2023-10-03 11:14:36 +08:00
## 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.
- < a href = "#api_nan_gc_callback" >< b >< code > NAN_GC_CALLBACK()</ code ></ b ></ a >
- < a href = "#api_nan_add_gc_epilogue_callback" >< b >< code > Nan::AddGCEpilogueCallback()</ code ></ b ></ a >
- < a href = "#api_nan_remove_gc_epilogue_callback" >< b >< code > Nan::RemoveGCEpilogueCallback()</ code ></ b ></ a >
- < a href = "#api_nan_add_gc_prologue_callback" >< b >< code > Nan::AddGCPrologueCallback()</ code ></ b ></ a >
- < a href = "#api_nan_remove_gc_prologue_callback" >< b >< code > Nan::RemoveGCPrologueCallback()</ code ></ b ></ a >
- < a href = "#api_nan_get_heap_statistics" >< b >< code > Nan::GetHeapStatistics()</ code ></ b ></ a >
- < a href = "#api_nan_set_counter_function" >< b >< code > Nan::SetCounterFunction()</ code ></ b ></ a >
- < a href = "#api_nan_set_create_histogram_function" >< b >< code > Nan::SetCreateHistogramFunction()</ code ></ b ></ a >
- < a href = "#api_nan_set_add_histogram_sample_function" >< b >< code > Nan::SetAddHistogramSampleFunction()</ code ></ b ></ a >
- < a href = "#api_nan_idle_notification" >< b >< code > Nan::IdleNotification()</ code ></ b ></ a >
- < a href = "#api_nan_low_memory_notification" >< b >< code > Nan::LowMemoryNotification()</ code ></ b ></ a >
- < a href = "#api_nan_context_disposed_notification" >< b >< code > Nan::ContextDisposedNotification()</ code ></ b ></ a >
- < a href = "#api_nan_get_internal_field_pointer" >< b >< code > Nan::GetInternalFieldPointer()</ code ></ b ></ a >
- < a href = "#api_nan_set_internal_field_pointer" >< b >< code > Nan::SetInternalFieldPointer()</ code ></ b ></ a >
- < a href = "#api_nan_adjust_external_memory" >< b >< code > Nan::AdjustExternalMemory()</ code ></ b ></ a >
< a name = "api_nan_gc_callback" > < / a >
### 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< 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(To< Function > (args[0]).ToLocalChecked());
Nan::AddGCPrologueCallback(gcPrologueCallback);
info.GetReturnValue().Set(info.Holder());
}
```
< a name = "api_nan_add_gc_epilogue_callback" > < / a >
### Nan::AddGCEpilogueCallback()
Signature:
```c++
void Nan::AddGCEpilogueCallback(v8::Isolate::GCEpilogueCallback callback, v8::GCType gc_type_filter = v8::kGCTypeAll)
```
Calls V8's [`AddGCEpilogueCallback()` ](https://v8docs.nodesource.com/node-8.16/d5/dda/classv8_1_1_isolate.html#a580f976e4290cead62c2fc4dd396be3e ).
< a name = "api_nan_remove_gc_epilogue_callback" > < / a >
### Nan::RemoveGCEpilogueCallback()
Signature:
```c++
void Nan::RemoveGCEpilogueCallback(v8::Isolate::GCEpilogueCallback callback)
```
Calls V8's [`RemoveGCEpilogueCallback()` ](https://v8docs.nodesource.com/node-8.16/d5/dda/classv8_1_1_isolate.html#adca9294555a3908e9f23c7bb0f0f284c ).
< a name = "api_nan_add_gc_prologue_callback" > < / a >
### Nan::AddGCPrologueCallback()
Signature:
```c++
void Nan::AddGCPrologueCallback(v8::Isolate::GCPrologueCallback, v8::GCType gc_type_filter callback)
```
Calls V8's [`AddGCPrologueCallback()` ](https://v8docs.nodesource.com/node-8.16/d5/dda/classv8_1_1_isolate.html#a6dbef303603ebdb03da6998794ea05b8 ).
< a name = "api_nan_remove_gc_prologue_callback" > < / a >
### Nan::RemoveGCPrologueCallback()
Signature:
```c++
void Nan::RemoveGCPrologueCallback(v8::Isolate::GCPrologueCallback callback)
```
Calls V8's [`RemoveGCPrologueCallback()` ](https://v8docs.nodesource.com/node-8.16/d5/dda/classv8_1_1_isolate.html#a5f72c7cda21415ce062bbe5c58abe09e ).
