
}

void Heap::StartIncrementalMarkingIfAllocationLimitIsReached(
    LocalHeap* local_heap, GCFlags gc_flags,
    const GCCallbackFlags gc_callback_flags) {
  if (incremental_marking()->IsStopped() &&
      incremental_marking()->CanAndShouldBeStarted()) {
    auto [limit, reason] = IncrementalMarkingLimitReached();
    switch (limit) {
      case IncrementalMarkingLimit::kHardLimit:
        if (local_heap->is_main_thread_for(this)) {
          StartIncrementalMarking(
              gc_flags,
              OldGenerationSpaceAvailable() <= NewSpaceTargetCapacity()
                  ? GarbageCollectionReason::kAllocationLimit
                  : GarbageCollectionReason::kGlobalAllocationLimit,
              gc_callback_flags, GarbageCollector::MARK_COMPACTOR, reason);
        } else {
          ExecutionAccess access(isolate());
          isolate()->stack_guard()->RequestStartIncrementalMarking();
          if (auto* job = incremental_marking()->incremental_marking_job()) {
            job->ScheduleTask();
          }
        }
        break;
      case IncrementalMarkingLimit::kSoftLimit:
        if (auto* job = incremental_marking()->incremental_marking_job()) {
          job->ScheduleTask();
        }
        break;
      case IncrementalMarkingLimit::kFallbackForEmbedderLimit:
        // This is a fallback case where no appropriate limits have been
        // configured yet.
        if (local_heap->is_main_thread_for(this) &&
            memory_reducer() != nullptr) {
          memory_reducer()->NotifyPossibleGarbage();
        }
        break;
      case IncrementalMarkingLimit::kNoLimit:
        break;
    }
  }
}

namespace {

template <typename TSlot, typename AtomicOp, typename NonAtomicOp>
void CopyOrMoveRangeImpl(Heap* heap, Tagged<HeapObject> dst_object,
                         const TSlot dst_slot, const TSlot src_slot, int len,
                         WriteBarrierMode mode, AtomicOp atomic_op,
                         NonAtomicOp non_atomic_op) {
  DCHECK_GT(len, 0);
  DCHECK_NE(dst_object->map(), ReadOnlyRoots(heap).fixed_cow_array_map());

  MemoryChunk* dst_chunk = MemoryChunk::FromHeapObject(dst_object);
  // Young generation object with marking being off, we can use plain memcopy
  // without write barriers.
  if (!dst_chunk->PointersFromHereAreInteresting()) {
    non_atomic_op(dst_slot, src_slot, len);
    return;
  }

  const TSlot dst_end(dst_slot + len);
  // Falling through here means either old generation object or marking being
  // on.
  DCHECK_IMPLIES(heap->sweeper()->IsIteratingPromotedPages(),
                 v8_flags.minor_ms);
  if ((heap->incremental_marking()->IsMarking() &&
       v8_flags.concurrent_marking) ||
      (v8_flags.minor_ms && heap->sweeper()->IsIteratingPromotedPages())) {
    atomic_op(dst_slot, dst_end, src_slot, len);
  } else {
    non_atomic_op(dst_slot, src_slot, len);
  }
  if (mode == SKIP_WRITE_BARRIER) {
    return;
  }
  WriteBarrier::ForRange(heap, dst_object, dst_slot, dst_end);
}

}  // namespace

template <typename TSlot>
void Heap::MoveRange(Tagged<HeapObject> dst_object, const TSlot dst_slot,
                     const TSlot src_slot, uint32_t len,
                     WriteBarrierMode mode) {
  // Ensure no range overflow.
  DCHECK(dst_slot < TSlot(dst_slot + len));
  DCHECK(src_slot < src_slot + len);

  const auto atomic_callback = [](TSlot dst_slot, TSlot dst_end, TSlot src_slot,
                                  uint32_t len) {
    if (dst_slot < src_slot) {
      // Copy tagged values forward using relaxed load/stores that do not
      // involve value decompression.
      const AtomicSlot atomic_dst_end(dst_end);
      AtomicSlot dst(dst_slot);
      AtomicSlot src(src_slot);
      while (dst < atomic_dst_end) {
        *dst = *src;
        ++dst;
        ++src;
      }
    } else {
      // Copy tagged values backwards using relaxed load/stores that do not
      // involve value decompression.
      const AtomicSlot atomic_dst_begin(dst_slot);
      AtomicSlot dst(dst_slot + len - 1);
      AtomicSlot src(src_slot + len - 1);
      while (dst >= atomic_dst_begin) {
        *dst = *src;
        --dst;
        --src;
      }
    }
  };
  const auto non_atomic_callback = [](TSlot dst_slot, TSlot src_slot,
                                      uint32_t len) {
    MemMove(dst_slot.ToVoidPtr(), src_slot.ToVoidPtr(), len * kTaggedSize);
  };
  CopyOrMoveRangeImpl(this, dst_object, dst_slot, src_slot, len, mode,
                      atomic_callback, non_atomic_callback);
}

template V8_EXPORT_PRIVATE void Heap::MoveRange<ObjectSlot>(
    Tagged<HeapObject> dst_object, ObjectSlot dst_slot, ObjectSlot src_slot,
    uint32_t len, WriteBarrierMode mode);
template V8_EXPORT_PRIVATE void Heap::MoveRange<MaybeObjectSlot>(
    Tagged<HeapObject> dst_object, MaybeObjectSlot dst_slot,
    MaybeObjectSlot src_slot, uint32_t len, WriteBarrierMode mode);

template <typename TSlot>
void Heap::CopyRange(Tagged<HeapObject> dst_object, const TSlot dst_slot,
                     const TSlot src_slot, uint32_t len,
                     WriteBarrierMode mode) {
  // Ensure ranges do not overlap.
  DCHECK(TSlot(dst_slot + len) <= src_slot || (src_slot + len) <= dst_slot);

  const auto atomic_callback = [](TSlot dst_slot, TSlot dst_end, TSlot src_slot,
                                  int len) {
    const AtomicSlot atomic_dst_end(dst_end);
    AtomicSlot dst(dst_slot);
    AtomicSlot src(src_slot);
    while (dst < atomic_dst_end) {
      *dst = *src;
      ++dst;
      ++src;
    }
  };
  const auto non_atomic_callback = [](TSlot dst_slot, TSlot src_slot,
                                      uint32_t len) {
    MemCopy(dst_slot.ToVoidPtr(), src_slot.ToVoidPtr(), len * kTaggedSize);
  };
  CopyOrMoveRangeImpl(this, dst_object, dst_slot, src_slot, len, mode,
                      atomic_callback, non_atomic_callback);
}

template V8_EXPORT_PRIVATE void Heap::CopyRange<ObjectSlot>(
    Tagged<HeapObject> dst_object, ObjectSlot dst_slot, ObjectSlot src_slot,
    uint32_t len, WriteBarrierMode mode);
template V8_EXPORT_PRIVATE void Heap::CopyRange<MaybeObjectSlot>(
    Tagged<HeapObject> dst_object, MaybeObjectSlot dst_slot,
    MaybeObjectSlot src_slot, uint32_t len, WriteBarrierMode mode);

bool Heap::CollectionRequested() {
  return collection_barrier_->RequestedGC().has_value();
}

void Heap::RestoreHeapLimit(size_t heap_limit) {
  // Do not set the limit lower than the live size + some slack.
  size_t min_limit = SizeOfObjects() + SizeOfObjects() / 4;
  limits()->SetMaximumSizes(std::min(limits()->max_old_generation_size(),
                                     std::max(heap_limit, min_limit)),
                            physical_memory());
}

void Heap::CollectGarbageWithRetry(AllocationSpace space, GCFlags gc_flags,
                                   GarbageCollectionReason gc_reason,
                                   const GCCallbackFlags gc_callback_flags) {
  std::ignore = allocator()->RetryCustomAllocate(
      [&]() { return !ReachedHeapLimit(); },
      space == NEW_SPACE ? AllocationType::kYoung : AllocationType::kOld);
}

void Heap::PerformRequestedGC(LocalHeap* local_heap) {
  CHECK(local_heap->is_main_thread());
  auto requested_gc = collection_barrier_->RequestedGC();
  if (!requested_gc) {
    return;
  }
  if (*requested_gc == RequestedGCKind::kMajor) {
    CollectAllGarbage(current_gc_flags_,
                      GarbageCollectionReason::kBackgroundAllocationFailure,
                      kNoGCCallbackFlags, PerformHeapLimitCheck::kYes);
  } else {
    CollectAllAvailableGarbage(GarbageCollectionReason::kLastResort);
  }
}

void Heap::UpdateSurvivalStatistics(int start_new_space_size) {
  if (start_new_space_size == 0) return;

  promotion_ratio_ = (static_cast<double>(promoted_objects_size_) /
                      static_cast<double>(start_new_space_size) * 100);

  if (previous_new_space_surviving_object_size_ > 0) {
    promotion_rate_ =
        (static_cast<double>(promoted_objects_size_) /
         static_cast<double>(previous_new_space_surviving_object_size_) * 100);
  } else {
    promotion_rate_ = 0;
  }

  new_space_surviving_rate_ =
      (static_cast<double>(new_space_surviving_object_size_) /
       static_cast<double>(start_new_space_size) * 100);

  double survival_rate = promotion_ratio_ + new_space_surviving_rate_;
  tracer()->AddSurvivalRatio(survival_rate);
}

namespace {

GCTracer::Scope::ScopeId CollectorScopeId(GarbageCollector collector) {
  switch (collector) {
    case GarbageCollector::MARK_COMPACTOR:
      return GCTracer::Scope::ScopeId::MARK_COMPACTOR;
    case GarbageCollector::MINOR_MARK_SWEEPER:
      return GCTracer::Scope::ScopeId::MINOR_MARK_SWEEPER;
    case GarbageCollector::SCAVENGER:
      return GCTracer::Scope::ScopeId::SCAVENGER;
  }
  UNREACHABLE();
}

void ClearStubCaches(Isolate* isolate) {
  isolate->load_stub_cache()->Clear();
  isolate->store_stub_cache()->Clear();
  isolate->define_own_stub_cache()->Clear();

  if (isolate->is_shared_space_isolate()) {
    isolate->global_safepoint()->IterateClientIsolates([](Isolate* client) {
      client->load_stub_cache()->Clear();
      client->store_stub_cache()->Clear();
      client->define_own_stub_cache()->Clear();
    });
  }
}

}  // namespace

void Heap::PerformGarbageCollection(GarbageCollector collector,
                                    GarbageCollectionReason gc_reason,
                                    const char* collector_reason) {
  if (IsYoungGenerationCollector(collector)) {
    if (v8_flags.sticky_mark_bits) {
      DCHECK_EQ(GarbageCollector::MINOR_MARK_SWEEPER, collector);
      // TODO(333906585): It's not necessary to complete full sweeping here.
      // Make sure that only the OLD_SPACE is swept.
      CompleteSweepingFull(CompleteSweepingReason::kMinorGC);
    } else {
      CompleteSweepingYoung(CompleteSweepingReason::kMinorGC);
      if (v8_flags.verify_heap) {
        // If heap verification is enabled, we want to ensure that sweeping is
        // completed here, as it will be triggered from Heap::Verify anyway.
        // In this way, sweeping finalization is accounted to the corresponding
        // full GC cycle.
        CompleteSweepingFull(CompleteSweepingReason::kTesting);
      }
    }
  } else if (!incremental_marking()->IsMajorMarking()) {
    DCHECK_EQ(GarbageCollector::MARK_COMPACTOR, collector);
    CompleteSweepingFull(CompleteSweepingReason::kMajorGC);
  }

  const base::TimeTicks atomic_pause_start_time = base::TimeTicks::Now();

  std::optional<SafepointScope> safepoint_scope;
  {
    AllowGarbageCollection allow_shared_gc;
    safepoint_scope.emplace(isolate(), kGlobalSafepointForSharedSpaceIsolate);
  }

  if (!incremental_marking_->IsMarking() ||
      (collector == GarbageCollector::SCAVENGER)) {
    tracer()->StartCycle(collector, gc_reason, collector_reason,
                         GCTracer::MarkingType::kAtomic);
  }

  tracer()->StartAtomicPause();
  if ((!Heap::IsYoungGenerationCollector(collector) || v8_flags.minor_ms) &&
      incremental_marking_->IsMarking()) {
    DCHECK_IMPLIES(Heap::IsYoungGenerationCollector(collector),
                   incremental_marking_->IsMinorMarking());
    tracer()->UpdateCurrentEvent(gc_reason, collector_reason);
  }

  DCHECK(tracer()->IsConsistentWithCollector(collector));
  TRACE_GC_EPOCH(tracer(), CollectorScopeId(collector), ThreadKind::kMain);

  collection_barrier_->StopTimeToCollectionTimer(RequestedGCKind::kMajor);

  std::vector<Isolate*> paused_clients =
      PauseConcurrentThreadsInClients(collector);

  FreeLinearAllocationAreas();

  tracer()->StartInSafepoint(atomic_pause_start_time);

  GarbageCollectionPrologueInSafepoint(collector);

  PerformHeapVerification();

  const size_t start_young_generation_size =
      NewSpaceSize() + (new_lo_space() ? new_lo_space()->SizeOfObjects() : 0);

  // Make sure allocation observers are disabled until the new new space
  // capacity is set in the epilogue.
  PauseAllocationObserversScope pause_observers(this);

  const size_t new_space_capacity_before_gc = NewSpaceTargetCapacity();

  if (collector == GarbageCollector::MARK_COMPACTOR) {
    MarkCompact();
  } else if (collector == GarbageCollector::MINOR_MARK_SWEEPER) {
    MinorMarkSweep();
  } else {
    DCHECK_EQ(GarbageCollector::SCAVENGER, collector);
    Scavenge();
  }

  if (IsYoungGenerationCollector(collector)) {
    // We don't want growing or shrinking of the current cycle to affect
    // pretenuring decisions. The numbers collected in the GC will be for the
    // capacity that was set before the GC.
    pretenuring_handler_.ProcessPretenuringFeedback(
        new_space_capacity_before_gc);
  }

  UpdateSurvivalStatistics(static_cast<int>(start_young_generation_size));
  if (!initial_size_overwritten_ && tracer()->SurvivalEventsRecorded()) {
    base::MutexGuard guard(old_space()->mutex());
    limits()->ShrinkAllocationLimitIfNotConfigured(CurrentHeapGrowingMode(),
                                                   OldGenerationConsumedBytes(),
                                                   GlobalConsumedBytes());
  }

  isolate_->counters()->objs_since_last_young()->Set(0);

  isolate_->eternal_handles()->PostGarbageCollectionProcessing();

  // Update relocatables.
  Relocatable::PostGarbageCollectionProcessing(isolate_);

  if (isolate_->is_shared_space_isolate()) {
    // Allows handle derefs for all threads/isolates from this thread.
    AllowHandleUsageOnAllThreads allow_all_handle_derefs;
    isolate()->global_safepoint()->IterateClientIsolates([](Isolate* client) {
      Relocatable::PostGarbageCollectionProcessing(client);
    });
  }

  // First round weak callbacks are not supposed to allocate and trigger
  // nested GCs.
  isolate_->global_handles()->InvokeFirstPassWeakCallbacks();

  if (cpp_heap() && (collector == GarbageCollector::MARK_COMPACTOR ||
                     collector == GarbageCollector::MINOR_MARK_SWEEPER)) {
    // TraceEpilogue may trigger operations that invalidate global handles. It
    // has to be called *after* all other operations that potentially touch
    // and reset global handles. It is also still part of the main garbage
    // collection pause and thus needs to be called *before* any operation
    // that can potentially trigger recursive garbage collections.
    TRACE_GC(tracer(), GCTracer::Scope::HEAP_EMBEDDER_TRACING_EPILOGUE);
    CppHeap::From(cpp_heap())->CompactAndSweep();
  }

  if (collector == GarbageCollector::MARK_COMPACTOR) {
    ClearStubCaches(isolate());
  }

  PerformHeapVerification();

  GarbageCollectionEpilogueInSafepoint(collector);

  const base::TimeTicks atomic_pause_end_time = base::TimeTicks::Now();
  tracer()->StopInSafepoint(atomic_pause_end_time);

  ResumeConcurrentThreadsInClients(std::move(paused_clients));

  // After every full GC the old generation allocation limit should be
  // configured.
  DCHECK_IMPLIES(!IsYoungGenerationCollector(collector),
                 !limits()->using_initial_limit());
}

void Heap::PerformHeapVerification() {
  HeapVerifier::VerifyHeapIfEnabled(this);

  if (isolate()->is_shared_space_isolate()) {
    // Allow handle creation for client isolates even if they are parked. This
    // is because some object verification methods create handles.
    AllowHandleUsageOnAllThreads allow_handle_creation;
    isolate()->global_safepoint()->IterateClientIsolates([](Isolate* client) {
      HeapVerifier::VerifyHeapIfEnabled(client->heap());
    });
  }
}

std::vector<Isolate*> Heap::PauseConcurrentThreadsInClients(
    GarbageCollector collector) {
  std::vector<Isolate*> paused_clients;

  if (isolate()->is_shared_space_isolate()) {
    isolate()->global_safepoint()->IterateClientIsolates(
        [collector, &paused_clients](Isolate* client) {
          CHECK(client->heap()->deserialization_complete());

          if (v8_flags.concurrent_marking &&
              client->heap()->concurrent_marking()->Pause()) {
            paused_clients.push_back(client);
          }

          if (collector == GarbageCollector::MARK_COMPACTOR) {
            Sweeper* const client_sweeper = client->heap()->sweeper();
            client_sweeper->ContributeAndWaitForPromotedPagesIteration();
          }
        });
  }

  return paused_clients;
}

void Heap::ResumeConcurrentThreadsInClients(
    std::vector<Isolate*> paused_clients) {
  if (isolate()->is_shared_space_isolate()) {
    for (Isolate* client : paused_clients) {
      client->heap()->concurrent_marking()->Resume();
    }
  } else {
    DCHECK(paused_clients.empty());
  }
}

bool Heap::CollectGarbageShared(LocalHeap* local_heap,
                                GarbageCollectionReason gc_reason) {
  DCHECK(isolate()->has_shared_space());

  if (V8_UNLIKELY(!deserialization_complete_)) {
    CHECK(always_allocate());
    FatalProcessOutOfMemory("GC during deserialization");
  }

  Isolate* shared_space_isolate = isolate()->shared_space_isolate();
  if (shared_space_isolate == isolate() && local_heap->is_main_thread()) {
    shared_space_isolate->heap()->CollectAllGarbage(
        current_gc_flags_, gc_reason, current_gc_callback_flags_);
    return true;
  } else {
    return shared_space_isolate->heap()
        ->TriggerAndWaitForGCFromBackgroundThread(local_heap,
                                                  RequestedGCKind::kMajor);
  }
}

bool Heap::TriggerAndWaitForGCFromBackgroundThread(LocalHeap* local_heap,
                                                   RequestedGCKind kind) {
  DCHECK(local_heap->IsRunning());

  if (V8_UNLIKELY(!deserialization_complete_)) {
    CHECK(always_allocate());
    FatalProcessOutOfMemory("GC during deserialization");
  }

  if (!collection_barrier_->TryRequestGC(kind)) return false;

  const LocalHeap::ThreadState old_state =
      main_thread_local_heap()->state_.SetCollectionRequested();

  if (old_state.IsRunning()) {
    const bool performed_gc =
        collection_barrier_->AwaitCollectionBackground(local_heap, kind);
    return performed_gc;
  } else {
    DCHECK(old_state.IsParked());
    return false;
  }
}

void Heap::CompleteSweepingYoung(CompleteSweepingReason reason) {
  DCHECK(!v8_flags.sticky_mark_bits);

  // If sweeping is in progress and there are no sweeper tasks running, finish
  // the sweeping here, to avoid having to pause and resume during the young
  // generation GC.
  FinishSweepingIfOutOfWork(reason);

  EnsureYoungSweepingCompleted();

#if defined(CPPGC_YOUNG_GENERATION)
  // Always complete sweeping if young generation is enabled.
  if (cpp_heap()) {
    if (auto* iheap = CppHeap::From(cpp_heap());
        iheap->generational_gc_supported())
      iheap->FinishSweepingIfRunning();
  }
#endif  // defined(CPPGC_YOUNG_GENERATION)
}

void Heap::EnsureSweepingCompletedForObject(Tagged<HeapObject> object) {
  if (!sweeping_in_progress()) return;

  MemoryChunk* chunk = MemoryChunk::FromHeapObject(object);
  if (chunk->InReadOnlySpace()) {
    return;
  }

  MutablePage* mutable_page = SbxCast<MutablePage>(chunk->Metadata());
  if (mutable_page->SweepingDone()) {
    return;
  }

  // SweepingDone() is always true for large pages.
  DCHECK(!mutable_page->is_large());

  NormalPage* page = SbxCast<NormalPage>(mutable_page);
  sweeper()->EnsurePageIsSwept(page);
}

void Heap::RecomputeLimits(GarbageCollector collector) {
  if (collector == GarbageCollector::MARK_COMPACTOR) {
    const LimitsComputationResult new_limits = limits()->UpdateAllocationLimits(
        CurrentHeapGrowingMode(), {}, "RecomputeLimitsAfterMajorGC");

    if (v8_flags.memory_balancer) {
      // Now recompute the new allocation limit.
      mb_->RecomputeLimits(new_limits.global_allocation_limit -
                               new_limits.old_generation_allocation_limit,
                           base::TimeTicks::Now());
    }
  } else if (v8_flags.scavenger_updates_allocation_limit &&
             IsYoungGenerationCollector(collector) &&
             HasLowYoungGenerationAllocationRate() &&
             !limits()->using_initial_limit()) {
    limits()->UpdateAllocationLimits(CurrentHeapGrowingMode(),
                                     limits()->AtMostCurrentLimits(),
                                     "RecomputeLimitsAfterMinorGC");
  }
}

void Heap::CallGCPrologueCallbacks(GCType gc_type, GCCallbackFlags flags,
                                   GCTracer::Scope::ScopeId scope_id) {
  if (gc_prologue_callbacks_.IsEmpty()) return;

  GCCallbacksScope scope(this);
  if (scope.CheckReenter()) {
    RCS_SCOPE(isolate(), RuntimeCallCounterId::kGCPrologueCallback);
    TRACE_GC(tracer(), scope_id);
    HandleScope handle_scope(isolate());
    gc_prologue_callbacks_.Invoke(gc_type, flags);
  }
}

void Heap::CallGCEpilogueCallbacks(GCType gc_type, GCCallbackFlags flags,
                                   GCTracer::Scope::ScopeId scope_id) {
  if (gc_epilogue_callbacks_.IsEmpty()) return;

  GCCallbacksScope scope(this);
  if (scope.CheckReenter()) {
    RCS_SCOPE(isolate(), RuntimeCallCounterId::kGCEpilogueCallback);
    TRACE_GC(tracer(), scope_id);
    HandleScope handle_scope(isolate());
    gc_epilogue_callbacks_.Invoke(gc_type, flags);
  }
}

void Heap::MarkCompact() {
  SetGCState(MARK_COMPACT);

  PROFILE(isolate_, CodeMovingGCEvent());

  UpdateOldGenerationAllocationCounter();
  uint64_t size_of_objects_before_gc = SizeOfObjects();

  mark_compact_collector()->Prepare();

  ms_count_++;
  contexts_disposed_ = 0;

  MarkCompactPrologue();

  mark_compact_collector()->CollectGarbage();

  MarkCompactEpilogue();

  if (v8_flags.allocation_site_pretenuring) {
    EvaluateOldSpaceLocalPretenuring(size_of_objects_before_gc);
  }
  // This should be updated before PostGarbageCollectionProcessing, which
  // can cause another GC. Take into account the objects promoted during
  // GC.
  old_generation_allocation_counter_at_last_gc_ +=
      static_cast<size_t>(promoted_objects_size_);
  limits()->UpdateConsumedAfterGC();
}

void Heap::MinorMarkSweep() {
  DCHECK(v8_flags.minor_ms);
  CHECK_EQ(NOT_IN_GC, gc_state());
  DCHECK(use_new_space());
  DCHECK(!incremental_marking()->IsMajorMarking());

  TRACE_GC(tracer(), GCTracer::Scope::MINOR_MS);

  SetGCState(MINOR_MARK_SWEEP);
  minor_mark_sweep_collector_->CollectGarbage();
  SetGCState(NOT_IN_GC);
}

void Heap::MarkCompactEpilogue() {
  TRACE_GC(tracer(), GCTracer::Scope::MC_EPILOGUE);
  SetGCState(NOT_IN_GC);

  isolate_->counters()->objs_since_last_full()->Set(0);
}

void Heap::MarkCompactPrologue() {
  TRACE_GC(tracer(), GCTracer::Scope::MC_PROLOGUE);
  isolate_->descriptor_lookup_cache()->Clear();
  RegExpResultsCache::Clear(string_split_cache());
  RegExpResultsCache::Clear(regexp_multiple_cache());
  RegExpResultsCache_MatchGlobalAtom::Clear(this);

  // Flush the number to string caches.
  smi_string_cache()->Clear();
  double_string_cache()->Clear();
}

void Heap::Scavenge() {
  DCHECK_NOT_NULL(new_space());
  DCHECK(!incremental_marking()->IsMarking());

  TRACE_GC(tracer(), GCTracer::Scope::SCAVENGER_SCAVENGE);
  SetGCState(SCAVENGE);

  // Implements Cheney's copying algorithm
  scavenger_collector_->CollectGarbage();

  SetGCState(NOT_IN_GC);
}

bool Heap::ExternalStringTable::Contains(Tagged<String> string) {
  for (size_t i = 0; i < old_strings_.size(); ++i) {
    if (old_strings_[i] == string) return true;
  }
  return false;
}

void Heap::UpdateExternalString(Tagged<String> string, size_t old_payload,
                                size_t new_payload) {
  DCHECK(IsExternalString(string));
}

void Heap::ExternalStringTable::Verify() {
#ifdef DEBUG
  std::set<Tagged<String>> visited_map;
  std::map<MutablePage*, size_t> size_map;

  for (size_t i = 0; i < old_strings_.size(); ++i) {
    Tagged<String> obj = Cast<String>(Tagged<Object>(old_strings_[i]));
    MutablePage* mc = MutablePage::FromHeapObject(heap_->isolate(), obj);
    DCHECK_IMPLIES(!v8_flags.sticky_mark_bits,
                   !mc->Chunk()->InYoungGeneration());
    DCHECK(!HeapLayout::InYoungGeneration(obj));
    DCHECK(!IsTheHole(obj, heap_->isolate()));
    DCHECK(IsExternalString(obj));
    // Note: we can have repeated elements in the table.
    DCHECK_EQ(0, visited_map.count(obj));
    visited_map.insert(obj);
    size_map[mc] += Cast<ExternalString>(obj)->ExternalPayloadSize();
  }
#endif
}

void Heap::ExternalStringTable::Iterate(RootVisitor* v) {
  if (!old_strings_.empty()) {
    v->VisitRootPointers(
        Root::kExternalStringsTable, nullptr,
        FullObjectSlot(old_strings_.data()),
        FullObjectSlot(old_strings_.data() + old_strings_.size()));
  }
}

void Heap::ExternalStringTable::UpdateReferences(
    Heap::ExternalStringTableUpdaterCallback updater_func) {
  if (!old_strings_.empty()) {
    FullObjectSlot start(old_strings_.data());
    FullObjectSlot end(old_strings_.data() + old_strings_.size());
    for (FullObjectSlot p = start; p < end; ++p)
      p.store(updater_func(heap_, p));
  }
}

void Heap::ProcessAllWeakReferences(WeakObjectRetainer* retainer) {
  ProcessNativeContexts(retainer);
  ProcessAllocationSites(retainer);
  ProcessDirtyJSFinalizationRegistries(retainer);
}

void Heap::ProcessNativeContexts(WeakObjectRetainer* retainer) {
  Tagged<Object> head =
      VisitWeakList<Context>(this, native_contexts_list(), retainer);
  // Update the head of the list of contexts.
  set_native_contexts_list(head);
}

void Heap::ProcessAllocationSites(WeakObjectRetainer* retainer) {
  Tagged<Object> allocation_site_obj =
      VisitWeakList<AllocationSiteWithWeakNext>(this, allocation_sites_list(),
                                                retainer);
  set_allocation_sites_list(
      Cast<UnionOf<Undefined, AllocationSiteWithWeakNext>>(
          allocation_site_obj));
}

void Heap::ProcessDirtyJSFinalizationRegistries(WeakObjectRetainer* retainer) {
  Tagged<Object> head = VisitWeakList<JSFinalizationRegistry>(
      this, dirty_js_finalization_registries_list(), retainer);
  set_dirty_js_finalization_registries_list(head);
  // If the list is empty, set the tail to undefined. Otherwise the tail is set
  // by WeakListVisitor<JSFinalizationRegistry>::VisitLiveObject.
  if (IsUndefined(head, isolate())) {
    set_dirty_js_finalization_registries_list_tail(head);
  }
}

void Heap::ProcessWeakListRoots(WeakObjectRetainer* retainer) {
  set_native_contexts_list(retainer->RetainAs(native_contexts_list()));
  set_allocation_sites_list(
      Cast<UnionOf<Smi, Undefined, AllocationSiteWithWeakNext>>(
          retainer->RetainAs(allocation_sites_list())));
  set_dirty_js_finalization_registries_list(
      retainer->RetainAs(dirty_js_finalization_registries_list()));
  set_dirty_js_finalization_registries_list_tail(
      retainer->RetainAs(dirty_js_finalization_registries_list_tail()));
}

void Heap::AddToWeakNativeContextList(Tagged<Context> context) {
  DCHECK(IsNativeContext(context));
  DCHECK(LocalHeap::Current()->is_main_thread());

