JS bindings questions

@ricardo wrote:

Hey @pandamicro @zhangxm and rest of the team. I have the following questions:

1) Allocation / Deallocation inconsistencies
Why the deallocation of the proxy is invoked by Ref::~Ref() and not by js_cocos2d_xxx_finalize() ?

The allocation is invoked in the js_cocos2dx_xxx_constructor()... so it makes sense to have the deallocation in js_cocos2d_xxx_finalize().

Example:

bool js_cocos2dx_Sprite_constructor(JSContext *cx, uint32_t argc, jsval *vp)
{
   ...
    js_proxy_t* p = jsb_new_proxy(cobj, obj);
    AddNamedObjectRoot(cx, &p->obj, "cocos2d::Sprite");
    ...
}

// finalize is empty
void js_cocos2d_Sprite_finalize(JSFreeOp *fop, JSObject *obj) {
    CCLOGINFO("jsbindings: finalizing JS object %p (Sprite)", obj);
}


// ~Ref calls this function... in any case, finalize should call it
void ScriptingCore::removeScriptObjectByObject(Ref* pObj)
{
    ...
    jsproxy = jsb_get_js_proxy(nproxy->obj);
    RemoveObjectRoot(cx, &jsproxy->obj);
    jsb_remove_proxy(nproxy, jsproxy);
    ...
}

This asymmetric allocation/deallocation is confusing.

2) we should avoid dynamic_cast
The automatic bindings are doing something like this:

    cocos2d::Sprite* cobj = new (std::nothrow) cocos2d::Sprite();
    cocos2d::Ref *_ccobj = dynamic_cast<cocos2d::Ref *>(cobj);
    if (_ccobj) {
        _ccobj->autorelease();
    }

There two "bugs" here:

• Ref is a base class, so there is no need is doing a dynamic cast.
• dynamic_cast is super expensive... we should avoid it.

I guess that code was added in case the Sprite is not a subclass of Ref, but that should be solved in another way... perhaps by adding a parameter in the config file saying "do not call autorelease(). As it is now, it is not optimal.
But if there are objects that are not subclass of Ref that are being used here, then they will leak since only ~Ref deallocs the proxy (see question #1)

I'm researching how to remove retain/release from JS, so expect from me more questions about Spidermonkey/bindings.

Posts: 10

Participants: 3

Read full topic