V8：爲什麼WeakReferenceCallback沒有被調用？

Question

當我嘗試使持久性句柄變弱時，爲什麼WeakReferenceCallback未被調用？請參見下面的示例：

void myWeakReferenceCallback(v8::Persistent<v8::Value> theValue, void *theParameter) 
{ 
    fprintf(stdout, "myWeakReferenceCallback"); 
} 

void testWeakReferenceCallback() 
{ 
    v8::Persistent<v8::Value> persistent_value; 
    { 
     v8::Persistent<v8::Context> context = v8::Context::New(); 
     v8::Context::Scope context_scope(context); 
     v8::HandleScope handle_scope; 
     v8::Local<v8::Value> local_value = v8::NumberObject::New(5.0); 
     persistent_value = v8::Persistent<v8::Value>::New(local_value); 
     persistent_value.MakeWeak(NULL, myWeakReferenceCallback); 
     context.Dispose(); 
    } 
    persistent_value.Dispose(); 
} 

Answer 1

我認爲有兩個問題：

1. 你處置弱手柄V8有機會來調用回調之前。你需要在裏面調用的回調。
2. V8在執行GC之前不會調用弱句柄回調。

試試這個：

void myWeakReferenceCallback(v8::Persistent<v8::Value> theValue, void *theParameter) 
{ 
    fprintf(stdout, "myWeakReferenceCallback"); 
    theValue.Dispose(); 
} 

void testWeakReferenceCallback() 
{ 
    v8::Persistent<v8::Value> persistent_value; 
    { 
     v8::Persistent<v8::Context> context = v8::Context::New(); 
     v8::Context::Scope context_scope(context); 
     v8::HandleScope handle_scope; 
     v8::Local<v8::Value> local_value = v8::NumberObject::New(5.0); 
     persistent_value = v8::Persistent<v8::Value>::New(local_value); 
     persistent_value.MakeWeak(NULL, myWeakReferenceCallback); 
     context.Dispose(); 
    } 
    //persistent_value.Dispose(); 
    while (!v8::V8::IdleNotification()); // force GC 
}