Subj : How does object persistance work over multiple contexts?
To   : netscape.public.mozilla.jseng
From : eboli
Date : Wed Nov 17 2004 07:34 pm

Hello, 

I am trying to embed Spidermonkey into a c++ application I am working
on and would like to know if somebody could explain how the contexts
work as far as object persistence is concerned. I think I am
misunderstanding this, but ultimately what I am trying to achieve is a
wrapper class which would load assorted scripts in a library style
fashion. Previously I have been creating and using objects on a single
context with all initialisation etc as per
(http://sourceforge.net/docman/display_doc.php?docid=10853&group_id=50913).
That works fine for the moment. As I understand it (and it works
through implementation) after a context is created other context's
subsequently have access to that object. Now what I figured would
happen (figured incorrectly) is that the lifetime for that object
would be limited to the context that created it (and/or while it was
being referenced by another object). So what I had tried was:

Create a new Runtime; 
Create a new Context1;
Create a new Context2;

Initialise an object on Context1; Call one of its methods from context
2; - This worked fine; So I figured if I deleted Context1 at this
point the reference to that object would be lost; and it would be
garbage collected; thus the subsequent call to that objects method on
Context2 would fail. Calling JS_DestroyContext(Context1); caused my
application to crash, I thought this was probably because as it
contained the global object; and the standard classes were also
initialised to it, it was probably just a bad thing to do :) So I
created a third context; and after destroying the second context the
object still persisted. So what I am doing is below;

Create a runtime;
Create a global context; 

Create a nonglobalcontext1; 
Create a nonglobalcontext2; 

Create an object on nonglobalcontext1;

function someObject()
{
	this.someValue = 22;
	this.someMethod = function() { return this.someValue; };
}

var someObjectInstance = new someObject();

Call JS_DestroyContext( nonglobalcontext1 ); 

Execute a method from someObjectInstance from the nonglobalcontext2;
var test = someObjectInstance.someMethod();

and rather then returning undefined or JS_FALSE in an error; I am
still getting the return value of the function as if the object is
persisting; additionally I have tried calling JS_GC(nonglobalcontext1)
before destroying it to no avail. Finally even when I create the
object definition / prototype on the first nonglobalcontext; then
destroy that context; I can still create an instance of that object;
and call its methods from another context (again w/wo JS_GC called)

So my question would be in two parts :) … what am I doing wrong; and /
or am I even on the correct track here?

Thanks for your time


Joesph

.