v8 WeakCallback 永远不会被调用

Posted 2023-04-01

【中文标题】v8 WeakCallback 永远不会被调用

【英文标题】：v8 WeakCallback never gets called

【发布时间】：2014-06-08 14:47:26

【问题描述】：

我知道这个问题很老，但我找到的所有答案都不起作用并且已经过时了。 但这是我的代码：

void Destroyed(const v8::WeakCallbackData<v8::Object, int>& info)

    std::cout << "d: " << *info.GetParameter() << std::endl;


std::vector<v8::Persistent<v8::Object, v8::CopyablePersistentTraits<v8::Object>>> persistent;
int i = 0;

void Constructor(const v8::FunctionCallbackInfo<v8::Value>& info)

    v8::HandleScope scope(v8::Isolate::GetCurrent());

    v8::Persistent<v8::Object, v8::CopyablePersistentTraits<v8::Object>> per;
    per = v8::Persistent<v8::Object>(v8::Isolate::GetCurrent(), info.This());

    per.SetWeak<int>(new int(i), Destroyed);

    persistent.push_back(per);

    ++i;

    while(!v8::V8::IdleNotification()) 


void TestV8()

    v8::Isolate* isolate = v8::Isolate::New();

    v8::Isolate::Scope isolateScope(isolate);

    v8::HandleScope scope(isolate);

    v8::Local<v8::Context> context = v8::Context::New(isolate);

    v8::Context::Scope contextScope(context);

    v8::Local<v8::FunctionTemplate> temp = v8::FunctionTemplate::New(isolate, Constructor);

    context->Global()->Set(v8::String::NewFromUtf8(isolate, "Object"), temp->GetFunction());

    v8::Local<v8::String> source = v8::String::NewFromUtf8(isolate, "while(true) new Object();");

    v8::Local<v8::Script> script = v8::Script::Compile(source);

    v8::Local<v8::Value> result = script->Run();

    std::cout << *v8::String::Utf8Value(result) << std::endl;

如果我不将持久性添加到向量中，则内存不会增加。 但是 Destroyed 永远不会被调用，我似乎无法弄清楚出了什么问题，请帮忙:)

【参考方案1】：

我在下面解决了它是工作代码。显然 Persistent 复制构造函数没有将其复制到弱引用的位置，因此将其转换为指针解决了它。

std::vector<v8::Persistent<v8::Object, v8::CopyablePersistentTraits<v8::Object>>*> persistent;
int i = 0;

void Destroyed(const v8::WeakCallbackData<v8::Object, int>& info)

    std::cout << "d: " << *info.GetParameter() << std::endl;

    persistent[*info.GetParameter()]->Reset();


void Constructor(const v8::FunctionCallbackInfo<v8::Value>& info)

    v8::HandleScope scope(v8::Isolate::GetCurrent());

    v8::Persistent<v8::Object, v8::CopyablePersistentTraits<v8::Object>>* per = new v8::Persistent<v8::Object, v8::CopyablePersistentTraits<v8::Object>>(v8::Isolate::GetCurrent(), info.This());
    per->SetWeak<int>(new int(i), Destroyed);
    persistent.push_back(per);

    ++i;

    while(!v8::V8::IdleNotification()) 


void TestV8()

    v8::Isolate* isolate = v8::Isolate::New();
    v8::Isolate::Scope isolateScope(isolate);

    v8::HandleScope scope(isolate);

    v8::Local<v8::Context> context = v8::Context::New(isolate);
    v8::Context::Scope contextScope(context);

    v8::Local<v8::FunctionTemplate> temp = v8::FunctionTemplate::New(isolate, Constructor);

    context->Global()->Set(v8::String::NewFromUtf8(isolate, "Object"), temp->GetFunction());

    v8::Local<v8::String> source = v8::String::NewFromUtf8(isolate, "while(true) new Object();");
    v8::Local<v8::Script> script = v8::Script::Compile(source);
    v8::Local<v8::Value> result = script->Run();

    std::cout << *v8::String::Utf8Value(result) << std::endl;

【讨论】：

这里真正的答案是“使用v8::Global”。 v8::CopyablePersistentTraits 非常糟糕

【参考方案2】：

您检查过SetWeak 的documentation 吗？它明确指出以下内容：

/**
 *  Install a finalization callback on this object.
 *  NOTE: There is no guarantee as to *when* or even *if* the callback is
 *  invoked. The invocation is performed solely on a best effort basis.
 *  As always, GC-based finalization should *not* be relied upon for any
 *  critical form of resource management!
 */
template<typename P>
V8_INLINE void SetWeak(
    P* parameter,
    typename WeakCallbackData<T, P>::Callback callback);

【讨论】：

是的，我有，但我不相信它会错过其中的 2GB。另外，当我没有为它们创建任何持久句柄时，它们会收集垃圾。那么当他们得到一个弱引用时，他们为什么不这样做呢？

据我所见，您将每个创建的对象的句柄存储到您的 persistent 向量中，这显然使所有对象都处于活动状态，因此它们都无法被收集。

是的，但我将它们设为弱，所以应该收集它们对吗？

我似乎发现了 per.IsWeak() 返回 1 的问题，但如果我键入 persistent.back().IsWeak() 它返回 0。将向量更改为包含指针它适用于一个至少。然后 (state() != NEAR_DEATH) 但嘿更近一步 :)