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// 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/cancelable-task.h"
#include "src/heap/heap.h"
#include "src/heap/incremental-marking-job.h"
#include "src/heap/mark-compact.h"
namespace v8 {
namespace internal {
class HeapObject;
class MarkBit;
class Map;
class Object;
class PagedSpace;
enum class StepOrigin { kV8, kTask };
enum class WorklistToProcess { kAll, kBailout };
class V8_EXPORT_PRIVATE IncrementalMarking {
enum CompletionAction { GC_VIA_STACK_GUARD, NO_GC_VIA_STACK_GUARD };
using MarkingState = IncrementalMarkingState;
using MarkingState = MajorNonAtomicMarkingState;
using AtomicMarkingState = MajorAtomicMarkingState;
using NonAtomicMarkingState = MajorNonAtomicMarkingState;
class PauseBlackAllocationScope {
explicit PauseBlackAllocationScope(IncrementalMarking* marking)
: marking_(marking), paused_(false) {
if (marking_->black_allocation()) {
paused_ = true;
~PauseBlackAllocationScope() {
if (paused_) {
IncrementalMarking* marking_;
bool paused_;
// It's hard to know how much work the incremental marker should do to make
// progress in the face of the mutator creating new work for it. We start
// of at a moderate rate of work and gradually increase the speed of the
// incremental marker until it completes.
// Do some marking every time this much memory has been allocated or that many
// heavy (color-checking) write barriers have been invoked.
static const size_t kYoungGenerationAllocatedThreshold = 64 * KB;
static const size_t kOldGenerationAllocatedThreshold = 256 * KB;
static const size_t kMinStepSizeInBytes = 64 * KB;
static const int kStepSizeInMs = 1;
static const int kMaxStepSizeInMs = 5;
#ifndef DEBUG
static const intptr_t kActivationThreshold = 8 * MB;
static const intptr_t kActivationThreshold = 0;
static const AccessMode kAtomicity = AccessMode::ATOMIC;
static const AccessMode kAtomicity = AccessMode::NON_ATOMIC;
IncrementalMarking(Heap* heap,
MarkCompactCollector::MarkingWorklist* marking_worklist);
MarkingState* marking_state() { return &marking_state_; }
AtomicMarkingState* atomic_marking_state() { return &atomic_marking_state_; }
NonAtomicMarkingState* non_atomic_marking_state() {
return &non_atomic_marking_state_;
void NotifyLeftTrimming(HeapObject* from, HeapObject* to);
V8_INLINE void TransferColor(HeapObject* from, HeapObject* to) {
if (atomic_marking_state()->IsBlack(to)) {
if (atomic_marking_state()->IsGrey(from)) {
bool success = atomic_marking_state()->WhiteToGrey(to);
} else if (atomic_marking_state()->IsBlack(from)) {
bool success = atomic_marking_state()->WhiteToBlack(to);
State state() const {
DCHECK(state_ == STOPPED || FLAG_incremental_marking);
return state_;
bool should_hurry() const { return should_hurry_; }
void set_should_hurry(bool val) { should_hurry_ = val; }
bool finalize_marking_completed() const {
return finalize_marking_completed_;
void SetWeakClosureWasOverApproximatedForTesting(bool val) {
finalize_marking_completed_ = val;
inline bool IsStopped() const { return state() == STOPPED; }
inline bool IsSweeping() const { return state() == SWEEPING; }
inline bool IsMarking() const { return state() >= MARKING; }
inline bool IsMarkingIncomplete() const { return state() == MARKING; }
inline bool IsComplete() const { return state() == COMPLETE; }
inline bool IsReadyToOverApproximateWeakClosure() const {
return request_type_ == FINALIZATION && !finalize_marking_completed_;
inline bool NeedsFinalization() {
return IsMarking() &&
(request_type_ == FINALIZATION || request_type_ == COMPLETE_MARKING);
GCRequestType request_type() const { return request_type_; }
void reset_request_type() { request_type_ = NONE; }
bool CanBeActivated();
bool WasActivated();
void Start(GarbageCollectionReason gc_reason);
void FinalizeIncrementally();
void UpdateMarkingWorklistAfterScavenge();
void UpdateMarkedBytesAfterScavenge(size_t dead_bytes_in_new_space);
void Hurry();
void Finalize();
void Stop();
void FinalizeMarking(CompletionAction action);
void MarkingComplete(CompletionAction action);
void Epilogue();
// Performs incremental marking steps until deadline_in_ms is reached. It
// returns the remaining time that cannot be used for incremental marking
// anymore because a single step would exceed the deadline.
double AdvanceIncrementalMarking(double deadline_in_ms,
CompletionAction completion_action,
StepOrigin step_origin);
void FinalizeSweeping();
size_t Step(size_t bytes_to_process, CompletionAction action,
StepOrigin step_origin,
WorklistToProcess worklist_to_process = WorklistToProcess::kAll);
inline void RestartIfNotMarking();
static int RecordWriteFromCode(HeapObject* obj, Object** slot,
Isolate* isolate);
// Record a slot for compaction. Returns false for objects that are
// guaranteed to be rescanned or not guaranteed to survive.
