blob: 81f2b0dd8c30d5411c969c3129f9ed79f9fcbca0 [file] [log] [blame]
// Copyright 2012 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_HEAP_HEAP_H_
#define V8_HEAP_HEAP_H_
#include <cmath>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <vector>
// Clients of this interface shouldn't depend on lots of heap internals.
// Do not include anything from src/heap here!
#include "include/v8-internal.h"
#include "include/v8.h"
#include "src/base/atomic-utils.h"
#include "src/builtins/accessors.h"
#include "src/common/assert-scope.h"
#include "src/common/globals.h"
#include "src/init/heap-symbols.h"
#include "src/objects/allocation-site.h"
#include "src/objects/fixed-array.h"
#include "src/objects/heap-object.h"
#include "src/objects/objects.h"
#include "src/objects/smi.h"
#include "src/objects/string-table.h"
#include "src/objects/visitors.h"
#include "src/roots/roots.h"
#include "src/utils/allocation.h"
#include "testing/gtest/include/gtest/gtest_prod.h"
namespace v8 {
namespace debug {
using OutOfMemoryCallback = void (*)(void* data);
} // namespace debug
namespace internal {
namespace heap {
class HeapTester;
class TestMemoryAllocatorScope;
} // namespace heap
class IncrementalMarking;
class JSArrayBuffer;
using v8::MemoryPressureLevel;
class AllocationObserver;
class ArrayBufferCollector;
class CodeLargeObjectSpace;
class ConcurrentMarking;
class GCIdleTimeHandler;
class GCIdleTimeHeapState;
class GCTracer;
class HeapObjectAllocationTracker;
class HeapObjectsFilter;
class HeapStats;
class Isolate;
class JSFinalizationGroup;
class LocalEmbedderHeapTracer;
class MemoryAllocator;
class MemoryReducer;
class MinorMarkCompactCollector;
class ObjectIterator;
class ObjectStats;
class Page;
class PagedSpace;
class ReadOnlyHeap;
class RootVisitor;
class ScavengeJob;
class Scavenger;
class ScavengerCollector;
class Space;
class StoreBuffer;
class StressScavengeObserver;
class TimedHistogram;
class WeakObjectRetainer;
enum ArrayStorageAllocationMode {
enum class ClearRecordedSlots { kYes, kNo };
enum class ClearFreedMemoryMode { kClearFreedMemory, kDontClearFreedMemory };
enum ExternalBackingStoreType { kArrayBuffer, kExternalString, kNumTypes };
enum class FixedArrayVisitationMode { kRegular, kIncremental };
enum class TraceRetainingPathMode { kEnabled, kDisabled };
enum class RetainingPathOption { kDefault, kTrackEphemeronPath };
enum class GarbageCollectionReason {
kUnknown = 0,
kAllocationFailure = 1,
kAllocationLimit = 2,
kContextDisposal = 3,
kCountersExtension = 4,
kDebugger = 5,
kDeserializer = 6,
kExternalMemoryPressure = 7,
kFinalizeMarkingViaStackGuard = 8,
kFinalizeMarkingViaTask = 9,
kFullHashtable = 10,
kHeapProfiler = 11,
kIdleTask = 12,
kLastResort = 13,
kLowMemoryNotification = 14,
kMakeHeapIterable = 15,
kMemoryPressure = 16,
kMemoryReducer = 17,
kRuntime = 18,
kSamplingProfiler = 19,
kSnapshotCreator = 20,
kTesting = 21,
kExternalFinalize = 22,
kGlobalAllocationLimit = 23,
// If you add new items here, then update the incremental_marking_reason,
// mark_compact_reason, and scavenge_reason counters in counters.h.
// Also update src/tools/metrics/histograms/histograms.xml in chromium.
enum class YoungGenerationHandling {
kRegularScavenge = 0,
kFastPromotionDuringScavenge = 1,
// Histogram::InspectConstructionArguments in chromium requires us to have at
// least three buckets.
kUnusedBucket = 2,
// If you add new items here, then update the young_generation_handling in
// counters.h.
// Also update src/tools/metrics/histograms/histograms.xml in chromium.
enum class GCIdleTimeAction : uint8_t;
class AllocationResult {
static inline AllocationResult Retry(AllocationSpace space = NEW_SPACE) {
return AllocationResult(space);
// Implicit constructor from Object.
AllocationResult(Object object) // NOLINT
: object_(object) {
// AllocationResults can't return Smis, which are used to represent
// failure and the space to retry in.
AllocationResult() : object_(Smi::FromInt(NEW_SPACE)) {}
inline bool IsRetry() { return object_.IsSmi(); }
inline HeapObject ToObjectChecked();
inline AllocationSpace RetrySpace();
template <typename T>
bool To(T* obj) {
if (IsRetry()) return false;
*obj = T::cast(object_);
return true;
explicit AllocationResult(AllocationSpace space)
: object_(Smi::FromInt(static_cast<int>(space))) {}
Object object_;
STATIC_ASSERT(sizeof(AllocationResult) == kSystemPointerSize);
#ifdef DEBUG
struct CommentStatistic {
const char* comment;
int size;
int count;
void Clear() {
comment = nullptr;
size = 0;
count = 0;
// Must be small, since an iteration is used for lookup.
static const int kMaxComments = 64;
using EphemeronRememberedSet =
std::unordered_map<EphemeronHashTable, std::unordered_set<int>,
class Heap {
// Stores ephemeron entries where the EphemeronHashTable is in old-space,
// and the key of the entry is in new-space. Such keys do not appear in the
// usual OLD_TO_NEW remembered set.
EphemeronRememberedSet ephemeron_remembered_set_;
enum FindMementoMode { kForRuntime, kForGC };
enum class HeapGrowingMode { kSlow, kConservative, kMinimal, kDefault };
enum HeapState {
using PretenuringFeedbackMap =
std::unordered_map<AllocationSite, size_t, Object::Hasher>;
// Taking this mutex prevents the GC from entering a phase that relocates
// object references.
base::Mutex* relocation_mutex() { return &relocation_mutex_; }
// Support for partial snapshots. After calling this we have a linear
// space to write objects in each space.
struct Chunk {
uint32_t size;
Address start;
Address end;
using Reservation = std::vector<Chunk>;
// 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.
static const int kPointerMultiplier = 1;
static const int kPointerMultiplier = i::kTaggedSize / 4;
static const size_t kMaxInitialOldGenerationSize =
256 * MB * kPointerMultiplier;
// These constants control heap configuration based on the physical memory.
static constexpr size_t kPhysicalMemoryToOldGenerationRatio = 4;
static constexpr size_t kOldGenerationToSemiSpaceRatio = 128;
static constexpr size_t kOldGenerationToSemiSpaceRatioLowMemory = 256;
static constexpr size_t kOldGenerationLowMemory =
128 * MB * kPointerMultiplier;
static constexpr size_t kNewLargeObjectSpaceToSemiSpaceRatio = 1;
static constexpr size_t kMinSemiSpaceSize = 512 * KB * kPointerMultiplier;
static constexpr size_t kMaxSemiSpaceSize = 8192 * KB * kPointerMultiplier;
STATIC_ASSERT(kMinSemiSpaceSize % (1 << kPageSizeBits) == 0);
STATIC_ASSERT(kMaxSemiSpaceSize % (1 << kPageSizeBits) == 0);
static const int kTraceRingBufferSize = 512;
static const int kStacktraceBufferSize = 512;
static const int kNoGCFlags = 0;
static const int kReduceMemoryFootprintMask = 1;
// The minimum size of a HeapObject on the heap.
static const int kMinObjectSizeInTaggedWords = 2;
static const int kMinPromotedPercentForFastPromotionMode = 90;
STATIC_ASSERT(static_cast<int>(RootIndex::kUndefinedValue) ==
STATIC_ASSERT(static_cast<int>(RootIndex::kTheHoleValue) ==
STATIC_ASSERT(static_cast<int>(RootIndex::kNullValue) ==
STATIC_ASSERT(static_cast<int>(RootIndex::kTrueValue) ==
STATIC_ASSERT(static_cast<int>(RootIndex::kFalseValue) ==
STATIC_ASSERT(static_cast<int>(RootIndex::kempty_string) ==
// Calculates the maximum amount of filler that could be required by the
// given alignment.
V8_EXPORT_PRIVATE static int GetMaximumFillToAlign(
AllocationAlignment alignment);
// Calculates the actual amount of filler required for a given address at the
// given alignment.
V8_EXPORT_PRIVATE static int GetFillToAlign(Address address,
AllocationAlignment alignment);
// Returns the size of the initial area of a code-range, which is marked
// writable and reserved to contain unwind information.
static size_t GetCodeRangeReservedAreaSize();
void FatalProcessOutOfMemory(const char* location);
// Checks whether the space is valid.
static bool IsValidAllocationSpace(AllocationSpace space);
// Zapping is needed for verify heap, and always done in debug builds.
static inline bool ShouldZapGarbage() {
#ifdef DEBUG
return true;
return FLAG_verify_heap;
return false;
// Helper function to get the bytecode flushing mode based on the flags. This
// is required because it is not safe to acess flags in concurrent marker.
static inline BytecodeFlushMode GetBytecodeFlushMode() {
if (FLAG_stress_flush_bytecode) {
return BytecodeFlushMode::kStressFlushBytecode;
} else if (FLAG_flush_bytecode) {
return BytecodeFlushMode::kFlushBytecode;
return BytecodeFlushMode::kDoNotFlushBytecode;
static uintptr_t ZapValue() {
return FLAG_clear_free_memory ? kClearedFreeMemoryValue : kZapValue;
static inline bool IsYoungGenerationCollector(GarbageCollector collector) {
return collector == SCAVENGER || collector == MINOR_MARK_COMPACTOR;
static inline GarbageCollector YoungGenerationCollector() {
static inline const char* CollectorName(GarbageCollector collector) {
switch (collector) {
return "Scavenger";
return "Mark-Compact";
return "Minor Mark-Compact";
return "Unknown collector";
// Copy block of memory from src to dst. Size of block should be aligned
// by pointer size.
