RE: [Java-gnome-developer] CVS: Problem with gdk_BaseObject.c and GTK_IS_OBJECT()

[Jeffrey M. <Jef...@Br...>]

I have struggled with this issue for some time and as
yet haven't found a solution.  I need to determine if
a void pointer is actually pointing to a GTK type.  All
macros and methods in GTK assume this is the case
(like the GTK_IS_OBJECT macro below).  Does anybody
have a suggestion?

-Jeff

> 
> In CVS version, in other/gdk_BaseObject.c:
> 
> jobject makeBaseObjectSubclass (JNIEnv *env, jclass cls, void *peer)
> {
>   if (peer == NULL)
>     return NULL;
>   else if (GTK_IS_OBJECT(peer))
>     return makeBaseObjectClass(env, peer);
>   else {
>     jobject result = (*env)->AllocObject (env, cls);
>     jlong result_jl;
> 
>     *(void **) &result_jl = peer;
>     (*env)->SetLongField (env, result, nativepeerFid, result_jl);
>     return result;
>   }
> }
> 
> The GTK_IS_OBJECT is a problem, if you try to create any 
> object not based
> on Gtk, like GdkGC:
> 
> 	xx = new GdkGC(yy);
> 
> leads to:
> 
> Program received signal SIGSEGV, Segmentation fault.
> 0x41383ed6 in makeBaseObjectSubclass (env=0x400887d4, cls=0x6,
> peer=0x81244f8)
>     at other/gdk_BaseObject.c:70
> 70        else if (GTK_IS_OBJECT(peer))
> 
> This, of course happens because "peer" in this context is not a Gtk
> object, but instead a GdkWindow, which isn't representable in the Gtk
> object system:
> 
> (gdb) p *(GdkGC*)peer
> $14 = {dummy_var = 1701080693}
> (gdb) p *((GtkObject*)peer)
> $15 = {klass = 0x65646e75, flags = 135415064, ref_count = 135220712,
>   object_data = 0x1}
> (gdb) p *((GtkObject*)peer)->klass
> Cannot access memory at address 0x65646e75
> 
> In noticed the GTK_IS_OBJECT was added in version 1.5 (of that file).
> Apparently this hasn't been noticed since the test and sample programs
> don't use GdkGC directly at all..
> 
> --
> sa...@ik...                    I have become death, 
> destroyer of the worlds.
> 
> 
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