Subj : Re: JS_NewObject
To   : netscape.public.mozilla.jseng
From : "Jochen Stier" <jstier@cs.uvic.ca>
Date : Mon Mar 29 2004 11:44 am

Hi Brendan,


With "internal class" I meant a C++ class for which I have created a
corresponding JavaScript
class using JS_DefineClass. Now I would like to instantiate an object of the
"internal class" from
within the C++ code and not the JavaScript. In the constructor of the
internal class I call
JS_NewObject to obtain a JSObject*. I can now use that JSObject* as one of
the parameters to
a JS_CallFunction and everything works fine. I can access the methods and
members of the internal
class via JavaScript. What I am confused about is the GC ? At what point
does the GC delete the
JSObject*, if at all ? I can certainly delete an object of the "internal
class" but there must be some call to
the Javascript engine to decrement the reference count to the JS_Object.
OpenInventor has
something like somevar->ref() and somevar->unref(). Am I correct to assume
that JS_AddRoot
and JS_RemoveRoot are equivalent to the the ref() and unref() calls of
OpenInventor ? What about
the JS_DeleteProperty that was mentioned by Sterling in the previous answer
?

> You have to tell the engine when you no longer have an "internal class"
> referring to the object returned from JS_NewObject.  See JS_RemoveRoot,
> which implies you have already called JS_AddNamedRoot passing the
> address of a pointer to the JSObject.  The pointer's storage must remain
> live till you call JS_RemoveRoot, of course.

I am confused about JS_AddRoot ? Do I have to call that after JS_NewObject
or does that call
happen automatically at least once when you call JS_NewObject ? It would
assume that I only
have to call JS_RemoveRoot in order to GC an object.


Anyways, thanks for your help. I am starting to realize that I may be using
the GC in a wrong way and
that this may cause some of the problem I experience with the error
reporting .....

Cheers
Jochen

"Brendan Eich" <brendan@meer.net> wrote in message
news:40677929.2070108@meer.net...
> Jochen Stier wrote:
> > Hi,
> >
> > I am us JS_NewObject inside my C++ app to create stubs for internal
classes.
>
>
> What do you mean, exactly, by "internal class"?  Can you show the code
> that calls JS_NewObject and stores its return value?
>
>
> > Is there a
> > a way to delete the JSObject when I delete my internal classes. I am
looking
> > for something like JS_DeleteObject ?
>
>
> There is no such API, nor should there be in a GC'd runtime's API.
>
>
> > I know there is GC in JavaScript, but the interpretor can not know
> > when I delete an internal class and the corresponding JS_Object is not
> > needed anymore.
>
>
> You have to tell the engine when you no longer have an "internal class"
> referring to the object returned from JS_NewObject.  See JS_RemoveRoot,
> which implies you have already called JS_AddNamedRoot passing the
> address of a pointer to the JSObject.  The pointer's storage must remain
> live till you call JS_RemoveRoot, of course.
>
> /be

.