static inline void CopyBlock(Address dst, Address src, int byte_size);
// Executes generational and/or marking write barrier for a [start, end) range
// of non-weak slots inside |object|.
template <typename TSlot>
V8_EXPORT_PRIVATE void WriteBarrierForRange(HeapObject object, TSlot start,
TSlot end);
V8_EXPORT_PRIVATE static void WriteBarrierForCodeSlow(Code host);
V8_EXPORT_PRIVATE static void GenerationalBarrierSlow(HeapObject object,
Address slot,
HeapObject value);
V8_EXPORT_PRIVATE inline void RecordEphemeronKeyWrite(
EphemeronHashTable table, Address key_slot);
V8_EXPORT_PRIVATE static void EphemeronKeyWriteBarrierFromCode(
Address raw_object, Address address, Isolate* isolate);
V8_EXPORT_PRIVATE static void GenerationalBarrierForCodeSlow(
Code host, RelocInfo* rinfo, HeapObject value);
V8_EXPORT_PRIVATE static void MarkingBarrierSlow(HeapObject object,
Address slot,
HeapObject value);
V8_EXPORT_PRIVATE static void MarkingBarrierForCodeSlow(Code host,
RelocInfo* rinfo,
HeapObject value);
V8_EXPORT_PRIVATE static void MarkingBarrierForDescriptorArraySlow(
Heap* heap, HeapObject host, HeapObject descriptor_array,
int number_of_own_descriptors);
V8_EXPORT_PRIVATE static bool PageFlagsAreConsistent(HeapObject object);
// Notifies the heap that is ok to start marking or other activities that
// should not happen during deserialization.
void NotifyDeserializationComplete();
void NotifyBootstrapComplete();
void NotifyOldGenerationExpansion();
inline Address* NewSpaceAllocationTopAddress();
inline Address* NewSpaceAllocationLimitAddress();
inline Address* OldSpaceAllocationTopAddress();
inline Address* OldSpaceAllocationLimitAddress();
// Move len non-weak tagged elements from src_slot to dst_slot of dst_object.
// The source and destination memory ranges can overlap.
void MoveRange(HeapObject dst_object, ObjectSlot dst_slot,
ObjectSlot src_slot, int len, WriteBarrierMode mode);
// Copy len non-weak tagged elements from src_slot to dst_slot of dst_object.
// The source and destination memory ranges must not overlap.
template <typename TSlot>
void CopyRange(HeapObject dst_object, TSlot dst_slot, TSlot src_slot, int len,
WriteBarrierMode mode);
// Initialize a filler object to keep the ability to iterate over the heap
// when introducing gaps within pages. If slots could have been recorded in
// the freed area, then pass ClearRecordedSlots::kYes as the mode. Otherwise,
// pass ClearRecordedSlots::kNo. If the memory after the object header of
// the filler should be cleared, pass in kClearFreedMemory. The default is
// kDontClearFreedMemory.
V8_EXPORT_PRIVATE HeapObject CreateFillerObjectAt(
Address addr, int size, ClearRecordedSlots clear_slots_mode,
ClearFreedMemoryMode clear_memory_mode =
template <typename T>
void CreateFillerForArray(T object, int elements_to_trim, int bytes_to_trim);
bool CanMoveObjectStart(HeapObject object);
bool IsImmovable(HeapObject object);
static bool IsLargeObject(HeapObject object);
// Trim the given array from the left. Note that this relocates the object
// start and hence is only valid if there is only a single reference to it.
V8_EXPORT_PRIVATE FixedArrayBase LeftTrimFixedArray(FixedArrayBase obj,
int elements_to_trim);
// Trim the given array from the right.
V8_EXPORT_PRIVATE void RightTrimFixedArray(FixedArrayBase obj,
int elements_to_trim);
void RightTrimWeakFixedArray(WeakFixedArray obj, int elements_to_trim);
// Converts the given boolean condition to JavaScript boolean value.
inline Oddball ToBoolean(bool condition);
// Notify the heap that a context has been disposed.
V8_EXPORT_PRIVATE int NotifyContextDisposed(bool dependant_context);
void set_native_contexts_list(Object object) {
native_contexts_list_ = object;
Object native_contexts_list() const { return native_contexts_list_; }
void set_allocation_sites_list(Object object) {
allocation_sites_list_ = object;
Object allocation_sites_list() { return allocation_sites_list_; }
// Used in CreateAllocationSiteStub and the (de)serializer.
Address allocation_sites_list_address() {
return reinterpret_cast<Address>(&allocation_sites_list_);
// Traverse all the allocaions_sites [nested_site and weak_next] in the list
// and foreach call the visitor
void ForeachAllocationSite(
Object list, const std::function<void(AllocationSite)>& visitor);
// Number of mark-sweeps.
int ms_count() const { return ms_count_; }
// Checks whether the given object is allowed to be migrated from it's
// current space into the given destination space. Used for debugging.
bool AllowedToBeMigrated(Map map, HeapObject object, AllocationSpace dest);
void CheckHandleCount();
// Number of "runtime allocations" done so far.
uint32_t allocations_count() { return allocations_count_; }
// Print short heap statistics.
void PrintShortHeapStatistics();
// Print statistics of freelists of old_space:
// with FLAG_trace_gc_freelists: summary of each FreeListCategory.
// with FLAG_trace_gc_freelists_verbose: also prints the statistics of each
// FreeListCategory of each page.
void PrintFreeListsStats();
// Dump heap statistics in JSON format.
void DumpJSONHeapStatistics(std::stringstream& stream);
bool write_protect_code_memory() const { return write_protect_code_memory_; }
uintptr_t code_space_memory_modification_scope_depth() {
return code_space_memory_modification_scope_depth_;
void increment_code_space_memory_modification_scope_depth() {
void decrement_code_space_memory_modification_scope_depth() {
void UnprotectAndRegisterMemoryChunk(MemoryChunk* chunk);
V8_EXPORT_PRIVATE void UnprotectAndRegisterMemoryChunk(HeapObject object);
void UnregisterUnprotectedMemoryChunk(MemoryChunk* chunk);
V8_EXPORT_PRIVATE void ProtectUnprotectedMemoryChunks();
void EnableUnprotectedMemoryChunksRegistry() {
unprotected_memory_chunks_registry_enabled_ = true;
void DisableUnprotectedMemoryChunksRegistry() {
unprotected_memory_chunks_registry_enabled_ = false;
bool unprotected_memory_chunks_registry_enabled() {
return unprotected_memory_chunks_registry_enabled_;
inline HeapState gc_state() { return gc_state_; }
void SetGCState(HeapState state);
bool IsTearingDown() const { return gc_state_ == TEAR_DOWN; }
inline bool IsInGCPostProcessing() { return gc_post_processing_depth_ > 0; }
// If an object has an AllocationMemento trailing it, return it, otherwise
// return a null AllocationMemento.
template <FindMementoMode mode>
inline AllocationMemento FindAllocationMemento(Map map, HeapObject object);
// Returns false if not able to reserve.
bool ReserveSpace(Reservation* reservations, std::vector<Address>* maps);
// Support for the API.
void CreateApiObjects();
// Implements the corresponding V8 API function.
bool IdleNotification(double deadline_in_seconds);
bool IdleNotification(int idle_time_in_ms);
V8_EXPORT_PRIVATE void MemoryPressureNotification(MemoryPressureLevel level,
bool is_isolate_locked);
void CheckMemoryPressure();
V8_EXPORT_PRIVATE void AddNearHeapLimitCallback(v8::NearHeapLimitCallback,
void* data);
V8_EXPORT_PRIVATE void RemoveNearHeapLimitCallback(
v8::NearHeapLimitCallback callback, size_t heap_limit);
V8_EXPORT_PRIVATE void AutomaticallyRestoreInitialHeapLimit(
double threshold_percent);
V8_EXPORT_PRIVATE double MonotonicallyIncreasingTimeInMs();
void RecordStats(HeapStats* stats, bool take_snapshot = false);
// Check new space expansion criteria and expand semispaces if it was hit.
void CheckNewSpaceExpansionCriteria();
void VisitExternalResources(v8::ExternalResourceVisitor* visitor);
// An object should be promoted if the object has survived a
// scavenge operation.
inline bool ShouldBePromoted(Address old_address);
void IncrementDeferredCount(v8::Isolate::UseCounterFeature feature);
inline int NextScriptId();
inline int NextDebuggingId();
inline int GetNextTemplateSerialNumber();
void SetSerializedObjects(FixedArray objects);
void SetSerializedGlobalProxySizes(FixedArray sizes);
// For post mortem debugging.
void RememberUnmappedPage(Address page, bool compacted);
int64_t external_memory_hard_limit() { return max_old_generation_size_ / 2; }
V8_INLINE int64_t external_memory();
V8_INLINE void update_external_memory(int64_t delta);
V8_INLINE void update_external_memory_concurrently_freed(intptr_t freed);
V8_INLINE void account_external_memory_concurrently_freed();
size_t backing_store_bytes() const { return backing_store_bytes_; }
void CompactWeakArrayLists(AllocationType allocation);
V8_EXPORT_PRIVATE void AddRetainedMap(Handle<Map> map);
// This event is triggered after successful allocation of a new object made
// by runtime. Allocations of target space for object evacuation do not
// trigger the event. In order to track ALL allocations one must turn off
// FLAG_inline_new.
inline void OnAllocationEvent(HeapObject object, int size_in_bytes);
// This event is triggered after object is moved to a new place.
void OnMoveEvent(HeapObject target, HeapObject source, int size_in_bytes);
inline bool CanAllocateInReadOnlySpace();
bool deserialization_complete() const { return deserialization_complete_; }
bool HasLowAllocationRate();
bool HasHighFragmentation();
bool HasHighFragmentation(size_t used, size_t committed);
void ActivateMemoryReducerIfNeeded();
V8_EXPORT_PRIVATE bool ShouldOptimizeForMemoryUsage();
bool HighMemoryPressure() {
return memory_pressure_level_ != MemoryPressureLevel::kNone;
void RestoreHeapLimit(size_t heap_limit) {
// Do not set the limit lower than the live size + some slack.
size_t min_limit = SizeOfObjects() + SizeOfObjects() / 4;
max_old_generation_size_ =
Min(max_old_generation_size_, Max(heap_limit, min_limit));
// ===========================================================================
// Initialization. ===========================================================
// ===========================================================================
void ConfigureHeap(const v8::ResourceConstraints& constraints);
void ConfigureHeapDefault();
// Prepares the heap, setting up for deserialization.
void SetUp();
// Sets read-only heap and space.
void SetUpFromReadOnlyHeap(ReadOnlyHeap* ro_heap);
// Sets up the heap memory without creating any objects.
void SetUpSpaces();
// (Re-)Initialize hash seed from flag or RNG.
void InitializeHashSeed();
// Bootstraps the object heap with the core set of objects required to run.
