[SOLVED] prolog ## V8 internals

## V8 internals

The hooks to access V8 internalsincluding GC and statisticsare 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`.

`c++
static Nan::Persistent callback;

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

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

### Nan::AddGCEpilogueCallback()

Signature:

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

Calls V8s [`AddGCEpilogueCallback()`](https://v8docs.nodesource.com/io.js-3.0/d5/dda/classv8_1_1_isolate.html#a90d1860babc76059c62514b422f56960).

### Nan::RemoveGCEpilogueCallback()

Signature:

`c++
void Nan::RemoveGCEpilogueCallback(v8::Isolate::GCEpilogueCallback callback)
`

Calls V8s [`RemoveGCEpilogueCallback()`](https://v8docs.nodesource.com/io.js-3.0/d5/dda/classv8_1_1_isolate.html#a05c60859fd4b8e96bfcd451281ed6c7c).

### Nan::AddGCPrologueCallback()

Signature:

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

Calls V8s [`AddGCPrologueCallback()`](https://v8docs.nodesource.com/io.js-3.0/d5/dda/classv8_1_1_isolate.html#ab4b87b8f9f8e5bf95eba4009357e001f).

### Nan::RemoveGCPrologueCallback()

Signature:

`c++
void Nan::RemoveGCPrologueCallback(v8::Isolate::GCPrologueCallback callback)
`

Calls V8s [`RemoveGCEpilogueCallback()`](https://v8docs.nodesource.com/io.js-3.0/d5/dda/classv8_1_1_isolate.html#a9f6c51932811593f81ff30b949124186).

### Nan::GetHeapStatistics()

Signature:

`c++
void Nan::GetHeapStatistics(v8::HeapStatistics *heap_statistics)
`

Calls V8s [`GetHeapStatistics()`](https://v8docs.nodesource.com/io.js-3.0/d5/dda/classv8_1_1_isolate.html#a5593ac74687b713095c38987e5950b34).

### Nan::SetCounterFunction()

Signature:

`c++
void Nan::SetCounterFunction(v8::CounterLookupCallback cb)
`

Calls V8s [`SetCounterFunction()`](https://v8docs.nodesource.com/io.js-3.0/d5/dda/classv8_1_1_isolate.html#a045d7754e62fa0ec72ae6c259b29af94).

### Nan::SetCreateHistogramFunction()

Signature:

`c++
void Nan::SetCreateHistogramFunction(v8::CreateHistogramCallback cb)
`

Calls V8s [`SetCreateHistogramFunction()`](https://v8docs.nodesource.com/io.js-3.0/d5/dda/classv8_1_1_isolate.html#a542d67e85089cb3f92aadf032f99e732).

### Nan::SetAddHistogramSampleFunction()

Signature:

`c++
void Nan::SetAddHistogramSampleFunction(v8::AddHistogramSampleCallback cb)
`

Calls V8s [`SetAddHistogramSampleFunction()`](https://v8docs.nodesource.com/io.js-3.0/d5/dda/classv8_1_1_isolate.html#aeb420b690bc2c216882d6fdd00ddd3ea).

### Nan::IdleNotification()

Signature:

`c++
void Nan::IdleNotification(v8::HeapStatistics *heap_statistics)
`

Calls V8s [`IdleNotification()` or `IdleNotificationDeadline()`](https://v8docs.nodesource.com/io.js-3.0/d5/dda/classv8_1_1_isolate.html#ad6a2a02657f5425ad460060652a5a118) depending on V8 version.

### Nan::LowMemoryNotification()

Signature:

`c++
void Nan::LowMemoryNotification()
`

Calls V8s [`IdleNotification()`](https://v8docs.nodesource.com/io.js-3.0/d5/dda/classv8_1_1_isolate.html#a24647f61d6b41f69668094bdcd6ea91f).

### Nan::ContextDisposedNotification()

Signature:

`c++
void Nan::ContextDisposedNotification()
`

Calls V8s [`ContextDisposedNotification()`](https://v8docs.nodesource.com/io.js-3.0/d5/dda/classv8_1_1_isolate.html#ad7f5dc559866343fe6cd8db1f134d48b).

### Nan::GetInternalFieldPointer()

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

Signature:

`c++
void* Nan::GetInternalFieldPointer(v8::Local object, int index)
`

Calls the Objects [`GetAlignedPointerFromInternalField()` or `GetPointerFromInternalField()`](https://v8docs.nodesource.com/io.js-3.0/db/d85/classv8_1_1_object.html#ab3c57184263cf29963ef0017bec82281) depending on the version of V8.

### Nan::SetInternalFieldPointer()

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

Signature:

`c++
void Nan::SetInternalFieldPointer(v8::Local object, int index, void* value)
`

Calls the Objects [`SetAlignedPointerInInternalField()` or `SetPointerInInternalField()`](https://v8docs.nodesource.com/io.js-3.0/d5/dda/classv8_1_1_isolate.html#ad7f5dc559866343fe6cd8db1f134d48b) depending on the version of V8.

### Nan::AdjustExternalMemory()

Signature:

`c++
int Nan::AdjustExternalMemory(int bytesChange)
`

Calls V8s [`AdjustAmountOfExternalAllocatedMemory()`](https://v8docs.nodesource.com/io.js-3.0/d5/dda/classv8_1_1_isolate.html#ae1a59cac60409d3922582c4af675473e).