Subj : Re: updated jsgen (maybe rc1?)
To   : netscape.public.mozilla.jseng
From : Marcello Bastea-Forte <marcello@TEHSPAMcellosoft.com>
Date : Thu Jan 01 2004 08:04 pm


> What context-dependent or -related data do you store in your classes? 
> That seems like a bug, to be fixed ASAP if possible.  It ought not be 
> necessary.

I'm not entirely sure if it will work with multiple contexts or not, I 
really don't know how I'd test it (perhaps some insight here would help).

I store a single JSObject * with the classes so you can get the JSObject 
from a C++ instance, although I'm looking at the Embedder's Guide, and 
it's saying that multiple contexts can access the same object (so a 
single JSObject* can be used on multiple contexts?)

Right now I'm caching the JSContext for the getJSObject routine (this 
either returns a previously made JSObject*, or makes a new one with 
JS_NewObject), but it only uses the cached context if a context isn't 
passed to getJSObject().

After looking at that code again, I think I'll take the caching out 
altogether, since it seems pointless and unnecessary now.

The problem I see is in the JSInit function that initializes a class 
into an object for use:

-----------------------------------------------------------------------
///// JavaScript Initialization Method
JSObject *JSTest::_JSInitObject = NULL; // static
JSObject *JSTest::JSInit(JSContext *cx, JSObject *obj, JSObject *proto) {
   if (!_JSInitObject)
     _JSInitObject = JS_InitClass(cx, obj, proto, &JSTest::_jsClass,
         JSTest::JSConstructor, 0,
         JSTest::_JSPropertySpec, JSTest::_JSFunctionSpec,
         JSTest::_JSPropertySpec_static, JSTest::_JSFunctionSpec_static);
   return _JSInitObject;
}
-----------------------------------------------------------------------

In my code, proto is NULL by default (I think I'll take out the extra 
prototype code as well), and if the class inherits from another class, 
the init function looks slightly different:

-----------------------------------------------------------------------
JSObject *JSTestChild::JSInit(JSContext *cx, JSObject *obj, JSObject 
*proto) {
   if (!_JSInitObject)
     _JSInitObject = JS_InitClass(cx, obj, proto ? proto : 
JSTest::JSInit(cx,obj), &JSTestChild::_jsClass, /* <- I'll take out that 
proto ? proto : stuff */
         JSTestChild::JSConstructor, 0,
         NULL, JSTestChild::_JSFunctionSpec,
         NULL, NULL);
	return _JSInitObject;
}
-----------------------------------------------------------------------

I don't know if that init object can be used across contexts, but 
looking at the code I see a bug.  You wouldn't be able to initialize the 
class for use in multiple (global) objects.  The problem is with 
JS_InitClass being called multiple times on the same class.

If you call getJSObject on the child class, it will call JS_NewObject 
with a prototype:

-----------------------------------------------------------------------
///// JavaScript Object Linking
JSObject *JSTestChild::getJSObject(JSContext *cx) {
   if (!cx) cx = _JSinternal.cx;
   else if (!_JSinternal.cx) _JSinternal.cx = cx;
   /*** Note the ugly context caching above that I'll take out ***/
   if (!cx) return NULL;
   if (!_JSinternal.o) {
     _JSinternal.o = JS_NewObject(cx, &JSTestChild::_jsClass, 
JSTest::_JSInitObject, NULL);
      if (!JS_SetPrivate(cx, _JSinternal.o, this))
        return NULL;
    }
    return _JSinternal.o;
}
-----------------------------------------------------------------------

Here I have to refer to the cached init object (I think), because JSInit 
requires an object to create it in.  Perhaps there's another way to do this?

In summary, those are the two problem points.  Is it a problem to be 
calling JS_InitClass for the same thing multiple times on the same 
object?  Should I be doing that instead?  (For example, a child class 
will call the init of its parent class for the prototype.)

I would also need some way to do deal with the prototype in the 
JS_NewObject for child classes.

Thanks,

Marcello

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