// Returns whether it succeeded.
bool CreateHeapObjects();
// Create ObjectStats if live_object_stats_ or dead_object_stats_ are nullptr.
void CreateObjectStats();
// Sets the TearDown state, so no new GC tasks get posted.
void StartTearDown();
// Destroys all memory allocated by the heap.
void TearDown();
// Returns whether SetUp has been called.
bool HasBeenSetUp();
// ===========================================================================
// Getters for spaces. =======================================================
// ===========================================================================
inline Address NewSpaceTop();
NewSpace* new_space() { return new_space_; }
OldSpace* old_space() { return old_space_; }
CodeSpace* code_space() { return code_space_; }
MapSpace* map_space() { return map_space_; }
LargeObjectSpace* lo_space() { return lo_space_; }
CodeLargeObjectSpace* code_lo_space() { return code_lo_space_; }
NewLargeObjectSpace* new_lo_space() { return new_lo_space_; }
ReadOnlySpace* read_only_space() { return read_only_space_; }
inline PagedSpace* paged_space(int idx);
inline Space* space(int idx);
// Returns name of the space.
V8_EXPORT_PRIVATE static const char* GetSpaceName(AllocationSpace space);
// ===========================================================================
// Getters to other components. ==============================================
// ===========================================================================
GCTracer* tracer() { return tracer_.get(); }
MemoryAllocator* memory_allocator() { return memory_allocator_.get(); }
inline Isolate* isolate();
MarkCompactCollector* mark_compact_collector() {
return mark_compact_collector_.get();
MinorMarkCompactCollector* minor_mark_compact_collector() {
return minor_mark_compact_collector_;
ArrayBufferCollector* array_buffer_collector() {
return array_buffer_collector_.get();
// ===========================================================================
// Root set access. ==========================================================
// ===========================================================================
// Shortcut to the roots table stored in the Isolate.
V8_INLINE RootsTable& roots_table();
// Heap root getters.
#define ROOT_ACCESSOR(type, name, CamelName) inline type name();
V8_INLINE void SetRootMaterializedObjects(FixedArray objects);
V8_INLINE void SetRootScriptList(Object value);
V8_INLINE void SetRootStringTable(StringTable value);
V8_INLINE void SetRootNoScriptSharedFunctionInfos(Object value);
V8_INLINE void SetMessageListeners(TemplateList value);
V8_INLINE void SetPendingOptimizeForTestBytecode(Object bytecode);
// Set the stack limit in the roots table. Some architectures generate
// code that looks here, because it is faster than loading from the static
// jslimit_/real_jslimit_ variable in the StackGuard.
void SetStackLimits();
// The stack limit is thread-dependent. To be able to reproduce the same
// snapshot blob, we need to reset it before serializing.
void ClearStackLimits();
void RegisterStrongRoots(FullObjectSlot start, FullObjectSlot end);
void UnregisterStrongRoots(FullObjectSlot start);
void SetBuiltinsConstantsTable(FixedArray cache);
// A full copy of the interpreter entry trampoline, used as a template to
// create copies of the builtin at runtime. The copies are used to create
// better profiling information for ticks in bytecode execution. Note that
// this is always a copy of the full builtin, i.e. not the off-heap
// trampoline.
// See also: FLAG_interpreted_frames_native_stack.
void SetInterpreterEntryTrampolineForProfiling(Code code);
// Add finalization_group into the dirty_js_finalization_groups list.
void AddDirtyJSFinalizationGroup(
JSFinalizationGroup finalization_group,
std::function<void(HeapObject object, ObjectSlot slot, Object target)>
V8_EXPORT_PRIVATE void KeepDuringJob(Handle<JSReceiver> target);
void ClearKeptObjects();
// ===========================================================================
// Inline allocation. ========================================================
// ===========================================================================
// Indicates whether inline bump-pointer allocation has been disabled.
bool inline_allocation_disabled() { return inline_allocation_disabled_; }
// Switch whether inline bump-pointer allocation should be used.
V8_EXPORT_PRIVATE void EnableInlineAllocation();
V8_EXPORT_PRIVATE void DisableInlineAllocation();
// ===========================================================================
// Methods triggering GCs. ===================================================
// ===========================================================================
// Performs garbage collection operation.
// Returns whether there is a chance that another major GC could
// collect more garbage.
V8_EXPORT_PRIVATE bool CollectGarbage(
AllocationSpace space, GarbageCollectionReason gc_reason,
const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags);
// Performs a full garbage collection.
V8_EXPORT_PRIVATE void CollectAllGarbage(
int flags, GarbageCollectionReason gc_reason,
const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags);
// Last hope GC, should try to squeeze as much as possible.
V8_EXPORT_PRIVATE void CollectAllAvailableGarbage(
GarbageCollectionReason gc_reason);
// Precise garbage collection that potentially finalizes already running
// incremental marking before performing an atomic garbage collection.
// Only use if absolutely necessary or in tests to avoid floating garbage!
V8_EXPORT_PRIVATE void PreciseCollectAllGarbage(
int flags, GarbageCollectionReason gc_reason,
const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags);
// Reports and external memory pressure event, either performs a major GC or
// completes incremental marking in order to free external resources.
void ReportExternalMemoryPressure();
using GetExternallyAllocatedMemoryInBytesCallback =
void SetGetExternallyAllocatedMemoryInBytesCallback(
GetExternallyAllocatedMemoryInBytesCallback callback) {
external_memory_callback_ = callback;
// Invoked when GC was requested via the stack guard.
void HandleGCRequest();
// ===========================================================================
// Builtins. =================================================================
// ===========================================================================
V8_EXPORT_PRIVATE Code builtin(int index);
Address builtin_address(int index);
void set_builtin(int index, Code builtin);
// ===========================================================================
// Iterators. ================================================================
// ===========================================================================
// None of these methods iterate over the read-only roots. To do this use
// ReadOnlyRoots::Iterate. Read-only root iteration is not necessary for
// garbage collection and is usually only performed as part of
// (de)serialization or heap verification.
// Iterates over the strong roots and the weak roots.
void IterateRoots(RootVisitor* v, VisitMode mode);
// Iterates over the strong roots.
void IterateStrongRoots(RootVisitor* v, VisitMode mode);
// Iterates over entries in the smi roots list. Only interesting to the
// serializer/deserializer, since GC does not care about smis.
void IterateSmiRoots(RootVisitor* v);
// Iterates over weak string tables.
void IterateWeakRoots(RootVisitor* v, VisitMode mode);
// Iterates over weak global handles.
void IterateWeakGlobalHandles(RootVisitor* v);
// Iterates over builtins.
void IterateBuiltins(RootVisitor* v);
// ===========================================================================
// Store buffer API. =========================================================
// ===========================================================================
// Used for query incremental marking status in generated code.
Address* IsMarkingFlagAddress() {
return reinterpret_cast<Address*>(&is_marking_flag_);
void SetIsMarkingFlag(uint8_t flag) { is_marking_flag_ = flag; }
Address* store_buffer_top_address();
static intptr_t store_buffer_mask_constant();
static Address store_buffer_overflow_function_address();
void ClearRecordedSlot(HeapObject object, ObjectSlot slot);
void ClearRecordedSlotRange(Address start, Address end);
#ifdef DEBUG
void VerifyClearedSlot(HeapObject object, ObjectSlot slot);
// ===========================================================================
// Incremental marking API. ==================================================
// ===========================================================================
int GCFlagsForIncrementalMarking() {
return ShouldOptimizeForMemoryUsage() ? kReduceMemoryFootprintMask
: kNoGCFlags;
// Start incremental marking and ensure that idle time handler can perform
// incremental steps.
V8_EXPORT_PRIVATE void StartIdleIncrementalMarking(
GarbageCollectionReason gc_reason,
GCCallbackFlags gc_callback_flags = GCCallbackFlags::kNoGCCallbackFlags);
// Starts incremental marking assuming incremental marking is currently
// stopped.
V8_EXPORT_PRIVATE void StartIncrementalMarking(
int gc_flags, GarbageCollectionReason gc_reason,
GCCallbackFlags gc_callback_flags = GCCallbackFlags::kNoGCCallbackFlags);
void StartIncrementalMarkingIfAllocationLimitIsReached(
int gc_flags,
GCCallbackFlags gc_callback_flags = GCCallbackFlags::kNoGCCallbackFlags);
void FinalizeIncrementalMarkingIfComplete(GarbageCollectionReason gc_reason);
// Synchronously finalizes incremental marking.
void FinalizeIncrementalMarkingAtomically(GarbageCollectionReason gc_reason);
void RegisterDeserializedObjectsForBlackAllocation(
Reservation* reservations, const std::vector<HeapObject>& large_objects,
const std::vector<Address>& maps);
IncrementalMarking* incremental_marking() {
return incremental_marking_.get();
// ===========================================================================
// Concurrent marking API. ===================================================
// ===========================================================================
ConcurrentMarking* concurrent_marking() { return concurrent_marking_.get(); }
// The runtime uses this function to notify potentially unsafe object layout
// changes that require special synchronization with the concurrent marker.
// The old size is the size of the object before layout change.
void NotifyObjectLayoutChange(HeapObject object, int old_size,
const DisallowHeapAllocation&);
// This function checks that either
// - the map transition is safe,
// - or it was communicated to GC using NotifyObjectLayoutChange.