#ifdef DEBUG
  {
    DCHECK(IsUndefined(context->next_context_link(), isolate()));
    // Check that context is not in the list yet.
    for (Tagged<Object> current = native_contexts_list();
         !IsUndefined(current, isolate());
         current = Cast<Context>(current)->next_context_link()) {
      DCHECK(current != context);
    }
  }
#endif
  context->SetNoCell(Context::NEXT_CONTEXT_LINK, native_contexts_list(),
                     UPDATE_WRITE_BARRIER);
  set_native_contexts_list(context);
}

void Heap::ForeachAllocationSite(
    Tagged<Object> list,
    const std::function<void(Tagged<AllocationSite>)>& visitor) {
  DisallowGarbageCollection no_gc;
  Tagged<Object> current = list;
  while (IsAllocationSite(current)) {
    Tagged<AllocationSiteWithWeakNext> site =
        Cast<AllocationSiteWithWeakNext>(current);
    visitor(site);
    Tagged<Object> current_nested = site->nested_site();
    while (IsAllocationSite(current_nested)) {
      Tagged<AllocationSite> nested_site = Cast<AllocationSite>(current_nested);
      visitor(nested_site);
      current_nested = nested_site->nested_site();
    }
    current = site->weak_next();
  }
}

void Heap::ResetAllAllocationSitesDependentCode(AllocationType allocation) {
  DisallowGarbageCollection no_gc_scope;
  bool marked = false;

  ForeachAllocationSite(
      allocation_sites_list(),
      [&marked, allocation, this](Tagged<AllocationSite> site) {
        if (site->GetAllocationType() == allocation) {
          site->ResetPretenureDecision();
          site->set_deopt_dependent_code(true);
          marked = true;
          pretenuring_handler_.RemoveAllocationSitePretenuringFeedback(site);
          return;
        }
      });
  if (marked) isolate_->stack_guard()->RequestDeoptMarkedAllocationSites();
}

void Heap::EvaluateOldSpaceLocalPretenuring(
    uint64_t size_of_objects_before_gc) {
  uint64_t size_of_objects_after_gc = SizeOfObjects();
  double old_generation_survival_rate =
      (static_cast<double>(size_of_objects_after_gc) * 100) /
      static_cast<double>(size_of_objects_before_gc);

  if (old_generation_survival_rate < kOldSurvivalRateLowThreshold) {
    // Too many objects died in the old generation, pretenuring of wrong
    // allocation sites may be the cause for that. We have to deopt all
    // dependent code registered in the allocation sites to re-evaluate
    // our pretenuring decisions.
    ResetAllAllocationSitesDependentCode(AllocationType::kOld);
    if (v8_flags.trace_pretenuring) {
      PrintF(
          "Deopt all allocation sites dependent code due to low survival "
          "rate in the old generation %f\n",
          old_generation_survival_rate);
    }
  }
}

static_assert(IsAligned(OFFSET_OF_DATA_START(FixedDoubleArray),
                        kDoubleAlignment));

#ifdef V8_COMPRESS_POINTERS
// TODO(ishell, v8:8875): When pointer compression is enabled the kHeaderSize
// is only kTaggedSize aligned but we can keep using unaligned access since
// both x64 and arm64 architectures (where pointer compression supported)
// allow unaligned access to doubles.
static_assert(IsAligned(OFFSET_OF_DATA_START(ByteArray), kTaggedSize));
#else
static_assert(IsAligned(OFFSET_OF_DATA_START(ByteArray), kDoubleAlignment));
#endif

int Heap::GetMaximumFillToAlign(AllocationAlignment alignment) {
  if (V8_COMPRESS_POINTERS_8GB_BOOL) return 0;
  switch (alignment) {
    case kTaggedAligned:
      return 0;
    case kDoubleAligned:
    case kDoubleUnaligned:
      return kDoubleSize - kTaggedSize;
    default:
      UNREACHABLE();
  }
}

// static
int Heap::GetFillToAlign(Address address, AllocationAlignment alignment) {
  if (V8_COMPRESS_POINTERS_8GB_BOOL) return 0;
  if (alignment == kDoubleAligned && (address & kDoubleAlignmentMask) != 0)
    return kTaggedSize;
  if (alignment == kDoubleUnaligned && (address & kDoubleAlignmentMask) == 0) {
    return kDoubleSize - kTaggedSize;  // No fill if double is always aligned.
  }
  return 0;
}

size_t Heap::GetCodeRangeReservedAreaSize() {
  return CodeRange::GetWritableReservedAreaSize();
}

Tagged<HeapObject> Heap::PrecedeWithFiller(Tagged<HeapObject> object,
                                           int filler_size) {
  CreateFillerObjectAt(object.address(), filler_size);
  return HeapObject::FromAddress(object.address() + filler_size);
}

Tagged<HeapObject> Heap::PrecedeWithFillerBackground(Tagged<HeapObject> object,
                                                     int filler_size) {
  CreateFillerObjectAtBackground(
      WritableFreeSpace::ForNonExecutableMemory(object.address(), filler_size));
  return HeapObject::FromAddress(object.address() + filler_size);
}

Tagged<HeapObject> Heap::AlignWithFillerBackground(
    Tagged<HeapObject> object, int object_size, int allocation_size,
    AllocationAlignment alignment) {
  const int filler_size = allocation_size - object_size;
  DCHECK_LT(0, filler_size);
  const int pre_filler = GetFillToAlign(object.address(), alignment);
  if (pre_filler) {
    object = PrecedeWithFillerBackground(object, pre_filler);
  }
  DCHECK_LE(0, filler_size - pre_filler);
  const int post_filler = filler_size - pre_filler;
  if (post_filler) {
    CreateFillerObjectAtBackground(WritableFreeSpace::ForNonExecutableMemory(
        object.address() + object_size, post_filler));
  }
  return object;
}

void* Heap::AllocateExternalBackingStore(
    const std::function<void*(size_t)>& allocate, size_t byte_length) {
  size_t max = isolate()->array_buffer_allocator()->MaxAllocationSize();
  DCHECK(max <= JSArrayBuffer::kMaxByteLength);
  if (byte_length > max) {
    return nullptr;
  }
  if (!always_allocate() && new_space()) {
    size_t new_space_backing_store_bytes = YoungExternalMemoryBytes();
    if ((!incremental_marking()->IsMajorMarking()) &&
        new_space_backing_store_bytes >=
            2 * DefaultMaxSemiSpaceSize(physical_memory()) &&
        new_space_backing_store_bytes >= byte_length) {
      // Performing a young generation GC amortizes over the allocated backing
      // store bytes and may free enough external bytes for this allocation.
      CollectGarbage(NEW_SPACE,
                     GarbageCollectionReason::kExternalMemoryPressure);
    }
  }
  void* result = allocate(byte_length);
  if (result || always_allocate()) {
    return result;
  }
  std::ignore = allocator()->RetryCustomAllocate(
      [&]() { return result = allocate(byte_length); }, AllocationType::kOld);
  return result;
}

size_t Heap::YoungExternalMemoryBytes() const {
  return array_buffer_sweeper()->YoungBytes();
}

void Heap::EnsureMinimumRemainingAllocationLimit(size_t at_least_remaining) {
  base::MutexGuard guard(old_space()->mutex());

  if (OldGenerationSpaceAvailable() > at_least_remaining &&
      GlobalSpaceAvailable() >
          HeapLimits::GlobalMemorySizeFromV8Size(at_least_remaining)) {
    return;
  }

  // At least with ArrayBufferExtensions, external memory could overflow size_t
  // on 32-bit. Use a saturated cast here to defend against this.
  size_t new_old_generation_allocation_limit = std::max(
      base::saturated_cast<size_t>(OldGenerationAllocationLimitConsumedBytes() +
                                   at_least_remaining),
      limits()->old_generation_allocation_limit());
  // We need to clamp the new limit between the allowed minimum and maximum
  // value. We do not currently cap allocated external memory, so either the old
  // or global bytes counter (depending on
  // v8_flags.external_memory_accounted_in_global_limit) could legitimately be
  // larger than the maximum allowed limit.
  new_old_generation_allocation_limit = std::clamp(
      new_old_generation_allocation_limit, limits()->min_old_generation_size(),
      limits()->max_old_generation_size());

  size_t current_global_bytes = GlobalConsumedBytes();
  if (!v8_flags.external_memory_accounted_in_global_limit) {
    // TODO(chromium:42203776): Without that flag external memory is added in
    // OldGenerationAllocationLimitConsumedBytes() but not in
    // GlobalConsumedBytes(). This can lead to cases where the allocation limit
    // for the old generation is higher than for global memory. We fix this here
    // by manually adding it.
    current_global_bytes += AllocatedExternalMemorySinceMarkCompact();
  }
  size_t new_global_allocation_limit =
      std::max(current_global_bytes +
                   HeapLimits::GlobalMemorySizeFromV8Size(at_least_remaining),
               limits()->global_allocation_limit());
  new_global_allocation_limit = std::clamp(new_global_allocation_limit,
                                           limits()->min_global_memory_size(),
                                           limits()->max_global_memory_size());

  TRACE_EVENT_INSTANT(
      TRACE_DISABLED_BY_DEFAULT("v8.gc"),
      "V8.GCEnsureMinimumRemainingAllocationLimit", "value",
      [&](perfetto::TracedValue ctx) {
        auto dict = std::move(ctx).WriteDictionary();
        dict.Add("old_gen_allocation_limit",
                 limits()->old_generation_allocation_limit());
        dict.Add("next_old_gen_allocation_limit",
                 new_old_generation_allocation_limit);
        dict.Add("global_allocation_limit",
                 limits()->global_allocation_limit());
        dict.Add("next_global_allocation_limit", new_global_allocation_limit);
        dict.Add("old_gen_allocation_limit_consumed_bytes",
                 OldGenerationAllocationLimitConsumedBytes());
        dict.Add("global_consumed_bytes", GlobalConsumedBytes());
        dict.Add("external_memory_since_mark_compact",
                 AllocatedExternalMemorySinceMarkCompact());
      });

  limits()->SetAllocationLimit(new_old_generation_allocation_limit,
                               new_global_allocation_limit);
}

namespace {

void CreateFillerObjectAtImpl(const WritableFreeSpace& free_space, Heap* heap,
                              ClearFreedMemoryMode clear_memory_mode) {
  int size = free_space.Size();
  if (size == 0) return;
  DCHECK_IMPLIES(V8_COMPRESS_POINTERS_8GB_BOOL,
                 IsAligned(free_space.Address(), kObjectAlignment8GbHeap));
  DCHECK_IMPLIES(V8_COMPRESS_POINTERS_8GB_BOOL,
                 IsAligned(size, kObjectAlignment8GbHeap));

  // TODO(v8:13070): Filler sizes are irrelevant for 8GB+ heaps. Adding them
  // should be avoided in this mode.
  ReadOnlyRoots roots(heap);
  if (size == kTaggedSize) {
    HeapObject::SetFillerMap(free_space,
                             roots.unchecked_one_pointer_filler_map());
    // Ensure the filler map is properly initialized.
    DCHECK(IsMap(
        HeapObject::FromAddress(free_space.Address())->map(heap->isolate())));
  } else if (size == 2 * kTaggedSize) {
    HeapObject::SetFillerMap(free_space,
                             roots.unchecked_two_pointer_filler_map());
    if (clear_memory_mode == ClearFreedMemoryMode::kClearFreedMemory) {
      free_space.ClearTagged<kTaggedSize>((size / kTaggedSize) - 1);
    }
    // Ensure the filler map is properly initialized.
    DCHECK(IsMap(
        HeapObject::FromAddress(free_space.Address())->map(heap->isolate())));
  } else {
    DCHECK_GT(size, 2 * kTaggedSize);
    HeapObject::SetFillerMap(free_space, roots.unchecked_free_space_map());
    FreeSpace::SetSize(free_space, size, kRelaxedStore);
    if (clear_memory_mode == ClearFreedMemoryMode::kClearFreedMemory) {
      free_space.ClearTagged<2 * kTaggedSize>((size / kTaggedSize) - 2);
    }

    // During bootstrapping we need to create a free space object before its
    // map is initialized. In this case we cannot access the map yet, as it
    // might be null, or not set up properly yet.
    DCHECK_IMPLIES(roots.is_initialized(RootIndex::kFreeSpaceMap),
                   IsMap(HeapObject::FromAddress(free_space.Address())
                             ->map(heap->isolate())));
  }
}

#ifdef DEBUG
void VerifyNoNeedToClearSlots(Address start, Address end) {
  MemoryChunk* chunk = MemoryChunk::FromAddress(start);
  if (chunk->InReadOnlySpace()) return;
  if (!v8_flags.sticky_mark_bits && chunk->InYoungGeneration()) return;
  MutablePage* mutable_page = SbxCast<MutablePage>(chunk->Metadata());
  BaseSpace* space = mutable_page->owner();
  space->heap()->VerifySlotRangeHasNoRecordedSlots(start, end);
}
#else
void VerifyNoNeedToClearSlots(Address start, Address end) {}
#endif  // DEBUG

}  // namespace

void Heap::CreateFillerObjectAtBackground(const WritableFreeSpace& free_space) {
  // TODO(leszeks): Verify that no slots need to be recorded.
  // Do not verify whether slots are cleared here: the concurrent thread is not
  // allowed to access the main thread's remembered set.
  CreateFillerObjectAtRaw(free_space,
                          ClearFreedMemoryMode::kDontClearFreedMemory,
                          ClearRecordedSlots::kNo, VerifyNoSlotsRecorded::kNo);
}

void Heap::CreateFillerObjectAt(Address addr, int size,
                                ClearFreedMemoryMode clear_memory_mode,
                                std::optional<AllocationType> allocation_type) {
  if (size == 0) {
    return;
  }
  const bool non_code_space =
      (allocation_type.has_value() &&
       allocation_type.value() != AllocationType::kCode) ||
      !MemoryChunk::FromAddress(addr)->Metadata(isolate())->is_executable();
  if (V8_LIKELY(non_code_space)) {
    WritableFreeSpace free_space =
        WritableFreeSpace::ForNonExecutableMemory(addr, size);
    CreateFillerObjectAtRaw(free_space, clear_memory_mode,
                            ClearRecordedSlots::kNo,
                            VerifyNoSlotsRecorded::kYes);
    return;
  }
  WritableJitPage jit_page(addr, size);
  WritableFreeSpace free_space = jit_page.FreeRange(addr, size);
  CreateFillerObjectAtRaw(free_space, clear_memory_mode,
                          ClearRecordedSlots::kNo, VerifyNoSlotsRecorded::kYes);
}

void Heap::CreateFillerObjectAtRaw(
    const WritableFreeSpace& free_space, ClearFreedMemoryMode clear_memory_mode,
    ClearRecordedSlots clear_slots_mode,
    VerifyNoSlotsRecorded verify_no_slots_recorded) {
  // TODO(mlippautz): It would be nice to DCHECK that we never call this
  // with {addr} pointing into large object space; however we currently do,
  // see, e.g., Factory::NewFillerObject and in many tests.
  size_t size = free_space.Size();
  if (size == 0) return;
  CreateFillerObjectAtImpl(free_space, this, clear_memory_mode);
  Address addr = free_space.Address();
  if (clear_slots_mode == ClearRecordedSlots::kYes) {
    ClearRecordedSlotRange(addr, addr + size);
  } else if (verify_no_slots_recorded == VerifyNoSlotsRecorded::kYes) {
    VerifyNoNeedToClearSlots(addr, addr + size);
  }
}

bool Heap::CanMoveObjectStart(Tagged<HeapObject> object) {
  if (!v8_flags.move_object_start) {
    return false;
  }

  // Sampling heap profiler may have a reference to the object.
  if (heap_profiler()->is_sampling_allocations()) {
    return false;
  }

  if (HeapLayout::InAnyLargeSpace(object)) {
    return false;
  }

  // Compilation jobs may have references to the object.
  if (isolate()->concurrent_recompilation_enabled() &&
      isolate()->optimizing_compile_dispatcher()->HasJobs()) {
    return false;
  }

  // Concurrent marking does not support moving object starts without snapshot
  // protocol.
  //
  // TODO(v8:13726): This can be improved via concurrently reading the contents
  // in the marker at the cost of some complexity.
  if (incremental_marking()->IsMarking()) {
    return false;
  }

  // Concurrent sweeper does not support moving object starts. It assumes that
  // markbits (black regions) and object starts are matching up.
  if (!MutablePage::FromHeapObject(isolate(), object)->SweepingDone()) {
    return false;
  }

  return true;
}

bool Heap::IsImmovable(Tagged<HeapObject> object) {
  const BasePage* metadata =
      MemoryChunk::FromHeapObject(object)->Metadata(isolate());
  return metadata->never_evacuate() || metadata->is_large();
}

#ifdef ENABLE_SLOW_DCHECKS
namespace {

class LeftTrimmerVerifierRootVisitor : public RootVisitor {
 public:
  explicit LeftTrimmerVerifierRootVisitor(Tagged<FixedArrayBase> to_check)
      : to_check_(to_check) {}

  LeftTrimmerVerifierRootVisitor(const LeftTrimmerVerifierRootVisitor&) =
      delete;
  LeftTrimmerVerifierRootVisitor& operator=(
      const LeftTrimmerVerifierRootVisitor&) = delete;

  void VisitRootPointers(Root root, const char* description,
                         FullObjectSlot start, FullObjectSlot end) override {
    for (FullObjectSlot p = start; p < end; ++p) {
      // V8_EXTERNAL_CODE_SPACE specific: we might be comparing
      // InstructionStream object with non-InstructionStream object here and it
      // might produce false positives because operator== for tagged values
      // compares only lower 32 bits when pointer compression is enabled.
      DCHECK_NE((*p).ptr(), to_check_.ptr());
    }
  }

  void VisitCompressedRootPointers(Root root, const char* description,
                                   OffHeapObjectSlot start,
                                   OffHeapObjectSlot end) override {
    DCHECK(root == Root::kStringTable ||
           root == Root::kSharedStructTypeRegistry);
    // We can skip iterating the string table and shared struct type registry,
    // they don't point to any fixed arrays.
  }

 private:
  Tagged<FixedArrayBase> to_check_;
};
}  // namespace
#endif  // ENABLE_SLOW_DCHECKS

namespace {
bool MayContainRecordedSlots(Tagged<HeapObject> object) {
  // New space object do not have recorded slots.
  if (HeapLayout::InYoungGeneration(object)) {
    return false;
  }
  // Allowlist objects that definitely do not have pointers.
  if (IsByteArray(object) || IsFixedDoubleArray(object)) return false;
  // Conservatively return true for other objects.
  return true;
}
}  // namespace

void Heap::OnMoveEvent(Tagged<HeapObject> source, Tagged<HeapObject> target,
                       int size_in_bytes) {
  if (heap_profiler()->is_tracking_object_moves()) {
    heap_profiler()->ObjectMoveEvent(source.address(), target.address(),
                                     size_in_bytes,
                                     /*is_embedder_object=*/false);
  }
  for (auto& tracker : allocation_trackers_) {
    tracker->MoveEvent(source.address(), target.address(), size_in_bytes);
  }
  if (IsSharedFunctionInfo(target, isolate_)) {
    LOG_CODE_EVENT(isolate_, SharedFunctionInfoMoveEvent(source.address(),
                                                         target.address()));
  } else if (IsNativeContext(target, isolate_)) {
    if (isolate_->current_embedder_state() != nullptr) {
      isolate_->current_embedder_state()->OnMoveEvent(source.address(),
                                                      target.address());
    }
    PROFILE(isolate_,
            NativeContextMoveEvent(source.address(), target.address()));
  } else if (IsMap(target, isolate_)) {
    LOG(isolate_, MapMoveEvent(Cast<Map>(source), Cast<Map>(target)));
  }
}

Tagged<FixedArrayBase> Heap::LeftTrimFixedArray(Tagged<FixedArrayBase> object,
                                                int elements_to_trim) {
  if (elements_to_trim == 0) {
    // This simplifies reasoning in the rest of the function.
    return object;
  }
  CHECK(!object.is_null());
  DCHECK(CanMoveObjectStart(object));
  // Add custom visitor to concurrent marker if new left-trimmable type
  // is added.
  DCHECK(IsFixedArray(object) || IsFixedDoubleArray(object));
  const int element_size = IsFixedArray(object) ? kTaggedSize : kDoubleSize;
  const int bytes_to_trim = elements_to_trim * element_size;
  Tagged<Map> map = object->map();

  // For now this trick is only applied to fixed arrays which may be in new
  // space or old space. In a large object space the object's start must
  // coincide with chunk and thus the trick is just not applicable.
  DCHECK(!HeapLayout::InAnyLargeSpace(object));
  DCHECK(object->map() != ReadOnlyRoots(this).fixed_cow_array_map());

  static_assert(offsetof(FixedArrayBase, map_) == 0);
  static_assert(offsetof(FixedArrayBase, length_) == kTaggedSize);
  static_assert(sizeof(FixedArrayBase) == 2 * kTaggedSize);

  const int len = object->length();
  DCHECK(elements_to_trim <= len);

  // Calculate location of new array start.
  Address old_start = object.address();
  Address new_start = old_start + bytes_to_trim;

  // Technically in new space this write might be omitted (except for
  // debug mode which iterates through the heap), but to play safer
  // we still do it.
  CreateFillerObjectAtRaw(
      WritableFreeSpace::ForNonExecutableMemory(old_start, bytes_to_trim),
      ClearFreedMemoryMode::kClearFreedMemory,
      MayContainRecordedSlots(object) ? ClearRecordedSlots::kYes
                                      : ClearRecordedSlots::kNo,
      VerifyNoSlotsRecorded::kYes);

  // Initialize header of the trimmed array. Since left trimming is only
  // performed on pages which are not concurrently swept creating a filler
  // object does not require synchronization.
  RELAXED_WRITE_FIELD(object, bytes_to_trim,
                      Tagged<Object>(MapWord::FromMap(map).ptr()));
  RELAXED_WRITE_FIELD(object, bytes_to_trim + kTaggedSize,
                      Smi::FromInt(len - elements_to_trim));

  Tagged<FixedArrayBase> new_object =
      Cast<FixedArrayBase>(HeapObject::FromAddress(new_start));

  if (isolate()->log_object_relocation()) {
    // Notify the heap profiler of change in object layout.
    OnMoveEvent(object, new_object, new_object->Size());
  }

#ifdef ENABLE_SLOW_DCHECKS
  if (v8_flags.enable_slow_asserts) {
    // Make sure the stack or other roots (e.g., Handles) don't contain pointers
    // to the original FixedArray (which is now the filler object).

    // Iterating roots forces us to safepoint here. The safepoint allows a
    // shared GC here though, while the JSArray holding the pointer to that
    // FixedArray is still pointing to the old object start. To fix this we only
    // safepoint here when we can grab the lock without blocking. This means we
    // can also only conditionally verify roots.
    std::optional<IsolateSafepointScope> safepoint_scope =
        safepoint()->ReachSafepointWithoutTriggeringGC();
    CHECK_IMPLIES(!isolate()->has_shared_space(), safepoint_scope.has_value());

    if (safepoint_scope.has_value()) {
      LeftTrimmerVerifierRootVisitor root_visitor(object);
      ReadOnlyRoots(this).Iterate(&root_visitor);

      // Stale references are allowed in some locations. IterateRoots() uses
      // ClearStaleLeftTrimmedPointerVisitor internally to clear such references
      // beforehand.
      IterateRoots(&root_visitor,
                   base::EnumSet<SkipRoot>{SkipRoot::kConservativeStack});
    }
  }
#endif  // ENABLE_SLOW_DCHECKS

  return new_object;
}

template <typename Array>
void Heap::RightTrimArray(Tagged<Array> object, uint32_t new_capacity_raw,
                          uint32_t old_capacity_raw) {
  int new_capacity = new_capacity_raw;
  int old_capacity = old_capacity_raw;
  DCHECK_EQ(old_capacity, object->capacity());
  DCHECK_LT(new_capacity, old_capacity);
  DCHECK_GE(new_capacity, 0);

  if constexpr (Array::kElementsAreMaybeObject) {
    // For MaybeObject elements, this function is safe to use only at the end
    // of the mark compact collection: When marking, we record the weak slots,
    // and shrinking invalidates them.
    DCHECK_EQ(gc_state(), MARK_COMPACT);
  }

  const int bytes_to_trim = (old_capacity - new_capacity) * Array::kElementSize;

  // Calculate location of new array end.
  const int old_size = Array::SizeFor(old_capacity);
  DCHECK_EQ(object->AllocatedSize(), old_size);
  Address old_end = object.address() + old_size;
  Address new_end = old_end - bytes_to_trim;

  const bool clear_slots = MayContainRecordedSlots(object);

  // Technically in new space this write might be omitted (except for debug
  // mode which iterates through the heap), but to play safer we still do it.
  // We do not create a filler for objects in a large object space.
  if (!HeapLayout::InAnyLargeSpace(object)) {
    NotifyObjectSizeChange(
        object, old_size, old_size - bytes_to_trim,
        clear_slots ? ClearRecordedSlots::kYes : ClearRecordedSlots::kNo);
    if (!v8_flags.black_allocated_pages) {
      Tagged<HeapObject> filler = HeapObject::FromAddress(new_end);
      // Clear the mark bits of the black area that belongs now to the filler.
      // This is an optimization. The sweeper will release black fillers anyway.
      if (incremental_marking()->black_allocation() &&
          marking_state()->IsMarked(filler)) {
        NormalPage* page = NormalPage::FromAddress(new_end);
        page->marking_bitmap()->ClearRange<AccessMode::ATOMIC>(
            MarkingBitmap::AddressToIndex(new_end),
            MarkingBitmap::LimitAddressToIndex(new_end + bytes_to_trim));
      }
    }
  } else if (clear_slots) {
    // Large objects are not swept, so it is not necessary to clear the
    // recorded slot.
    Relaxed_MemsetTagged(ObjectSlot(new_end),
                         Tagged<Object>(kClearedFreeMemoryValue),
                         (old_end - new_end) / kTaggedSize);
  }

  // Initialize header of the trimmed array. We are storing the new capacity
  // using release store after creating a filler for the left-over space to
  // avoid races with the sweeper thread.
  object->set_capacity(new_capacity, kReleaseStore);

  // Notify the heap object allocation tracker of change in object layout. The
  // array may not be moved during GC, and size has to be adjusted nevertheless.
  for (auto& tracker : allocation_trackers_) {
    tracker->UpdateObjectSizeEvent(object.address(),
                                   Array::SizeFor(new_capacity));
  }
}

#define DEF_RIGHT_TRIM(T)                                          \
  template EXPORT_TEMPLATE_DEFINE(V8_EXPORT_PRIVATE) void          \
  Heap::RightTrimArray<T>(Tagged<T> object, uint32_t new_capacity, \
                          uint32_t old_capacity);
RIGHT_TRIMMABLE_ARRAY_LIST(DEF_RIGHT_TRIM)
#undef DEF_RIGHT_TRIM

void Heap::MakeHeapIterable(CompleteSweepingReason reason) {
  EnsureSweepingCompleted(SweepingForcedFinalizationMode::kV8Only, reason);

  MakeLinearAllocationAreasIterable();
}

void Heap::MakeLinearAllocationAreasIterable() {
  allocator()->MakeLinearAllocationAreasIterable();

  safepoint()->IterateLocalHeaps([](LocalHeap* local_heap) {
    local_heap->MakeLinearAllocationAreasIterable();
  });

  if (isolate()->is_shared_space_isolate()) {
    isolate()->global_safepoint()->IterateClientIsolates([](Isolate* client) {
      client->heap()->MakeLinearAllocationAreasIterable();
    });
  }
}

void Heap::FreeLinearAllocationAreas() {
  FreeMainThreadLinearAllocationAreas();

  safepoint()->IterateLocalHeaps(
      [](LocalHeap* local_heap) { local_heap->FreeLinearAllocationAreas(); });

  if (isolate()->is_shared_space_isolate()) {
    isolate()->global_safepoint()->IterateClientIsolates(
        [](Isolate* client) { client->heap()->FreeLinearAllocationAreas(); });
  }
}

void Heap::FreeMainThreadLinearAllocationAreas() {
  allocator()->FreeLinearAllocationAreas();
}

void Heap::MarkSharedLinearAllocationAreasBlack() {
  DCHECK(!v8_flags.black_allocated_pages);
  allocator()->MarkSharedLinearAllocationAreasBlack();
  main_thread_local_heap()->MarkSharedLinearAllocationAreasBlack();

  safepoint()->IterateLocalHeaps([](LocalHeap* local_heap) {
    local_heap->MarkSharedLinearAllocationAreasBlack();
  });
}


void Heap::FreeSharedLinearAllocationAreasAndResetFreeLists() {
  DCHECK(v8_flags.black_allocated_pages);
  allocator()->FreeSharedLinearAllocationAreasAndResetFreeLists();
  main_thread_local_heap()->FreeSharedLinearAllocationAreasAndResetFreeLists();

  safepoint()->IterateLocalHeaps([](LocalHeap* local_heap) {
    local_heap->FreeSharedLinearAllocationAreasAndResetFreeLists();
  });
}

void Heap::Unmark() {
  DCHECK(v8_flags.sticky_mark_bits);
  DCHECK_NULL(new_space());

  auto unmark_space = [](auto& space) {
    for (auto* page : space) {
      page->marking_bitmap()->template Clear<AccessMode::NON_ATOMIC>();
      page->SetMajorGCInProgress();
      page->SetLiveBytes(0);
    }
  };

  unmark_space(*old_space());
  unmark_space(*lo_space());

  if (isolate()->is_shared_space_isolate()) {
    unmark_space(*shared_space());
    unmark_space(*shared_lo_space());
  }

