On Sat, May 16, 2009 at 12:10 PM, Marshall Greenblatt <
magreenbl...@gmail.com> wrote:
> On Sat, May 16, 2009 at 1:27 PM, Mike Belshe <mbel...@google.com> wrote:
>
>> You can create a weak reference to the object, and when the object is GC'd
>> in v8, the weak reference handler will get called. Check out the v8.h
>> documentation for weak references and it will probably make sense.
>> Mike
>>
>
> Hi Mike,
>
> So I guess the code would look like this:
>
> void MyDestructor(Persistent<Object> object, void*)
> {
> // do whatever cleanup is required
> }
>
> static v8::Handle<v8::Value> MyCallback(const v8::Arguments& args) {
> // Create a new V8 object template with one internal field.
> v8::Handle<v8::ObjectTemplate> my_templ = v8::ObjectTemplate::New();
> my_templ->SetInternalFieldCount(1);
>
> // Create a new MyClass instance.
> MyClass* my_class = ...;
>
> // Create a new persistent V8 object.
> v8::Persistent<v8::Object> obj =
> v8::Persistent<v8::Object>::New(my_templ->NewInstance());
>
> // Attach the MyClass instance to the V8 object.
> obj->SetInternalField(0, v8::External::New(my_class));
>
> // Make the V8 object a weak reference and assign the destructor.
> obj.MakeWeak(NULL, &MyDestructor);
>
> return obj;
> }
>
Yes, that code looks about right. I'd recommend testing it out in test
programs so you can see it all in action.
> In what circumstances, if any, would it be appropriate to make the
> ObjectTemplate a weak reference instead of the Object? Would any Objects
> created with a weak reference ObjectTemplate automatically have the
> destructor called for them?
>
In general, don't go too crazy with Weak handles. Use it when you need it.
Cases where you need it include:
a) You're churning through lots of large C++ objects, causing memory
usage to skyrocket because V8 doesn't realize the C++ side is holding onto
so much memory
b) You're holding onto some system resource (like a file, lock, etc) that
you want to clean up quickly.
I can't imagine cases where you'd want the ObjectTemplate itself to be weak
much - because I can't envision a case where (a) or (b) above is relevant to
the ObjectTemplate. But maybe I lack vision :-)
Mike
>
>
> Thanks,
> Marshall
>
>
>>
>>
>> On Fri, May 15, 2009 at 8:38 PM, Marshall Greenblatt <
>> magreenbl...@gmail.com> wrote:
>>
>>> Hi All,
>>>
>>> I'm seeking a way to trigger destruction (or reference decrement) of a
>>> C++ object attached to a V8 object when the V8 object is destroyed. For
>>> instance, consider the following code where I create and return a new V8
>>> object in a function template callback:
>>>
>>> static v8::Handle<v8::Value> MyCallback(const v8::Arguments& args) {
>>> // Create a new V8 object template with one internal field.
>>> v8::Handle<v8::ObjectTemplate> my_templ = v8::ObjectTemplate::New();
>>> my_templ->SetInternalFieldCount(1);
>>>
>>> // Create a new MyClass instance.
>>> MyClass* my_class = ...;
>>>
>>> // Create a new V8 object.
>>> v8::Local<v8::Object> obj = my_templ->NewInstance();
>>>
>>> // Attach the MyClass instance to the V8 object.
>>> obj->SetInternalField(0, v8::External::New(my_class));
>>>
>>> return obj;
>>> }
>>>
>>> How can I clean up the MyClass instance when the associated V8 object
>>> destroyed? Is there some way that I can assign a destructor callback for
>>> the V8 object?
>>>
>>> Thanks,
>>> Marshall
>>>
>>> >>>
>>>
>>
>
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