V8_EXPORT_PRIVATE void VerifyObjectLayoutChange(HeapObject object,
Map new_map);
// ===========================================================================
// Deoptimization support API. ===============================================
// ===========================================================================
// Setters for code offsets of well-known deoptimization targets.
void SetArgumentsAdaptorDeoptPCOffset(int pc_offset);
void SetConstructStubCreateDeoptPCOffset(int pc_offset);
void SetConstructStubInvokeDeoptPCOffset(int pc_offset);
void SetInterpreterEntryReturnPCOffset(int pc_offset);
// Invalidates references in the given {code} object that are referenced
// transitively from the deoptimization data. Mutates write-protected code.
void InvalidateCodeDeoptimizationData(Code code);
void DeoptMarkedAllocationSites();
bool DeoptMaybeTenuredAllocationSites();
// ===========================================================================
// Embedder heap tracer support. =============================================
// ===========================================================================
LocalEmbedderHeapTracer* local_embedder_heap_tracer() const {
return local_embedder_heap_tracer_.get();
void SetEmbedderHeapTracer(EmbedderHeapTracer* tracer);
EmbedderHeapTracer* GetEmbedderHeapTracer() const;
void RegisterExternallyReferencedObject(Address* location);
void SetEmbedderStackStateForNextFinalizaton(
EmbedderHeapTracer::EmbedderStackState stack_state);
EmbedderHeapTracer::TraceFlags flags_for_embedder_tracer() const;
// ===========================================================================
// External string table API. ================================================
// ===========================================================================
// Registers an external string.
inline void RegisterExternalString(String string);
// Called when a string's resource is changed. The size of the payload is sent
// as argument of the method.
V8_EXPORT_PRIVATE void UpdateExternalString(String string, size_t old_payload,
size_t new_payload);
// Finalizes an external string by deleting the associated external
// data and clearing the resource pointer.
inline void FinalizeExternalString(String string);
static String UpdateYoungReferenceInExternalStringTableEntry(
Heap* heap, FullObjectSlot pointer);
// ===========================================================================
// Methods checking/returning the space of a given object/address. ===========
// ===========================================================================
// Returns whether the object resides in new space.
static inline bool InYoungGeneration(Object object);
static inline bool InYoungGeneration(MaybeObject object);
static inline bool InYoungGeneration(HeapObject heap_object);
static inline bool InFromPage(Object object);
static inline bool InFromPage(MaybeObject object);
static inline bool InFromPage(HeapObject heap_object);
static inline bool InToPage(Object object);
static inline bool InToPage(MaybeObject object);
static inline bool InToPage(HeapObject heap_object);
// Returns whether the object resides in old space.
inline bool InOldSpace(Object object);
// Checks whether an address/object is in the non-read-only heap (including
// auxiliary area and unused area). Use IsValidHeapObject if checking both
// heaps is required.
V8_EXPORT_PRIVATE bool Contains(HeapObject value);
// Checks whether an address/object in a space.
// Currently used by tests, serialization and heap verification only.
V8_EXPORT_PRIVATE bool InSpace(HeapObject value, AllocationSpace space);
// Slow methods that can be used for verification as they can also be used
// with off-heap Addresses.
bool InSpaceSlow(Address addr, AllocationSpace space);
static inline Heap* FromWritableHeapObject(HeapObject obj);
// ===========================================================================
// Object statistics tracking. ===============================================
// ===========================================================================
// Returns the number of buckets used by object statistics tracking during a
// major GC. Note that the following methods fail gracefully when the bounds
// are exceeded though.
size_t NumberOfTrackedHeapObjectTypes();
// Returns object statistics about count and size at the last major GC.
// Objects are being grouped into buckets that roughly resemble existing
// instance types.
size_t ObjectCountAtLastGC(size_t index);
size_t ObjectSizeAtLastGC(size_t index);
// Retrieves names of buckets used by object statistics tracking.
bool GetObjectTypeName(size_t index, const char** object_type,
const char** object_sub_type);
// The total number of native contexts object on the heap.
size_t NumberOfNativeContexts();
// The total number of native contexts that were detached but were not
// garbage collected yet.
size_t NumberOfDetachedContexts();
// ===========================================================================
// Code statistics. ==========================================================
// ===========================================================================
// Collect code (Code and BytecodeArray objects) statistics.
void CollectCodeStatistics();
// ===========================================================================
// GC statistics. ============================================================
// ===========================================================================
// Returns the maximum amount of memory reserved for the heap.
V8_EXPORT_PRIVATE size_t MaxReserved();
size_t MaxSemiSpaceSize() { return max_semi_space_size_; }
size_t InitialSemiSpaceSize() { return initial_semispace_size_; }
size_t MaxOldGenerationSize() { return max_old_generation_size_; }
V8_EXPORT_PRIVATE static size_t HeapSizeFromPhysicalMemory(
uint64_t physical_memory);
V8_EXPORT_PRIVATE static void GenerationSizesFromHeapSize(
size_t heap_size, size_t* young_generation_size,
size_t* old_generation_size);
V8_EXPORT_PRIVATE static size_t YoungGenerationSizeFromOldGenerationSize(
size_t old_generation_size);
V8_EXPORT_PRIVATE static size_t YoungGenerationSizeFromSemiSpaceSize(
size_t semi_space_size);
V8_EXPORT_PRIVATE static size_t SemiSpaceSizeFromYoungGenerationSize(
size_t young_generation_size);
V8_EXPORT_PRIVATE static size_t MinYoungGenerationSize();
V8_EXPORT_PRIVATE static size_t MinOldGenerationSize();
V8_EXPORT_PRIVATE static size_t MaxOldGenerationSize(
uint64_t physical_memory);
// Returns the capacity of the heap in bytes w/o growing. Heap grows when
// more spaces are needed until it reaches the limit.
size_t Capacity();
// Returns the capacity of the old generation.
V8_EXPORT_PRIVATE size_t OldGenerationCapacity();
// Returns the amount of memory currently held alive by the unmapper.
size_t CommittedMemoryOfUnmapper();
// Returns the amount of memory currently committed for the heap.
size_t CommittedMemory();
// Returns the amount of memory currently committed for the old space.
size_t CommittedOldGenerationMemory();
// Returns the amount of executable memory currently committed for the heap.
size_t CommittedMemoryExecutable();
// Returns the amount of phyical memory currently committed for the heap.
size_t CommittedPhysicalMemory();
// Returns the maximum amount of memory ever committed for the heap.
size_t MaximumCommittedMemory() { return maximum_committed_; }
// Updates the maximum committed memory for the heap. Should be called
// whenever a space grows.
void UpdateMaximumCommitted();
// Returns the available bytes in space w/o growing.
// Heap doesn't guarantee that it can allocate an object that requires
// all available bytes. Check MaxHeapObjectSize() instead.
size_t Available();
// Returns of size of all objects residing in the heap.
V8_EXPORT_PRIVATE size_t SizeOfObjects();
void UpdateSurvivalStatistics(int start_new_space_size);
inline void IncrementPromotedObjectsSize(size_t object_size) {
promoted_objects_size_ += object_size;
inline size_t promoted_objects_size() { return promoted_objects_size_; }
inline void IncrementSemiSpaceCopiedObjectSize(size_t object_size) {
semi_space_copied_object_size_ += object_size;
inline size_t semi_space_copied_object_size() {
return semi_space_copied_object_size_;
inline size_t SurvivedYoungObjectSize() {
return promoted_objects_size_ + semi_space_copied_object_size_;
inline void IncrementNodesDiedInNewSpace() { nodes_died_in_new_space_++; }
inline void IncrementNodesCopiedInNewSpace() { nodes_copied_in_new_space_++; }
inline void IncrementNodesPromoted() { nodes_promoted_++; }
inline void IncrementYoungSurvivorsCounter(size_t survived) {
survived_last_scavenge_ = survived;
survived_since_last_expansion_ += survived;
inline uint64_t OldGenerationObjectsAndPromotedExternalMemorySize() {
return OldGenerationSizeOfObjects() + PromotedExternalMemorySize();
inline void UpdateNewSpaceAllocationCounter();
inline size_t NewSpaceAllocationCounter();
// This should be used only for testing.
void set_new_space_allocation_counter(size_t new_value) {
new_space_allocation_counter_ = new_value;
void UpdateOldGenerationAllocationCounter() {
old_generation_allocation_counter_at_last_gc_ =
old_generation_size_at_last_gc_ = 0;
size_t OldGenerationAllocationCounter() {
return old_generation_allocation_counter_at_last_gc_ +
size_t EmbedderAllocationCounter() const;
// This should be used only for testing.
void set_old_generation_allocation_counter_at_last_gc(size_t new_value) {
old_generation_allocation_counter_at_last_gc_ = new_value;
size_t PromotedSinceLastGC() {
size_t old_generation_size = OldGenerationSizeOfObjects();
DCHECK_GE(old_generation_size, old_generation_size_at_last_gc_);
return old_generation_size - old_generation_size_at_last_gc_;
// This is called by the sweeper when it discovers more free space
// than expected at the end of the preceding GC.
void NotifyRefinedOldGenerationSize(size_t decreased_bytes) {
if (old_generation_size_at_last_gc_ != 0) {
// OldGenerationSizeOfObjects() is now smaller by |decreased_bytes|.
// Adjust old_generation_size_at_last_gc_ too, so that PromotedSinceLastGC
// continues to increase monotonically, rather than decreasing here.
DCHECK_GE(old_generation_size_at_last_gc_, decreased_bytes);
old_generation_size_at_last_gc_ -= decreased_bytes;
int gc_count() const { return gc_count_; }
bool is_current_gc_forced() const { return is_current_gc_forced_; }
// Returns the size of objects residing in non-new spaces.
// Excludes external memory held by those objects.