  {
    RwxMemoryWriteScope scope("For writing flags.");
    unmark_space(*code_space());
    unmark_space(*code_lo_space());
  }

  unmark_space(*trusted_space());
  unmark_space(*trusted_lo_space());
}

void Heap::DeactivateMajorGCInProgressFlag() {
  DCHECK(v8_flags.sticky_mark_bits);
  DCHECK_NULL(new_space());

  auto deactivate_space = [](auto& space) {
    for (auto* metadata : space) {
      metadata->ResetMajorGCInProgress();
    }
  };

  deactivate_space(*old_space());
  deactivate_space(*lo_space());

  {
    RwxMemoryWriteScope scope("For writing flags.");
    deactivate_space(*code_space());
    deactivate_space(*code_lo_space());
  }

  if (isolate()->is_shared_space_isolate()) {
    deactivate_space(*shared_space());
    deactivate_space(*shared_lo_space());
  }

  deactivate_space(*trusted_space());
  deactivate_space(*trusted_lo_space());
}

namespace {

double ComputeMutatorUtilizationImpl(double mutator_speed,
                                     std::optional<double> gc_speed) {
  constexpr double kMinMutatorUtilization = 0.0;
  constexpr double kConservativeGcSpeedInBytesPerMillisecond = 200000;
  if (mutator_speed == 0) return kMinMutatorUtilization;
  if (!gc_speed) gc_speed = kConservativeGcSpeedInBytesPerMillisecond;
  // Derivation:
  // mutator_utilization = mutator_time / (mutator_time + gc_time)
  // mutator_time = 1 / mutator_speed
  // gc_time = 1 / gc_speed
  // mutator_utilization = (1 / mutator_speed) /
  //                       (1 / mutator_speed + 1 / gc_speed)
  // mutator_utilization = gc_speed / (mutator_speed + gc_speed)
  return *gc_speed / (mutator_speed + *gc_speed);
}

}  // namespace

double Heap::ComputeMutatorUtilization(const char* tag, double mutator_speed,
                                       std::optional<double> gc_speed) {
  double result = ComputeMutatorUtilizationImpl(mutator_speed, gc_speed);
  if (v8_flags.trace_mutator_utilization) {
    isolate()->PrintWithTimestamp(
        "%s mutator utilization = %.3f ("
        "mutator_speed=%.f, gc_speed=%.f)\n",
        tag, result, mutator_speed, gc_speed.value_or(0));
  }
  return result;
}

bool Heap::HasLowYoungGenerationAllocationRate() {
  double mu = ComputeMutatorUtilization(
      "Young generation",
      tracer()->NewSpaceAllocationThroughputInBytesPerMillisecond(),
      tracer()->YoungGenerationSpeedInBytesPerMillisecond(
          YoungGenerationSpeedMode::kOnlyAtomicPause));
  constexpr double kHighMutatorUtilization = 0.993;
  return mu > kHighMutatorUtilization;
}

bool Heap::HasLowOldGenerationAllocationRate() {
  double mu = ComputeMutatorUtilization(
      "Old generation",
      tracer()->OldGenerationAllocationThroughputInBytesPerMillisecond(),
      tracer()->OldGenerationSpeedInBytesPerMillisecond());
  const double kHighMutatorUtilization = 0.993;
  return mu > kHighMutatorUtilization;
}

bool Heap::HasLowEmbedderAllocationRate() {
  double mu = ComputeMutatorUtilization(
      "Embedder", tracer()->EmbedderAllocationThroughputInBytesPerMillisecond(),
      tracer()->EmbedderSpeedInBytesPerMillisecond());
  const double kHighMutatorUtilization = 0.993;
  return mu > kHighMutatorUtilization;
}

bool Heap::HasLowAllocationRate() {
  return HasLowYoungGenerationAllocationRate() &&
         HasLowOldGenerationAllocationRate() && HasLowEmbedderAllocationRate();
}

size_t Heap::OldGenerationSpaceAvailable() {
  uint64_t bytes = OldGenerationAllocationLimitConsumedBytes();
  if (limits()->old_generation_allocation_limit() <= bytes) return 0;
  return limits()->old_generation_allocation_limit() -
         static_cast<size_t>(bytes);
}

size_t Heap::GlobalSpaceAvailable() {
  size_t global_size = GlobalConsumedBytes();
  size_t global_limit = limits()->global_allocation_limit();

  if (global_size < global_limit) {
    return global_limit - global_size;
  } else {
    return 0;
  }
}

bool Heap::IsIneffectiveMarkCompact(size_t old_generation_size,
                                    size_t global_size,
                                    double mutator_utilization) {
  bool high_heap_ratio =
      (old_generation_size >= v8_flags.ineffective_gc_size_threshold *
                                  limits()->max_old_generation_size());
  if (v8_flags.ineffective_gc_includes_global) {
    high_heap_ratio |= (global_size >= v8_flags.ineffective_gc_size_threshold *
                                           limits()->max_global_memory_size());
  }
  return high_heap_ratio &&
         mutator_utilization <
             v8_flags.ineffective_gc_mutator_utilization_threshold;
}

namespace {
static constexpr int kMaxConsecutiveIneffectiveMarkCompacts = 4;
}

void Heap::CheckIneffectiveMarkCompact(size_t old_generation_size,
                                       size_t global_size,
                                       double mutator_utilization) {
  if (!v8_flags.detect_ineffective_gcs_near_heap_limit) return;
  if (!IsIneffectiveMarkCompact(old_generation_size, global_size,
                                mutator_utilization)) {
    consecutive_ineffective_mark_compacts_ = 0;
    return;
  }
  if (++consecutive_ineffective_mark_compacts_ ==
      kMaxConsecutiveIneffectiveMarkCompacts) {
    if (InvokeNearHeapLimitCallback()) {
      // The callback increased the heap limit.
      consecutive_ineffective_mark_compacts_ = 0;
      return;
    }
    if (v8_flags.heap_snapshot_on_oom) {
      heap_profiler()->WriteSnapshotToDiskAfterGC();
    }
    FatalProcessOutOfMemory("Ineffective mark-compacts near heap limit");
  }
}

bool Heap::HasHighFragmentation() {
  const size_t used = OldGenerationSizeOfObjects();
  const size_t committed = CommittedOldGenerationMemory();

  // Background thread allocation could result in committed memory being less
  // than used memory in some situations.
  if (committed < used) return false;

  constexpr size_t kSlack = 16 * MB;

  // Fragmentation is high if committed > 2 * used + kSlack.
  // Rewrite the expression to avoid overflow.
  return committed - used > used + kSlack;
}

bool Heap::ShouldOptimizeForMemoryUsage() {
  return isolate()->priority() == v8::Isolate::Priority::kBestEffort ||
         ShouldOptimizeForMemoryUsageIgnoringPriority();
}

bool Heap::ShouldOptimizeForMemoryUsageIgnoringPriority() {
  const size_t kOldGenerationSlack = limits()->max_old_generation_size() / 8;
  return isolate()->MemorySaverModeEnabled() || HighMemoryPressure() ||
         !CanExpandOldGeneration(kOldGenerationSlack);
}

class ActivateMemoryReducerTask : public CancelableTask {
 public:
  explicit ActivateMemoryReducerTask(Heap* heap)
      : CancelableTask(heap->isolate()), heap_(heap) {}

  ~ActivateMemoryReducerTask() override = default;
  ActivateMemoryReducerTask(const ActivateMemoryReducerTask&) = delete;
  ActivateMemoryReducerTask& operator=(const ActivateMemoryReducerTask&) =
      delete;

 private:
  // v8::internal::CancelableTask overrides.
  void RunInternal() override {
    heap_->ActivateMemoryReducerIfNeededOnMainThread();
  }

  Heap* heap_;
};

void Heap::ActivateMemoryReducerIfNeeded() {
  if (memory_reducer_ == nullptr) return;
  // This method may be called from any thread. Post a task to run it on the
  // isolate's main thread to avoid synchronization.
  task_runner_->PostTask(std::make_unique<ActivateMemoryReducerTask>(this));
}

void Heap::ActivateMemoryReducerIfNeededOnMainThread() {
  // Activate memory reducer when switching to background if
  // - there was no mark compact since the start.
  // - the committed memory can be potentially reduced.
  // 2 pages for the old, code, and map space + 1 page for new space.
  const int kMinCommittedMemory = 7 * NormalPage::kPageSize;
  if (ms_count_ == 0 && CommittedMemory() > kMinCommittedMemory &&
      isolate()->is_backgrounded()) {
    memory_reducer_->NotifyPossibleGarbage();
  }
}

Heap::ResizeNewSpaceMode Heap::ShouldResizeNewSpace() {
  if (ShouldReduceMemory()) {
    return (v8_flags.predictable) ? ResizeNewSpaceMode::kNone
                                  : ResizeNewSpaceMode::kShrink;
  }

  static const size_t kLowAllocationThroughput = 1000;
  const double allocation_throughput =
      tracer_->AllocationThroughputInBytesPerMillisecond();
  const bool should_shrink = !v8_flags.predictable &&
                             (allocation_throughput != 0) &&
                             (allocation_throughput < kLowAllocationThroughput);

  const bool should_grow =
      (new_space_->TotalCapacity() < new_space_->MaximumCapacity()) &&
      (survived_since_last_expansion_ > new_space_->TotalCapacity());

  if (should_grow) survived_since_last_expansion_ = 0;

  if (should_grow == should_shrink) return ResizeNewSpaceMode::kNone;
  return should_grow ? ResizeNewSpaceMode::kGrow : ResizeNewSpaceMode::kShrink;
}

namespace {
size_t ComputeReducedNewSpaceSize(NewSpace* new_space) {
  size_t new_capacity =
      std::max(new_space->MinimumCapacity(), 2 * new_space->Size());
  size_t rounded_new_capacity = ::RoundUp(new_capacity, NormalPage::kPageSize);
  DCHECK_LE(new_space->TotalCapacity(), new_space->MaximumCapacity());
  return std::min(new_space->TotalCapacity(), rounded_new_capacity);
}
}  // anonymous namespace

void Heap::StartResizeNewSpace() {
  DCHECK_EQ(ResizeNewSpaceMode::kNone, resize_new_space_mode_);
  DCHECK(v8_flags.minor_ms);
  resize_new_space_mode_ = ShouldResizeNewSpace();
  if (resize_new_space_mode_ == ResizeNewSpaceMode::kShrink) {
    size_t reduced_capacity = ComputeReducedNewSpaceSize(new_space());
    paged_new_space()->StartShrinking(reduced_capacity);
  }
}

void Heap::ResizeNewSpace() {
  DCHECK_IMPLIES(!v8_flags.minor_ms,
                 resize_new_space_mode_ == ResizeNewSpaceMode::kNone);
  const ResizeNewSpaceMode mode =
      v8_flags.minor_ms ? resize_new_space_mode_ : ShouldResizeNewSpace();
  resize_new_space_mode_ = ResizeNewSpaceMode::kNone;

  switch (mode) {
    case ResizeNewSpaceMode::kShrink:
      ReduceNewSpaceSize();
      break;
    case ResizeNewSpaceMode::kGrow:
      ExpandNewSpaceSize();
      break;
    case ResizeNewSpaceMode::kNone:
      break;
  }
}

void Heap::ReduceNewSpaceSizeForTesting() { ReduceNewSpaceSize(); }
void Heap::ExpandNewSpaceSizeForTesting() { ExpandNewSpaceSize(); }

void Heap::ExpandNewSpaceSize() {
  // Grow the size of new space if there is room to grow, and enough data
  // has survived scavenge since the last expansion.
  const size_t suggested_capacity =
      static_cast<size_t>(v8_flags.semi_space_growth_factor) *
      new_space_->TotalCapacity();
  const size_t chosen_capacity =
      std::min(suggested_capacity, new_space_->MaximumCapacity());
  DCHECK(IsAligned(chosen_capacity, NormalPage::kPageSize));

  if (chosen_capacity > new_space_->TotalCapacity()) {
    new_space_->Grow(chosen_capacity);
    new_lo_space()->SetCapacity(new_space()->TotalCapacity());
  }
}

void Heap::ReduceNewSpaceSize() {
  if (!v8_flags.minor_ms) {
    const size_t reduced_capacity = ComputeReducedNewSpaceSize(new_space());
    semi_space_new_space()->Shrink(reduced_capacity);
  } else {
    // MinorMS starts shrinking new space as part of sweeping.
    paged_new_space()->FinishShrinking();
  }
  new_lo_space_->SetCapacity(new_space()->TotalCapacity());
}

size_t Heap::NewSpaceSize() {
  if (v8_flags.sticky_mark_bits) {
    return sticky_space()->young_objects_size();
  }
  return new_space() ? new_space()->Size() : 0;
}

size_t Heap::NewSpaceCapacity() const {
  if (v8_flags.sticky_mark_bits) {
    return sticky_space()->Capacity() - sticky_space()->young_objects_size();
  }
  return new_space() ? new_space()->Capacity() : 0;
}

size_t Heap::NewSpaceTargetCapacity() const {
  if (v8_flags.sticky_mark_bits) {
    // TODO(333906585): Adjust target capacity for new sticky-space.
    return sticky_space()->Capacity() - sticky_space()->young_objects_size();
  }
  return new_space() ? new_space()->TotalCapacity() : 0;
}

void Heap::FinalizeIncrementalMarkingAtomically(
    GarbageCollectionReason gc_reason) {
  DCHECK(!incremental_marking()->IsStopped());
  CollectAllGarbage(current_gc_flags_, gc_reason, current_gc_callback_flags_);
}

void Heap::FinalizeIncrementalMarkingAtomicallyIfRunning(
    GarbageCollectionReason gc_reason) {
  if (!incremental_marking()->IsStopped()) {
    FinalizeIncrementalMarkingAtomically(gc_reason);
  }
}

void Heap::InvokeIncrementalMarkingPrologueCallbacks() {
  AllowGarbageCollection allow_allocation;
  VMState<EXTERNAL> state(isolate_);
  CallGCPrologueCallbacks(kGCTypeIncrementalMarking, kNoGCCallbackFlags,
                          GCTracer::Scope::MC_INCREMENTAL_EXTERNAL_PROLOGUE);
}

void Heap::InvokeIncrementalMarkingEpilogueCallbacks() {
  AllowGarbageCollection allow_allocation;
  VMState<EXTERNAL> state(isolate_);
  CallGCEpilogueCallbacks(kGCTypeIncrementalMarking, kNoGCCallbackFlags,
                          GCTracer::Scope::MC_INCREMENTAL_EXTERNAL_EPILOGUE);
}

namespace {
thread_local Address pending_layout_change_object_address = kNullAddress;

#ifdef V8_ENABLE_SANDBOX
class ExternalPointerSlotInvalidator
    : public HeapVisitor<ExternalPointerSlotInvalidator> {
 public:
  explicit ExternalPointerSlotInvalidator(Isolate* isolate)
      : HeapVisitor(isolate), isolate_(isolate) {}

  void VisitPointers(Tagged<HeapObject> host, ObjectSlot start,
                     ObjectSlot end) override {}
  void VisitPointers(Tagged<HeapObject> host, MaybeObjectSlot start,
                     MaybeObjectSlot end) override {}
  void VisitInstructionStreamPointer(Tagged<Code> host,
                                     InstructionStreamSlot slot) override {}
  void VisitMapPointer(Tagged<HeapObject> host) override {}

  void VisitExternalPointer(Tagged<HeapObject> host,
                            ExternalPointerSlot slot) override {
    DCHECK_EQ(target_, host);
    ExternalPointerTable::Space* space =
        IsolateForSandbox(isolate_).GetExternalPointerTableSpaceFor(
            slot.tag_range(), host.address());
    space->NotifyExternalPointerFieldInvalidated(slot.address(),
                                                 slot.tag_range());
    num_invalidated_slots++;
  }

  int Visit(Tagged<HeapObject> target) {
    target_ = target;
    num_invalidated_slots = 0;
    HeapVisitor::Visit(target);
    return num_invalidated_slots;
  }

 private:
  Isolate* isolate_;
  Tagged<HeapObject> target_;
  int num_invalidated_slots = 0;
};
#endif  // V8_ENABLE_SANDBOX

}  // namespace

void Heap::NotifyObjectLayoutChange(
    Tagged<HeapObject> object, const DisallowGarbageCollection&,
    InvalidateRecordedSlots invalidate_recorded_slots,
    InvalidateExternalPointerSlots invalidate_external_pointer_slots,
    int new_size) {
  if (invalidate_recorded_slots == InvalidateRecordedSlots::kYes) {
    const bool may_contain_recorded_slots = MayContainRecordedSlots(object);
    MutablePage* const page = MutablePage::FromHeapObject(isolate(), object);
    // Do not remove the recorded slot in the map word as this one can never be
    // invalidated.
    const Address clear_range_start = object.address() + kTaggedSize;
    // Only slots in the range of the new object size (which is potentially
    // smaller than the original one) can be invalidated. Clearing of recorded
    // slots up to the original object size even conflicts with concurrent
    // sweeping.
    const Address clear_range_end = object.address() + new_size;

    if (incremental_marking()->IsMarking()) {
      ObjectLock::Lock(isolate(), object);
      DCHECK_EQ(pending_layout_change_object_address, kNullAddress);
      pending_layout_change_object_address = object.address();
      if (may_contain_recorded_slots && incremental_marking()->IsCompacting()) {
        RememberedSet<OLD_TO_OLD>::RemoveRange(
            page, clear_range_start, clear_range_end,
            SlotSet::EmptyBucketMode::KEEP_EMPTY_BUCKETS);
      }
    }

    if (may_contain_recorded_slots) {
      RememberedSet<OLD_TO_NEW>::RemoveRange(
          page, clear_range_start, clear_range_end,
          SlotSet::EmptyBucketMode::KEEP_EMPTY_BUCKETS);
      RememberedSet<OLD_TO_NEW_BACKGROUND>::RemoveRange(
          page, clear_range_start, clear_range_end,
          SlotSet::EmptyBucketMode::KEEP_EMPTY_BUCKETS);
      RememberedSet<OLD_TO_SHARED>::RemoveRange(
          page, clear_range_start, clear_range_end,
          SlotSet::EmptyBucketMode::KEEP_EMPTY_BUCKETS);
    }

    DCHECK(!page->is_trusted());
  }

  // During external pointer table compaction, the external pointer table
  // records addresses of fields that index into the external pointer table. As
  // such, it needs to be informed when such a field is invalidated.
  if (invalidate_external_pointer_slots ==
      InvalidateExternalPointerSlots::kYes) {
    // Currently, the only time this function receives
    // InvalidateExternalPointerSlots::kYes is when an external string
    // transitions to a thin string.  If this ever changed to happen for array
    // buffer extension slots, we would have to run the invalidator in
    // pointer-compression-but-no-sandbox configurations as well.
    DCHECK(IsString(object));
#ifdef V8_ENABLE_SANDBOX
    if (V8_ENABLE_SANDBOX_BOOL) {
      ExternalPointerSlotInvalidator slot_invalidator(isolate());
      int num_invalidated_slots = slot_invalidator.Visit(object);
      USE(num_invalidated_slots);
      DCHECK_GT(num_invalidated_slots, 0);
    }

    // During concurrent marking for a minor GC, the heap also builds up a
    // RememberedSet of external pointer field locations, and uses that set to
    // evacuate external pointer table entries when promoting objects.  Here we
    // would need to invalidate that set too; until we do, assert that
    // NotifyObjectLayoutChange is never called on young objects.
    CHECK(!HeapLayout::InYoungGeneration(object));
#endif
  }

#ifdef VERIFY_HEAP
  if (v8_flags.verify_heap) {
    HeapVerifier::SetPendingLayoutChangeObject(this, object);
  }
#endif
}

// static
void Heap::NotifyObjectLayoutChangeDone(Tagged<HeapObject> object) {
  if (pending_layout_change_object_address != kNullAddress) {
    DCHECK_EQ(pending_layout_change_object_address, object.address());
    ObjectLock::Unlock(Isolate::Current(), object);
    pending_layout_change_object_address = kNullAddress;
  }
}

void Heap::NotifyObjectSizeChange(Tagged<HeapObject> object, int old_size,
                                  int new_size,
                                  ClearRecordedSlots clear_recorded_slots) {
  old_size = ALIGN_TO_ALLOCATION_ALIGNMENT(old_size);
  new_size = ALIGN_TO_ALLOCATION_ALIGNMENT(new_size);
  DCHECK_LE(new_size, old_size);
  DCHECK(!HeapLayout::InAnyLargeSpace(object));
  if (new_size == old_size) return;

  const LocalHeap* current = LocalHeap::TryGetCurrent();
  DCHECK_IMPLIES(!current, gc_state() == MARK_COMPACT);
  const bool is_non_main_thread = current && !current->is_main_thread();
  DCHECK_IMPLIES(is_non_main_thread,
                 clear_recorded_slots == ClearRecordedSlots::kNo);

  const auto verify_no_slots_recorded = !is_non_main_thread
                                            ? VerifyNoSlotsRecorded::kYes
                                            : VerifyNoSlotsRecorded::kNo;

  const auto clear_memory_mode = ClearFreedMemoryMode::kDontClearFreedMemory;

  const Address filler = object.address() + new_size;
  const int filler_size = old_size - new_size;
  CreateFillerObjectAtRaw(
      WritableFreeSpace::ForNonExecutableMemory(filler, filler_size),
      clear_memory_mode, clear_recorded_slots, verify_no_slots_recorded);
}

double Heap::MonotonicallyIncreasingTimeInMs() const {
  return V8::GetCurrentPlatform()->MonotonicallyIncreasingTime() *
         static_cast<double>(base::Time::kMillisecondsPerSecond);
}

#if DEBUG
void Heap::VerifyNewSpaceTop() {
  if (!new_space()) return;
  allocator()->new_space_allocator()->Verify();
}
#endif  // DEBUG

class MemoryPressureInterruptTask : public CancelableTask {
 public:
  explicit MemoryPressureInterruptTask(Heap* heap)
      : CancelableTask(heap->isolate()), heap_(heap) {}

  ~MemoryPressureInterruptTask() override = default;
  MemoryPressureInterruptTask(const MemoryPressureInterruptTask&) = delete;
  MemoryPressureInterruptTask& operator=(const MemoryPressureInterruptTask&) =
      delete;

 private:
  // v8::internal::CancelableTask overrides.
  void RunInternal() override { heap_->CheckMemoryPressure(); }

  Heap* heap_;
};

void Heap::CheckMemoryPressure() {
  if (HighMemoryPressure()) {
    FreeCachesOnMemoryPressure(isolate());
  }
  // Reset the memory pressure level to avoid recursive GCs triggered by
  // CheckMemoryPressure from AdjustAmountOfExternalMemory called by
  // the finalizers.
  MemoryPressureLevel memory_pressure_level = memory_pressure_level_.exchange(
      MemoryPressureLevel::kNone, std::memory_order_relaxed);
  if (memory_pressure_level == MemoryPressureLevel::kCritical) {
    TRACE_EVENT0("devtools.timeline,v8", "V8.CheckMemoryPressure");
    CollectGarbageOnMemoryPressure();
  } else if (memory_pressure_level == MemoryPressureLevel::kModerate) {
    if (v8_flags.incremental_marking && incremental_marking()->IsStopped()) {
      TRACE_EVENT0("devtools.timeline,v8", "V8.CheckMemoryPressure");
      StartIncrementalMarking(GCFlag::kReduceMemoryFootprint,
                              GarbageCollectionReason::kMemoryPressure);
    }
  }
}

void Heap::CollectGarbageOnMemoryPressure() {
  const int kGarbageThresholdInBytes = 8 * MB;
  const double kGarbageThresholdAsFractionOfTotalMemory = 0.1;
  // This constant is the maximum response time in RAIL performance model.
  const double kMaxMemoryPressurePauseMs = 100;
  const GarbageCollectionReason gc_reason =
      GarbageCollectionReason::kMemoryPressure;

  double start = MonotonicallyIncreasingTimeInMs();
  CollectAllGarbage(GCFlag::kReduceMemoryFootprint, gc_reason,
                    kGCCallbackFlagCollectAllAvailableGarbage);
  FlushLiftoffCode(gc_reason);
  CompleteArrayBufferSweeping();
  double end = MonotonicallyIncreasingTimeInMs();

  // Estimate how much memory we can free.
  int64_t potential_garbage =
      (CommittedMemory() - SizeOfObjects()) + external_memory();
  // If we can potentially free large amount of memory, then start GC right
  // away instead of waiting for memory reducer.
  if (potential_garbage >= kGarbageThresholdInBytes &&
      potential_garbage >=
          CommittedMemory() * kGarbageThresholdAsFractionOfTotalMemory) {
    // If we spent less than half of the time budget, then perform full GC
    // Otherwise, start incremental marking.
    if (end - start < kMaxMemoryPressurePauseMs / 2) {
      CollectAllGarbage(GCFlag::kReduceMemoryFootprint, gc_reason,
                        kGCCallbackFlagCollectAllAvailableGarbage);
    } else {
      if (v8_flags.incremental_marking && incremental_marking()->IsStopped()) {
        StartIncrementalMarking(GCFlag::kReduceMemoryFootprint, gc_reason);
      }
    }
  }
}

void Heap::MemoryPressureNotification(MemoryPressureLevel level,
                                      bool is_isolate_locked) {
  TRACE_EVENT1("devtools.timeline,v8", "V8.MemoryPressureNotification", "level",
               static_cast<int>(level));
  MemoryPressureLevel previous =
      memory_pressure_level_.exchange(level, std::memory_order_relaxed);
  if ((previous != MemoryPressureLevel::kCritical &&
       level == MemoryPressureLevel::kCritical) ||
      (previous == MemoryPressureLevel::kNone &&
       level == MemoryPressureLevel::kModerate)) {
    if (is_isolate_locked) {
      CheckMemoryPressure();
    } else {
      ExecutionAccess access(isolate());
      isolate()->stack_guard()->RequestGC();
      task_runner_->PostTask(
          std::make_unique<MemoryPressureInterruptTask>(this));
    }
  }
}

void Heap::FlushLiftoffCode(GarbageCollectionReason gc_reason) {
#if V8_ENABLE_WEBASSEMBLY
  const bool should_flush =
      gc_reason == GarbageCollectionReason::kLastResort ||
      gc_reason == GarbageCollectionReason::kMemoryPressure;
  if (should_flush && v8_flags.flush_liftoff_code) {
    wasm::GetWasmEngine()->FlushLiftoffCode();
  }
#endif  // V8_ENABLE_WEBASSEMBLY
}

void Heap::AddNearHeapLimitCallback(v8::NearHeapLimitCallback callback,
                                    void* data) {
  const size_t kMaxCallbacks = 100;
  CHECK_LT(near_heap_limit_callbacks_.size(), kMaxCallbacks);
  for (auto callback_data : near_heap_limit_callbacks_) {
    CHECK_NE(callback_data.first, callback);
  }
  near_heap_limit_callbacks_.push_back(std::make_pair(callback, data));
}

void Heap::RemoveNearHeapLimitCallback(v8::NearHeapLimitCallback callback,
                                       size_t heap_limit) {
  for (size_t i = 0; i < near_heap_limit_callbacks_.size(); i++) {
    if (near_heap_limit_callbacks_[i].first == callback) {
      near_heap_limit_callbacks_.erase(near_heap_limit_callbacks_.begin() + i);
      if (heap_limit) {
        RestoreHeapLimit(heap_limit);
      }
      return;
    }
  }
  UNREACHABLE();
}

void Heap::AppendArrayBufferExtension(ArrayBufferExtension* extension) {
  // ArrayBufferSweeper is managing all counters and updating Heap counters.
  array_buffer_sweeper_->Append(extension);
}

void Heap::ResizeArrayBufferExtension(ArrayBufferExtension* extension,
                                      int64_t delta) {
  // ArrayBufferSweeper is managing all counters and updating Heap counters.
  array_buffer_sweeper_->Resize(extension, delta);
}

void Heap::DetachArrayBufferExtension(ArrayBufferExtension* extension) {
  // ArrayBufferSweeper is managing all counters and updating Heap counters.
  return array_buffer_sweeper_->Detach(extension);
}

void Heap::AutomaticallyRestoreInitialHeapLimit(double threshold_percent) {
  initial_max_old_generation_size_threshold_ =
      limits()->initial_max_old_generation_size() * threshold_percent;
}

bool Heap::InvokeNearHeapLimitCallback() {
  if (!near_heap_limit_callbacks_.empty()) {
    AllowGarbageCollection allow_gc;
    TRACE_GC(tracer(), GCTracer::Scope::HEAP_EXTERNAL_NEAR_HEAP_LIMIT);
    VMState<EXTERNAL> callback_state(isolate());
    HandleScope scope(isolate());
    v8::NearHeapLimitCallback callback =
        near_heap_limit_callbacks_.back().first;
    void* data = near_heap_limit_callbacks_.back().second;
    size_t heap_limit = callback(data, limits()->max_old_generation_size(),
                                 limits()->initial_max_old_generation_size());
    if (heap_limit > limits()->max_old_generation_size()) {
      limits()->SetMaximumSizes(
          std::min(heap_limit,
                   AllocatorLimitOnMaxOldGenerationSize(physical_memory())),
          physical_memory());
      return true;
    }
  }
  return false;
}

bool Heap::MeasureMemory(std::unique_ptr<v8::MeasureMemoryDelegate> delegate,
                         v8::MeasureMemoryExecution execution) {
  HandleScope handle_scope(isolate());
  std::vector<Handle<NativeContext>> contexts = FindAllNativeContexts();
  std::vector<Handle<NativeContext>> to_measure;
  for (auto& current : contexts) {
    if (delegate->ShouldMeasure(v8::Utils::ToLocal(current))) {
      to_measure.push_back(current);
    }
  }
  return memory_measurement_->EnqueueRequest(std::move(delegate), execution,
                                             to_measure);
}

std::unique_ptr<v8::MeasureMemoryDelegate>
Heap::CreateDefaultMeasureMemoryDelegate(
    v8::Local<v8::Context> context, v8::Local<v8::Promise::Resolver> promise,
    v8::MeasureMemoryMode mode) {
  return i::MemoryMeasurement::DefaultDelegate(
      reinterpret_cast<v8::Isolate*>(isolate_), context, promise, mode);
}

void Heap::CollectCodeStatistics() {
  TRACE_EVENT0("v8", "Heap::CollectCodeStatistics");
  SafepointScope safepoint_scope(isolate(),
                                 kGlobalSafepointForSharedSpaceIsolate);
  MakeHeapIterable(CompleteSweepingReason::kCollectCodeStatistics);
  CodeStatistics::ResetCodeAndMetadataStatistics(isolate());
  // We do not look for code in new space, or map space.  If code
  // somehow ends up in those spaces, we would miss it here.
  CodeStatistics::CollectCodeStatistics(code_space_, isolate());
  CodeStatistics::CollectCodeStatistics(old_space_, isolate());
  CodeStatistics::CollectCodeStatistics(code_lo_space_, isolate());
  CodeStatistics::CollectCodeStatistics(trusted_space_, isolate());
  CodeStatistics::CollectCodeStatistics(trusted_lo_space_, isolate());
}