< a name = "api_nan_get_heap_statistics" > < / a >
### Nan::GetHeapStatistics()
Signature:
```c++
void Nan::GetHeapStatistics(v8::HeapStatistics *heap_statistics)
```
Calls V8's [`GetHeapStatistics()` ](https://v8docs.nodesource.com/node-8.16/d5/dda/classv8_1_1_isolate.html#a5593ac74687b713095c38987e5950b34 ).
< a name = "api_nan_set_counter_function" > < / a >
### Nan::SetCounterFunction()
Signature:
```c++
void Nan::SetCounterFunction(v8::CounterLookupCallback cb)
```
Calls V8's [`SetCounterFunction()` ](https://v8docs.nodesource.com/node-8.16/d5/dda/classv8_1_1_isolate.html#a045d7754e62fa0ec72ae6c259b29af94 ).
< a name = "api_nan_set_create_histogram_function" > < / a >
### Nan::SetCreateHistogramFunction()
Signature:
```c++
void Nan::SetCreateHistogramFunction(v8::CreateHistogramCallback cb)
```
Calls V8's [`SetCreateHistogramFunction()` ](https://v8docs.nodesource.com/node-8.16/d5/dda/classv8_1_1_isolate.html#a542d67e85089cb3f92aadf032f99e732 ).
< a name = "api_nan_set_add_histogram_sample_function" > < / a >
### Nan::SetAddHistogramSampleFunction()
Signature:
```c++
void Nan::SetAddHistogramSampleFunction(v8::AddHistogramSampleCallback cb)
```
Calls V8's [`SetAddHistogramSampleFunction()` ](https://v8docs.nodesource.com/node-8.16/d5/dda/classv8_1_1_isolate.html#aeb420b690bc2c216882d6fdd00ddd3ea ).
< a name = "api_nan_idle_notification" > < / a >
### Nan::IdleNotification()
Signature:
```c++
bool Nan::IdleNotification(int idle_time_in_ms)
```
Calls V8's [`IdleNotification()` or `IdleNotificationDeadline()` ](https://v8docs.nodesource.com/node-8.16/d5/dda/classv8_1_1_isolate.html#ad6a2a02657f5425ad460060652a5a118 ) depending on V8 version.
< a name = "api_nan_low_memory_notification" > < / a >
### Nan::LowMemoryNotification()
Signature:
```c++
void Nan::LowMemoryNotification()
```
Calls V8's [`LowMemoryNotification()` ](https://v8docs.nodesource.com/node-8.16/d5/dda/classv8_1_1_isolate.html#a24647f61d6b41f69668094bdcd6ea91f ).
< a name = "api_nan_context_disposed_notification" > < / a >
### Nan::ContextDisposedNotification()
Signature:
```c++
void Nan::ContextDisposedNotification()
```
Calls V8's [`ContextDisposedNotification()` ](https://v8docs.nodesource.com/node-8.16/d5/dda/classv8_1_1_isolate.html#ad7f5dc559866343fe6cd8db1f134d48b ).
< a name = "api_nan_get_internal_field_pointer" > < / a >
### Nan::GetInternalFieldPointer()
Gets a pointer to the internal field with at `index` from a V8 `Object` handle.
Signature:
```c++
void* Nan::GetInternalFieldPointer(v8::Local< v8::Object > object, int index)
```
Calls the Object's [`GetAlignedPointerFromInternalField()` or `GetPointerFromInternalField()` ](https://v8docs.nodesource.com/node-8.16/db/d85/classv8_1_1_object.html#a580ea84afb26c005d6762eeb9e3c308f ) depending on the version of V8.
< a name = "api_nan_set_internal_field_pointer" > < / a >
### Nan::SetInternalFieldPointer()
Sets the value of the internal field at `index` on a V8 `Object` handle.
Signature:
```c++
void Nan::SetInternalFieldPointer(v8::Local< v8::Object > object, int index, void* value)
```
Calls the Object's [`SetAlignedPointerInInternalField()` or `SetPointerInInternalField()` ](https://v8docs.nodesource.com/node-8.16/db/d85/classv8_1_1_object.html#ab3c57184263cf29963ef0017bec82281 ) depending on the version of V8.
< a name = "api_nan_adjust_external_memory" > < / a >
### Nan::AdjustExternalMemory()
Signature:
```c++
int Nan::AdjustExternalMemory(int bytesChange)
```
Calls V8's [`AdjustAmountOfExternalAllocatedMemory()` ](https://v8docs.nodesource.com/node-8.16/d5/dda/classv8_1_1_isolate.html#ae1a59cac60409d3922582c4af675473e ).