V8_EXPORT_PRIVATE size_t OldGenerationSizeOfObjects();
V8_EXPORT_PRIVATE size_t GlobalSizeOfObjects();
// We allow incremental marking to overshoot the V8 and global allocation
// limit for performace reasons. If the overshoot is too large then we are
// more eager to finalize incremental marking.
bool AllocationLimitOvershotByLargeMargin();
// ===========================================================================
// Prologue/epilogue callback methods.========================================
// ===========================================================================
void AddGCPrologueCallback(v8::Isolate::GCCallbackWithData callback,
GCType gc_type_filter, void* data);
void RemoveGCPrologueCallback(v8::Isolate::GCCallbackWithData callback,
void* data);
void AddGCEpilogueCallback(v8::Isolate::GCCallbackWithData callback,
GCType gc_type_filter, void* data);
void RemoveGCEpilogueCallback(v8::Isolate::GCCallbackWithData callback,
void* data);
void CallGCPrologueCallbacks(GCType gc_type, GCCallbackFlags flags);
void CallGCEpilogueCallbacks(GCType gc_type, GCCallbackFlags flags);
// ===========================================================================
// Allocation methods. =======================================================
// ===========================================================================
// Creates a filler object and returns a heap object immediately after it.
PrecedeWithFiller(HeapObject object, int filler_size);
// Creates a filler object if needed for alignment and returns a heap object
// immediately after it. If any space is left after the returned object,
// another filler object is created so the over allocated memory is iterable.
AlignWithFiller(HeapObject object, int object_size, int allocation_size,
AllocationAlignment alignment);
// ===========================================================================
// ArrayBuffer tracking. =====================================================
// ===========================================================================
// TODO(gc): API usability: encapsulate mutation of JSArrayBuffer::is_external
// in the registration/unregistration APIs. Consider dropping the "New" from
// "RegisterNewArrayBuffer" because one can re-register a previously
// unregistered buffer, too, and the name is confusing.
void RegisterNewArrayBuffer(JSArrayBuffer buffer);
void UnregisterArrayBuffer(JSArrayBuffer buffer);
// ===========================================================================
// Allocation site tracking. =================================================
// ===========================================================================
// Updates the AllocationSite of a given {object}. The entry (including the
// count) is cached on the local pretenuring feedback.
inline void UpdateAllocationSite(
Map map, HeapObject object, PretenuringFeedbackMap* pretenuring_feedback);
// Merges local pretenuring feedback into the global one. Note that this
// method needs to be called after evacuation, as allocation sites may be
// evacuated and this method resolves forward pointers accordingly.
void MergeAllocationSitePretenuringFeedback(
const PretenuringFeedbackMap& local_pretenuring_feedback);
// ===========================================================================
// Allocation tracking. ======================================================
// ===========================================================================
// Adds {new_space_observer} to new space and {observer} to any other space.
void AddAllocationObserversToAllSpaces(
AllocationObserver* observer, AllocationObserver* new_space_observer);
// Removes {new_space_observer} from new space and {observer} from any other
// space.
void RemoveAllocationObserversFromAllSpaces(
AllocationObserver* observer, AllocationObserver* new_space_observer);
bool allocation_step_in_progress() { return allocation_step_in_progress_; }
void set_allocation_step_in_progress(bool val) {
allocation_step_in_progress_ = val;
// ===========================================================================
// Heap object allocation tracking. ==========================================
// ===========================================================================
void AddHeapObjectAllocationTracker(HeapObjectAllocationTracker* tracker);
void RemoveHeapObjectAllocationTracker(HeapObjectAllocationTracker* tracker);
bool has_heap_object_allocation_tracker() const {
return !allocation_trackers_.empty();
// ===========================================================================
// Retaining path tracking. ==================================================
// ===========================================================================
// Adds the given object to the weak table of retaining path targets.
// On each GC if the marker discovers the object, it will print the retaining
// path. This requires --track-retaining-path flag.
void AddRetainingPathTarget(Handle<HeapObject> object,
RetainingPathOption option);
// ===========================================================================
// Stack frame support. ======================================================
// ===========================================================================
// Returns the Code object for a given interior pointer.
Code GcSafeFindCodeForInnerPointer(Address inner_pointer);
// Returns true if {addr} is contained within {code} and false otherwise.
// Mostly useful for debugging.
bool GcSafeCodeContains(Code code, Address addr);
// Casts a heap object to a code object and checks if the inner_pointer is
// within the object.
Code GcSafeCastToCode(HeapObject object, Address inner_pointer);
// Returns the map of an object. Can be used during garbage collection, i.e.
// it supports a forwarded map. Fails if the map is not the code map.
Map GcSafeMapOfCodeSpaceObject(HeapObject object);
// =============================================================================
// Verify the heap is in its normal state before or after a GC.
V8_EXPORT_PRIVATE void Verify();
// Verify the read-only heap after all read-only heap objects have been
// created.
void VerifyReadOnlyHeap();
void VerifyRememberedSetFor(HeapObject object);
void set_allocation_timeout(int timeout) { allocation_timeout_ = timeout; }
#ifdef DEBUG
void VerifyCountersAfterSweeping();
void VerifyCountersBeforeConcurrentSweeping();
void Print();
void PrintHandles();
// Report code statistics.
void ReportCodeStatistics(const char* title);
void* GetRandomMmapAddr() {
void* result = v8::internal::GetRandomMmapAddr();
// The Darwin kernel [as of macOS 10.12.5] does not clean up page
// directory entries [PDE] created from mmap or mach_vm_allocate, even
// after the region is destroyed. Using a virtual address space that is
// too large causes a leak of about 1 wired [can never be paged out] page
// per call to mmap(). The page is only reclaimed when the process is
// killed. Confine the hint to a 32-bit section of the virtual address
// space. See
uintptr_t offset =
reinterpret_cast<uintptr_t>(v8::internal::GetRandomMmapAddr()) &
result = reinterpret_cast<void*>(mmap_region_base_ + offset);
#endif // V8_OS_MACOSX
#endif // V8_TARGET_ARCH_X64
return result;
static const char* GarbageCollectionReasonToString(
GarbageCollectionReason gc_reason);
// Calculates the nof entries for the full sized number to string cache.
inline int MaxNumberToStringCacheSize() const;
class SkipStoreBufferScope;
using ExternalStringTableUpdaterCallback = String (*)(Heap* heap,
FullObjectSlot pointer);
// External strings table is a place where all external strings are
// registered. We need to keep track of such strings to properly
// finalize them.
class ExternalStringTable {
explicit ExternalStringTable(Heap* heap) : heap_(heap) {}
// Registers an external string.
inline void AddString(String string);
bool Contains(String string);
void IterateAll(RootVisitor* v);
void IterateYoung(RootVisitor* v);
void PromoteYoung();
// Restores internal invariant and gets rid of collected strings. Must be
// called after each Iterate*() that modified the strings.
void CleanUpAll();
void CleanUpYoung();
// Finalize all registered external strings and clear tables.
void TearDown();
void UpdateYoungReferences(
Heap::ExternalStringTableUpdaterCallback updater_func);
void UpdateReferences(
Heap::ExternalStringTableUpdaterCallback updater_func);
void Verify();
void VerifyYoung();
Heap* const heap_;
// To speed up scavenge collections young string are kept separate from old
// strings.
std::vector<Object> young_strings_;
std::vector<Object> old_strings_;
struct StrongRootsList;
struct StringTypeTable {
InstanceType type;
int size;
RootIndex index;
struct ConstantStringTable {
const char* contents;
RootIndex index;
struct StructTable {
InstanceType type;
int size;
RootIndex index;
struct GCCallbackTuple {
GCCallbackTuple(v8::Isolate::GCCallbackWithData callback, GCType gc_type,
void* data)
: callback(callback), gc_type(gc_type), data(data) {}
bool operator==(const GCCallbackTuple& other) const;
GCCallbackTuple& operator=(const GCCallbackTuple& other) V8_NOEXCEPT;
v8::Isolate::GCCallbackWithData callback;
GCType gc_type;
void* data;
static const int kInitialStringTableSize = StringTable::kMinCapacity;
static const int kInitialEvalCacheSize = 64;
static const int kInitialNumberStringCacheSize = 256;
static const int kRememberedUnmappedPages = 128;
static const StringTypeTable string_type_table[];
static const ConstantStringTable constant_string_table[];
static const StructTable struct_table[];
static const int kYoungSurvivalRateHighThreshold = 90;
static const int kYoungSurvivalRateAllowedDeviation = 15;
static const int kOldSurvivalRateLowThreshold = 10;
static const int kMaxMarkCompactsInIdleRound = 7;
static const int kIdleScavengeThreshold = 5;
static const int kInitialFeedbackCapacity = 256;
static bool IsRegularObjectAllocation(AllocationType allocation) {
return AllocationType::kYoung == allocation ||
AllocationType::kOld == allocation;
static size_t DefaultGetExternallyAllocatedMemoryInBytesCallback() {
return 0;
#define ROOT_ACCESSOR(type, name, CamelName) inline void set_##name(type value);
StoreBuffer* store_buffer() { return store_buffer_.get(); }
void set_current_gc_flags(int flags) {
current_gc_flags_ = flags;
inline bool ShouldReduceMemory() const {
return (current_gc_flags_ & kReduceMemoryFootprintMask) != 0;
int NumberOfScavengeTasks();
// Checks whether a global GC is necessary
GarbageCollector SelectGarbageCollector(AllocationSpace space,
const char** reason);
// Make sure there is a filler value behind the top of the new space
// so that the GC does not confuse some unintialized/stale memory
// with the allocation memento of the object at the top
void EnsureFillerObjectAtTop();
// Ensure that we have swept all spaces in such a way that we can iterate
// over all objects. May cause a GC.
void MakeHeapIterable();
// Performs garbage collection
// Returns whether there is a chance another major GC could
// collect more garbage.
bool PerformGarbageCollection(
GarbageCollector collector,
const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags);
inline void UpdateOldSpaceLimits();
bool CreateInitialMaps();
void CreateInternalAccessorInfoObjects();
void CreateInitialObjects();
// Commits from space if it is uncommitted.
void EnsureFromSpaceIsCommitted();
// Uncommit unused semi space.
V8_EXPORT_PRIVATE bool UncommitFromSpace();
// Fill in bogus values in from space
void ZapFromSpace();
// Zaps the memory of a code object.