#ifdef DEBUG

void Heap::Print() {
  if (!HasBeenSetUp()) return;
  for (SpaceIterator it(this); it.HasNext();) {
    it.Next()->Print();
  }
}

void Heap::ReportCodeStatistics(const char* title) {
  PrintF("###### Code Stats (%s) ######\n", title);
  CollectCodeStatistics();
  CodeStatistics::ReportCodeStatistics(isolate());
}

#endif  // DEBUG

bool Heap::Contains(Tagged<HeapObject> value) const {
  if (HeapLayout::InReadOnlySpace(value)) {
    return false;
  }
  if (HeapLayout::InWritableSharedSpace(value) &&
      !isolate()->is_shared_space_isolate()) {
    return false;
  }

  CHECK(HasBeenSetUp());
  // Must be somewhere on the heap.
  CHECK(!memory_allocator()->IsOutsideAllocatedSpace(value.address()));

  const auto space =
      MemoryChunk::FromHeapObject(value)->Metadata(isolate())->owner_identity();
  switch (space) {
    case NEW_SPACE:
      return new_space_->Contains(value);
    case OLD_SPACE:
      return old_space_->Contains(value);
    case CODE_SPACE:
      return code_space_->Contains(value);
    case SHARED_SPACE:
      return shared_space_->Contains(value);
    case TRUSTED_SPACE:
      return trusted_space_->Contains(value);
    case SHARED_TRUSTED_SPACE:
      return shared_trusted_space_->Contains(value);
    case LO_SPACE:
      return lo_space_->Contains(value);
    case CODE_LO_SPACE:
      return code_lo_space_->Contains(value);
    case NEW_LO_SPACE:
      return new_lo_space_->Contains(value);
    case SHARED_LO_SPACE:
      return shared_lo_space_->Contains(value);
    case SHARED_TRUSTED_LO_SPACE:
      return shared_trusted_lo_space_->Contains(value);
    case TRUSTED_LO_SPACE:
      return trusted_lo_space_->Contains(value);
    case RO_SPACE:
      UNREACHABLE();
  }
  UNREACHABLE();
}

bool Heap::ContainsCode(Tagged<HeapObject> value) const {
  // TODO(v8:11880): support external code space.
  if (memory_allocator()->IsOutsideAllocatedSpace(value.address(),
                                                  EXECUTABLE)) {
    return false;
  }
  return HasBeenSetUp() &&
         (code_space_->Contains(value) || code_lo_space_->Contains(value));
}

bool Heap::SharedHeapContains(Tagged<HeapObject> value) const {
  if (shared_allocation_space_) {
    if (shared_allocation_space_->Contains(value)) return true;
    if (shared_lo_allocation_space_->Contains(value)) return true;
    if (shared_trusted_allocation_space_->Contains(value)) return true;
    if (shared_trusted_lo_allocation_space_->Contains(value)) return true;
  }

  return false;
}

bool Heap::MustBeInSharedOldSpace(Tagged<HeapObject> value) {
  if (isolate()->OwnsStringTables()) return false;
  if (ReadOnlyHeap::Contains(value)) return false;
  if (HeapLayout::InYoungGeneration(value)) return false;
  if (IsExternalString(value)) return false;
  if (IsInternalizedString(value)) return true;
  return false;
}

bool Heap::InSpace(Tagged<HeapObject> value, AllocationSpace space) const {
  if (memory_allocator()->IsOutsideAllocatedSpace(
          value.address(),
          IsAnyCodeSpace(space) ? EXECUTABLE : NOT_EXECUTABLE)) {
    return false;
  }
  if (!HasBeenSetUp()) return false;

  switch (space) {
    case NEW_SPACE:
      return new_space_->Contains(value);
    case OLD_SPACE:
      return old_space_->Contains(value);
    case CODE_SPACE:
      return code_space_->Contains(value);
    case SHARED_SPACE:
      return shared_space_->Contains(value);
    case TRUSTED_SPACE:
      return trusted_space_->Contains(value);
    case SHARED_TRUSTED_SPACE:
      return shared_trusted_space_->Contains(value);
    case LO_SPACE:
      return lo_space_->Contains(value);
    case CODE_LO_SPACE:
      return code_lo_space_->Contains(value);
    case NEW_LO_SPACE:
      return new_lo_space_->Contains(value);
    case SHARED_LO_SPACE:
      return shared_lo_space_->Contains(value);
    case SHARED_TRUSTED_LO_SPACE:
      return shared_trusted_lo_space_->Contains(value);
    case TRUSTED_LO_SPACE:
      return trusted_lo_space_->Contains(value);
    case RO_SPACE:
      return ReadOnlyHeap::Contains(value);
  }
  UNREACHABLE();
}

bool Heap::InSpaceSlow(Address addr, AllocationSpace space) const {
  if (memory_allocator()->IsOutsideAllocatedSpace(
          addr, IsAnyCodeSpace(space) ? EXECUTABLE : NOT_EXECUTABLE)) {
    return false;
  }
  if (!HasBeenSetUp()) return false;

  switch (space) {
    case NEW_SPACE:
      return new_space_->ContainsSlow(addr);
    case OLD_SPACE:
      return old_space_->ContainsSlow(addr);
    case CODE_SPACE:
      return code_space_->ContainsSlow(addr);
    case SHARED_SPACE:
      return shared_space_->ContainsSlow(addr);
    case TRUSTED_SPACE:
      return trusted_space_->ContainsSlow(addr);
    case SHARED_TRUSTED_SPACE:
      return shared_trusted_space_->ContainsSlow(addr);
    case LO_SPACE:
      return lo_space_->ContainsSlow(addr);
    case CODE_LO_SPACE:
      return code_lo_space_->ContainsSlow(addr);
    case NEW_LO_SPACE:
      return new_lo_space_->ContainsSlow(addr);
    case SHARED_LO_SPACE:
      return shared_lo_space_->ContainsSlow(addr);
    case SHARED_TRUSTED_LO_SPACE:
      return shared_trusted_lo_space_->ContainsSlow(addr);
    case TRUSTED_LO_SPACE:
      return trusted_lo_space_->ContainsSlow(addr);
    case RO_SPACE:
      return read_only_space_->ContainsSlow(addr);
  }
  UNREACHABLE();
}

bool Heap::CanReferenceHeapObject(Tagged<HeapObject> obj) {
  MemoryChunk* chunk = MemoryChunk::FromHeapObject(obj);
  // Objects in read-only space are allowed to be used in any isolate.
  if (chunk->InReadOnlySpace()) {
    return true;
  }
  // `heap()` below is not necessarily `this` as the object may be on a shared
  // page.
  Heap* obj_heap = chunk->Metadata(isolate())->heap();
  Heap* expected_heap = chunk->InWritableSharedSpace()
                            ? isolate()->shared_space_isolate()->heap()
                            : this;
  return obj_heap == expected_heap;
}

#ifdef DEBUG
void Heap::VerifyCountersAfterSweeping() {
  MakeHeapIterable(CompleteSweepingReason::kTesting);
  PagedSpaceIterator spaces(this);
  for (PagedSpace* space = spaces.Next(); space != nullptr;
       space = spaces.Next()) {
    space->VerifyCountersAfterSweeping(this);
  }
}

void Heap::VerifyCountersBeforeConcurrentSweeping(GarbageCollector collector) {
  if (v8_flags.minor_ms && new_space()) {
    PagedSpaceBase* space = paged_new_space()->paged_space();
    space->RefillFreeList();
    space->VerifyCountersBeforeConcurrentSweeping();
  }
  if (collector != GarbageCollector::MARK_COMPACTOR) return;
  PagedSpaceIterator spaces(this);
  for (PagedSpace* space = spaces.Next(); space != nullptr;
       space = spaces.Next()) {
    // We need to refine the counters on pages that are already swept and have
    // not been moved over to the actual space. Otherwise, the AccountingStats
    // are just an over approximation.
    space->RefillFreeList();
    space->VerifyCountersBeforeConcurrentSweeping();
  }
}

void Heap::VerifyCommittedPhysicalMemory() {
  PagedSpaceIterator spaces(this);
  for (PagedSpace* space = spaces.Next(); space != nullptr;
       space = spaces.Next()) {
    space->VerifyCommittedPhysicalMemory();
  }
  if (v8_flags.minor_ms && new_space()) {
    paged_new_space()->paged_space()->VerifyCommittedPhysicalMemory();
  }
}
#endif  // DEBUG

void Heap::IterateWeakRoots(RootVisitor* v, base::EnumSet<SkipRoot> options) {
  DCHECK(!options.contains(SkipRoot::kWeak));

  if (!options.contains(SkipRoot::kUnserializable)) {
    // Isolate::topmost_script_having_context_address is treated weakly.
    v->VisitRootPointer(
        Root::kWeakRoots, nullptr,
        FullObjectSlot(isolate()->topmost_script_having_context_address()));
  }

  if (!options.contains(SkipRoot::kOldGeneration) &&
      !options.contains(SkipRoot::kUnserializable) &&
      isolate()->OwnsStringTables()) {
    // Do not visit for the following reasons.
    // - Serialization, since the string table is custom serialized.
    // - If we are skipping old generation, since all internalized strings
    //   are in old space.
    // - If the string table is shared and this is not the shared heap,
    //   since all internalized strings are in the shared heap.
    isolate()->string_table()->IterateElements(v);
  }
  v->Synchronize(VisitorSynchronization::kStringTable);
  if (!options.contains(SkipRoot::kExternalStringTable) &&
      !options.contains(SkipRoot::kUnserializable)) {
    // Scavenge collections have special processing for this.
    // Do not visit for serialization, since the external string table will
    // be populated from scratch upon deserialization.
    external_string_table_.Iterate(v);
  }
  v->Synchronize(VisitorSynchronization::kExternalStringsTable);
  if (!options.contains(SkipRoot::kOldGeneration) &&
      !options.contains(SkipRoot::kUnserializable) &&
      isolate()->is_shared_space_isolate() &&
      isolate()->shared_struct_type_registry()) {
    isolate()->shared_struct_type_registry()->IterateElements(isolate(), v);
  }
  v->Synchronize(VisitorSynchronization::kSharedStructTypeRegistry);
}

void Heap::IterateSmiRoots(RootVisitor* v) {
  // Acquire execution access since we are going to read stack limit values.
  ExecutionAccess access(isolate());
  v->VisitRootPointers(Root::kSmiRootList, nullptr,
                       roots_table().smi_roots_begin(),
                       roots_table().smi_roots_end());
  v->Synchronize(VisitorSynchronization::kSmiRootList);
}

void ClearStaleLeftTrimmedPointerVisitor::ClearLeftTrimmedOrForward(
    Root root, const char* description, FullObjectSlot p) {
  if (!IsHeapObject(*p)) return;

  if (IsLeftTrimmed(p)) {
    p.store(Smi::zero());
  } else {
    visitor_->VisitRootPointer(root, description, p);
  }
}

namespace {
bool IsInterestingObjectStart(MapWord map_word) {
  // Scavenge tasks may run concurrently to this function and therefore
  // could introduce forwarding pointers at any moment. This is the reason
  // why we pass the Map from the MapWord to
  // InstanceTypeChecker::IsFreeSpaceOrFiller.
  return map_word.IsForwardingAddress() ||
         !InstanceTypeChecker::IsFreeSpaceOrFiller(map_word.ToMap());
}
}  // namespace

bool ClearStaleLeftTrimmedPointerVisitor::IsLeftTrimmed(FullObjectSlot p) {
  Tagged<HeapObject> current;
  if (!TryCast<HeapObject>(*p, &current)) return false;
  // Using MapWord instead of `current` directly defends against concurrent
  // Scavenge tasks installing forward pointers on `current`.
  MapWord map_word = current->map_word(cage_base(), kRelaxedLoad);
  if (!IsInterestingObjectStart(map_word)) {
#ifdef DEBUG
      // We need to find a FixedArrayBase map after walking the fillers.
      while (!IsInterestingObjectStart(map_word)) {
        Address next = current.ptr();
        Tagged<Map> map = map_word.ToMap();
        if (map == ReadOnlyRoots(heap_).one_pointer_filler_map()) {
          next += kTaggedSize;
        } else if (map == ReadOnlyRoots(heap_).two_pointer_filler_map()) {
          next += 2 * kTaggedSize;
        } else {
          next += current->SizeFromMap(map);
        }
        current = Cast<HeapObject>(Tagged<Object>(next));
        map_word = current->map_word(cage_base(), kRelaxedLoad);
      }
      // Scavenge tasks may run concurrently to this function and therefore
      // could introduce forwarding pointers at any moment. This is the reason
      // why we pass the Map from the MapWord to
      // InstanceTypeChecker::IsFreeSpaceOrFiller.
      DCHECK(map_word.IsForwardingAddress() ||
             InstanceTypeChecker::IsFixedArrayBase(map_word.ToMap()));
#endif  // DEBUG
      return true;
  } else {
    return false;
  }
}

ClearStaleLeftTrimmedPointerVisitor::ClearStaleLeftTrimmedPointerVisitor(
    Heap* heap, RootVisitor* visitor)
    : heap_(heap),
      visitor_(visitor)
#if V8_COMPRESS_POINTERS
      ,
      cage_base_(heap->isolate())
#endif  // V8_COMPRESS_POINTERS
{
  USE(heap_);
}

void ClearStaleLeftTrimmedPointerVisitor::VisitRootPointer(
    Root root, const char* description, FullObjectSlot p) {
  ClearLeftTrimmedOrForward(root, description, p);
}

void ClearStaleLeftTrimmedPointerVisitor::VisitRootPointers(
    Root root, const char* description, FullObjectSlot start,
    FullObjectSlot end) {
  for (FullObjectSlot p = start; p < end; ++p) {
    ClearLeftTrimmedOrForward(root, description, p);
  }
}

void ClearStaleLeftTrimmedPointerVisitor::VisitRunningCode(
    FullObjectSlot code_slot, FullObjectSlot istream_or_smi_zero_slot) {
  // Directly forward to actual visitor here. Code objects and instruction
  // stream will not be left-trimmed.
  DCHECK(!IsLeftTrimmed(code_slot));
  DCHECK(!IsLeftTrimmed(istream_or_smi_zero_slot));
  visitor_->VisitRunningCode(code_slot, istream_or_smi_zero_slot);
}

void Heap::IterateRoots(RootVisitor* v, base::EnumSet<SkipRoot> options,
                        IterateRootsMode roots_mode) {
  v->VisitRootPointers(Root::kStrongRootList, nullptr,
                       roots_table().strong_roots_begin(),
                       roots_table().strong_roots_end());
  v->Synchronize(VisitorSynchronization::kStrongRootList);

  isolate_->bootstrapper()->Iterate(v);
  v->Synchronize(VisitorSynchronization::kBootstrapper);
  Relocatable::Iterate(isolate_, v);
  v->Synchronize(VisitorSynchronization::kRelocatable);
  isolate_->debug()->Iterate(v);
  v->Synchronize(VisitorSynchronization::kDebug);

  isolate_->compilation_cache()->Iterate(v);
  v->Synchronize(VisitorSynchronization::kCompilationCache);

  const bool skip_iterate_builtins =
      options.contains(SkipRoot::kOldGeneration) ||
      (Builtins::kCodeObjectsAreInROSpace &&
       options.contains(SkipRoot::kReadOnlyBuiltins) &&
       // Prior to ReadOnlyPromotion, builtins may be on the mutable heap.
       !isolate_->serializer_enabled());
  if (!skip_iterate_builtins) {
    IterateBuiltins(v);
    v->Synchronize(VisitorSynchronization::kBuiltins);
  }

  // Iterate over pointers being held by inactive threads.
  isolate_->thread_manager()->Iterate(v);
  v->Synchronize(VisitorSynchronization::kThreadManager);

  // Visitors in this block only run when not serializing. These include:
  //
  // - Thread-local and stack.
  // - Handles.
  // - Microtasks.
  // - The startup object cache.
  //
  // When creating real startup snapshot, these areas are expected to be empty.
  // It is also possible to create a snapshot of a *running* isolate for testing
  // purposes. In this case, these areas are likely not empty and will simply be
  // skipped.
  //
  // The general guideline for adding visitors to this section vs. adding them
  // above is that non-transient heap state is always visited, transient heap
  // state is visited only when not serializing.
  if (!options.contains(SkipRoot::kUnserializable)) {
    if (!options.contains(SkipRoot::kTracedHandles)) {
      // Young GCs always skip traced handles and visit them manually.
      DCHECK(!options.contains(SkipRoot::kOldGeneration));

      isolate_->traced_handles()->Iterate(v);
    }

    if (!options.contains(SkipRoot::kGlobalHandles)) {
      // Young GCs always skip global handles and visit them manually.
      DCHECK(!options.contains(SkipRoot::kOldGeneration));

      if (options.contains(SkipRoot::kWeak)) {
        isolate_->global_handles()->IterateStrongRoots(v);
      } else {
        isolate_->global_handles()->IterateAllRoots(v);
      }
    }
    v->Synchronize(VisitorSynchronization::kGlobalHandles);

    if (!options.contains(SkipRoot::kStack)) {
      ClearStaleLeftTrimmedPointerVisitor left_trim_visitor(this, v);
      IterateStackRoots(&left_trim_visitor);
      if (!options.contains(SkipRoot::kConservativeStack)) {
        IterateConservativeStackRoots(v, roots_mode);
      }
      v->Synchronize(VisitorSynchronization::kStackRoots);
    }

    // Iterate over main thread handles in handle scopes.
    if (!options.contains(SkipRoot::kMainThreadHandles)) {
      // Clear main thread handles with stale references to left-trimmed
      // objects. The GC would crash on such stale references.
      ClearStaleLeftTrimmedPointerVisitor left_trim_visitor(this, v);
      isolate_->handle_scope_implementer()->Iterate(&left_trim_visitor);
    }
    // Iterate local handles for all local heaps.
    safepoint_->Iterate(v);
    // Iterates all persistent handles.
    isolate_->persistent_handles_list()->Iterate(v, isolate_);
    v->Synchronize(VisitorSynchronization::kHandleScope);

    if (options.contains(SkipRoot::kOldGeneration)) {
      isolate_->eternal_handles()->IterateYoungRoots(v);
    } else {
      isolate_->eternal_handles()->IterateAllRoots(v);
    }
    v->Synchronize(VisitorSynchronization::kEternalHandles);

    // Iterate over pending Microtasks stored in MicrotaskQueues.
    MicrotaskQueue* default_microtask_queue =
        isolate_->default_microtask_queue();
    if (default_microtask_queue) {
      MicrotaskQueue* microtask_queue = default_microtask_queue;
      do {
        microtask_queue->IterateMicrotasks(v);
        microtask_queue = microtask_queue->next();
      } while (microtask_queue != default_microtask_queue);
    }
    v->Synchronize(VisitorSynchronization::kMicroTasks);

    // Iterate over other strong roots (currently only identity maps and
    // deoptimization entries).
    for (StrongRootsEntry* current = strong_roots_head_; current;
         current = current->next) {
      v->VisitRootPointers(Root::kStrongRoots, current->label, current->start,
                           current->end);
    }

    v->Synchronize(VisitorSynchronization::kStrongRoots);

    for (GCRootsProvider* provider : global_gc_roots_providers_) {
      provider->Iterate(v);
    }

    v->Synchronize(VisitorSynchronization::kStrongRoots);

    // Iterate over the startup and shared heap object caches unless
    // serializing or deserializing.
    SerializerDeserializer::IterateStartupObjectCache(isolate_, v);
    v->Synchronize(VisitorSynchronization::kStartupObjectCache);

    // Iterate over shared heap object cache when the isolate owns this data
    // structure. Isolates which own the shared heap object cache are:
    //   * All isolates when not using --shared-string-table.
    //   * Shared space/main isolate with --shared-string-table.
    //
    // Isolates which do not own the shared heap object cache should not iterate
    // it.
    if (isolate_->OwnsStringTables()) {
      SerializerDeserializer::IterateSharedHeapObjectCache(isolate_, v);
      v->Synchronize(VisitorSynchronization::kSharedHeapObjectCache);
    }
  }

  if (!options.contains(SkipRoot::kWeak)) {
    IterateWeakRoots(v, options);
  }
}

void Heap::IterateRootsIncludingClients(RootVisitor* v,
                                        base::EnumSet<SkipRoot> options) {
  IterateRoots(v, options, IterateRootsMode::kMainIsolate);

  if (isolate()->is_shared_space_isolate()) {
    ClientRootVisitor<> client_root_visitor(v);
    isolate()->global_safepoint()->IterateClientIsolates(
        [v = &client_root_visitor, options](Isolate* client) {
          client->heap()->IterateRoots(v, options,
                                       IterateRootsMode::kClientIsolate);
        });
  }
}

void Heap::IterateWeakGlobalHandles(RootVisitor* v) {
  isolate_->global_handles()->IterateWeakRoots(v);
  isolate_->traced_handles()->Iterate(v);
}

void Heap::IterateBuiltins(RootVisitor* v) {
  Builtins* builtins = isolate()->builtins();
  for (Builtin builtin = Builtins::kFirst; builtin <= Builtins::kLast;
       ++builtin) {
    const char* name = Builtins::name(builtin);
    v->VisitRootPointer(Root::kBuiltins, name, builtins->builtin_slot(builtin));
  }

  for (Builtin builtin = Builtins::kFirst; builtin <= Builtins::kLastTier0;
       ++builtin) {
    v->VisitRootPointer(Root::kBuiltins, Builtins::name(builtin),
                        builtins->builtin_tier0_slot(builtin));
  }

  // The entry table doesn't need to be updated since all builtins are embedded.
  static_assert(Builtins::AllBuiltinsAreIsolateIndependent());
}

void Heap::IterateStackRoots(RootVisitor* v) { isolate_->Iterate(v); }

void Heap::IterateConservativeStackRoots(RootVisitor* root_visitor,
                                         IterateRootsMode roots_mode) {
  const StackScanMode stack_scan_mode =
      ConservativeStackScanningModeForMajorGC();
  if (stack_scan_mode == StackScanMode::kNone || !IsGCWithStack()) {
    return;
  }

  // In case of a shared GC, we're interested in the main isolate for CSS.
  Isolate* main_isolate = roots_mode == IterateRootsMode::kClientIsolate
                              ? isolate()->shared_space_isolate()
                              : isolate();

  ConservativeStackVisitor stack_visitor(main_isolate, root_visitor);

  IterateConservativeStackRoots(&stack_visitor, stack_scan_mode);
}

void Heap::IterateConservativeStackRoots(
    ::heap::base::StackVisitor* stack_visitor, StackScanMode stack_scan_mode) {
  DCHECK(IsGCWithStack());
  DCHECK_NE(stack_scan_mode, StackScanMode::kNone);

  if (stack_scan_mode == StackScanMode::kSelective) {
    DCHECK(IsGCWithMainThreadStack());
    DCHECK(selective_stack_scan_start_address_.has_value());
    stack().IteratePointersFromAddressUntilMarker(
        stack_visitor, selective_stack_scan_start_address_.value());
    return;
  }

  DCHECK_EQ(stack_scan_mode, StackScanMode::kFull);
  if (IsGCWithMainThreadStack()) {
    stack().IteratePointersUntilMarker(stack_visitor);
  }
  stack().IterateBackgroundStacks(stack_visitor);
}

void Heap::IterateRootsForPrecisePinning(RootVisitor* visitor) {
  IterateStackRoots(visitor);
  isolate()->handle_scope_implementer()->Iterate(visitor);
}

#if V8_OS_ANDROID
// static
bool Heap::IsHighEndAndroid(uint64_t physical_memory) {
#if defined(V8_TARGET_ARCH_32_BIT)
  return false;
#else
  if (v8_flags.high_end_android) {
    return true;
  }

  return (physical_memory / GB) >=
         v8_flags.high_end_android_physical_memory_threshold;
#endif  // defined(V8_TARGET_ARCH_32_BIT)
}
#endif  // V8_OS_ANDROID

// static
size_t Heap::HeapLimitMultiplier(uint64_t physical_memory) {
#if V8_OS_ANDROID
  // Don't apply pointer multiplier on Android since it has no swap space and
  // should instead adapt it's heap size based on available physical memory.
  if (!IsHighEndAndroid(physical_memory)) {
    return 1;
  }
#endif

  // The heap limit needs to be computed based on the system pointer size
  // because we want a pointer-compressed heap to have larger limit than
  // an ordinary 32-bit which that is constrained by 2GB virtual address space.
  return kSystemPointerSize / 4;
}

// static
size_t Heap::DefaultInitialOldGenerationSize(uint64_t physical_memory) {
  return 256 * MB * HeapLimitMultiplier(physical_memory);
}

// static
size_t Heap::DefaultMinSemiSpaceSize() {
  return RoundUp(512 * KB, NormalPage::kPageSize);
}

// static
size_t Heap::DefaultMaxSemiSpaceSize(uint64_t physical_memory) {
  if (v8_flags.minor_ms) {
    static constexpr size_t kMinorMsMaxCapacity = 72 * MB;
    return RoundUp(kMinorMsMaxCapacity, NormalPage::kPageSize);
  }

  // Compute default max semi space size for Scavenger.
  static constexpr size_t kScavengerDefaultMaxCapacity = 32 * MB;
  size_t max_semi_space_size = kScavengerDefaultMaxCapacity;

#if defined(ANDROID)
  if (!IsHighEndAndroid(physical_memory)) {
    static constexpr size_t kAndroidNonHighEndMaxCapacity = 8 * MB;
    max_semi_space_size = kAndroidNonHighEndMaxCapacity;
  }
#endif

  return RoundUp(max_semi_space_size, NormalPage::kPageSize);
}

// static
size_t Heap::DefaultMinHeapSize(uint64_t physical_memory) {
  if (v8_flags.new_old_generation_heap_size) {
    return 256u * MB;
  }
  return 128u * HeapLimitMultiplier(physical_memory) * MB;
}

// static
size_t Heap::DefaultMaxHeapSize(uint64_t physical_memory) {
  return 1024u * HeapLimitMultiplier(physical_memory) * MB;
}

// static
size_t Heap::HeapSizeToSemiSpaceRatio(uint64_t physical_memory) {
  // The ratio is determined so that we hit DefaultMaxSemiSpaceSize()
  // at about `heap_size = 256MB`, which corresponds to
  // `physical_memory = 1GB`.
  if (v8_flags.minor_ms) {
    return 4;  // DefaultMaxSemiSpaceSize() = 72MB would give a ratio of 3.55
  }
#if defined(ANDROID)
  if (!IsHighEndAndroid(physical_memory)) {
    return 128;  // DefaultMaxSemiSpaceSize() = 8MB
  }
#endif
  return 32;  // DefaultMaxSemiSpaceSize() = 32MB
}

void Heap::ConfigureHeap(const v8::ResourceConstraints& constraints,
                         v8::CppHeap* cpp_heap) {
  CHECK(!configured_);
  physical_memory_ = constraints.physical_memory_size_in_bytes();

