Re: action->get_proxies during connect-proxy emit

[Torsten Schoenfeld <kaffeetisch gmx de>]

Kevin Ryde wrote:
> Test case and what I did about it below.  get_proxies isn't a
> constructor, so if I'm not mistaken its object returns shouldn't be
> subject to ref_sink.

That appears do be due to GtkAction not holding a real ref on the proxies but 
just a weak ref.  When connect_proxy in gtkaction.c calls the connect-proxy 
signal, the proxies weren't added to any container yet and are thus still 
floating.  So gtk_action_get_proxies ends up handing out objects with a floating 
reference.  When gtk2perl_new_gtkobject sees those, it sinks them and thus 
assumes ownership of the floating ref.  When the signal callback returns, the SV 
wrappers for the proxies go out of scope and that causes destruction of the 
proxies.  Later, some code in gtk+ tries to use the destroyed proxies and things 
go wrong.

I'm not yet sure who's at fault here: gtk_action_get_proxies for handing out 
objects that are potentially floating, or us for assuming we can sink any 
floating objects returned by gtk_action_get_proxies.  This and the hard code 
freeze we're in make me think we should punt on this issue until after the 
stable releases later today.

> But I don't know if this is enough.  In particular I turned on NOISY in
> GtkObject.xs and it got a segv ... but perhaps that's something else.

That's something else, yes.  The debug code in gtk2perl_new_gtkobject segfaults 
on NULL objects.  The attached patch fixes this for me.  Will commit when the 
code freeze is over.

--
-Torsten

Index: xs/GtkObject.xs
===================================================================
RCS file: /cvsroot/gtk2-perl/gtk2-perl-xs/Gtk2/xs/GtkObject.xs,v
retrieving revision 1.17
diff -u -d -p -r1.17 GtkObject.xs
--- xs/GtkObject.xs     16 Jan 2006 22:28:25 -0000      1.17
+++ xs/GtkObject.xs     20 Sep 2008 12:31:55 -0000
@@ -50,12 +50,16 @@ SV *
 gtk2perl_new_gtkobject (GtkObject * object)
 {
 #ifdef NOISY
-       warn ("gtk2perl_new_gtkobject (%s(%p)[%d])\n",
-             G_OBJECT_TYPE_NAME (object),
-             object,
-             G_OBJECT (object)->ref_count);
-       g_signal_connect (object, "destroy", G_CALLBACK (destroy_notify), NULL);
-       g_object_weak_ref (object, weak_ref, NULL);
+       if (object) {
+               warn ("gtk2perl_new_gtkobject (%s(%p)[%d])\n",
+                     G_OBJECT_TYPE_NAME (object),
+                     object,
+                     G_OBJECT (object)->ref_count);
+               g_signal_connect (object, "destroy", G_CALLBACK (destroy_notify), NULL);
+               g_object_weak_ref (G_OBJECT (object), weak_ref, NULL);
+       } else {
+               warn ("gtk2perl_new_gtkobject (NULL)\n");
+       }
 #endif
        /* always sink the object.  if it's not floating, then nothing
         * happens and we get a ref.  if it is floating, then the