V8_EXPORT_PRIVATE void ZapCodeObject(Address start_address,
int size_in_bytes);
// Range write barrier implementation.
template <int kModeMask, typename TSlot>
V8_INLINE void WriteBarrierForRangeImpl(MemoryChunk* source_page,
HeapObject object, TSlot start_slot,
TSlot end_slot);
// Deopts all code that contains allocation instruction which are tenured or
// not tenured. Moreover it clears the pretenuring allocation site statistics.
void ResetAllAllocationSitesDependentCode(AllocationType allocation);
// Evaluates local pretenuring for the old space and calls
// ResetAllTenuredAllocationSitesDependentCode if too many objects died in
// the old space.
void EvaluateOldSpaceLocalPretenuring(uint64_t size_of_objects_before_gc);
// Record statistics after garbage collection.
void ReportStatisticsAfterGC();
// Flush the number to string cache.
void FlushNumberStringCache();
void ConfigureInitialOldGenerationSize();
double ComputeMutatorUtilization(const char* tag, double mutator_speed,
double gc_speed);
bool HasLowYoungGenerationAllocationRate();
bool HasLowOldGenerationAllocationRate();
bool HasLowEmbedderAllocationRate();
void ReduceNewSpaceSize();
GCIdleTimeHeapState ComputeHeapState();
bool PerformIdleTimeAction(GCIdleTimeAction action,
GCIdleTimeHeapState heap_state,
double deadline_in_ms);
void IdleNotificationEpilogue(GCIdleTimeAction action,
GCIdleTimeHeapState heap_state, double start_ms,
double deadline_in_ms);
int NextAllocationTimeout(int current_timeout = 0);
inline void UpdateAllocationsHash(HeapObject object);
inline void UpdateAllocationsHash(uint32_t value);
void PrintAllocationsHash();
void PrintMaxMarkingLimitReached();
void PrintMaxNewSpaceSizeReached();
int NextStressMarkingLimit();
void AddToRingBuffer(const char* string);
void GetFromRingBuffer(char* buffer);
void CompactRetainedMaps(WeakArrayList retained_maps);
void CollectGarbageOnMemoryPressure();
void EagerlyFreeExternalMemory();
bool InvokeNearHeapLimitCallback();
void ComputeFastPromotionMode();
// Attempt to over-approximate the weak closure by marking object groups and
// implicit references from global handles, but don't atomically complete
// marking. If we continue to mark incrementally, we might have marked
// objects that die later.
void FinalizeIncrementalMarkingIncrementally(
GarbageCollectionReason gc_reason);
// Returns the timer used for a given GC type.
// - GCScavenger: young generation GC
// - GCCompactor: full GC
// - GCFinalzeMC: finalization of incremental full GC
// - GCFinalizeMCReduceMemory: finalization of incremental full GC with
// memory reduction
TimedHistogram* GCTypeTimer(GarbageCollector collector);
TimedHistogram* GCTypePriorityTimer(GarbageCollector collector);
// ===========================================================================
// Pretenuring. ==============================================================
// ===========================================================================
// Pretenuring decisions are made based on feedback collected during new space
// evacuation. Note that between feedback collection and calling this method
// object in old space must not move.
void ProcessPretenuringFeedback();
// Removes an entry from the global pretenuring storage.
void RemoveAllocationSitePretenuringFeedback(AllocationSite site);
// ===========================================================================
// Actual GC. ================================================================
// ===========================================================================
// Code that should be run before and after each GC. Includes some
// reporting/verification activities when compiled with DEBUG set.
void GarbageCollectionPrologue();
void GarbageCollectionEpilogue();
// Performs a major collection in the whole heap.
void MarkCompact();
// Performs a minor collection of just the young generation.
void MinorMarkCompact();
// Code to be run before and after mark-compact.
void MarkCompactPrologue();
void MarkCompactEpilogue();
// Performs a minor collection in new generation.
void Scavenge();
void EvacuateYoungGeneration();
void UpdateYoungReferencesInExternalStringTable(
ExternalStringTableUpdaterCallback updater_func);
void UpdateReferencesInExternalStringTable(
ExternalStringTableUpdaterCallback updater_func);
void ProcessAllWeakReferences(WeakObjectRetainer* retainer);
void ProcessYoungWeakReferences(WeakObjectRetainer* retainer);
void ProcessNativeContexts(WeakObjectRetainer* retainer);
void ProcessAllocationSites(WeakObjectRetainer* retainer);
void ProcessWeakListRoots(WeakObjectRetainer* retainer);
// ===========================================================================
// GC statistics. ============================================================
// ===========================================================================
inline size_t OldGenerationSpaceAvailable() {
if (old_generation_allocation_limit_ <=
return 0;
return old_generation_allocation_limit_ -
void UpdateTotalGCTime(double duration);
bool MaximumSizeScavenge() { return maximum_size_scavenges_ > 0; }
bool IsIneffectiveMarkCompact(size_t old_generation_size,
double mutator_utilization);
void CheckIneffectiveMarkCompact(size_t old_generation_size,
double mutator_utilization);
inline void IncrementExternalBackingStoreBytes(ExternalBackingStoreType type,
size_t amount);
inline void DecrementExternalBackingStoreBytes(ExternalBackingStoreType type,
size_t amount);
// ===========================================================================
// Growing strategy. =========================================================
// ===========================================================================
MemoryReducer* memory_reducer() { return memory_reducer_.get(); }
// For some webpages RAIL mode does not switch from PERFORMANCE_LOAD.
// This constant limits the effect of load RAIL mode on GC.
// The value is arbitrary and chosen as the largest load time observed in
// v8 browsing benchmarks.
static const int kMaxLoadTimeMs = 7000;
bool ShouldOptimizeForLoadTime();
size_t old_generation_allocation_limit() const {
return old_generation_allocation_limit_;
size_t global_allocation_limit() const { return global_allocation_limit_; }
bool always_allocate() { return always_allocate_scope_count_ != 0; }
V8_EXPORT_PRIVATE bool CanExpandOldGeneration(size_t size);
bool ShouldExpandOldGenerationOnSlowAllocation();
HeapGrowingMode CurrentHeapGrowingMode();
enum class IncrementalMarkingLimit { kNoLimit, kSoftLimit, kHardLimit };
IncrementalMarkingLimit IncrementalMarkingLimitReached();
bool UseGlobalMemoryScheduling() const {
return FLAG_global_gc_scheduling && local_embedder_heap_tracer();
size_t GlobalMemoryAvailable();
void RecomputeLimits(GarbageCollector collector);
// ===========================================================================
// Idle notification. ========================================================
// ===========================================================================
bool RecentIdleNotificationHappened();
void ScheduleIdleScavengeIfNeeded(int bytes_allocated);
// ===========================================================================
// Allocation methods. =======================================================
// ===========================================================================
// Allocates a JS Map in the heap.
V8_WARN_UNUSED_RESULT AllocationResult
AllocateMap(InstanceType instance_type, int instance_size,
ElementsKind elements_kind = TERMINAL_FAST_ELEMENTS_KIND,
int inobject_properties = 0);
// Allocate an uninitialized object. The memory is non-executable if the
// hardware and OS allow. This is the single choke-point for allocations
// performed by the runtime and should not be bypassed (to extend this to
// inlined allocations, use the Heap::DisableInlineAllocation() support).
V8_WARN_UNUSED_RESULT inline AllocationResult AllocateRaw(
int size_in_bytes, AllocationType allocation,
AllocationAlignment aligment = kWordAligned);
// This method will try to perform an allocation of a given size of a given
// AllocationType. If the allocation fails, a regular full garbage collection
// is triggered and the allocation is retried. This is performed multiple
// times. If after that retry procedure the allocation still fails nullptr is
// returned.
HeapObject AllocateRawWithLightRetry(
int size, AllocationType allocation,
AllocationAlignment alignment = kWordAligned);
// This method will try to perform an allocation of a given size of a given
// AllocationType. If the allocation fails, a regular full garbage collection
// is triggered and the allocation is retried. This is performed multiple
// times. If after that retry procedure the allocation still fails a "hammer"
// garbage collection is triggered which tries to significantly reduce memory.
// If the allocation still fails after that a fatal error is thrown.
HeapObject AllocateRawWithRetryOrFail(
int size, AllocationType allocation,
AllocationAlignment alignment = kWordAligned);
HeapObject AllocateRawCodeInLargeObjectSpace(int size);
// Allocates a heap object based on the map.
V8_WARN_UNUSED_RESULT AllocationResult Allocate(Map map,
AllocationType allocation);
// Takes a code object and checks if it is on memory which is not subject to
// compaction. This method will return a new code object on an immovable
// memory location if the original code object was movable.
HeapObject EnsureImmovableCode(HeapObject heap_object, int object_size);
// Allocates a partial map for bootstrapping.
V8_WARN_UNUSED_RESULT AllocationResult
AllocatePartialMap(InstanceType instance_type, int instance_size);
void FinalizePartialMap(Map map);
// Allocate empty fixed typed array of given type.
V8_WARN_UNUSED_RESULT AllocationResult
AllocateEmptyFixedTypedArray(ExternalArrayType array_type);
void set_force_oom(bool value) { force_oom_ = value; }
// ===========================================================================
// Retaining path tracing ====================================================
// ===========================================================================
void AddRetainer(HeapObject retainer, HeapObject object);
void AddEphemeronRetainer(HeapObject retainer, HeapObject object);
void AddRetainingRoot(Root root, HeapObject object);
// Returns true if the given object is a target of retaining path tracking.
// Stores the option corresponding to the object in the provided *option.
bool IsRetainingPathTarget(HeapObject object, RetainingPathOption* option);
void PrintRetainingPath(HeapObject object, RetainingPathOption option);
#ifdef DEBUG
V8_EXPORT_PRIVATE void IncrementObjectCounters();
#endif // DEBUG
// The amount of memory that has been freed concurrently.
std::atomic<intptr_t> external_memory_concurrently_freed_{0};
// This can be calculated directly from a pointer to the heap; however, it is
// more expedient to get at the isolate directly from within Heap methods.
