EmbedderHeapTracer Class Reference

#include <v8.h>

Collaboration diagram for EmbedderHeapTracer:

Data Structures
class	TracedGlobalHandleVisitor
struct	TraceSummary

Public Types
enum	TraceFlags : uint64_t { kNoFlags = 0, kReduceMemory = 1 << 0 }
enum	EmbedderStackState { kUnknown, kNonEmpty, kEmpty }

Public Member Functions
virtual	~EmbedderHeapTracer ()=default
void	IterateTracedGlobalHandles (TracedGlobalHandleVisitor *visitor)
void	SetStackStart (void *stack_start)
void	NotifyEmptyEmbedderStack ()
virtual void	RegisterV8References (const std::vector< std::pair< void *, void *> > &embedder_fields)=0
void	RegisterEmbedderReference (const TracedReferenceBase< v8::Data > &ref)
virtual void	TracePrologue (TraceFlags flags)
virtual bool	AdvanceTracing (double deadline_in_ms)=0
virtual bool	IsTracingDone ()=0
virtual void	TraceEpilogue (TraceSummary *trace_summary)
virtual void	EnterFinalPause (EmbedderStackState stack_state)=0
void	FinalizeTracing ()
virtual bool	IsRootForNonTracingGC (const v8::TracedReference< v8::Value > &handle)
virtual bool	IsRootForNonTracingGC (const v8::TracedGlobal< v8::Value > &handle)
virtual void	ResetHandleInNonTracingGC (const v8::TracedReference< v8::Value > &handle)
void	GarbageCollectionForTesting (EmbedderStackState stack_state)
void	IncreaseAllocatedSize (size_t bytes)
void	DecreaseAllocatedSize (size_t bytes)
v8::Isolate *	isolate () const

Protected Attributes
v8::Isolate *	isolate_ = nullptr

Friends
class	internal::LocalEmbedderHeapTracer

Detailed Description

Interface for tracing through the embedder heap. During a V8 garbage collection, V8 collects hidden fields of all potential wrappers, and at the end of its marking phase iterates the collection and asks the embedder to trace through its heap and use reporter to report each JavaScript object reachable from any of the given wrappers.

Definition at line 7837 of file v8.h.

Member Enumeration Documentation

EmbedderStackState

enum EmbedderStackState

Enumerator
kUnknown
kNonEmpty
kEmpty

Definition at line 7845 of file v8.h.

TraceFlags

enum TraceFlags : uint64_t

Enumerator
kNoFlags
kReduceMemory

Definition at line 7839 of file v8.h.

Constructor & Destructor Documentation

~EmbedderHeapTracer()

virtual ~EmbedderHeapTracer ( )

virtualdefault

Member Function Documentation

AdvanceTracing()

virtual bool AdvanceTracing ( double  deadline_in_ms )

pure virtual

Called to advance tracing in the embedder.

The embedder is expected to trace its heap starting from wrappers reported by RegisterV8References method, and report back all reachable wrappers. Furthermore, the embedder is expected to stop tracing by the given deadline. A deadline of infinity means that tracing should be finished.

Returns |true| if tracing is done, and false otherwise.

DecreaseAllocatedSize()

void DecreaseAllocatedSize

(

size_t

bytes

)

EnterFinalPause()

virtual void EnterFinalPause ( EmbedderStackState  stack_state )

pure virtual

Called upon entering the final marking pause. No more incremental marking steps will follow this call.

FinalizeTracing()

void FinalizeTracing

(

)

GarbageCollectionForTesting()

void GarbageCollectionForTesting

(

EmbedderStackState

stack_state

)

IncreaseAllocatedSize()

void IncreaseAllocatedSize

(

size_t

bytes

)

isolate()

v8::Isolate* isolate ( ) const

inline

Definition at line 8011 of file v8.h.

References EmbedderHeapTracer::isolate_.

IsRootForNonTracingGC() [1/2]

virtual bool IsRootForNonTracingGC ( const v8::TracedReference< v8::Value > &  handle )

virtual

Returns true if the TracedGlobal handle should be considered as root for the currently running non-tracing garbage collection and false otherwise. The default implementation will keep all TracedGlobal references as roots.

If this returns false, then V8 may decide that the object referred to by such a handle is reclaimed. In that case:

• No action is required if handles are used with destructors, i.e., by just using |TracedGlobal|.
• When run without destructors, i.e., by using |TracedReference|, V8 calls |ResetHandleInNonTracingGC|.

Note that the |handle| is different from the handle that the embedder holds for retaining the object. The embedder may use |WrapperClassId()| to distinguish cases where it wants handles to be treated as roots from not being treated as roots.

IsRootForNonTracingGC() [2/2]

virtual bool IsRootForNonTracingGC ( const v8::TracedGlobal< v8::Value > &  handle )

virtual

IsTracingDone()

virtual bool IsTracingDone ( )

pure virtual

IterateTracedGlobalHandles()

void IterateTracedGlobalHandles

(

TracedGlobalHandleVisitor *

visitor

)

Iterates all TracedGlobal handles created for the v8::Isolate the tracer is attached to.

NotifyEmptyEmbedderStack()

void NotifyEmptyEmbedderStack

(

)

Called by the embedder to notify V8 of an empty execution stack.

RegisterEmbedderReference()

void RegisterEmbedderReference

(

const TracedReferenceBase< v8::Data > &

ref

)

RegisterV8References()

virtual void RegisterV8References ( const std::vector< std::pair< void *, void *> > &  embedder_fields )

pure virtual

Called by v8 to register internal fields of found wrappers.

The embedder is expected to store them somewhere and trace reachable wrappers from them when called through |AdvanceTracing|.

ResetHandleInNonTracingGC()

virtual void ResetHandleInNonTracingGC ( const v8::TracedReference< v8::Value > &  handle )

virtual

Used in combination with |IsRootForNonTracingGC|. Called by V8 when an object that is backed by a handle is reclaimed by a non-tracing garbage collection. It is up to the embedder to reset the original handle.

Note that the |handle| is different from the handle that the embedder holds for retaining the object. It is up to the embedder to find the original handle via the object or class id.

SetStackStart()

void SetStackStart

(

void *

stack_start

)

Called by the embedder to set the start of the stack which is e.g. used by V8 to determine whether handles are used from stack or heap.

TraceEpilogue()

virtual void TraceEpilogue ( TraceSummary *  trace_summary )

inlinevirtual

Called at the end of a GC cycle.

Note that allocation is not allowed within |TraceEpilogue|. Can be overriden to fill a |TraceSummary| that is used by V8 to schedule future garbage collections.

Definition at line 7939 of file v8.h.

TracePrologue()

virtual void TracePrologue ( TraceFlags  flags )

inlinevirtual

Called at the beginning of a GC cycle.

Definition at line 7912 of file v8.h.

Friends And Related Function Documentation

internal::LocalEmbedderHeapTracer

friend class internal::LocalEmbedderHeapTracer

friend

Definition at line 8016 of file v8.h.

Field Documentation

isolate_

v8::Isolate* isolate_ = nullptr

protected

Definition at line 8014 of file v8.h.

Referenced by EmbedderHeapTracer::isolate().

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The documentation for this class was generated from the following file:

• include/v8.h