  // Initialize max_semi_space_size_.
  {
    max_semi_space_size_ =
        DefaultMaxSemiSpaceSize(constraints.physical_memory_size_in_bytes());
    if (constraints.max_young_generation_size_in_bytes() > 0) {
      max_semi_space_size_ = SemiSpaceSizeFromYoungGenerationSize(
          constraints.max_young_generation_size_in_bytes());
    }
    if (v8_flags.max_semi_space_size > 0) {
      max_semi_space_size_ =
          static_cast<size_t>(v8_flags.max_semi_space_size) * MB;
    } else if (v8_flags.max_heap_size > 0) {
      size_t max_heap_size = static_cast<size_t>(v8_flags.max_heap_size) * MB;
      size_t young_generation_size, old_generation_size;
      if (v8_flags.max_old_space_size > 0) {
        old_generation_size =
            static_cast<size_t>(v8_flags.max_old_space_size) * MB;
        young_generation_size = max_heap_size > old_generation_size
                                    ? max_heap_size - old_generation_size
                                    : 0;
      } else {
        GenerationSizesFromHeapSize(constraints.physical_memory_size_in_bytes(),
                                    max_heap_size, &young_generation_size,
                                    &old_generation_size);
      }
      max_semi_space_size_ =
          SemiSpaceSizeFromYoungGenerationSize(young_generation_size);
    }
    if (v8_flags.stress_compaction) {
      // This will cause more frequent GCs when stressing.
      max_semi_space_size_ = MB;
    }
    if (!v8_flags.minor_ms) {
      // TODO(dinfuehr): Rounding to a power of 2 is technically no longer
      // needed but yields best performance on Pixel2.
      max_semi_space_size_ =
          static_cast<size_t>(base::bits::RoundUpToPowerOfTwo64(
              static_cast<uint64_t>(max_semi_space_size_)));
    }
    max_semi_space_size_ =
        std::max(max_semi_space_size_, DefaultMinSemiSpaceSize());
    max_semi_space_size_ =
        RoundDown<NormalPage::kPageSize>(max_semi_space_size_);
    static constexpr size_t max_possible_heap_size =
#ifdef V8_COMPRESS_POINTERS
        kPtrComprCageReservationSize;
#else   // !V8_COMPRESS_POINTERS
        std::numeric_limits<Tagged_t>::max();
#endif  // !V8_COMPRESS_POINTERS
    // Check that the semi space size doesn't exceed the max possible size of
    // the heap. In Scavenger, 2 semi space are needed so semi space should not
    // exceed half the max heap size.
    const size_t max_possible_semi_space_size =
        max_possible_heap_size / (v8_flags.minor_ms ? 1 : 2);
    max_semi_space_size_ =
        std::min(max_semi_space_size_, max_possible_semi_space_size);
  }

  CHECK_NO_SECURITY_IMPACT(v8_flags.max_heap_size == 0 ||
                           v8_flags.max_semi_space_size == 0 ||
                           v8_flags.max_old_space_size == 0);

  // Initialize min_semispace_size_.
  {
    min_semi_space_size_ = DefaultMinSemiSpaceSize();
    if (!v8_flags.optimize_for_size) {
      // Start with at least 1*MB semi-space on machines with a lot of memory.
      min_semi_space_size_ =
          std::max(min_semi_space_size_, static_cast<size_t>(1 * MB));
    }
    DCHECK_GE(min_semi_space_size_, DefaultMinSemiSpaceSize());
    if (v8_flags.min_semi_space_size > 0) {
      min_semi_space_size_ =
          static_cast<size_t>(v8_flags.min_semi_space_size) * MB;
    }
    min_semi_space_size_ = std::min(min_semi_space_size_, max_semi_space_size_);
    min_semi_space_size_ =
        RoundDown<NormalPage::kPageSize>(min_semi_space_size_);
  }

  // Initialize initial_semispace_size_.
  {
    initial_semispace_size_ = min_semi_space_size_;
    if (constraints.initial_young_generation_size_in_bytes() > 0) {
      initial_semispace_size_ = SemiSpaceSizeFromYoungGenerationSize(
          constraints.initial_young_generation_size_in_bytes());
    }
    if (v8_flags.initial_heap_size > 0) {
      size_t young_generation, old_generation;
      Heap::GenerationSizesFromHeapSize(
          constraints.physical_memory_size_in_bytes(),
          static_cast<size_t>(v8_flags.initial_heap_size) * MB,
          &young_generation, &old_generation);
      initial_semispace_size_ =
          SemiSpaceSizeFromYoungGenerationSize(young_generation);
    }
    initial_semispace_size_ =
        std::min(initial_semispace_size_, max_semi_space_size_);
    initial_semispace_size_ =
        std::max(initial_semispace_size_, min_semi_space_size_);
    initial_semispace_size_ =
        RoundDown<NormalPage::kPageSize>(initial_semispace_size_);
  }

  DCHECK_LE(min_semi_space_size_, initial_semispace_size_);
  DCHECK_LE(initial_semispace_size_, max_semi_space_size_);

  if (v8_flags.lazy_new_space_shrinking) {
    initial_semispace_size_ = max_semi_space_size_;
  }

  // Initialize max_old_generation_size_ and max_global_memory_.
  {
    size_t max_old_generation_size = 700ul * (kSystemPointerSize / 4) * MB;
    if (constraints.max_old_generation_size_in_bytes() > 0) {
      max_old_generation_size = constraints.max_old_generation_size_in_bytes();
    }
    if (v8_flags.max_old_space_size > 0) {
      max_old_generation_size =
          static_cast<size_t>(v8_flags.max_old_space_size) * MB;
    } else if (v8_flags.max_heap_size > 0) {
      size_t max_heap_size = static_cast<size_t>(v8_flags.max_heap_size) * MB;
      size_t young_generation_size =
          YoungGenerationSizeFromSemiSpaceSize(max_semi_space_size_);
      max_old_generation_size = max_heap_size > young_generation_size
                                    ? max_heap_size - young_generation_size
                                    : 0;
    }
    max_old_generation_size =
        std::clamp(max_old_generation_size, MinOldGenerationSize(),
                   AllocatorLimitOnMaxOldGenerationSize(
                       constraints.physical_memory_size_in_bytes()));
    max_old_generation_size =
        RoundDown<NormalPage::kPageSize>(max_old_generation_size);

    // Initialize initial_old_space_size_.
    std::optional<size_t> initial_old_generation_size =
        [&]() -> std::optional<size_t> {
      if (v8_flags.initial_old_space_size > 0) {
        return static_cast<size_t>(v8_flags.initial_old_space_size) * MB;
      }
      if (v8_flags.initial_heap_size > 0) {
        size_t initial_heap_size =
            static_cast<size_t>(v8_flags.initial_heap_size) * MB;
        size_t young_generation_size =
            YoungGenerationSizeFromSemiSpaceSize(initial_semispace_size_);
        return initial_heap_size > young_generation_size
                   ? initial_heap_size - young_generation_size
                   : 0;
      }
      return std::nullopt;
    }();

    if (initial_old_generation_size.has_value()) {
      initial_size_overwritten_ = true;
    } else if (v8_flags.preconfigured_old_space_size > 0) {
      initial_size_overwritten_ = true;
      initial_old_generation_size =
          static_cast<size_t>(v8_flags.preconfigured_old_space_size) * MB;
      preconfigured_old_generation_size_ = true;
    } else {
      initial_old_generation_size = Heap::DefaultInitialOldGenerationSize(
          constraints.physical_memory_size_in_bytes());
      if (constraints.initial_old_generation_size_in_bytes() > 0) {
        initial_old_generation_size =
            constraints.initial_old_generation_size_in_bytes();
      }
    }
    initial_old_generation_size =
        std::min(*initial_old_generation_size, max_old_generation_size / 2);
    initial_old_generation_size =
        RoundDown<NormalPage::kPageSize>(*initial_old_generation_size);

    limits_.reset(new HeapLimits(this, constraints, max_old_generation_size,
                                 *initial_old_generation_size));
    if (initial_size_overwritten_ && !preconfigured_old_generation_size_) {
      // If the embedder pre-configures the initial old generation size,
      // then allow V8 to skip full GCs below that threshold.
      limits()->SetMinimumSizes(*initial_old_generation_size,
                                constraints.physical_memory_size_in_bytes());
    }
  }

  // We rely on being able to allocate new arrays in paged spaces.
  DCHECK(kMaxRegularHeapObjectSize >=
         (JSArray::kHeaderSize +
          FixedArray::SizeFor(JSArray::kInitialMaxFastElementArray) +
          ALIGN_TO_ALLOCATION_ALIGNMENT(sizeof(AllocationMemento))));

  code_range_size_ = constraints.code_range_size_in_bytes();

  heap_profiler_ = std::make_unique<HeapProfiler>(this);
  if (cpp_heap) {
    AttachCppHeap(cpp_heap);
    owning_cpp_heap_.reset(CppHeap::From(cpp_heap));
  }

  configured_ = true;
}

void Heap::AddToRingBuffer(const char* string) {
  size_t first_part =
      std::min(strlen(string), kTraceRingBufferSize - ring_buffer_end_);
  memcpy(trace_ring_buffer_ + ring_buffer_end_, string, first_part);
  ring_buffer_end_ += first_part;
  if (first_part < strlen(string)) {
    ring_buffer_full_ = true;
    size_t second_part = strlen(string) - first_part;
    memcpy(trace_ring_buffer_, string + first_part, second_part);
    ring_buffer_end_ = second_part;
  }
}

void Heap::GetFromRingBuffer(char* buffer) {
  size_t copied = 0;
  if (ring_buffer_full_) {
    copied = kTraceRingBufferSize - ring_buffer_end_;
    memcpy(buffer, trace_ring_buffer_ + ring_buffer_end_, copied);
  }
  memcpy(buffer + copied, trace_ring_buffer_, ring_buffer_end_);
}

void Heap::ConfigureHeapDefault() {
  v8::ResourceConstraints constraints;
  ConfigureHeap(constraints, nullptr);
}

namespace {

void RecordStatsForCage(VirtualMemoryCage* cage, CageStats* stats) {
  stats->start = HexAddress(cage->base());
  stats->size = ByteSize(cage->size());
  base::BoundedPageAllocator::Stats allocator_stats =
      cage->page_allocator()->RecordStats();
  stats->free_size = ByteSize(allocator_stats.free_size);
  stats->largest_free_region = ByteSize(allocator_stats.largest_free_region);
  stats->last_allocation_status = allocator_stats.allocation_status;
}

}  // anonymous namespace

void Heap::RecordStats(HeapStats* stats) {
  stats->start_marker = HeapStats::kStartMarker;
  stats->end_marker = HeapStats::kEndMarker;
  stats->ro_space_size = ByteSize(read_only_space_->Size());
  stats->ro_space_capacity = ByteSize(read_only_space_->Capacity());
  stats->new_space_size = ByteSize(NewSpaceSize());
  stats->new_space_capacity = ByteSize(NewSpaceCapacity());
  stats->old_space_size = ByteSize(old_space_->SizeOfObjects());
  stats->old_space_capacity = ByteSize(old_space_->Capacity());
  stats->code_space_size = ByteSize(code_space_->SizeOfObjects());
  stats->code_space_capacity = ByteSize(code_space_->Capacity());
  stats->map_space_size = ByteSize(0);
  stats->map_space_capacity = ByteSize(0);
  stats->lo_space_size = ByteSize(lo_space_->Size());
  stats->code_lo_space_size = ByteSize(code_lo_space_->Size());
  isolate_->global_handles()->RecordStats(stats);
  size_t memory_allocator_size = memory_allocator()->Size();
  stats->memory_allocator_size = ByteSize(memory_allocator_size);
  stats->memory_allocator_capacity =
      ByteSize(memory_allocator_size + memory_allocator()->Available());
  stats->isolate_count = isolate_->isolate_group()->GetIsolateCount();
  stats->last_os_error = base::OS::GetLastError();
  const size_t allocator_memory =
      isolate_->allocator()->GetCurrentMemoryUsage() +
      isolate_->string_table()->GetCurrentMemoryUsage();
  stats->malloced_memory = ByteSize(allocator_memory);
  stats->is_main_isolate =
      isolate_->isolate_group()->main_isolate() == isolate_;
#if V8_COMPRESS_POINTERS
  RecordStatsForCage(isolate_->isolate_group()->GetPtrComprCage(),
                     &stats->main_cage);
  RecordStatsForCage(isolate_->isolate_group()->GetTrustedPtrComprCage(),
                     &stats->trusted_cage);
#endif
  if (CodeRange* code_cage = isolate_->isolate_group()->GetCodeRange()) {
    RecordStatsForCage(code_cage, &stats->code_cage);
  }

#if V8_ENABLE_WEBASSEMBLY
  stats->malloced_memory =
      ByteSize(stats->malloced_memory.value() +
               i::wasm::GetWasmEngine()->allocator()->GetCurrentMemoryUsage());
#endif  // V8_ENABLE_WEBASSEMBLY
  stats->malloced_peak_memory =
      ByteSize(isolate_->allocator()->GetMaxMemoryUsage());
  GetFromRingBuffer(stats->last_few_messages);
}

size_t Heap::OldGenerationSizeOfObjects() const {
  size_t total = 0;
  if (v8_flags.sticky_mark_bits)
    total += sticky_space()->old_objects_size();
  else
    total += old_space()->SizeOfObjects();
  total += lo_space()->SizeOfObjects();
  total += code_space()->SizeOfObjects();
  total += code_lo_space()->SizeOfObjects();
  if (shared_space()) {
    total += shared_space()->SizeOfObjects();
  }
  if (shared_lo_space()) {
    total += shared_lo_space()->SizeOfObjects();
  }
  total += trusted_space()->SizeOfObjects();
  total += trusted_lo_space()->SizeOfObjects();
  return total;
}

namespace {
constexpr char kCrashKeyPrefix[] = "v8-oom-";
constexpr size_t kCrashKeyPrefixLen = sizeof(kCrashKeyPrefix) - 1;

// Turn a field name like `last_few_messages` into the crash key
// `v8-oom-last-few-messages`. The result needs to be static because of the
// CrashKey API.
template <size_t N>
consteval std::array<char, kCrashKeyPrefixLen + N> BuildCrashKeyName(
    const char (&name)[N]) {
  std::array<char, kCrashKeyPrefixLen + N> data{};
  for (size_t i = 0; i < kCrashKeyPrefixLen; ++i) data[i] = kCrashKeyPrefix[i];
  for (size_t i = 0; i < N; ++i) {
    char c = name[i];
    data[kCrashKeyPrefixLen + i] = (c == '_') ? '-' : c;
  }
  return data;
}
}  // anonymous namespace

void Heap::ReportStatsAsCrashKeys(const HeapStats& heap_stats) {
  if (!isolate()->HasCrashKeyStringCallbacks()) {
    return;
  }

  Isolate* isolate = this->isolate();
  auto add_crash_key = absl::Overload(
      [isolate](const char* name, const ByteSize& value) {
        constexpr size_t kBufferSize = 32;
        char buffer[kBufferSize];
        const size_t bytes = value.value();
        size_t len;
        if (bytes >= MB) {
          len = std::snprintf(buffer, kBufferSize, "%.2fMB",
                              static_cast<double>(bytes) / MB);
        } else if (bytes >= KB) {
          len = std::snprintf(buffer, kBufferSize, "%.2fKB",
                              static_cast<double>(bytes) / KB);
        } else {
          len = std::snprintf(buffer, kBufferSize, "%zuB", bytes);
        }
        isolate->AddCrashKeyString(name, CrashKeySize::Size32,
                                   std::string_view(buffer, len));
      },
      [isolate](const char* name, const size_t& value) {
        constexpr size_t kBufferSize = 32;
        char buffer[kBufferSize];
        size_t len = std::snprintf(buffer, kBufferSize, "%zu", value);
        isolate->AddCrashKeyString(name, CrashKeySize::Size32,
                                   std::string_view(buffer, len));
      },
      [isolate](const char* name, const HexAddress& value) {
        constexpr size_t kBufferSize = 32;
        char buffer[kBufferSize];
        size_t len = std::snprintf(buffer, kBufferSize, "0x%zx", *value);
        isolate->AddCrashKeyString(name, CrashKeySize::Size32,
                                   std::string_view(buffer, len));
      },
      [isolate](const char* name, const TraceRingBuffer& value) {
        std::string_view value_view(value, std::strlen(value));
        isolate->AddCrashKeyString(name, CrashKeySize::Size1024, value_view);
      },
      [isolate](const char* name, bool value) {
        isolate->AddCrashKeyString(name, CrashKeySize::Size32,
                                   value ? "true" : "false");
      },
      [isolate](const char* name,
                base::BoundedPageAllocator::AllocationStatus value) {
        isolate->AddCrashKeyString(name, CrashKeySize::Size64, ToString(value));
      },
      []<typename T>(const char*, const T&) {
        static_assert(std::is_void_v<T>);
      });

#define HANDLE_PRIMITIVE_FIELD(name, value)                          \
  static constexpr auto crash_key_##name = BuildCrashKeyName(#name); \
  add_crash_key(crash_key_##name.data(), value);

#define HANDLE_CAGE_STATS_FIELD(name, value)                 \
  HANDLE_PRIMITIVE_FIELD(name##_start, value.start);         \
  HANDLE_PRIMITIVE_FIELD(name##_size, value.size);           \
  HANDLE_PRIMITIVE_FIELD(name##_free_size, value.free_size); \
  HANDLE_PRIMITIVE_FIELD(name##_largest_free_region,         \
                         value.largest_free_region);         \
  HANDLE_PRIMITIVE_FIELD(name##_last_alloc_status,           \
                         value.last_allocation_status);

#define HANDLE_GENERIC_FIELD(type, name)           \
  do {                                             \
    auto visitor = absl::Overload(                 \
        [&add_crash_key](const CageStats& value) { \
          HANDLE_CAGE_STATS_FIELD(name, value)     \
        },                                         \
        [&add_crash_key](const auto& value) {      \
          HANDLE_PRIMITIVE_FIELD(name, value)      \
        });                                        \
    visitor(heap_stats.name);                      \
  } while (false);
  HEAP_STATS_FIELDS(HANDLE_GENERIC_FIELD);
#undef HANDLE_GENERIC_FIELD
#undef HANDLE_CAGE_STATS_FIELD
#undef HANDLE_PRIMITIVE_FIELD
}

size_t Heap::OldGenerationWastedBytes() const {
  PagedSpaceIterator spaces(this);
  size_t total = 0;
  for (PagedSpace* space = spaces.Next(); space != nullptr;
       space = spaces.Next()) {
    total += space->Waste();
  }
  return total;
}

size_t Heap::OldGenerationConsumedBytes() const {
  return OldGenerationSizeOfObjects() + OldGenerationWastedBytes();
}

size_t Heap::YoungGenerationSizeOfObjects() const {
  DCHECK_NOT_NULL(new_space());
  DCHECK_NOT_NULL(new_lo_space());
  if (v8_flags.sticky_mark_bits) {
    return sticky_space()->young_objects_size() +
           new_lo_space()->SizeOfObjects();
  }
  DCHECK_NOT_NULL(new_lo_space());
  return new_space()->SizeOfObjects() + new_lo_space()->SizeOfObjects();
}

size_t Heap::YoungGenerationWastedBytes() const {
  DCHECK_NOT_NULL(new_space());
  DCHECK(v8_flags.minor_ms);
  return paged_new_space()->paged_space()->Waste();
}

size_t Heap::YoungGenerationConsumedBytes() const {
  if (!new_space()) {
    return 0;
  }
  DCHECK_NOT_NULL(new_lo_space());
  if (v8_flags.minor_ms) {
    return YoungGenerationSizeOfObjects() + YoungGenerationWastedBytes();
  }
  // When using Scavenger, memory is compacted. Thus wasted space is always 0.
  // The diff between `new_space()->SizeOfObjects()` and
  // `new_space()->CurrentCapacitySafe()` is less than one page. Using capacity
  // here is also easier for concurrency since this method is reachable from
  // background old allocations.
  return semi_space_new_space()->CurrentCapacitySafe() +
         new_lo_space()->SizeOfObjects();
}

size_t Heap::EmbedderSizeOfObjects() const {
  return cpp_heap_ ? CppHeap::From(cpp_heap_)->used_size() : 0;
}

size_t Heap::GlobalSizeOfObjects() const {
  return OldGenerationSizeOfObjects() + EmbedderSizeOfObjects() +
         (v8_flags.external_memory_accounted_in_global_limit ? external_memory()
                                                             : 0);
}

size_t Heap::GlobalWastedBytes() const { return OldGenerationWastedBytes(); }

size_t Heap::GlobalConsumedBytes() const {
  return GlobalSizeOfObjects() + GlobalWastedBytes();
}

size_t Heap::OldGenerationAllocationLimitForTesting() const {
  return limits()->old_generation_allocation_limit();
}

size_t Heap::GlobalAllocationLimitForTesting() const {
  return limits()->global_allocation_limit();
}

uint64_t Heap::AllocatedExternalMemorySinceMarkCompact() const {
  uint64_t total_bytes = external_memory_total_.load(std::memory_order_relaxed);
  uint64_t low_since_mark_compact_bytes =
      limits()->external_memory_low_since_last_gc();

  if (total_bytes <= low_since_mark_compact_bytes) {
    return 0;
  }
  return total_bytes - low_since_mark_compact_bytes;
}

bool Heap::AllocationLimitOvershotByLargeMargin() const {
  uint64_t old_generation_consumed =
      OldGenerationAllocationLimitConsumedBytes();
  if (incremental_marking()->IsMajorMarking()) {
    // No interleaved GCs, so we count young gen as part of old gen.
    old_generation_consumed += YoungGenerationConsumedBytes();
  }
  size_t global_consumed = GlobalConsumedBytes();

  const size_t old_generation_limit =
      limits()->old_generation_allocation_limit();
  const size_t old_generation_overshoot =
      old_generation_limit < old_generation_consumed
          ? old_generation_consumed - old_generation_limit
          : 0;

  const size_t global_limit = limits()->global_allocation_limit();
  const size_t global_overshoot =
      global_limit < global_consumed ? global_consumed - global_limit : 0;

  // Bail out if the V8 and global sizes are still below their respective
  // limits.
  if (old_generation_overshoot == 0 && global_overshoot == 0) {
    return false;
  }

  return old_generation_overshoot >=
             limits()->old_generation_overshoot_margin() ||
         global_overshoot >= limits()->global_overshoot_margin();
}

namespace {
uint64_t GetFixedMarginForInputHandlingBytes() {
  DCHECK(v8_flags.optimize_for_input_handling);
  const int fixed_margin = std::clamp(
      static_cast<int>(v8_flags.fixed_margin_for_input_handling), 0, 64);
  return fixed_margin * MB;
}
}  // namespace

bool Heap::AllocationLimitOvershotByFixedMargin(
    const uint64_t overshoot_margin) const {
  uint64_t old_generation_size = OldGenerationAllocationLimitConsumedBytes();
  if (incremental_marking()->IsMajorMarking()) {
    // No interleaved GCs, so we count young gen as part of old gen.
    old_generation_size += YoungGenerationConsumedBytes();
  }

  const size_t old_gen_limit = limits()->old_generation_allocation_limit();
  if (old_generation_size > old_gen_limit + overshoot_margin) {
    return true;
  }

  if (GlobalConsumedBytes() >
      limits()->global_allocation_limit() + overshoot_margin) {
    return true;
  }

  return false;
}

bool Heap::ShouldOptimizeForLoadTime() const {
  return IsLoading() && !AllocationLimitOvershotByLargeMargin();
}

bool Heap::ShouldOptimizeForInputHandlingResponsiveness() const {
  if (!v8_flags.optimize_for_input_handling) {
    return false;
  }
  // TODO(crbug.com/444705203): The current implementation of input mode tracks
  // our state, regardless of if the flag is enabled or not. This is to allow us
  // to add metrics. If we end up not needing this for metrics, consider
  // simplifying the state here.
  return IsInputHandling() && !(AllocationLimitOvershotByFixedMargin(
                                    GetFixedMarginForInputHandlingBytes()) ||
                                AllocationLimitOvershotByLargeMargin());
}

bool Heap::GCHintState::IsInitialized() const {
  const double start_time = start_time_ms_.load(std::memory_order_relaxed);
  return start_time != kInactive;
}

bool Heap::GCHintState::IsActive(const Heap* heap) const {
  const double start_time = start_time_ms_.load(std::memory_order_relaxed);
  return start_time != kInactive &&
         heap->MonotonicallyIncreasingTimeInMs() < start_time + max_time();
}

bool Heap::IsLoading() const { return loading_state_.IsActive(this); }

bool Heap::IsInputHandling() const {
  return input_handling_state_.IsActive(this);
}

bool Heap::IsLoadingInitialized() const {
  return loading_state_.IsInitialized();
}

bool Heap::IsInputHandlingInitialized() const {
  return input_handling_state_.IsInitialized();
}

// This predicate is called when an old generation space cannot allocated from
// the free list and is about to add a new page. Returning false will cause a
// major GC. It happens when the old generation allocation limit is reached and
// - either we need to optimize for memory usage,
// - or the incremental marking is not in progress and we cannot start it.
bool Heap::ShouldExpandOldGenerationOnSlowAllocation(LocalHeap* local_heap,
                                                     AllocationOrigin origin) {
  if (always_allocate()) {
    return true;
  }
  // Under external_memory_accounted_in_global_limit, we also consider the
  // global limit.
  if (OldGenerationSpaceAvailable() > 0 &&
      (!v8_flags.external_memory_accounted_in_global_limit ||
       GlobalSpaceAvailable() > 0)) {
    return true;
  }
  // We reached the old generation or global allocation limit.