Isolate* isolate_ = nullptr;
// These limits are initialized in Heap::ConfigureHeap based on the resource
// constraints and flags.
size_t code_range_size_ = 0;
size_t max_semi_space_size_ = 0;
size_t initial_semispace_size_ = 0;
// Full garbage collections can be skipped if the old generation size
// is below this threshold.
size_t min_old_generation_size_ = 0;
// If the old generation size exceeds this limit, then V8 will
// crash with out-of-memory error.
size_t max_old_generation_size_ = 0;
// TODO(mlippautz): Clarify whether this should take some embedder
// configurable limit into account.
size_t min_global_memory_size_ = 0;
size_t max_global_memory_size_ = 0;
size_t initial_max_old_generation_size_ = 0;
size_t initial_max_old_generation_size_threshold_ = 0;
size_t initial_old_generation_size_ = 0;
bool old_generation_size_configured_ = false;
size_t maximum_committed_ = 0;
size_t old_generation_capacity_after_bootstrap_ = 0;
// Backing store bytes (array buffers and external strings).
std::atomic<size_t> backing_store_bytes_{0};
// For keeping track of how much data has survived
// scavenge since last new space expansion.
size_t survived_since_last_expansion_ = 0;
// ... and since the last scavenge.
size_t survived_last_scavenge_ = 0;
// This is not the depth of nested AlwaysAllocateScope's but rather a single
// count, as scopes can be acquired from multiple tasks (read: threads).
std::atomic<size_t> always_allocate_scope_count_{0};
// Stores the memory pressure level that set by MemoryPressureNotification
// and reset by a mark-compact garbage collection.
std::atomic<MemoryPressureLevel> memory_pressure_level_;
std::vector<std::pair<v8::NearHeapLimitCallback, void*> >
// For keeping track of context disposals.
int contexts_disposed_ = 0;
// The length of the retained_maps array at the time of context disposal.
// This separates maps in the retained_maps array that were created before
// and after context disposal.
int number_of_disposed_maps_ = 0;
NewSpace* new_space_ = nullptr;
OldSpace* old_space_ = nullptr;
CodeSpace* code_space_ = nullptr;
MapSpace* map_space_ = nullptr;
LargeObjectSpace* lo_space_ = nullptr;
CodeLargeObjectSpace* code_lo_space_ = nullptr;
NewLargeObjectSpace* new_lo_space_ = nullptr;
ReadOnlySpace* read_only_space_ = nullptr;
// Map from the space id to the space.
Space* space_[LAST_SPACE + 1];
// Determines whether code space is write-protected. This is essentially a
// race-free copy of the {FLAG_write_protect_code_memory} flag.
bool write_protect_code_memory_ = false;
// Holds the number of open CodeSpaceMemoryModificationScopes.
uintptr_t code_space_memory_modification_scope_depth_ = 0;
HeapState gc_state_ = NOT_IN_GC;
int gc_post_processing_depth_ = 0;
// Returns the amount of external memory registered since last global gc.
V8_EXPORT_PRIVATE uint64_t PromotedExternalMemorySize();
// How many "runtime allocations" happened.
uint32_t allocations_count_ = 0;
// Running hash over allocations performed.
uint32_t raw_allocations_hash_ = 0;
// Starts marking when stress_marking_percentage_% of the marking start limit
// is reached.
int stress_marking_percentage_ = 0;
// Observer that causes more frequent checks for reached incremental marking
// limit.
AllocationObserver* stress_marking_observer_ = nullptr;
// Observer that can cause early scavenge start.
StressScavengeObserver* stress_scavenge_observer_ = nullptr;
bool allocation_step_in_progress_ = false;
// The maximum percent of the marking limit reached wihout causing marking.
// This is tracked when specyfing --fuzzer-gc-analysis.
double max_marking_limit_reached_ = 0.0;
// How many mark-sweep collections happened.
unsigned int ms_count_ = 0;
// How many gc happened.
unsigned int gc_count_ = 0;
// The number of Mark-Compact garbage collections that are considered as
// ineffective. See IsIneffectiveMarkCompact() predicate.
int consecutive_ineffective_mark_compacts_ = 0;
static const uintptr_t kMmapRegionMask = 0xFFFFFFFFu;
uintptr_t mmap_region_base_ = 0;
// For post mortem debugging.
int remembered_unmapped_pages_index_ = 0;
Address remembered_unmapped_pages_[kRememberedUnmappedPages];
// Limit that triggers a global GC on the next (normally caused) GC. This
// is checked when we have already decided to do a GC to help determine
// which collector to invoke, before expanding a paged space in the old
// generation and on every allocation in large object space.
size_t old_generation_allocation_limit_ = 0;
size_t global_allocation_limit_ = 0;
// Indicates that inline bump-pointer allocation has been globally disabled
// for all spaces. This is used to disable allocations in generated code.
bool inline_allocation_disabled_ = false;
// Weak list heads, threaded through the objects.
// List heads are initialized lazily and contain the undefined_value at start.
Object native_contexts_list_;
Object allocation_sites_list_;
std::vector<GCCallbackTuple> gc_epilogue_callbacks_;
std::vector<GCCallbackTuple> gc_prologue_callbacks_;
GetExternallyAllocatedMemoryInBytesCallback external_memory_callback_;
int deferred_counters_[v8::Isolate::kUseCounterFeatureCount];
size_t promoted_objects_size_ = 0;
double promotion_ratio_ = 0.0;
double promotion_rate_ = 0.0;
size_t semi_space_copied_object_size_ = 0;
size_t previous_semi_space_copied_object_size_ = 0;
double semi_space_copied_rate_ = 0.0;
int nodes_died_in_new_space_ = 0;
int nodes_copied_in_new_space_ = 0;
int nodes_promoted_ = 0;
// This is the pretenuring trigger for allocation sites that are in maybe
// tenure state. When we switched to the maximum new space size we deoptimize
// the code that belongs to the allocation site and derive the lifetime
// of the allocation site.
unsigned int maximum_size_scavenges_ = 0;
// Total time spent in GC.
double total_gc_time_ms_;
// Last time an idle notification happened.
double last_idle_notification_time_ = 0.0;
// Last time a garbage collection happened.
double last_gc_time_ = 0.0;
std::unique_ptr<GCTracer> tracer_;
std::unique_ptr<MarkCompactCollector> mark_compact_collector_;
MinorMarkCompactCollector* minor_mark_compact_collector_ = nullptr;
std::unique_ptr<ScavengerCollector> scavenger_collector_;
std::unique_ptr<ArrayBufferCollector> array_buffer_collector_;
std::unique_ptr<MemoryAllocator> memory_allocator_;
std::unique_ptr<StoreBuffer> store_buffer_;
std::unique_ptr<IncrementalMarking> incremental_marking_;
std::unique_ptr<ConcurrentMarking> concurrent_marking_;
std::unique_ptr<GCIdleTimeHandler> gc_idle_time_handler_;
std::unique_ptr<MemoryReducer> memory_reducer_;
std::unique_ptr<ObjectStats> live_object_stats_;
std::unique_ptr<ObjectStats> dead_object_stats_;
std::unique_ptr<ScavengeJob> scavenge_job_;
std::unique_ptr<AllocationObserver> idle_scavenge_observer_;
std::unique_ptr<LocalEmbedderHeapTracer> local_embedder_heap_tracer_;
StrongRootsList* strong_roots_list_ = nullptr;
// This counter is increased before each GC and never reset.
// To account for the bytes allocated since the last GC, use the
// NewSpaceAllocationCounter() function.
size_t new_space_allocation_counter_ = 0;
// This counter is increased before each GC and never reset. To
// account for the bytes allocated since the last GC, use the
// OldGenerationAllocationCounter() function.
size_t old_generation_allocation_counter_at_last_gc_ = 0;
// The size of objects in old generation after the last MarkCompact GC.
size_t old_generation_size_at_last_gc_ = 0;
// The feedback storage is used to store allocation sites (keys) and how often
// they have been visited (values) by finding a memento behind an object. The
// storage is only alive temporary during a GC. The invariant is that all
// pointers in this map are already fixed, i.e., they do not point to
// forwarding pointers.
PretenuringFeedbackMap global_pretenuring_feedback_;
char trace_ring_buffer_[kTraceRingBufferSize];
// Used as boolean.
uint8_t is_marking_flag_ = 0;
// If it's not full then the data is from 0 to ring_buffer_end_. If it's
// full then the data is from ring_buffer_end_ to the end of the buffer and
// from 0 to ring_buffer_end_.
bool ring_buffer_full_ = false;
size_t ring_buffer_end_ = 0;
// Flag is set when the heap has been configured. The heap can be repeatedly
// configured through the API until it is set up.
bool configured_ = false;
// Currently set GC flags that are respected by all GC components.
int current_gc_flags_ = Heap::kNoGCFlags;
// Currently set GC callback flags that are used to pass information between
// the embedder and V8's GC.
