v8_internals.md

V8 internals

The hooks to access V8 internals—including GC and statistics—are different across the supported versions of V8, therefore NAN provides its own hooks that call the appropriate V8 methods.

• NAN_GC_CALLBACK()
• Nan::AddGCEpilogueCallback()
• Nan::RemoveGCEpilogueCallback()
• Nan::AddGCPrologueCallback()
• Nan::RemoveGCPrologueCallback()
• Nan::GetHeapStatistics()
• Nan::SetCounterFunction()
• Nan::SetCreateHistogramFunction()
• Nan::SetAddHistogramSampleFunction()
• Nan::IdleNotification()
• Nan::LowMemoryNotification()
• Nan::ContextDisposedNotification()
• Nan::GetInternalFieldPointer()
• Nan::SetInternalFieldPointer()
• Nan::AdjustExternalMemory()

NAN_GC_CALLBACK(callbackname)

Use NAN_GC_CALLBACK to declare your callbacks for Nan::AddGCPrologueCallback() and Nan::AddGCEpilogueCallback(). Your new method receives the arguments v8::GCType type and v8::GCCallbackFlags flags.

static Nan::Persistent<Function> callback;

NAN_GC_CALLBACK(gcPrologueCallback) {
  v8::Local<Value> argv[] = { Nan::New("prologue").ToLocalChecked() };
  Nan::MakeCallback(Nan::GetCurrentContext()->Global(), Nan::New(callback), 1, argv);
}

NAN_METHOD(Hook) {
  callback.Reset(args[0].As<Function>());
  Nan::AddGCPrologueCallback(gcPrologueCallback);
  info.GetReturnValue().Set(info.Holder());
}

Nan::AddGCEpilogueCallback()

Signature:

void Nan::AddGCEpilogueCallback(v8::Isolate::GCEpilogueCallback callback, v8::GCType gc_type_filter = v8::kGCTypeAll)

Calls V8's AddGCEpilogueCallback().

Nan::RemoveGCEpilogueCallback()

Signature:

void Nan::RemoveGCEpilogueCallback(v8::Isolate::GCEpilogueCallback callback)

Calls V8's RemoveGCEpilogueCallback().

Nan::AddGCPrologueCallback()

Signature:

void Nan::AddGCPrologueCallback(v8::Isolate::GCPrologueCallback, v8::GCType gc_type_filter callback)

Calls V8's AddGCPrologueCallback().

Nan::RemoveGCPrologueCallback()

Signature:

void Nan::RemoveGCPrologueCallback(v8::Isolate::GCPrologueCallback callback)

Calls V8's RemoveGCEpilogueCallback().

Nan::GetHeapStatistics()

Signature:

void Nan::GetHeapStatistics(v8::HeapStatistics *heap_statistics)

Calls V8's GetHeapStatistics().

Nan::SetCounterFunction()

Signature:

void Nan::SetCounterFunction(v8::CounterLookupCallback cb)

Calls V8's SetCounterFunction().

Nan::SetCreateHistogramFunction()

Signature:

void Nan::SetCreateHistogramFunction(v8::CreateHistogramCallback cb) 

Calls V8's SetCreateHistogramFunction().

Nan::SetAddHistogramSampleFunction()

Signature:

void Nan::SetAddHistogramSampleFunction(v8::AddHistogramSampleCallback cb) 

Calls V8's SetAddHistogramSampleFunction().

Nan::IdleNotification()

Signature:

void Nan::IdleNotification(v8::HeapStatistics *heap_statistics)

Calls V8's IdleNotification() or IdleNotificationDeadline() depending on V8 version.

Nan::LowMemoryNotification()

Signature:

void Nan::LowMemoryNotification() 

Calls V8's IdleNotification().

Nan::ContextDisposedNotification()

Signature:

void Nan::ContextDisposedNotification()

Calls V8's ContextDisposedNotification().

Nan::GetInternalFieldPointer()

Gets a pointer to the internal field with at index from a V8 Object handle.

Signature:

void* Nan::GetInternalFieldPointer(v8::Local<v8::Object> object, int index) 

Calls the Object's GetAlignedPointerFromInternalField() or GetPointerFromInternalField() depending on the version of V8.

Nan::SetInternalFieldPointer()

Sets the value of the internal field at index on a V8 Object handle.

Signature:

void Nan::SetInternalFieldPointer(v8::Local<v8::Object> object, int index, void* value)

Calls the Object's SetAlignedPointerInInternalField() or SetPointerInInternalField() depending on the version of V8.

Nan::AdjustExternalMemory()

Signature:

int Nan::AdjustExternalMemory(int bytesChange)

Calls V8's AdjustAmountOfExternalAllocatedMemory().