  // Allocations in the GC should always succeed if possible.
  if (origin == AllocationOrigin::kGC) return true;

  // Background threads need to be allowed to allocate without GC after teardown
  // was initiated.
  if (gc_state() == TEAR_DOWN) return true;

  // Allocations need to succeed during isolate deserialization. With shared
  // heap allocations, a client isolate may perform shared heap allocations
  // during isolate deserialization as well.
  if (!deserialization_complete() ||
      !local_heap->heap()->deserialization_complete()) {
    return true;
  }

  // Make it more likely that retry of allocations succeeds.
  if (local_heap->IsRetryOfFailedAllocation()) return true;

  // Background thread requested GC, allocation should fail
  if (CollectionRequested()) return false;

  if (v8_flags.enable_allocation_failures_optimize_memory) {
    DCHECK(
        !v8_flags.enable_allocation_failures_optimize_memory_ignoring_priority);
    if (ShouldOptimizeForMemoryUsage()) {
      return false;
    }
  } else if (
      v8_flags.enable_allocation_failures_optimize_memory_ignoring_priority) {
    if (ShouldOptimizeForMemoryUsageIgnoringPriority()) {
      return false;
    }
  } else {
    // This is allowed behind an experiment arm, where we want to skip
    // both forms of ShouldOptimizeForMemoryUsage().
  }

  if (ShouldOptimizeForLoadTime()) return true;

  if (ShouldOptimizeForInputHandlingResponsiveness()) return true;

  if (incremental_marking()->IsMajorMarking() &&
      AllocationLimitOvershotByLargeMargin()) {
    return false;
  }

  if (incremental_marking()->IsStopped()) {
    auto [limit, reason] = IncrementalMarkingLimitReached();

    if (limit == IncrementalMarkingLimit::kNoLimit) {
      // We cannot start incremental marking.
      return false;
    }
  }
  return true;
}

// This predicate is called when an young generation space cannot allocated
// from the free list and is about to add a new page. Returning false will
// cause a GC.
bool Heap::ShouldExpandYoungGenerationOnSlowAllocation(size_t allocation_size) {
  DCHECK(deserialization_complete());

  if (always_allocate()) return true;

  if (gc_state() == TEAR_DOWN) return true;

  if (!CanPromoteYoungAndExpandOldGeneration(allocation_size)) {
    // Assuming all of new space is alive, doing a full GC and promoting all
    // objects should still succeed. Don't let new space grow if it means it
    // will exceed the available size of old space.
    return false;
  }

  if (incremental_marking()->IsMajorMarking() &&
      !AllocationLimitOvershotByLargeMargin()) {
    // Allocate a new page during full GC incremental marking to avoid
    // prematurely finalizing the incremental GC. Once the full GC is over, new
    // space will be empty and capacity will be reset.
    return true;
  }

  return false;
}

bool Heap::IsNewSpaceAllowedToGrowAboveTargetCapacity() const {
  return always_allocate() || gc_state() == TEAR_DOWN ||
         incremental_marking()->IsMarking();
}

Heap::HeapGrowingMode Heap::CurrentHeapGrowingMode() {
  if (ShouldReduceMemory() || v8_flags.stress_compaction) {
    return Heap::HeapGrowingMode::kMinimal;
  }

  if (ShouldOptimizeForMemoryUsage()) {
    return Heap::HeapGrowingMode::kConservative;
  }

  if (memory_reducer() != nullptr && memory_reducer()->ShouldGrowHeapSlowly()) {
    return Heap::HeapGrowingMode::kSlow;
  }

  return Heap::HeapGrowingMode::kDefault;
}

namespace {

double PercentToLimit(size_t size_at_gc, size_t size_now, size_t limit) {
  if (size_now < size_at_gc) {
    return 0.0;
  }
  if (size_now > limit) {
    return 100.0;
  }
  const size_t current_bytes = size_now - size_at_gc;
  const size_t total_bytes = limit - size_at_gc;
  DCHECK_LE(current_bytes, total_bytes);
  return static_cast<double>(current_bytes) * 100 / total_bytes;
}

}  // namespace

double Heap::PercentToOldGenerationLimit() const {
  return PercentToLimit(limits()->OldGenerationConsumedBytesAtLastGC(),
                        OldGenerationConsumedBytes(),
                        limits()->old_generation_allocation_limit());
}

double Heap::PercentToGlobalMemoryLimit() const {
  return PercentToLimit(limits()->GlobalConsumedBytesAtLastGC(),
                        GlobalConsumedBytes(),
                        limits()->global_allocation_limit());
}

// - kNoLimit means that either incremental marking is disabled or it is too
// early to start incremental marking.
// - kSoftLimit means that incremental marking should be started soon.
// - kHardLimit means that incremental marking should be started immediately.
// - kFallbackForEmbedderLimit means that incremental marking should be
// started as soon as the embedder does not allocate with high throughput
// anymore.
std::pair<Heap::IncrementalMarkingLimit, const char*>
Heap::IncrementalMarkingLimitReached() {
  // InstructionStream using an AlwaysAllocateScope assumes that the GC state
  // does not change; that implies that no marking steps must be performed.
  if (!incremental_marking()->CanAndShouldBeStarted() || always_allocate()) {
    // Incremental marking is disabled or it is too early to start.
    return std::make_pair(IncrementalMarkingLimit::kNoLimit, "always allocate");
  }
  if (v8_flags.stress_incremental_marking) {
    return std::make_pair(IncrementalMarkingLimit::kHardLimit,
                          "stress incremental marking");
  }
  if (incremental_marking()->IsBelowActivationThresholds()) {
    // Incremental marking is disabled or it is too early to start.
    return std::make_pair(IncrementalMarkingLimit::kNoLimit,
                          "below activation threshold");
  }
  if (ShouldStressCompaction() || HighMemoryPressure()) {
    // If there is high memory pressure or stress testing is enabled, then
    // start marking immediately.
    return std::make_pair(IncrementalMarkingLimit::kHardLimit,
                          "high memory pressure");
  }

  if (v8_flags.stress_marking > 0) {
    int current_percent = static_cast<int>(
        std::max(PercentToOldGenerationLimit(), PercentToGlobalMemoryLimit()));
    if (current_percent > 0) {
      if (v8_flags.trace_stress_marking) {
        isolate()->PrintWithTimestamp(
            "[IncrementalMarking] %d%% of the memory limit reached\n",
            current_percent);
      }
      if (v8_flags.fuzzer_gc_analysis) {
        // Skips values >=100% since they already trigger marking.
        if (current_percent < 100) {
          double max_marking_limit_reached =
              max_marking_limit_reached_.load(std::memory_order_relaxed);
          while (current_percent > max_marking_limit_reached) {
            max_marking_limit_reached_.compare_exchange_weak(
                max_marking_limit_reached, current_percent,
                std::memory_order_relaxed);
          }
        }
      } else if (current_percent >= stress_marking_percentage_) {
        return std::make_pair(IncrementalMarkingLimit::kHardLimit,
                              "stress marking percentage");
      }
    }
  }

  if (v8_flags.incremental_marking_soft_trigger > 0 ||
      v8_flags.incremental_marking_hard_trigger > 0) {
    int current_percent = static_cast<int>(
        std::max(PercentToOldGenerationLimit(), PercentToGlobalMemoryLimit()));
    if (current_percent > v8_flags.incremental_marking_hard_trigger &&
        v8_flags.incremental_marking_hard_trigger > 0) {
      return std::make_pair(IncrementalMarkingLimit::kHardLimit,
                            "hard trigger");
    }
    if (current_percent > v8_flags.incremental_marking_soft_trigger &&
        v8_flags.incremental_marking_soft_trigger > 0) {
      return std::make_pair(IncrementalMarkingLimit::kSoftLimit,
                            "soft trigger");
    }
    return std::make_pair(IncrementalMarkingLimit::kNoLimit, "not triggered");
  }

  tracer()->RecordGCSizeCounters();
  const size_t old_generation_space_available = OldGenerationSpaceAvailable();
  const size_t global_memory_available = GlobalSpaceAvailable();
  const size_t new_space_target_capacity = NewSpaceTargetCapacity();

  if (old_generation_space_available > new_space_target_capacity &&
      (global_memory_available > new_space_target_capacity)) {
    if (cpp_heap() && gc_count_ == kInitialGCEpoch &&
        limits()->using_initial_limit()) {
      // At this point the embedder memory is above the activation
      // threshold. No GC happened so far and it's thus unlikely to get a
      // configured heap any time soon. Start a memory reducer in this case
      // which will wait until the allocation rate is low to trigger garbage
      // collection.
      return std::make_pair(IncrementalMarkingLimit::kFallbackForEmbedderLimit,
                            "fallback for embedder limit");
    }
    return std::make_pair(IncrementalMarkingLimit::kNoLimit,
                          "enough space available");
  }
  if (ShouldOptimizeForMemoryUsage()) {
    return std::make_pair(IncrementalMarkingLimit::kHardLimit,
                          "optimize for memory");
  }
  if (ShouldOptimizeForLoadTime()) {
    return std::make_pair(IncrementalMarkingLimit::kNoLimit,
                          "optimize for load time");
  }
  if (ShouldOptimizeForInputHandlingResponsiveness()) {
    return std::make_pair(IncrementalMarkingLimit::kNoLimit,
                          "optimize for input handling responsiveness");
  }
  if (old_generation_space_available == 0) {
    return std::make_pair(IncrementalMarkingLimit::kHardLimit,
                          "old generation allocation limit reached");
  }
  if (global_memory_available == 0) {
    return std::make_pair(IncrementalMarkingLimit::kHardLimit,
                          "global allocation limit reached");
  }

  if (global_memory_available > new_space_target_capacity) {
    DCHECK_LE(old_generation_space_available, new_space_target_capacity);
    return std::make_pair(IncrementalMarkingLimit::kSoftLimit,
                          "approaching old generation allocation limit");
  } else {
    DCHECK_LE(global_memory_available, new_space_target_capacity);
    return std::make_pair(IncrementalMarkingLimit::kSoftLimit,
                          "approaching global allocation limit");
  }
}

bool Heap::ShouldStressCompaction() const {
  return v8_flags.stress_compaction && (gc_count_.value() & 1) != 0;
}

void Heap::EnableInlineAllocation() { inline_allocation_enabled_ = true; }

void Heap::DisableInlineAllocation() {
  inline_allocation_enabled_ = false;
  FreeMainThreadLinearAllocationAreas();
}

void Heap::SetUp(LocalHeap* main_thread_local_heap) {
  DCHECK_NULL(main_thread_local_heap_);
  DCHECK_NULL(heap_allocator_);
  main_thread_local_heap_ = main_thread_local_heap;
  heap_allocator_ = &main_thread_local_heap->heap_allocator_;
  DCHECK_NOT_NULL(heap_allocator_);

  // Set the stack start for the main thread that sets up the heap.
  SetStackStart();

#ifdef V8_ENABLE_ALLOCATION_TIMEOUT
  heap_allocator_->UpdateAllocationTimeout();
#endif  // V8_ENABLE_ALLOCATION_TIMEOUT

  // Initialize heap spaces and initial maps and objects.
  //
  // If the heap is not yet configured (e.g. through the API), configure it.
  // Configuration is based on the flags new-space-size (really the semispace
  // size) and old-space-size if set or the initial values of semispace_size_
  // and old_generation_size_ otherwise.
  if (!configured_) ConfigureHeapDefault();

  mmap_region_base_ =
      reinterpret_cast<uintptr_t>(v8::internal::GetRandomMmapAddr()) &
      ~kMmapRegionMask;

  v8::PageAllocator* code_page_allocator;
  if (isolate_->RequiresCodeRange() || code_range_size_ != 0) {
    const size_t requested_size =
        code_range_size_ == 0 ? kMaximalCodeRangeSize : code_range_size_;
    // When a target requires the code range feature, we put all code objects in
    // a contiguous range of virtual address space, so that they can call each
    // other with near calls.
#ifdef V8_COMPRESS_POINTERS
    // When pointer compression is enabled, isolates in the same group share the
    // same CodeRange, owned by the IsolateGroup.
    code_range_ = isolate_->isolate_group()->EnsureCodeRange(requested_size);
#else
    // Otherwise, each isolate has its own CodeRange, owned by the heap.
    code_range_ = std::make_unique<CodeRange>();
    if (!code_range_->InitReservation(isolate_->page_allocator(),
                                      requested_size, false)) {
      V8::FatalProcessOutOfMemory(
          isolate_, "Failed to reserve virtual memory for CodeRange");
    }
#endif  // V8_COMPRESS_POINTERS

    LOG(isolate_,
        NewEvent("CodeRange",
                 reinterpret_cast<void*>(code_range_->reservation()->address()),
                 code_range_size_));

    isolate_->AddCodeRange(code_range_->reservation()->region().begin(),
                           code_range_->reservation()->region().size());
    code_page_allocator = code_range_->page_allocator();
  } else {
    code_page_allocator = isolate_->page_allocator();
  }

  v8::PageAllocator* trusted_page_allocator;
#ifdef V8_ENABLE_SANDBOX
  trusted_page_allocator =
      isolate_->isolate_group()->GetTrustedPtrComprCage()->page_allocator();
#else
  trusted_page_allocator = isolate_->page_allocator();
#endif

  task_runner_ = V8::GetCurrentPlatform()->GetForegroundTaskRunner(
      reinterpret_cast<v8::Isolate*>(isolate()));

  collection_barrier_.reset(new CollectionBarrier(this, this->task_runner_));

  // Set up memory allocator.
  memory_allocator_.reset(new MemoryAllocator(
      isolate_, code_page_allocator, trusted_page_allocator,
      isolate_->isolate_group()->memory_pool(), MaxReserved()));

  sweeper_.reset(new Sweeper(this));

  mark_compact_collector_.reset(new MarkCompactCollector(this));

  scavenger_collector_.reset(new ScavengerCollector(this));
  minor_mark_sweep_collector_.reset(new MinorMarkSweepCollector(this));
  ephemeron_remembered_set_.reset(new EphemeronRememberedSet());

  incremental_marking_.reset(
      new IncrementalMarking(this, mark_compact_collector_->weak_objects()));

  if (v8_flags.concurrent_marking || v8_flags.parallel_marking) {
    concurrent_marking_.reset(
        new ConcurrentMarking(this, mark_compact_collector_->weak_objects()));
  } else {
    concurrent_marking_.reset(new ConcurrentMarking(this, nullptr));
  }

  // Set up layout tracing callback.
  if (V8_UNLIKELY(v8_flags.trace_gc_heap_layout)) {
    v8::GCType gc_type = kGCTypeMarkSweepCompact;
    if (V8_UNLIKELY(!v8_flags.trace_gc_heap_layout_ignore_minor_gc)) {
      gc_type = static_cast<v8::GCType>(gc_type | kGCTypeScavenge |
                                        kGCTypeMinorMarkSweep);
    }
    AddGCPrologueCallback(HeapLayoutTracer::GCProloguePrintHeapLayout, gc_type,
                          nullptr);
    AddGCEpilogueCallback(HeapLayoutTracer::GCEpiloguePrintHeapLayout, gc_type,
                          nullptr);
  }
}

void Heap::SetUpFromReadOnlyHeap(ReadOnlyHeap* ro_heap) {
  DCHECK_NOT_NULL(ro_heap);
  DCHECK_IMPLIES(read_only_space_ != nullptr,
                 read_only_space_ == ro_heap->read_only_space());
  DCHECK_NULL(space_[RO_SPACE].get());
  read_only_space_ = ro_heap->read_only_space();
  heap_allocator_->SetReadOnlySpace(read_only_space_);
}

void Heap::ReplaceReadOnlySpace(SharedReadOnlySpace* space) {
  if (read_only_space_) {
    read_only_space_->TearDown(memory_allocator());
    delete read_only_space_;
  }

  read_only_space_ = space;
  heap_allocator_->SetReadOnlySpace(read_only_space_);
}

class StressConcurrentAllocationTask : public CancelableTask {
 public:
  explicit StressConcurrentAllocationTask(Isolate* isolate)
      : CancelableTask(isolate), isolate_(isolate) {}

  void RunInternal() override {
    Heap* heap = isolate_->heap();
    LocalHeap local_heap(heap, ThreadKind::kBackground);
    UnparkedScope unparked_scope(&local_heap);

    const int kNumIterations = 2000;
    const int kSmallObjectSize = 10 * kTaggedSize;
    const int kMediumObjectSize = 8 * KB;
    const int kLargeObjectSize =
        static_cast<int>(NormalPage::kPageSize -
                         MemoryChunkLayout::ObjectStartOffsetInDataPage());

    for (int i = 0; i < kNumIterations; i++) {
      // Isolate tear down started, stop allocation...
      if (heap->gc_state() == Heap::TEAR_DOWN) return;

      AllocationResult result = local_heap.AllocateRaw(
          kSmallObjectSize, AllocationType::kOld, AllocationOrigin::kRuntime,
          AllocationAlignment::kTaggedAligned);
      if (!result.IsFailure()) {
        heap->CreateFillerObjectAtBackground(
            WritableFreeSpace::ForNonExecutableMemory(result.ToAddress(),
                                                      kSmallObjectSize));
      } else {
        heap->TriggerAndWaitForGCFromBackgroundThread(&local_heap,
                                                      RequestedGCKind::kMajor);
      }

      result = local_heap.AllocateRaw(kMediumObjectSize, AllocationType::kOld,
                                      AllocationOrigin::kRuntime,
                                      AllocationAlignment::kTaggedAligned);
      if (!result.IsFailure()) {
        heap->CreateFillerObjectAtBackground(
            WritableFreeSpace::ForNonExecutableMemory(result.ToAddress(),
                                                      kMediumObjectSize));
      } else {
        heap->TriggerAndWaitForGCFromBackgroundThread(&local_heap,
                                                      RequestedGCKind::kMajor);
      }

      result = local_heap.AllocateRaw(kLargeObjectSize, AllocationType::kOld,
                                      AllocationOrigin::kRuntime,
                                      AllocationAlignment::kTaggedAligned);
      if (!result.IsFailure()) {
        heap->CreateFillerObjectAtBackground(
            WritableFreeSpace::ForNonExecutableMemory(result.ToAddress(),
                                                      kLargeObjectSize));
      } else {
        heap->TriggerAndWaitForGCFromBackgroundThread(&local_heap,
                                                      RequestedGCKind::kMajor);
      }
      local_heap.Safepoint();
    }

    Schedule(isolate_);
  }

  // Schedules task on background thread
  static void Schedule(Isolate* isolate) {
    auto task = std::make_unique<StressConcurrentAllocationTask>(isolate);
    const double kDelayInSeconds = 0.1;
    V8::GetCurrentPlatform()->PostDelayedTaskOnWorkerThread(
        TaskPriority::kUserVisible, std::move(task), kDelayInSeconds);
  }

 private:
  Isolate* isolate_;
};

class StressConcurrentAllocationObserver : public AllocationObserver {
 public:
  explicit StressConcurrentAllocationObserver(Heap* heap)
      : AllocationObserver(1024), heap_(heap) {}

  void Step(int bytes_allocated, Address, size_t) override {
    DCHECK(heap_->deserialization_complete());
    if (v8_flags.stress_concurrent_allocation) {
      // Only schedule task if --stress-concurrent-allocation is enabled. This
      // allows tests to disable flag even when Isolate was already initialized.
      StressConcurrentAllocationTask::Schedule(heap_->isolate());
    }
    heap_->RemoveAllocationObserversFromAllSpaces(this, this);
    heap_->need_to_remove_stress_concurrent_allocation_observer_ = false;
  }

 private:
  Heap* heap_;
};

namespace {

size_t ReturnNull() { return 0; }

}  // namespace

void Heap::SetUpSpaces() {
  // Ensure SetUpFromReadOnlySpace has been ran.
  DCHECK_NOT_NULL(read_only_space_);

  if (v8_flags.sticky_mark_bits) {
    space_[OLD_SPACE] = std::make_unique<StickySpace>(this);
    old_space_ = static_cast<OldSpace*>(space_[OLD_SPACE].get());
  } else {
    space_[OLD_SPACE] = std::make_unique<OldSpace>(this);
    old_space_ = static_cast<OldSpace*>(space_[OLD_SPACE].get());
  }

  if (!v8_flags.single_generation) {
    if (!v8_flags.sticky_mark_bits) {
      if (v8_flags.minor_ms) {
        space_[NEW_SPACE] = std::make_unique<PagedNewSpace>(
            this, initial_semispace_size_, min_semi_space_size_,
            max_semi_space_size_);
      } else {
        space_[NEW_SPACE] = std::make_unique<SemiSpaceNewSpace>(
            this, initial_semispace_size_, min_semi_space_size_,
            max_semi_space_size_);
      }
      new_space_ = static_cast<NewSpace*>(space_[NEW_SPACE].get());
    }

    space_[NEW_LO_SPACE] =
        std::make_unique<NewLargeObjectSpace>(this, NewSpaceCapacity());
    new_lo_space_ =
        static_cast<NewLargeObjectSpace*>(space_[NEW_LO_SPACE].get());
  }

  space_[CODE_SPACE] = std::make_unique<CodeSpace>(this);
  code_space_ = static_cast<CodeSpace*>(space_[CODE_SPACE].get());

  space_[LO_SPACE] = std::make_unique<OldLargeObjectSpace>(this);
  lo_space_ = static_cast<OldLargeObjectSpace*>(space_[LO_SPACE].get());

  space_[CODE_LO_SPACE] = std::make_unique<CodeLargeObjectSpace>(this);
  code_lo_space_ =
      static_cast<CodeLargeObjectSpace*>(space_[CODE_LO_SPACE].get());

  space_[TRUSTED_SPACE] = std::make_unique<TrustedSpace>(this);
  trusted_space_ = static_cast<TrustedSpace*>(space_[TRUSTED_SPACE].get());

  space_[TRUSTED_LO_SPACE] = std::make_unique<TrustedLargeObjectSpace>(this);
  trusted_lo_space_ =
      static_cast<TrustedLargeObjectSpace*>(space_[TRUSTED_LO_SPACE].get());

  if (isolate()->is_shared_space_isolate()) {
    DCHECK(!v8_flags.sticky_mark_bits);

    space_[SHARED_SPACE] = std::make_unique<SharedSpace>(this);
    shared_space_ = static_cast<SharedSpace*>(space_[SHARED_SPACE].get());

    space_[SHARED_LO_SPACE] = std::make_unique<SharedLargeObjectSpace>(this);
    shared_lo_space_ =
        static_cast<SharedLargeObjectSpace*>(space_[SHARED_LO_SPACE].get());

    space_[SHARED_TRUSTED_SPACE] = std::make_unique<SharedTrustedSpace>(this);
    shared_trusted_space_ =
        static_cast<SharedTrustedSpace*>(space_[SHARED_TRUSTED_SPACE].get());

    space_[SHARED_TRUSTED_LO_SPACE] =
        std::make_unique<SharedTrustedLargeObjectSpace>(this);
    shared_trusted_lo_space_ = static_cast<SharedTrustedLargeObjectSpace*>(
        space_[SHARED_TRUSTED_LO_SPACE].get());
  }

  if (isolate()->has_shared_space()) {
    Heap* heap = isolate()->shared_space_isolate()->heap();
    shared_allocation_space_ = heap->shared_space_;
    shared_lo_allocation_space_ = heap->shared_lo_space_;

    shared_trusted_allocation_space_ = heap->shared_trusted_space_;
    shared_trusted_lo_allocation_space_ = heap->shared_trusted_lo_space_;
  }

  main_thread_local_heap()->SetUpMainThread();

  base::TimeTicks startup_time = base::TimeTicks::Now();

  tracer_.reset(new GCTracer(this, startup_time));
  array_buffer_sweeper_.reset(new ArrayBufferSweeper(this));
  memory_measurement_.reset(new MemoryMeasurement(isolate()));
  if (v8_flags.memory_reducer) memory_reducer_.reset(new MemoryReducer(this));
  if (V8_UNLIKELY(TracingFlags::is_gc_stats_enabled())) {
    live_object_stats_.reset(new ObjectStats(this));
    dead_object_stats_.reset(new ObjectStats(this));
  }
  if (Heap::AllocationTrackerForDebugging::IsNeeded()) {
    allocation_tracker_for_debugging_ =
        std::make_unique<Heap::AllocationTrackerForDebugging>(this);
  }

  LOG(isolate_, IntPtrTEvent("heap-capacity", Capacity()));
  LOG(isolate_, IntPtrTEvent("heap-available", Available()));

  SetGetExternallyAllocatedMemoryInBytesCallback(ReturnNull);

  if (new_space() || v8_flags.sticky_mark_bits) {
    minor_gc_job_.reset(new MinorGCJob(this));
  }

  if (v8_flags.stress_marking > 0) {
    stress_marking_percentage_ = NextStressMarkingLimit();
  }
  if (IsStressingScavenge()) {
    stress_scavenge_observer_ = new StressScavengeObserver(this);
    allocator()->new_space_allocator()->AddAllocationObserver(
        stress_scavenge_observer_);
  }

  if (v8_flags.memory_balancer) {
    mb_.reset(new MemoryBalancer(this, startup_time));
  }
}

std::shared_ptr<v8::TaskRunner> Heap::GetForegroundTaskRunner(
    TaskPriority priority) const {
  return V8::GetCurrentPlatform()->GetForegroundTaskRunner(
      reinterpret_cast<v8::Isolate*>(isolate()), priority);
}

// static
void Heap::InitializeOncePerProcess() {
#ifdef V8_ENABLE_ALLOCATION_TIMEOUT
  HeapAllocator::InitializeOncePerProcess();
#endif
  MemoryAllocator::InitializeOncePerProcess();
  if (v8_flags.predictable) {
    ::heap::base::WorklistBase::EnforcePredictableOrder();
  }
}

void Heap::PrintMaxMarkingLimitReached() {
  PrintF("\n### Maximum marking limit reached = %.02lf\n",
         max_marking_limit_reached_.load(std::memory_order_relaxed));
}

void Heap::PrintMaxNewSpaceSizeReached() {
  PrintF("\n### Maximum new space size reached = %.02lf\n",
         stress_scavenge_observer_->MaxNewSpaceSizeReached());
}

int Heap::NextStressMarkingLimit() {
  return isolate()->fuzzer_rng()->NextInt(v8_flags.stress_marking + 1);
}

void Heap::WeakenDescriptorArrays(
    GlobalHandleVector<DescriptorArray> strong_descriptor_arrays) {
  if (incremental_marking()->IsMajorMarking()) {
    // During incremental/concurrent marking regular DescriptorArray objects are
    // treated with custom weakness. This weakness depends on
    // DescriptorArray::raw_gc_state() which is not set up properly upon
    // deserialization. The strong arrays are transitioned to weak ones at the
    // end of the GC.
    mark_compact_collector()->RecordStrongDescriptorArraysForWeakening(
        std::move(strong_descriptor_arrays));
    return;
  }

  // No GC is running, weaken the arrays right away.
  DisallowGarbageCollection no_gc;
  Tagged<Map> descriptor_array_map =
      ReadOnlyRoots(isolate()).descriptor_array_map();
  for (auto it = strong_descriptor_arrays.begin();
       it != strong_descriptor_arrays.end(); ++it) {
    Tagged<DescriptorArray> array = it.raw();
    DCHECK(IsStrongDescriptorArray(array));
    array->set_map_safe_transition_no_write_barrier(isolate(),
                                                    descriptor_array_map);
    DCHECK_EQ(array->raw_gc_state(kRelaxedLoad), 0);
  }
}

void Heap::NotifyDeserializationComplete() {
  // There are no concurrent/background threads yet.
  safepoint()->AssertMainThreadIsOnlyThread();

  FreeMainThreadLinearAllocationAreas();

#if DEBUG
  PagedSpaceIterator spaces(this);
  for (PagedSpace* s = spaces.Next(); s != nullptr; s = spaces.Next()) {
    // All pages right after bootstrapping must be marked as never-evacuate.
    for (NormalPage* p : *s) {
      DCHECK(p->never_evacuate());
    }
  }
#endif  // DEBUG

  if (v8_flags.stress_concurrent_allocation) {
    stress_concurrent_allocation_observer_.reset(
        new StressConcurrentAllocationObserver(this));
    AddAllocationObserversToAllSpaces(
        stress_concurrent_allocation_observer_.get(),
        stress_concurrent_allocation_observer_.get());
    need_to_remove_stress_concurrent_allocation_observer_ = true;
  }

  // Deserialization will never create objects in new space.
  DCHECK_IMPLIES(new_space(), new_space()->Size() == 0);
  DCHECK_IMPLIES(new_lo_space(), new_lo_space()->Size() == 0);

  deserialization_complete_ = true;
}

void Heap::NotifyBootstrapComplete() {
  // This function is invoked for each native context creation. We are
  // interested only in the first native context.
  if (old_generation_capacity_after_bootstrap_ == 0) {
    old_generation_capacity_after_bootstrap_ = OldGenerationCapacity();
  }
}

void Heap::NotifyOldGenerationExpansion(
    LocalHeap* local_heap, AllocationSpace space, MutablePage* chunk_metadata,
    OldGenerationExpansionNotificationOrigin notification_origin) {
  // Pages created during bootstrapping may contain immortal immovable objects.
  if (!deserialization_complete()) {
    DCHECK_NE(NEW_SPACE, chunk_metadata->owner()->identity());
    chunk_metadata->MarkNeverEvacuate();
  }
  if (IsAnyCodeSpace(space)) {
    isolate()->AddCodeMemoryChunk(chunk_metadata);
  }

  // Don't notify MemoryReducer when calling from client heap as otherwise not
  // thread safe.
  const size_t kMemoryReducerActivationThreshold = 1 * MB;
  if (local_heap->is_main_thread_for(this) && memory_reducer() != nullptr &&
      old_generation_capacity_after_bootstrap_ && ms_count_ == 0 &&
      OldGenerationCapacity() >= old_generation_capacity_after_bootstrap_ +
                                     kMemoryReducerActivationThreshold &&
      (notification_origin ==
       OldGenerationExpansionNotificationOrigin::kFromSameHeap) &&
      v8_flags.memory_reducer_for_small_heaps) {
    memory_reducer()->NotifyPossibleGarbage();
  }
}

void Heap::SetEmbedderRootsHandler(EmbedderRootsHandler* handler) {
  embedder_roots_handler_ = handler;
}

EmbedderRootsHandler* Heap::GetEmbedderRootsHandler() const {
  return embedder_roots_handler_;
}

void Heap::AttachCppHeap(v8::CppHeap* cpp_heap) {
  // Only a single CppHeap can be attached at a time.
  CHECK(!owning_cpp_heap_);

  CHECK_IMPLIES(incremental_marking(), !incremental_marking()->IsMarking());
  CppHeap::From(cpp_heap)->AttachIsolate(isolate());
  cpp_heap_ = cpp_heap;
}

std::optional<StackState> Heap::overridden_stack_state() const {
  if (!embedder_stack_state_origin_) return {};
  return embedder_stack_state_;
}

void Heap::SetStackStart() {
  // If no main thread local heap has been set up (we're still in the
  // deserialization process), we don't need to set the stack start.
  if (main_thread_local_heap_ == nullptr) return;
  stack().SetStackStart();
}

::heap::base::Stack& Heap::stack() {
  CHECK_NOT_NULL(main_thread_local_heap_);
  return main_thread_local_heap_->stack_;
}

const ::heap::base::Stack& Heap::stack() const {
  CHECK_NOT_NULL(main_thread_local_heap_);
  return main_thread_local_heap_->stack_;
}

void Heap::StartTearDown() {
  if (cpp_heap_) {
    // This may invoke a GC in case marking is running to get us into a
    // well-defined state for tear down.
    CppHeap::From(cpp_heap_)->StartDetachingIsolate();
  }

  // Stressing incremental marking should make it likely to force a GC here with
  // a CppHeap present. Stress compaction serves as a more deterministic way to
  // trigger such a GC.
  if (v8_flags.stress_compaction) {
    CollectGarbage(OLD_SPACE, GarbageCollectionReason::kTesting);
  }

  // the heap during teardown.
  CompleteSweepingFull(CompleteSweepingReason::kTearDown);

  if (v8_flags.concurrent_marking) {
    concurrent_marking()->Pause();
  }

  SetGCState(TEAR_DOWN);

  // Background threads may allocate and block until GC is performed. However
  // this might never happen when the main thread tries to quit and doesn't
  // process the event queue anymore. Avoid this deadlock by allowing all
  // allocations after tear down was requested to make sure all background
  // threads finish.
  collection_barrier_->NotifyShutdownRequested();

  // Main thread isn't going to allocate anymore.
  main_thread_local_heap()->FreeLinearAllocationAreas();

  FreeMainThreadLinearAllocationAreas();
}

void Heap::TearDownWithSharedHeap() {
  DCHECK_EQ(gc_state(), TEAR_DOWN);

  // Assert that there are no background threads left and no executable memory
  // chunks are unprotected.
  safepoint()->AssertMainThreadIsOnlyThread();

  // Now that all threads are stopped, verify the heap before tearing down the
  // heap/isolate.
  HeapVerifier::VerifyHeapIfEnabled(this);

  // Might use the external pointer which might be in the shared heap.
  external_string_table_.TearDown();

  // Publish shared object worklist for the main thread if incremental marking
  // is enabled for the shared heap.
  main_thread_local_heap()->marking_barrier()->PublishSharedIfNeeded();
}

void Heap::TearDown() {
  DCHECK_EQ(gc_state(), TEAR_DOWN);

  // Assert that there are no background threads left and no executable memory
  // chunks are unprotected.
  safepoint()->AssertMainThreadIsOnlyThread();

  DCHECK(concurrent_marking()->IsStopped());

  // It's too late for Heap::Verify() here, as parts of the Isolate are
  // already gone by the time this is called.