GCCallbackFlags current_gc_callback_flags_ =
bool is_current_gc_forced_ = false;
ExternalStringTable external_string_table_;
base::Mutex relocation_mutex_;
int gc_callbacks_depth_ = 0;
bool deserialization_complete_ = false;
bool fast_promotion_mode_ = false;
// Used for testing purposes.
bool force_oom_ = false;
bool delay_sweeper_tasks_for_testing_ = false;
HeapObject pending_layout_change_object_;
base::Mutex unprotected_memory_chunks_mutex_;
std::unordered_set<MemoryChunk*> unprotected_memory_chunks_;
bool unprotected_memory_chunks_registry_enabled_ = false;
// If the --gc-interval flag is set to a positive value, this
// variable holds the value indicating the number of allocations
// remain until the next failure and garbage collection.
int allocation_timeout_ = 0;
std::map<HeapObject, HeapObject, Object::Comparer> retainer_;
std::map<HeapObject, Root, Object::Comparer> retaining_root_;
// If an object is retained by an ephemeron, then the retaining key of the
// ephemeron is stored in this map.
std::map<HeapObject, HeapObject, Object::Comparer> ephemeron_retainer_;
// For each index inthe retaining_path_targets_ array this map
// stores the option of the corresponding target.
std::map<int, RetainingPathOption> retaining_path_target_option_;
std::vector<HeapObjectAllocationTracker*> allocation_trackers_;
// Classes in "heap" can be friends.
friend class AlwaysAllocateScope;
friend class ArrayBufferCollector;
friend class ConcurrentMarking;
friend class GCCallbacksScope;
friend class GCTracer;
friend class HeapObjectIterator;
friend class IdleScavengeObserver;
friend class IncrementalMarking;
friend class IncrementalMarkingJob;
friend class LargeObjectSpace;
template <FixedArrayVisitationMode fixed_array_mode,
TraceRetainingPathMode retaining_path_mode, typename MarkingState>
friend class MarkingVisitor;
friend class MarkCompactCollector;
friend class MarkCompactCollectorBase;
friend class MinorMarkCompactCollector;
friend class NewLargeObjectSpace;
friend class NewSpace;
friend class ObjectStatsCollector;
friend class Page;
friend class PagedSpace;
friend class ReadOnlyRoots;
friend class Scavenger;
friend class ScavengerCollector;
friend class Space;
friend class StoreBuffer;
friend class Sweeper;
friend class heap::TestMemoryAllocatorScope;
// The allocator interface.
friend class Factory;
// The Isolate constructs us.
friend class Isolate;
// Used in cctest.
friend class heap::HeapTester;
class HeapStats {
static const int kStartMarker = 0xDECADE00;
static const int kEndMarker = 0xDECADE01;
intptr_t* start_marker; // 0
size_t* ro_space_size; // 1
size_t* ro_space_capacity; // 2
size_t* new_space_size; // 3
size_t* new_space_capacity; // 4
size_t* old_space_size; // 5
size_t* old_space_capacity; // 6
size_t* code_space_size; // 7
size_t* code_space_capacity; // 8
size_t* map_space_size; // 9
size_t* map_space_capacity; // 10
size_t* lo_space_size; // 11
size_t* code_lo_space_size; // 12
size_t* global_handle_count; // 13
size_t* weak_global_handle_count; // 14
size_t* pending_global_handle_count; // 15
size_t* near_death_global_handle_count; // 16
size_t* free_global_handle_count; // 17
size_t* memory_allocator_size; // 18
size_t* memory_allocator_capacity; // 19
size_t* malloced_memory; // 20
size_t* malloced_peak_memory; // 21
size_t* objects_per_type; // 22
size_t* size_per_type; // 23
int* os_error; // 24
char* last_few_messages; // 25
char* js_stacktrace; // 26
intptr_t* end_marker; // 27
class AlwaysAllocateScope {
explicit inline AlwaysAllocateScope(Heap* heap);
explicit inline AlwaysAllocateScope(Isolate* isolate);
inline ~AlwaysAllocateScope();
Heap* heap_;
// The CodeSpaceMemoryModificationScope can only be used by the main thread.
class CodeSpaceMemoryModificationScope {
explicit inline CodeSpaceMemoryModificationScope(Heap* heap);
inline ~CodeSpaceMemoryModificationScope();
Heap* heap_;
// The CodePageCollectionMemoryModificationScope can only be used by the main
// thread. It will not be enabled if a CodeSpaceMemoryModificationScope is
// already active.
class CodePageCollectionMemoryModificationScope {
explicit inline CodePageCollectionMemoryModificationScope(Heap* heap);
inline ~CodePageCollectionMemoryModificationScope();
Heap* heap_;
// The CodePageMemoryModificationScope does not check if tansitions to
// writeable and back to executable are actually allowed, i.e. the MemoryChunk
// was registered to be executable. It can be used by concurrent threads.
class CodePageMemoryModificationScope {
explicit inline CodePageMemoryModificationScope(MemoryChunk* chunk);
inline ~CodePageMemoryModificationScope();
MemoryChunk* chunk_;
bool scope_active_;
// Disallow any GCs inside this scope, as a relocation of the underlying
// object would change the {MemoryChunk} that this scope targets.
// Visitor class to verify interior pointers in spaces that do not contain
// or care about intergenerational references. All heap object pointers have to
// point into the heap to a location that has a map pointer at its first word.
// Caveat: Heap::Contains is an approximation because it can return true for
// objects in a heap space but above the allocation pointer.
class VerifyPointersVisitor : public ObjectVisitor, public RootVisitor {
explicit VerifyPointersVisitor(Heap* heap) : heap_(heap) {}
void VisitPointers(HeapObject host, ObjectSlot start,
ObjectSlot end) override;
void VisitPointers(HeapObject host, MaybeObjectSlot start,
MaybeObjectSlot end) override;
void VisitCodeTarget(Code host, RelocInfo* rinfo) override;
void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override;
void VisitRootPointers(Root root, const char* description,
FullObjectSlot start, FullObjectSlot end) override;
V8_INLINE void VerifyHeapObjectImpl(HeapObject heap_object);
template <typename TSlot>
V8_INLINE void VerifyPointersImpl(TSlot start, TSlot end);
virtual void VerifyPointers(HeapObject host, MaybeObjectSlot start,
MaybeObjectSlot end);
Heap* heap_;
// Verify that all objects are Smis.
class VerifySmisVisitor : public RootVisitor {
void VisitRootPointers(Root root, const char* description,
FullObjectSlot start, FullObjectSlot end) override;
// Space iterator for iterating over all the paged spaces of the heap: Map
// space, old space and code space. Returns each space in turn, and null when it
// is done.
class V8_EXPORT_PRIVATE PagedSpaceIterator {
explicit PagedSpaceIterator(Heap* heap) : heap_(heap), counter_(OLD_SPACE) {}
PagedSpace* Next();
Heap* heap_;
int counter_;
class V8_EXPORT_PRIVATE SpaceIterator : public Malloced {
explicit SpaceIterator(Heap* heap);
virtual ~SpaceIterator();
bool HasNext();
Space* Next();
Heap* heap_;
int current_space_; // from enum AllocationSpace.
// A HeapObjectIterator provides iteration over the entire non-read-only heap.
// It aggregates the specific iterators for the different spaces as these can
// only iterate over one space only.
// HeapObjectIterator ensures there is no allocation during its lifetime (using
// an embedded DisallowHeapAllocation instance).
// HeapObjectIterator can skip free list nodes (that is, de-allocated heap
// objects that still remain in the heap). As implementation of free nodes
// filtering uses GC marks, it can't be used during MS/MC GC phases. Also, it is
// forbidden to interrupt iteration in this mode, as this will leave heap
// objects marked (and thus, unusable).
// See ReadOnlyHeapObjectIterator if you need to iterate over read-only space
// objects, or CombinedHeapObjectIterator if you need to iterate over both
// heaps.
class V8_EXPORT_PRIVATE HeapObjectIterator {
enum HeapObjectsFiltering { kNoFiltering, kFilterUnreachable };
explicit HeapObjectIterator(Heap* heap,
HeapObjectsFiltering filtering = kNoFiltering);
HeapObject Next();
HeapObject NextObject();
Heap* heap_;
HeapObjectsFiltering filtering_;
HeapObjectsFilter* filter_;
// Space iterator for iterating all the spaces.
SpaceIterator* space_iterator_;
// Object iterator for the space currently being iterated.
std::unique_ptr<ObjectIterator> object_iterator_;
// Abstract base class for checking whether a weak object should be retained.
class WeakObjectRetainer {
virtual ~WeakObjectRetainer() = default;
// Return whether this object should be retained. If nullptr is returned the
// object has no references. Otherwise the address of the retained object
// should be returned as in some GC situations the object has been moved.
virtual Object RetainAs(Object object) = 0;
// -----------------------------------------------------------------------------
// Allows observation of allocations.
class AllocationObserver {
explicit AllocationObserver(intptr_t step_size)
: step_size_(step_size), bytes_to_next_step_(step_size) {
DCHECK_LE(kTaggedSize, step_size);
virtual ~AllocationObserver() = default;
// Called each time the observed space does an allocation step. This may be
// more frequently than the step_size we are monitoring (e.g. when there are
// multiple observers, or when page or space boundary is encountered.)
void AllocationStep(int bytes_allocated, Address soon_object, size_t size);
intptr_t step_size() const { return step_size_; }
intptr_t bytes_to_next_step() const { return bytes_to_next_step_; }
// Pure virtual method provided by the subclasses that gets called when at
// least step_size bytes have been allocated. soon_object is the address just
// allocated (but not yet initialized.) size is the size of the object as
// requested (i.e. w/o the alignment fillers). Some complexities to be aware
// of:
// 1) soon_object will be nullptr in cases where we end up observing an
// allocation that happens to be a filler space (e.g. page boundaries.)
// 2) size is the requested size at the time of allocation. Right-trimming
// may change the object size dynamically.
// 3) soon_object may actually be the first object in an allocation-folding
// group. In such a case size is the size of the group rather than the
// first object.
virtual void Step(int bytes_allocated, Address soon_object, size_t size) = 0;
// Subclasses can override this method to make step size dynamic.
virtual intptr_t GetNextStepSize() { return step_size_; }
intptr_t step_size_;
intptr_t bytes_to_next_step_;
friend class Space;
// -----------------------------------------------------------------------------
// Allows observation of heap object allocations.
class HeapObjectAllocationTracker {
virtual void AllocationEvent(Address addr, int size) = 0;
virtual void MoveEvent(Address from, Address to, int size) {}
virtual void UpdateObjectSizeEvent(Address addr, int size) {}
virtual ~HeapObjectAllocationTracker() = default;
template <typename T>
T ForwardingAddress(T heap_obj) {
MapWord map_word = heap_obj.map_word();
if (map_word.IsForwardingAddress()) {
return T::cast(map_word.ToForwardingAddress());
} else if (Heap::InFromPage(heap_obj)) {
return T();
} else {
// TODO(ulan): Support minor mark-compactor here.
return heap_obj;
} // namespace internal
} // namespace v8
#endif // V8_HEAP_HEAP_H_