Subj : xpconnect object lifetime using nsIXPCScriptable
To   : netscape.public.mozilla.jseng
From : Ulrich von Zadow <u.zadow@gmx.de>
Date : Wed Sep 17 2003 11:05 pm

Hi,

we have xpcom components here that inherit from nsIXPCScriptable and
we've run into a situation where we can't seem to get rid of a memory
leak. Basically, we're returning an xpcom component from GetProperty:

NS_IMETHODIMP
acXPCDynamicProperties::GetProperty
         (nsIXPConnectWrappedNative *wrapper,
          JSContext * cx, JSObject * obj, jsval id,
          jsval * vp, PRBool *_retval)
{
     [...]

     scope= ???
     nsISupports * native = ...

     {
         nsCOMPtr<nsIXPConnectJSObjectHolder> holder;

         nsresult rv = getXPConnect()->WrapNative(cx, scope, native,
                 aIID, getter_AddRefs(holder));
         NS_ENSURE_SUCCESS(rv, rv);

         JSObject* obj = nsnull;
         rv = holder->GetJSObject(&obj);
         NS_ENSURE_SUCCESS(rv, rv);

         *vp = OBJECT_TO_JSVAL(obj);
     }
     [...]
}

On the native side, we seem to be reference counting correctly. In the
WrapNative() call, the reference count goes up by two - I have no way
of verifying that that is as intended.

We're also unsure about what to pass as scope. Since we're returning a
value, the reference to that value should be gone when the stack frame
is discarded. How is this accomplished? Is WrapNative the correct 
function to call at all if we want the object to be rooted locally?

Thanks for any help,

   Uli

.