// No slots in white objects should be recorded, as some slots are typed and
// cannot be interpreted correctly if the underlying object does not survive
// the incremental cycle (stays white).
V8_INLINE bool BaseRecordWrite(HeapObject* obj, Object* value);
V8_INLINE void RecordWrite(HeapObject* obj, Object** slot, Object* value);
V8_INLINE void RecordWriteIntoCode(Code* host, RelocInfo* rinfo,
Object* value);
V8_INLINE void RecordWrites(HeapObject* obj);
void RecordWriteSlow(HeapObject* obj, Object** slot, Object* value);
void RecordWriteIntoCodeSlow(Code* host, RelocInfo* rinfo, Object* value);
// Returns true if the function succeeds in transitioning the object
// from white to grey.
bool WhiteToGreyAndPush(HeapObject* obj);
// This function is used to color the object black before it undergoes an
// unsafe layout change. This is a part of synchronization protocol with
// the concurrent marker.
void MarkBlackAndPush(HeapObject* obj);
inline void SetOldSpacePageFlags(MemoryChunk* chunk) {
SetOldSpacePageFlags(chunk, IsMarking(), IsCompacting());
inline void SetNewSpacePageFlags(Page* chunk) {
SetNewSpacePageFlags(chunk, IsMarking());
bool IsCompacting() { return IsMarking() && is_compacting_; }
void ActivateGeneratedStub(Code* stub);
void NotifyIncompleteScanOfObject(int unscanned_bytes) {
unscanned_bytes_of_large_object_ = unscanned_bytes;
void ProcessBlackAllocatedObject(HeapObject* obj);
Heap* heap() const { return heap_; }
IncrementalMarkingJob* incremental_marking_job() {
return &incremental_marking_job_;
bool black_allocation() { return black_allocation_; }
void StartBlackAllocationForTesting() {
if (!black_allocation_) {
void AbortBlackAllocation();
MarkCompactCollector::MarkingWorklist* marking_worklist() const {
return marking_worklist_;
void Deactivate();
class Observer : public AllocationObserver {
Observer(IncrementalMarking& incremental_marking, intptr_t step_size)
: AllocationObserver(step_size),
incremental_marking_(incremental_marking) {}
void Step(int bytes_allocated, Address, size_t) override;
IncrementalMarking& incremental_marking_;
static void SetOldSpacePageFlags(MemoryChunk* chunk, bool is_marking,
bool is_compacting);
static void SetNewSpacePageFlags(MemoryChunk* chunk, bool is_marking);
void StartMarking();
void StartBlackAllocation();
void PauseBlackAllocation();
void FinishBlackAllocation();
void MarkRoots();
// Retain dying maps for <FLAG_retain_maps_for_n_gc> garbage collections to
// increase chances of reusing of map transition tree in future.
void RetainMaps();
void ActivateIncrementalWriteBarrier(PagedSpace* space);
void ActivateIncrementalWriteBarrier(NewSpace* space);
void ActivateIncrementalWriteBarrier();
void DeactivateIncrementalWriteBarrierForSpace(PagedSpace* space);
void DeactivateIncrementalWriteBarrierForSpace(NewSpace* space);
void DeactivateIncrementalWriteBarrier();
template <WorklistToProcess worklist_to_process = WorklistToProcess::kAll>
V8_INLINE intptr_t ProcessMarkingWorklist(
intptr_t bytes_to_process,
ForceCompletionAction completion = DO_NOT_FORCE_COMPLETION);
V8_INLINE bool IsFixedArrayWithProgressBar(HeapObject* object);
// Visits the object and returns its size.
V8_INLINE int VisitObject(Map* map, HeapObject* obj);
void RevisitObject(HeapObject* obj);
void IncrementIdleMarkingDelayCounter();
void AdvanceIncrementalMarkingOnAllocation();
size_t StepSizeToKeepUpWithAllocations();
size_t StepSizeToMakeProgress();
void SetState(State s) {
state_ = s;
heap_->SetIsMarkingFlag(s >= MARKING);
Heap* const heap_;
MarkCompactCollector::MarkingWorklist* const marking_worklist_;
double start_time_ms_;
size_t initial_old_generation_size_;
size_t old_generation_allocation_counter_;
size_t bytes_allocated_;
size_t bytes_marked_ahead_of_schedule_;
// A sample of concurrent_marking()->TotalMarkedBytes() at the last
// incremental marking step. It is used for updating
// bytes_marked_ahead_of_schedule_ with contribution of concurrent marking.
size_t bytes_marked_concurrently_;
size_t unscanned_bytes_of_large_object_;
// Must use SetState() above to update state_
State state_;
bool is_compacting_;
bool should_hurry_;
bool was_activated_;
bool black_allocation_;
bool finalize_marking_completed_;
bool trace_wrappers_toggle_;
IncrementalMarkingJob incremental_marking_job_;
GCRequestType request_type_;
Observer new_generation_observer_;
Observer old_generation_observer_;
MarkingState marking_state_;
AtomicMarkingState atomic_marking_state_;
NonAtomicMarkingState non_atomic_marking_state_;
} // namespace internal
} // namespace v8