  UpdateMaximumCommitted();

  if (v8_flags.fuzzer_gc_analysis) {
    if (v8_flags.stress_marking > 0) {
      PrintMaxMarkingLimitReached();
    }
    if (IsStressingScavenge()) {
      PrintMaxNewSpaceSizeReached();
    }
  }

  if (cpp_heap_) {
    CppHeap::From(cpp_heap_)->DetachIsolate();
    cpp_heap_ = nullptr;
    isolate_->RunReleaseCppHeapCallback(std::move(owning_cpp_heap_));
  }

  minor_gc_job_.reset();

  if (need_to_remove_stress_concurrent_allocation_observer_) {
    RemoveAllocationObserversFromAllSpaces(
        stress_concurrent_allocation_observer_.get(),
        stress_concurrent_allocation_observer_.get());
  }
  stress_concurrent_allocation_observer_.reset();

  if (IsStressingScavenge()) {
    allocator()->new_space_allocator()->RemoveAllocationObserver(
        stress_scavenge_observer_);
    delete stress_scavenge_observer_;
    stress_scavenge_observer_ = nullptr;
  }

  if (mark_compact_collector_) {
    mark_compact_collector_->TearDown();
    mark_compact_collector_.reset();
  }

  if (minor_mark_sweep_collector_) {
    minor_mark_sweep_collector_->TearDown();
    minor_mark_sweep_collector_.reset();
  }

  sweeper_->TearDown();
  sweeper_.reset();

  scavenger_collector_.reset();
  array_buffer_sweeper_.reset();
  incremental_marking_.reset();
  concurrent_marking_.reset();

  memory_measurement_.reset();
  allocation_tracker_for_debugging_.reset();
  ephemeron_remembered_set_.reset();

  if (memory_reducer_ != nullptr) {
    memory_reducer_->TearDown();
    memory_reducer_.reset();
  }

  live_object_stats_.reset();
  dead_object_stats_.reset();

  embedder_roots_handler_ = nullptr;

  tracer_.reset();

  pretenuring_handler_.reset();

  for (int i = FIRST_MUTABLE_SPACE; i <= LAST_MUTABLE_SPACE; i++) {
    space_[i].reset();
  }

  read_only_space_ = nullptr;

  memory_allocator()->TearDown();

  StrongRootsEntry* next = nullptr;
  for (StrongRootsEntry* current = strong_roots_head_; current;
       current = next) {
    next = current->next;
    delete current;
  }
  strong_roots_head_ = nullptr;

  memory_allocator_.reset();
  limits_.reset();

  heap_profiler_.reset();

#if defined(V8_USE_PERFETTO)
  if (perfetto::Tracing::IsInitialized()) {
    TrackEvent::EraseTrackDescriptor(tracing_track_);
  }
#endif
}

bool Heap::IsFreeSpaceValid(const FreeSpace* object) const {
  Tagged<Object> free_space_map = isolate()->root(RootIndex::kFreeSpaceMap);
  CHECK(!deserialization_complete() ||
        object->map_slot().contains_map_value(free_space_map.ptr()));
  CHECK_LE(offsetof(FreeSpace, next_) + kTaggedSize,
           object->size(kRelaxedLoad));
  return true;
}

void Heap::AddGCPrologueCallback(v8::Isolate::GCCallbackWithData callback,
                                 GCType gc_type, void* data) {
  gc_prologue_callbacks_.Add(
      callback, reinterpret_cast<v8::Isolate*>(isolate()), gc_type, data);
}

void Heap::RemoveGCPrologueCallback(v8::Isolate::GCCallbackWithData callback,
                                    void* data) {
  gc_prologue_callbacks_.Remove(callback, data);
}

void Heap::AddGCEpilogueCallback(v8::Isolate::GCCallbackWithData callback,
                                 GCType gc_type, void* data) {
  gc_epilogue_callbacks_.Add(
      callback, reinterpret_cast<v8::Isolate*>(isolate()), gc_type, data);
}

void Heap::RemoveGCEpilogueCallback(v8::Isolate::GCCallbackWithData callback,
                                    void* data) {
  gc_epilogue_callbacks_.Remove(callback, data);
}

void Heap::AddGlobalGCRootsProvider(GCRootsProvider* provider) {
  base::MutexGuard guard(&global_gc_roots_providers_mutex_);
  global_gc_roots_providers_.push_back(provider);
}

void Heap::RemoveGlobalGCRootsProvider(GCRootsProvider* provider) {
  base::MutexGuard guard(&global_gc_roots_providers_mutex_);
  auto it = std::find(global_gc_roots_providers_.begin(),
                      global_gc_roots_providers_.end(), provider);
  DCHECK_NE(it, global_gc_roots_providers_.end());
  *it = global_gc_roots_providers_.back();
  global_gc_roots_providers_.pop_back();
}

namespace {
Handle<WeakArrayList> CompactWeakArrayList(Heap* heap,
                                           Handle<WeakArrayList> array,
                                           AllocationType allocation) {
  if (array->length() == 0) {
    return array;
  }
  int new_length = array->CountLiveWeakReferences();
  if (new_length == array->length()) {
    return array;
  }

  Handle<WeakArrayList> new_array = WeakArrayList::EnsureSpace(
      heap->isolate(),
      handle(ReadOnlyRoots(heap).empty_weak_array_list(), heap->isolate()),
      new_length, allocation);
  // Allocation might have caused GC and turned some of the elements into
  // cleared weak heap objects. Count the number of live references again and
  // fill in the new array.
  int copy_to = 0;
  for (int i = 0; i < array->length(); i++) {
    Tagged<MaybeObject> element = array->Get(i);
    if (element.IsCleared()) continue;
    new_array->Set(copy_to++, element);
  }
  new_array->set_length(copy_to);
  return new_array;
}

}  // anonymous namespace

void Heap::CompactWeakArrayLists() {
  // Find known PrototypeUsers and compact them.
  std::vector<Handle<PrototypeInfo>> prototype_infos;
  {
    HeapObjectIterator iterator(this);
    for (Tagged<HeapObject> o = iterator.Next(); !o.is_null();
         o = iterator.Next()) {
      if (IsPrototypeInfo(*o)) {
        Tagged<PrototypeInfo> prototype_info = Cast<PrototypeInfo>(o);
        if (IsWeakArrayList(prototype_info->prototype_users())) {
          prototype_infos.emplace_back(handle(prototype_info, isolate()));
        }
      }
    }
  }
  for (auto& prototype_info : prototype_infos) {
    DirectHandle<WeakArrayList> array(
        Cast<WeakArrayList>(prototype_info->prototype_users()), isolate());
    DCHECK(InOldSpace(*array) ||
           *array == ReadOnlyRoots(this).empty_weak_array_list());
    Tagged<WeakArrayList> new_array = PrototypeUsers::Compact(
        array, this, JSObject::PrototypeRegistryCompactionCallback,
        AllocationType::kOld);
    prototype_info->set_prototype_users(new_array);
  }

  // Find known WeakArrayLists and compact them.
  Handle<WeakArrayList> scripts(script_list(), isolate());
  DCHECK(InOldSpace(*scripts));
  scripts = CompactWeakArrayList(this, scripts, AllocationType::kOld);
  set_script_list(*scripts);
}

void Heap::AddRetainedMaps(DirectHandle<NativeContext> context,
                           GlobalHandleVector<Map> maps) {
  Handle<WeakArrayList> array(Cast<WeakArrayList>(context->retained_maps()),
                              isolate());
  int new_maps_size = static_cast<int>(maps.size()) * kRetainMapEntrySize;
  if (array->length() + new_maps_size > array->capacity()) {
    CompactRetainedMaps(*array);
  }
  int cur_length = array->length();
  array =
      WeakArrayList::EnsureSpace(isolate(), array, cur_length + new_maps_size);
  if (*array != context->retained_maps()) {
    context->set_retained_maps(*array);
  }

  {
    DisallowGarbageCollection no_gc;
    Tagged<WeakArrayList> raw_array = *array;
    for (DirectHandle<Map> map : maps) {
      DCHECK(!HeapLayout::InAnySharedSpace(*map));

      if (map->is_in_retained_map_list()) {
        continue;
      }

      raw_array->Set(cur_length, MakeWeak(*map));
      raw_array->Set(cur_length + 1,
                     Smi::FromInt(v8_flags.retain_maps_for_n_gc));
      cur_length += kRetainMapEntrySize;
      raw_array->set_length(cur_length);

      map->set_is_in_retained_map_list(true);
    }
  }
}

void Heap::CompactRetainedMaps(Tagged<WeakArrayList> retained_maps) {
  int length = retained_maps->length();
  int new_length = 0;
  // This loop compacts the array by removing cleared weak cells.
  for (int i = 0; i < length; i += kRetainMapEntrySize) {
    Tagged<MaybeObject> maybe_object = retained_maps->Get(i);
    if (maybe_object.IsCleared()) {
      continue;
    }

    DCHECK(maybe_object.IsWeak());

    Tagged<MaybeObject> age = retained_maps->Get(i + 1);
    DCHECK(IsSmi(age));
    if (i != new_length) {
      retained_maps->Set(new_length, maybe_object);
      retained_maps->Set(new_length + 1, age);
    }
    new_length += kRetainMapEntrySize;
  }
  Tagged<HeapObject> undefined = ReadOnlyRoots(this).undefined_value();
  for (int i = new_length; i < length; i++) {
    retained_maps->Set(i, undefined);
  }
  if (new_length != length) retained_maps->set_length(new_length);
}

void Heap::FatalProcessOutOfMemory(const char* location) {
  V8::FatalProcessOutOfMemory(isolate(), location, V8::kHeapOOM);
}

#ifdef DEBUG

class PrintHandleVisitor : public RootVisitor {
 public:
  void VisitRootPointers(Root root, const char* description,
                         FullObjectSlot start, FullObjectSlot end) override {
    for (FullObjectSlot p = start; p < end; ++p)
      PrintF("  handle %p to %p\n", p.ToVoidPtr(),
             reinterpret_cast<void*>((*p).ptr()));
  }
};

void Heap::PrintHandles() {
  PrintF("Handles:\n");
  PrintHandleVisitor v;
  isolate_->handle_scope_implementer()->Iterate(&v);
}

#endif

class CheckHandleCountVisitor : public RootVisitor {
 public:
  CheckHandleCountVisitor() : handle_count_(0) {}
  ~CheckHandleCountVisitor() override {
    CHECK_GT(HandleScope::kCheckHandleThreshold, handle_count_);
  }
  void VisitRootPointers(Root root, const char* description,
                         FullObjectSlot start, FullObjectSlot end) override {
    handle_count_ += end - start;
  }

 private:
  ptrdiff_t handle_count_;
};

void Heap::CheckHandleCount() {
  CheckHandleCountVisitor v;
  isolate_->handle_scope_implementer()->Iterate(&v);
}

// static
int Heap::InsertIntoRememberedSetFromCode(MutablePage* chunk,
                                          size_t slot_offset) {
  // This is called during runtime by a builtin, therefore it is run in the main
  // thread.
  DCHECK(LocalHeap::Current()->is_main_thread());
  RememberedSet<OLD_TO_NEW>::Insert<AccessMode::NON_ATOMIC>(chunk, slot_offset);
  return 0;
}

#ifdef DEBUG
void Heap::VerifySlotRangeHasNoRecordedSlots(Address start, Address end) {
#ifndef V8_DISABLE_WRITE_BARRIERS
  MutablePage* page = MutablePage::FromAddress(start);
  RememberedSet<OLD_TO_NEW>::CheckNoneInRange(page, start, end);
  RememberedSet<OLD_TO_NEW_BACKGROUND>::CheckNoneInRange(page, start, end);
  RememberedSet<OLD_TO_SHARED>::CheckNoneInRange(page, start, end);
#endif
}
#endif

// static
void Heap::VerifySkippedWriteBarrier(Address object, Address value) {
#if V8_VERIFY_WRITE_BARRIERS
  DCHECK(v8_flags.verify_write_barriers);
  Tagged<Object> tagged(object);
  Tagged<HeapObject> heap_object;
  HeapObjectReferenceType reference_type;

  if (tagged.GetHeapObject(&heap_object, &reference_type)) {
    CHECK_EQ(reference_type, HeapObjectReferenceType::STRONG);
    CHECK(!WriteBarrier::IsRequired(heap_object, Tagged<Object>(value)));
  } else {
    CHECK(tagged.IsSmi());
  }
#else
  UNREACHABLE();
#endif  // V8_VERIFY_WRITE_BARRIERS
}

// static
void Heap::VerifySkippedIndirectWriteBarrier(Address object) {
#if V8_VERIFY_WRITE_BARRIERS
  DCHECK(v8_flags.verify_write_barriers);
  LocalHeap* local_heap = LocalHeap::Current();
  HeapAllocator* allocator = local_heap->allocator();
  CHECK(allocator->IsMostRecentYoungAllocation(object));
#else
  UNREACHABLE();
#endif  // V8_VERIFY_WRITE_BARRIERS
}

void Heap::ClearRecordedSlotRange(Address start, Address end) {
#ifndef V8_DISABLE_WRITE_BARRIERS
  MemoryChunk* chunk = MemoryChunk::FromAddress(start);
  DCHECK(!chunk->IsLargePage());
#if !V8_ENABLE_STICKY_MARK_BITS_BOOL
  if (!chunk->InYoungGeneration())
#endif
  {
    NormalPage* page = SbxCast<NormalPage>(chunk->Metadata());
    // This method will be invoked on objects in shared space for
    // internalization and string forwarding during GC.
    DCHECK(page->owner_identity() == OLD_SPACE ||
           page->owner_identity() == TRUSTED_SPACE ||
           page->owner_identity() == SHARED_SPACE);

    if (!page->SweepingDone()) {
      RememberedSet<OLD_TO_NEW>::RemoveRange(page, start, end,
                                             SlotSet::KEEP_EMPTY_BUCKETS);
      RememberedSet<OLD_TO_NEW_BACKGROUND>::RemoveRange(
          page, start, end, SlotSet::KEEP_EMPTY_BUCKETS);
      RememberedSet<OLD_TO_SHARED>::RemoveRange(page, start, end,
                                                SlotSet::KEEP_EMPTY_BUCKETS);
    }
  }
#endif
}

PagedSpace* PagedSpaceIterator::Next() {
  DCHECK_GE(counter_, FIRST_GROWABLE_PAGED_SPACE);
  while (counter_ <= LAST_GROWABLE_PAGED_SPACE) {
    PagedSpace* space = heap_->paged_space(counter_++);
    if (space) return space;
  }
  return nullptr;
}

class HeapObjectsFilter {
 public:
  virtual ~HeapObjectsFilter() = default;
  virtual bool SkipObject(Tagged<HeapObject> object) = 0;
};

class UnreachableObjectsFilter : public HeapObjectsFilter {
 public:
  explicit UnreachableObjectsFilter(Heap* heap) : heap_(heap) {
    MarkReachableObjects();
  }

  ~UnreachableObjectsFilter() override = default;

  bool SkipObject(Tagged<HeapObject> object) override {
    // Space object iterators should skip free space or filler objects.
    DCHECK(!IsFreeSpaceOrFiller(object));
    // If the bucket corresponding to the object's chunk does not exist, or the
    // object is not found in the bucket, return true.
    BasePage* chunk = BasePage::FromHeapObject(heap_->isolate(), object);
    if (reachable_.count(chunk) == 0) return true;
    return reachable_[chunk]->count(object) == 0;
  }

 private:
  using BucketType = std::unordered_set<Tagged<HeapObject>, Object::Hasher>;

  bool MarkAsReachable(Tagged<HeapObject> object) {
    // If the bucket corresponding to the object's chunk does not exist, then
    // create an empty bucket.
    BasePage* chunk = BasePage::FromHeapObject(heap_->isolate(), object);
    if (reachable_.count(chunk) == 0) {
      reachable_[chunk] = std::make_unique<BucketType>();
    }
    // Insert the object if not present; return whether it was indeed inserted.
    if (reachable_[chunk]->count(object)) return false;
    reachable_[chunk]->insert(object);
    return true;
  }

  class MarkingVisitor : public ObjectVisitorWithCageBases, public RootVisitor {
   public:
    explicit MarkingVisitor(UnreachableObjectsFilter* filter)
        : ObjectVisitorWithCageBases(filter->heap_), filter_(filter) {}

    void VisitMapPointer(Tagged<HeapObject> object) override {
      MarkHeapObject(UncheckedCast<Map>(object->map(cage_base())));
    }
    void VisitPointers(Tagged<HeapObject> host, ObjectSlot start,
                       ObjectSlot end) override {
      MarkPointersImpl(start, end);
    }

    void VisitPointers(Tagged<HeapObject> host, MaybeObjectSlot start,
                       MaybeObjectSlot end) final {
      MarkPointersImpl(start, end);
    }

    void VisitInstructionStreamPointer(Tagged<Code> host,
                                       InstructionStreamSlot slot) override {
      Tagged<Object> maybe_code = slot.load(code_cage_base());
      Tagged<HeapObject> heap_object;
      if (maybe_code.GetHeapObject(&heap_object)) {
        MarkHeapObject(heap_object);
      }
    }

    void VisitCodeTarget(Tagged<InstructionStream> host,
                         RelocInfo* rinfo) final {
      Tagged<InstructionStream> target =
          InstructionStream::FromTargetAddress(rinfo->target_address());
      MarkHeapObject(target);
    }
    void VisitEmbeddedPointer(Tagged<InstructionStream> host,
                              RelocInfo* rinfo) final {
      MarkHeapObject(rinfo->target_object(cage_base()));
    }

    void VisitRootPointers(Root root, const char* description,
                           FullObjectSlot start, FullObjectSlot end) override {
      MarkPointersImpl(start, end);
    }
    void VisitCompressedRootPointers(Root root, const char* description,
                                     OffHeapObjectSlot start,
                                     OffHeapObjectSlot end) override {
      MarkPointersImpl(start, end);
    }

    void TransitiveClosure() {
      while (!marking_stack_.empty()) {
        Tagged<HeapObject> obj = marking_stack_.back();
        marking_stack_.pop_back();
        VisitObject(filter_->heap_->isolate(), obj, this);
      }
    }

   private:
    template <typename TSlot>
    V8_INLINE void MarkPointersImpl(TSlot start, TSlot end) {
      // Treat weak references as strong.
      for (TSlot p = start; p < end; ++p) {
        typename TSlot::TObject object = p.load(cage_base());
#ifdef V8_ENABLE_DIRECT_HANDLE
        if (object.ptr() == kTaggedNullAddress) continue;
#endif
        Tagged<HeapObject> heap_object;
        if (object.GetHeapObject(&heap_object)) {
          MarkHeapObject(heap_object);
        }
      }
    }

    V8_INLINE void MarkHeapObject(Tagged<HeapObject> heap_object) {
      if (filter_->MarkAsReachable(heap_object)) {
        marking_stack_.push_back(heap_object);
      }
    }

    UnreachableObjectsFilter* filter_;
    std::vector<Tagged<HeapObject>> marking_stack_;
  };

  friend class MarkingVisitor;

  void MarkReachableObjects() {
    MarkingVisitor visitor(this);
    heap_->stack().SetMarkerIfNeededAndCallback(
        [this, &visitor]() { heap_->IterateRoots(&visitor, {}); });
    visitor.TransitiveClosure();
  }

  Heap* heap_;
  DISALLOW_GARBAGE_COLLECTION(no_gc_)
  std::unordered_map<BasePage*, std::unique_ptr<BucketType>,
                     base::hash<BasePage*>>
      reachable_;
};

HeapObjectIterator::HeapObjectIterator(
    Heap* heap, HeapObjectIterator::HeapObjectsFiltering filtering)
    : HeapObjectIterator(
          heap,
          new SafepointScope(heap->isolate(),
                             kGlobalSafepointForSharedSpaceIsolate),
          filtering) {}

HeapObjectIterator::HeapObjectIterator(Heap* heap,
                                       const SafepointScope& safepoint_scope,
                                       HeapObjectsFiltering filtering)
    : HeapObjectIterator(heap, nullptr, filtering) {}

HeapObjectIterator::HeapObjectIterator(
    Heap* heap, SafepointScope* safepoint_scope_or_nullptr,
    HeapObjectsFiltering filtering)
    : heap_(heap),
      safepoint_scope_(safepoint_scope_or_nullptr),
      space_iterator_(heap_) {
  heap_->MakeHeapIterable(CompleteSweepingReason::kHeapObjectIterator);
  switch (filtering) {
    case kFilterUnreachable:
      filter_ = std::make_unique<UnreachableObjectsFilter>(heap_);
      break;
    default:
      break;
  }
  // Start the iteration.
  CHECK(space_iterator_.HasNext());
  object_iterator_ = space_iterator_.Next()->GetObjectIterator(heap_);
}

HeapObjectIterator::~HeapObjectIterator() = default;

Tagged<HeapObject> HeapObjectIterator::Next() {
  if (!filter_) return NextObject();

  Tagged<HeapObject> obj = NextObject();
  while (!obj.is_null() && filter_->SkipObject(obj)) obj = NextObject();
  return obj;
}

Tagged<HeapObject> HeapObjectIterator::NextObject() {
  // No iterator means we are done.
  if (!object_iterator_) return Tagged<HeapObject>();

  Tagged<HeapObject> obj = object_iterator_->Next();
  // If the current iterator has more objects we are fine.
  if (!obj.is_null()) return obj;
  // Go though the spaces looking for one that has objects.
  while (space_iterator_.HasNext()) {
    object_iterator_ = space_iterator_.Next()->GetObjectIterator(heap_);
    obj = object_iterator_->Next();
    if (!obj.is_null()) return obj;
  }
  // Done with the last space.
  object_iterator_.reset();
  return Tagged<HeapObject>();
}

void Heap::UpdateTotalGCTime(base::TimeDelta duration) {
  total_gc_time_ms_ += duration;
}

size_t Heap::GetExternalStrinBytesForTesting() const {
  return external_string_table_.GetBytes();
}

void Heap::ExternalStringTable::CleanUp() {
  size_t last = 0;
  size_t bytes = 0;
  Isolate* isolate = heap_->isolate();
  for (size_t i = 0; i < old_strings_.size(); ++i) {
    Tagged<Object> o = old_strings_[i];
    if (IsTheHole(o, isolate)) {
      continue;
    }
    // The real external string is already in one of these vectors and was or
    // will be processed. Re-processing it will add a duplicate to the vector.
    if (IsThinString(o)) continue;
    DCHECK(IsExternalString(o));
    DCHECK(!HeapLayout::InYoungGeneration(o));
    old_strings_[last++] = o;
    bytes += Cast<ExternalString>(o)->length();
  }
  old_strings_.resize(last);
  bytes_ = bytes;
  if (v8_flags.verify_heap) {
    Verify();
  }
}

void Heap::ExternalStringTable::TearDown() {
  for (size_t i = 0; i < old_strings_.size(); ++i) {
    Tagged<Object> o = old_strings_[i];
    // Dont finalize thin strings.
    if (IsThinString(o)) continue;
    heap_->FinalizeExternalString(Cast<ExternalString>(o));
  }
  old_strings_.clear();
}

void Heap::RememberUnmappedPage(Address page, bool compacted) {
  // Tag the page pointer to make it findable in the dump file.
  if (compacted) {
    page ^= 0xC1EAD & (NormalPage::kPageSize - 1);  // Cleared.
  } else {
    page ^= 0x1D1ED & (NormalPage::kPageSize - 1);  // I died.
  }
  remembered_unmapped_pages_[remembered_unmapped_pages_index_] = page;
  remembered_unmapped_pages_index_++;
  remembered_unmapped_pages_index_ %= kRememberedUnmappedPages;
}

uint64_t Heap::UpdateExternalMemory(int64_t delta) {
  const uint64_t total_before =
      external_memory_total_.fetch_add(delta, std::memory_order_relaxed);
  CHECK_GE(static_cast<int64_t>(total_before), -delta);

  uint64_t total_after = total_before + delta;
  uint64_t low_since_mark_compact =
      limits()->external_memory_low_since_last_gc();
  if (total_after < low_since_mark_compact) {
    limits()->UpdateExternalMemoryLowSinceLastGC(total_after);
  }
  return total_after;
}

uint64_t Heap::backing_store_bytes() const {
  return external_string_table_.GetBytes() + array_buffer_sweeper_->GetBytes();
}

StrongRootsEntry* Heap::RegisterStrongRoots(const char* label,
                                            FullObjectSlot start,
                                            FullObjectSlot end) {
  // We're either on the main thread, or in a background thread with an active
  // local heap.
  DCHECK(LocalHeap::Current()->IsRunning());

  base::MutexGuard guard(&strong_roots_mutex_);

  StrongRootsEntry* entry = new StrongRootsEntry(label);
  entry->start = start;
  entry->end = end;
  entry->prev = nullptr;
  entry->next = strong_roots_head_;

  if (strong_roots_head_) {
    DCHECK_NULL(strong_roots_head_->prev);
    strong_roots_head_->prev = entry;
  }
  strong_roots_head_ = entry;

  return entry;
}

void Heap::UpdateStrongRoots(StrongRootsEntry* entry, FullObjectSlot start,
                             FullObjectSlot end) {
  entry->start = start;
  entry->end = end;
}

void Heap::UnregisterStrongRoots(StrongRootsEntry* entry) {
  // We're either on the main thread, or in a background thread with an active
  // local heap.
  DCHECK(gc_state() == MARK_COMPACT || LocalHeap::Current()->IsRunning());

  base::MutexGuard guard(&strong_roots_mutex_);

  StrongRootsEntry* prev = entry->prev;
  StrongRootsEntry* next = entry->next;

  if (prev) prev->next = next;
  if (next) next->prev = prev;

  if (strong_roots_head_ == entry) {
    DCHECK_NULL(prev);
    strong_roots_head_ = next;
  }

  delete entry;
}

void Heap::SetBuiltinsConstantsTable(Tagged<FixedArray> cache) {
  set_builtins_constants_table(cache);
}

void Heap::SetDetachedContexts(Tagged<WeakArrayList> detached_contexts) {
  set_detached_contexts(detached_contexts);
}

bool Heap::HasDirtyJSFinalizationRegistries() {
  return !IsUndefined(dirty_js_finalization_registries_list(), isolate());
}

void Heap::PostFinalizationRegistryCleanupTaskIfNeeded() {
  // Only one cleanup task is posted at a time.
  if (!HasDirtyJSFinalizationRegistries() ||
      is_finalization_registry_cleanup_task_posted_) {
    return;
  }
  auto task = std::make_unique<FinalizationRegistryCleanupTask>(this);
  task_runner_->PostNonNestableTask(std::move(task));
  is_finalization_registry_cleanup_task_posted_ = true;
}

void Heap::EnqueueDirtyJSFinalizationRegistry(
    Tagged<JSFinalizationRegistry> finalization_registry,
    std::function<void(Tagged<HeapObject> object, ObjectSlot slot,
                       Tagged<HeapObject> target)>
        gc_notify_updated_slot,
    WriteBarrierMode write_barrier_mode) {
  // Add a FinalizationRegistry to the tail of the dirty list.
  DCHECK(!HasDirtyJSFinalizationRegistries() ||
         IsJSFinalizationRegistry(dirty_js_finalization_registries_list()));
  DCHECK(IsUndefined(finalization_registry->next_dirty(), isolate()));
  DCHECK(!finalization_registry->scheduled_for_cleanup());
  finalization_registry->set_scheduled_for_cleanup(true);
  if (IsUndefined(dirty_js_finalization_registries_list_tail(), isolate())) {
    DCHECK(IsUndefined(dirty_js_finalization_registries_list(), isolate()));
    set_dirty_js_finalization_registries_list(finalization_registry);
    // dirty_js_finalization_registries_list_ is rescanned by
    // ProcessWeakListRoots.
  } else {
    Tagged<JSFinalizationRegistry> tail = Cast<JSFinalizationRegistry>(
        dirty_js_finalization_registries_list_tail());
    tail->set_next_dirty(finalization_registry, write_barrier_mode);
    gc_notify_updated_slot(
        tail, tail->RawField(JSFinalizationRegistry::kNextDirtyOffset),
        finalization_registry);
  }
  set_dirty_js_finalization_registries_list_tail(finalization_registry);
  // dirty_js_finalization_registries_list_tail_ is rescanned by
  // ProcessWeakListRoots.
}

MaybeDirectHandle<JSFinalizationRegistry>
Heap::DequeueDirtyJSFinalizationRegistry() {
  // Take a FinalizationRegistry from the head of the dirty list for fairness.
  if (HasDirtyJSFinalizationRegistries()) {
    DirectHandle<JSFinalizationRegistry> head(
        Cast<JSFinalizationRegistry>(dirty_js_finalization_registries_list()),
        isolate());
    set_dirty_js_finalization_registries_list(head->next_dirty());
    head->set_next_dirty(ReadOnlyRoots(this).undefined_value());
    if (*head == dirty_js_finalization_registries_list_tail()) {
      set_dirty_js_finalization_registries_list_tail(
          ReadOnlyRoots(this).undefined_value());
    }
    return head;
  }
  return {};
}

void Heap::RemoveDirtyFinalizationRegistriesOnContext(
    Tagged<NativeContext> context) {
  DisallowGarbageCollection no_gc;

  Isolate* isolate = this->isolate();
  Tagged<Object> prev = ReadOnlyRoots(isolate).undefined_value();
  Tagged<Object> current = dirty_js_finalization_registries_list();
  while (!IsUndefined(current, isolate)) {
    Tagged<JSFinalizationRegistry> finalization_registry =
        Cast<JSFinalizationRegistry>(current);
    if (finalization_registry->native_context() == context) {
      if (IsUndefined(prev, isolate)) {
        set_dirty_js_finalization_registries_list(
            finalization_registry->next_dirty());
      } else {
        Cast<JSFinalizationRegistry>(prev)->set_next_dirty(
            finalization_registry->next_dirty());
      }
      finalization_registry->set_scheduled_for_cleanup(false);
      current = finalization_registry->next_dirty();
      finalization_registry->set_next_dirty(
          ReadOnlyRoots(isolate).undefined_value());
    } else {
      prev = current;
      current = finalization_registry->next_dirty();
    }
  }
  set_dirty_js_finalization_registries_list_tail(prev);
}

void Heap::KeepDuringJob(DirectHandle<HeapObject> target) {
  DCHECK(IsUndefined(weak_refs_keep_during_job()) ||
         IsOrderedHashSet(weak_refs_keep_during_job()));
  Handle<OrderedHashSet> table;
  if (IsUndefined(weak_refs_keep_during_job(), isolate())) {
    table = isolate()->factory()->NewOrderedHashSet();
  } else {
    table =
        handle(Cast<OrderedHashSet>(weak_refs_keep_during_job()), isolate());
  }
  MaybeHandle<OrderedHashSet> maybe_table =
      OrderedHashSet::Add(isolate(), table, target);
  if (!maybe_table.ToHandle(&table)) {
    FatalProcessOutOfMemory(
        "Fatal JavaScript error: Too many distinct WeakRef objects "
        "created or dereferenced during single event loop turn.");
  }
  set_weak_refs_keep_during_job(*table);
}

void Heap::ClearKeptObjects() {
  set_weak_refs_keep_during_job(ReadOnlyRoots(isolate()).undefined_value());
}

size_t Heap::NumberOfTrackedHeapObjectTypes() {
  return ObjectStats::OBJECT_STATS_COUNT;
}

size_t Heap::ObjectCountAtLastGC(size_t index) {
  if (live_object_stats_ == nullptr || index >= ObjectStats::OBJECT_STATS_COUNT)
    return 0;
  return live_object_stats_->object_count_last_gc(index);
}

size_t Heap::ObjectSizeAtLastGC(size_t index) {
  if (live_object_stats_ == nullptr || index >= ObjectStats::OBJECT_STATS_COUNT)
    return 0;
  return live_object_stats_->object_size_last_gc(index);
}

bool Heap::GetObjectTypeName(size_t index, const char** object_type,
                             const char** object_sub_type) {
  if (index >= ObjectStats::OBJECT_STATS_COUNT) return false;

  switch (static_cast<int>(index)) {
#define COMPARE_AND_RETURN_NAME(name) \
  case name:                          \
    *object_type = #name;             \
    *object_sub_type = "";            \
    return true;
    INSTANCE_TYPE_LIST(COMPARE_AND_RETURN_NAME)
#undef COMPARE_AND_RETURN_NAME

#define COMPARE_AND_RETURN_NAME(name)                           \
  case ObjectStats::FIRST_VIRTUAL_TYPE +                        \
      static_cast<int>(ObjectStats::VirtualInstanceType::name): \
    *object_type = #name;                                       \
    *object_sub_type = "";                                      \
    return true;
    VIRTUAL_INSTANCE_TYPE_LIST(COMPARE_AND_RETURN_NAME)
#undef COMPARE_AND_RETURN_NAME
  }
  return false;
}

size_t Heap::NumberOfNativeContexts() {
  int result = 0;
  Tagged<Object> context = native_contexts_list();
  while (!IsUndefined(context, isolate())) {
    ++result;
    Tagged<Context> native_context = Cast<Context>(context);
    context = native_context->next_context_link();
  }
  return result;
}

std::vector<Handle<NativeContext>> Heap::FindAllNativeContexts() {
  std::vector<Handle<NativeContext>> result;
  Tagged<Object> context = native_contexts_list();
  while (!IsUndefined(context, isolate())) {
    Tagged<NativeContext> native_context = Cast<NativeContext>(context);
    result.push_back(handle(native_context, isolate()));
    context = native_context->next_context_link();
  }
  return result;
}

std::vector<Tagged<WeakArrayList>> Heap::FindAllRetainedMaps() {
  std::vector<Tagged<WeakArrayList>> result;
  Tagged<Object> context = native_contexts_list();
  while (!IsUndefined(context, isolate())) {
    Tagged<NativeContext> native_context = Cast<NativeContext>(context);
    result.push_back(Cast<WeakArrayList>(native_context->retained_maps()));
    context = native_context->next_context_link();
  }
  return result;
}

size_t Heap::NumberOfDetachedContexts() {
  // The detached_contexts() array has two entries per detached context.
  return detached_contexts()->length() / 2;
}

bool Heap::AllowedToBeMigrated(Tagged<Map> map, Tagged<HeapObject> object,
                               AllocationSpace dst) {
  // Object migration is governed by the following rules:
  //
  // 1) Objects in new-space can be migrated to the old space
  //    that matches their target space or they stay in new-space.
  // 2) Objects in old-space stay in the same space when migrating.
  // 3) Fillers (two or more words) can migrate due to left-trimming of
  //    fixed arrays in new-space or old space.
  // 4) Fillers (one word) can never migrate, they are skipped by
  //    incremental marking explicitly to prevent invalid pattern.
  //
  // Since this function is used for debugging only, we do not place
  // asserts here, but check everything explicitly.
  if (map == ReadOnlyRoots(this).one_pointer_filler_map()) {
    return false;
  }
  InstanceType type = map->instance_type();
  MutablePage* chunk = MutablePage::FromHeapObject(isolate(), object);
  AllocationSpace src = chunk->owner_identity();
  switch (src) {
    case NEW_SPACE:
      return dst == NEW_SPACE || dst == OLD_SPACE;
    case OLD_SPACE:
      return dst == OLD_SPACE;
    case CODE_SPACE:
      return dst == CODE_SPACE && type == INSTRUCTION_STREAM_TYPE;
    case SHARED_SPACE:
      return dst == SHARED_SPACE;
    case TRUSTED_SPACE:
      return dst == TRUSTED_SPACE;
    case SHARED_TRUSTED_SPACE:
      return dst == SHARED_TRUSTED_SPACE;
    case LO_SPACE:
    case CODE_LO_SPACE:
    case NEW_LO_SPACE:
    case SHARED_LO_SPACE:
    case TRUSTED_LO_SPACE:
    case SHARED_TRUSTED_LO_SPACE:
    case RO_SPACE:
      return false;
  }
  UNREACHABLE();
}

size_t Heap::EmbedderAllocationCounter() const {
  return cpp_heap_ ? CppHeap::From(cpp_heap_)->allocated_size() : 0;
}

void Heap::CreateObjectStats() {
  if (V8_LIKELY(!TracingFlags::is_gc_stats_enabled())) return;
  if (!live_object_stats_) {
    live_object_stats_.reset(new ObjectStats(this));
  }
  if (!dead_object_stats_) {
    dead_object_stats_.reset(new ObjectStats(this));
  }
}

Tagged<Map> Heap::GcSafeMapOfHeapObject(Tagged<HeapObject> object) {
  PtrComprCageBase cage_base(isolate());
  MapWord map_word = object->map_word(cage_base, kRelaxedLoad);
  if (map_word.IsForwardingAddress()) {
    return map_word.ToForwardingAddress(object)->map(cage_base);
  }
  return map_word.ToMap();
}

Tagged<GcSafeCode> Heap::GcSafeGetCodeFromInstructionStream(
    Tagged<HeapObject> instruction_stream, Address inner_pointer) {
  Tagged<InstructionStream> istream =
      UncheckedCast<InstructionStream>(instruction_stream);
  DCHECK(!istream.is_null());
  DCHECK(GcSafeInstructionStreamContains(istream, inner_pointer));
  return UncheckedCast<GcSafeCode>(istream->raw_code(kAcquireLoad));
}

bool Heap::GcSafeInstructionStreamContains(
    Tagged<InstructionStream> instruction_stream, Address addr) {
  Tagged<Map> map = GcSafeMapOfHeapObject(instruction_stream);
  DCHECK_EQ(map, ReadOnlyRoots(this).instruction_stream_map());

  Builtin builtin_lookup_result =
      OffHeapInstructionStream::TryLookupCode(isolate(), addr);
  if (Builtins::IsBuiltinId(builtin_lookup_result)) {
    // Builtins don't have InstructionStream objects.
    DCHECK(!Builtins::IsBuiltinId(
        instruction_stream->code(kAcquireLoad)->builtin_id()));
    return false;
  }

  Address start = instruction_stream.address();
  Address end = start + instruction_stream->SizeFromMap(map);
  return start <= addr && addr < end;
}

std::optional<Tagged<InstructionStream>>
Heap::GcSafeTryFindInstructionStreamForInnerPointer(Address inner_pointer) {
  std::optional<Address> start =
      ThreadIsolation::StartOfJitAllocationAt(inner_pointer);
  if (start.has_value()) {
    return UncheckedCast<InstructionStream>(HeapObject::FromAddress(*start));
  }

  return {};
}

std::optional<Tagged<GcSafeCode>> Heap::GcSafeTryFindCodeForInnerPointer(
    Address inner_pointer) {
  Builtin maybe_builtin =
      OffHeapInstructionStream::TryLookupCode(isolate(), inner_pointer);
  if (Builtins::IsBuiltinId(maybe_builtin)) {
    return Cast<GcSafeCode>(isolate()->builtins()->code(maybe_builtin));
  }

  std::optional<Tagged<InstructionStream>> maybe_istream =
      GcSafeTryFindInstructionStreamForInnerPointer(inner_pointer);
  if (!maybe_istream) return {};

  return GcSafeGetCodeFromInstructionStream(*maybe_istream, inner_pointer);
}

Tagged<Code> Heap::FindCodeForInnerPointer(Address inner_pointer) {
  return GcSafeFindCodeForInnerPointer(inner_pointer)->UnsafeCastToCode();
}

Tagged<GcSafeCode> Heap::GcSafeFindCodeForInnerPointer(Address inner_pointer) {
  std::optional<Tagged<GcSafeCode>> maybe_code =
      GcSafeTryFindCodeForInnerPointer(inner_pointer);
  // Callers expect that the code object is found.
  CHECK(maybe_code.has_value());
  return UncheckedCast<GcSafeCode>(maybe_code.value());
}

std::optional<Tagged<Code>> Heap::TryFindCodeForInnerPointerForPrinting(
    Address inner_pointer) {
  if (InSpaceSlow(inner_pointer, i::CODE_SPACE) ||
      InSpaceSlow(inner_pointer, i::CODE_LO_SPACE) ||
      i::OffHeapInstructionStream::PcIsOffHeap(isolate(), inner_pointer)) {
    std::optional<Tagged<GcSafeCode>> maybe_code =
        GcSafeTryFindCodeForInnerPointer(inner_pointer);
    if (maybe_code.has_value()) {
      return maybe_code.value()->UnsafeCastToCode();
    }
  }
  return {};
}

#ifdef DEBUG
void Heap::IncrementObjectCounters() {
  isolate_->counters()->objs_since_last_full()->Increment();
  isolate_->counters()->objs_since_last_young()->Increment();
}
#endif  // DEBUG

bool Heap::IsStressingScavenge() {
  return v8_flags.stress_scavenge > 0 && new_space();
}

void Heap::SetIsMarkingFlag(bool value) {
  isolate()->isolate_data()->is_marking_flag_ = value;
}

uint8_t* Heap::IsMarkingFlagAddress() {
  return &isolate()->isolate_data()->is_marking_flag_;
}

void Heap::SetIsMinorMarkingFlag(bool value) {
  isolate()->isolate_data()->is_minor_marking_flag_ = value;
}

size_t Heap::PromotedSinceLastGC() {
  return limits()->PromotedSinceLastGC(OldGenerationSizeOfObjects());
}

uint8_t* Heap::IsMinorMarkingFlagAddress() {
  return &isolate()->isolate_data()->is_minor_marking_flag_;
}

StrongRootAllocatorBase::StrongRootAllocatorBase(LocalHeap* heap)
    : StrongRootAllocatorBase(heap->heap()) {}
StrongRootAllocatorBase::StrongRootAllocatorBase(Isolate* isolate)
    : StrongRootAllocatorBase(isolate->heap()) {}
StrongRootAllocatorBase::StrongRootAllocatorBase(v8::Isolate* isolate)
    : StrongRootAllocatorBase(reinterpret_cast<Isolate*>(isolate)) {}
StrongRootAllocatorBase::StrongRootAllocatorBase(LocalIsolate* isolate)
    : StrongRootAllocatorBase(isolate->heap()) {}

// StrongRootBlocks are allocated as a block of addresses, prefixed with a
// StrongRootsEntry pointer:
//
//   | StrongRootsEntry*
//   | Address 1
//   | ...
//   | Address N
//
// The allocate method registers the range "Address 1" to "Address N" with the
// heap as a strong root array, saves that entry in StrongRootsEntry*, and
// returns a pointer to Address 1.
Address* StrongRootAllocatorBase::allocate_impl(size_t n) {
  void* block = base::Malloc(sizeof(StrongRootsEntry*) + n * sizeof(Address));

  StrongRootsEntry** header = reinterpret_cast<StrongRootsEntry**>(block);
  Address* ret = reinterpret_cast<Address*>(reinterpret_cast<char*>(block) +
                                            sizeof(StrongRootsEntry*));

  memset(ret, kNullAddress, n * sizeof(Address));
  *header = heap()->RegisterStrongRoots(
      "StrongRootAllocator", FullObjectSlot(ret), FullObjectSlot(ret + n));

  return ret;
}

void StrongRootAllocatorBase::deallocate_impl(Address* p, size_t n) noexcept {
  // The allocate method returns a pointer to Address 1, so the deallocate
  // method has to offset that pointer back by sizeof(StrongRootsEntry*).
  void* block = reinterpret_cast<char*>(p) - sizeof(StrongRootsEntry*);
  StrongRootsEntry** header = reinterpret_cast<StrongRootsEntry**>(block);

  heap()->UnregisterStrongRoots(*header);

  base::Free(block);
}

#ifdef V8_ENABLE_ALLOCATION_TIMEOUT
void Heap::set_allocation_timeout(int allocation_timeout) {
  heap_allocator_->SetAllocationTimeout(allocation_timeout);
}
#endif  // V8_ENABLE_ALLOCATION_TIMEOUT

void Heap::FinishSweepingIfOutOfWork(CompleteSweepingReason reason) {
  if (sweeper()->major_sweeping_in_progress() &&
      sweeper()->UsingMajorSweeperTasks() &&
      !sweeper()->AreMajorSweeperTasksRunning()) {
    // At this point we know that all concurrent sweeping tasks have run
    // out of work and quit: all pages are swept. The main thread still needs
    // to complete sweeping though.
    DCHECK_IMPLIES(!delay_sweeper_tasks_for_testing_,
                   !sweeper()->HasUnsweptPagesForMajorSweeping());
    EnsureSweepingCompleted(SweepingForcedFinalizationMode::kV8Only, reason);
    if (v8_flags.external_memory_accounted_in_global_limit &&
        !limits()->using_initial_limit()) {
      // Ensure that we don't update limits when starting incremental marking.
      // Shrinking limits there could lead to finalizing incremental marking
      // prematurely.
      DCHECK_NE(reason, CompleteSweepingReason::kStartMajorMarking);
      DCHECK_NE(reason, CompleteSweepingReason::kMajorGC);
      // Make sure we don't increase heap limits here.
      HeapLimitBounds bounds = limits()->AtMostCurrentLimits();
      // But don't go below the soft limits for starting incremental marking.
      const size_t new_space_capacity = NewSpaceCapacity();
      bounds.AtLeast(
          OldGenerationAllocationLimitConsumedBytes() + new_space_capacity,
          GlobalConsumedBytes() + new_space_capacity);
      limits()->UpdateAllocationLimits(CurrentHeapGrowingMode(), bounds);
    }
  }
  if (cpp_heap()) {
    // Ensure that sweeping is also completed for the C++ managed heap, if one
    // exists and it's out of work.
    CppHeap::From(cpp_heap())->FinishSweepingIfOutOfWork();
  }
}

void Heap::EnsureSweepingCompleted(SweepingForcedFinalizationMode mode,
                                   CompleteSweepingReason reason) {
  TRACE_GC_EPOCH(tracer(), GCTracer::Scope::HEAP_ENSURE_SWEEPING_COMPLETED,
                 ThreadKind::kMain, "value", [&](perfetto::TracedValue ctx) {
                   auto dict = std::move(ctx).WriteDictionary();
                   dict.Add("sweeping_reason", ToString(reason));
                   dict.Add("mode", ToString(mode));
                   dict.Add("epoch", tracer()->CurrentEpoch());
                 });

  CompleteArrayBufferSweeping();

  EnsureQuarantinedPagesSweepingCompleted();

  if (sweeper()->sweeping_in_progress()) {
    bool was_minor_sweeping_in_progress = minor_sweeping_in_progress();
    bool was_major_sweeping_in_progress = major_sweeping_in_progress();
    sweeper()->EnsureMajorCompleted();

    if (was_major_sweeping_in_progress) {
      old_space()->RefillFreeList();
      code_space()->RefillFreeList();
      if (shared_space()) {
        shared_space()->RefillFreeList();
        shared_trusted_space()->RefillFreeList();
      }

      trusted_space()->RefillFreeList();
    } else if (v8_flags.sticky_mark_bits) {
      // With sticky markbits there is no separate young gen. Minor sweeping
      // will thus sweep pages in old space, so old space freelist should be
      // refilled.
      DCHECK(was_minor_sweeping_in_progress);
      old_space()->RefillFreeList();
    }

    if (!v8_flags.sticky_mark_bits && v8_flags.minor_ms && use_new_space() &&
        was_minor_sweeping_in_progress) {
      TRACE_GC_EPOCH_WITH_FLOW(
          tracer(), GCTracer::Scope::MINOR_MS_COMPLETE_SWEEPING,
          ThreadKind::kMain,
          sweeper_->GetTraceIdForFlowEvent(
              GCTracer::Scope::MINOR_MS_COMPLETE_SWEEPING),
          TRACE_EVENT_FLAG_FLOW_IN | TRACE_EVENT_FLAG_FLOW_OUT);
      paged_new_space()->paged_space()->RefillFreeList();
    }

    tracer()->NotifyFullSweepingCompletedAndStopCycleIfFinished();

#ifdef VERIFY_HEAP
    if (v8_flags.verify_heap) {
      EvacuationVerifier verifier(this);
      verifier.Run();
    }
#endif
  }

  if (mode == SweepingForcedFinalizationMode::kUnifiedHeap && cpp_heap()) {
    // Ensure that sweeping is also completed for the C++ managed heap, if one
    // exists.
    CppHeap::From(cpp_heap())->FinishSweepingIfRunning();
    DCHECK(!CppHeap::From(cpp_heap())->sweeper().IsSweepingInProgress());
  }

  DCHECK_IMPLIES(
      mode == SweepingForcedFinalizationMode::kUnifiedHeap || !cpp_heap(),
      !tracer()->IsSweepingInProgress());
}

void Heap::EnsureQuarantinedPagesSweepingCompleted() {
  if (v8_flags.minor_ms) {
    return;
  }
  scavenger_collector_->CompleteSweepingQuarantinedPagesIfNeeded();
}

void Heap::EnsureYoungSweepingCompleted() {
  CompleteArrayBufferSweeping();

  EnsureQuarantinedPagesSweepingCompleted();

  if (!sweeper()->minor_sweeping_in_progress()) return;
  DCHECK(!v8_flags.sticky_mark_bits);

  TRACE_GC_EPOCH_WITH_FLOW(
      tracer(), GCTracer::Scope::MINOR_MS_COMPLETE_SWEEPING, ThreadKind::kMain,
      sweeper_->GetTraceIdForFlowEvent(
          GCTracer::Scope::MINOR_MS_COMPLETE_SWEEPING),
      TRACE_EVENT_FLAG_FLOW_IN);

  sweeper()->EnsureMinorCompleted();
  paged_new_space()->paged_space()->RefillFreeList();

  tracer()->NotifyYoungSweepingCompletedAndStopCycleIfFinished();
}

void Heap::NotifyLoadingStarted() { loading_state_.NotifyStarted(this); }

void Heap::NotifyLoadingEnded(LeaveHeapState context) {
  loading_state_.NotifyEnded(this);
  if (context == LeaveHeapState::kNotify) {
    if (auto* job = incremental_marking()->incremental_marking_job()) {
      // The task will start incremental marking (if needed not already started)
      // and advance marking if incremental marking is active.
      job->ScheduleTask();
    }
  } else {
    DCHECK_EQ(context, LeaveHeapState::kReachedTimeout);
    // Nothing to do here because we only trigger this from a GC.
  }
}

void Heap::NotifyInputHandlingStarted() {
  if (IsInputHandling()) return;
  input_handling_state_.NotifyStarted(this);
}

void Heap::NotifyInputHandlingEnded(LeaveHeapState context) {
  input_handling_state_.NotifyEnded(this);
  // TODO(crbug.com/444705203): Merge this function with |NotifyLoadingEnded|
  // once the feature flag is removed.
  if (!v8_flags.optimize_for_input_handling) {
    return;
  }
  if (context == LeaveHeapState::kNotify) {
    if (auto* job = incremental_marking()->incremental_marking_job()) {
      // The task will start incremental marking (if needed not already
      // started) and advance marking if incremental marking is active.
      job->ScheduleTask();
    }
  } else {
    DCHECK_EQ(context, LeaveHeapState::kReachedTimeout);
    // Nothing to do here because we only trigger this from a GC.
  }
}

void Heap::GCHintState::NotifyStarted(Heap* heap) {
  if (IsInitialized()) {
    TRACE_EVENT_END(TRACE_DISABLED_BY_DEFAULT("v8.gc"), track_);
  }
  TRACE_EVENT_BEGIN(TRACE_DISABLED_BY_DEFAULT("v8.gc"), tag_, track_);
  double now_ms = heap->MonotonicallyIncreasingTimeInMs();
  DCHECK_NE(now_ms, kInactive);
  start_time_ms_.store(now_ms, std::memory_order_relaxed);
}

void Heap::GCHintState::NotifyEnded(Heap* heap) {
  start_time_ms_.store(kInactive, std::memory_order_relaxed);
  TRACE_EVENT_END(TRACE_DISABLED_BY_DEFAULT("v8.gc"), track_);
}

int Heap::NextScriptId() {
  FullObjectSlot last_script_id_slot(&roots_table()[RootIndex::kLastScriptId]);
  Tagged<Smi> last_id = Cast<Smi>(last_script_id_slot.Relaxed_Load());
  Tagged<Smi> new_id, last_id_before_cas;
  do {
    if (last_id.value() == Smi::kMaxValue) {
      static_assert(v8::UnboundScript::kNoScriptId == 0);
      new_id = Smi::FromInt(1);
    } else {
      new_id = Smi::FromInt(last_id.value() + 1);
    }

    // CAS returns the old value on success, and the current value in the slot
    // on failure. Therefore, we want to break if the returned value matches the
    // old value (last_id), and keep looping (with the new last_id value) if it
    // doesn't.
    last_id_before_cas = last_id;
    last_id =
        Cast<Smi>(last_script_id_slot.Relaxed_CompareAndSwap(last_id, new_id));
  } while (last_id != last_id_before_cas);

  return new_id.value();
}

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::NextStackTraceId() {
  int last_id = last_stack_trace_id().value();
  if (last_id == Smi::kMaxValue) {
    last_id = 0;
  }
  last_id++;
  set_last_stack_trace_id(Smi::FromInt(last_id));
  return last_id;
}

uint64_t Heap::GetTotalAllocatedBytes() {
  return total_allocated_bytes_.load(std::memory_order_relaxed);
}

EmbedderStackStateScope::EmbedderStackStateScope(
    Heap* heap, EmbedderStackStateOrigin origin, StackState stack_state)
    : heap_(heap),
      old_stack_state_(heap_->embedder_stack_state_),
      old_origin_(heap->embedder_stack_state_origin_) {
  // Explicit scopes take precedence over implicit scopes.
  if (origin == EmbedderStackStateOrigin::kExplicitInvocation ||
      heap_->embedder_stack_state_origin_ !=
          EmbedderStackStateOrigin::kExplicitInvocation) {
    heap_->embedder_stack_state_ = stack_state;
    heap_->embedder_stack_state_origin_ = origin;
  }
}

EmbedderStackStateScope::~EmbedderStackStateScope() {
  heap_->embedder_stack_state_ = old_stack_state_;
  heap_->embedder_stack_state_origin_ = old_origin_;
}

CppClassNamesAsHeapObjectNameScope::CppClassNamesAsHeapObjectNameScope(
    v8::CppHeap* heap)
    : scope_(std::make_unique<cppgc::internal::ClassNameAsHeapObjectNameScope>(
          *CppHeap::From(heap))) {}

CppClassNamesAsHeapObjectNameScope::~CppClassNamesAsHeapObjectNameScope() =
    default;

#if V8_HEAP_USE_PTHREAD_JIT_WRITE_PROTECT || \
    V8_HEAP_USE_PKU_JIT_WRITE_PROTECT || V8_HEAP_USE_BECORE_JIT_WRITE_PROTECT

CodePageMemoryModificationScopeForDebugging::
    CodePageMemoryModificationScopeForDebugging(Heap* heap,
                                                VirtualMemory* reservation,
                                                base::AddressRegion region)
    : rwx_write_scope_("Write access for zapping.") {
#if !defined(DEBUG) && !defined(VERIFY_HEAP) && !defined(USE_SIMULATOR)
  UNREACHABLE();
#endif
}

CodePageMemoryModificationScopeForDebugging::
    CodePageMemoryModificationScopeForDebugging(BasePage* chunk)
    : rwx_write_scope_("Write access for zapping.") {
#if !defined(DEBUG) && !defined(VERIFY_HEAP) && !defined(USE_SIMULATOR)
  UNREACHABLE();
#endif
}

CodePageMemoryModificationScopeForDebugging::
    ~CodePageMemoryModificationScopeForDebugging() {}

#else  // V8_HEAP_USE_PTHREAD_JIT_WRITE_PROTECT ||
       // V8_HEAP_USE_PKU_JIT_WRITE_PROTECT ||
       // V8_HEAP_USE_BECORE_JIT_WRITE_PROTECT

CodePageMemoryModificationScopeForDebugging::
    CodePageMemoryModificationScopeForDebugging(Heap* heap,
                                                VirtualMemory* reservation,
                                                base::AddressRegion region) {
#if !defined(DEBUG) && !defined(VERIFY_HEAP) && !defined(USE_SIMULATOR)
  UNREACHABLE();
#endif
}

CodePageMemoryModificationScopeForDebugging::
    CodePageMemoryModificationScopeForDebugging(BasePage* page) {
#if !defined(DEBUG) && !defined(VERIFY_HEAP) && !defined(USE_SIMULATOR)
  UNREACHABLE();
#endif
}

CodePageMemoryModificationScopeForDebugging::
    ~CodePageMemoryModificationScopeForDebugging() {}

#endif

ConservativePinningScope::ConservativePinningScope(Heap* heap) : heap_(heap) {
  DCHECK(::heap::base::Stack::IsOnCurrentStack(this));
  DCHECK(!heap_->selective_stack_scan_start_address_.has_value());
  // `frame_address` should be higher than `this`, but we observed that this
  // may not hold in some cases (e.g. due to missing inlining or unexpected
  // frame layouts). In such cases, we scan the stack either from the last
  // c_entry_fp or the whole stack.
  const Address c_entry_fp = *heap_->isolate()->c_entry_fp_address();
  const void* frame_address =
      (c_entry_fp == kNullAddress)
          ? static_cast<void*>(v8::base::Stack::GetStackStart())
          : reinterpret_cast<const void*>(c_entry_fp);
  // The stack segment covered by this scope should include the scope itself.
  DCHECK_NOT_NULL(frame_address);
  DCHECK_LE(this, frame_address);
  DCHECK(::heap::base::Stack::IsOnCurrentStack(frame_address));
  heap_->selective_stack_scan_start_address_ = frame_address;
}
ConservativePinningScope::~ConservativePinningScope() {
  DCHECK(heap_->selective_stack_scan_start_address_.has_value());
  heap_->selective_stack_scan_start_address_.reset();
}

#include "src/objects/object-macros-undef.h"

}  // namespace v8::internal