Let's take a look at a typical foo_accessible_get_type() function as found in many GNOME modules, e.g. gtk+, evolution, libgail-gnome, gucharmap, control-centre, libgnomeui, gnome-media, eel, goocanvas, evince, ...:

static GType
gtk_icon_view_accessible_get_type (void)
{
  static GType type = 0;

  if (!type)
    {
      static GTypeInfo tinfo =
      {
        0, /* class size */
        (GBaseInitFunc) NULL, /* base init */
        (GBaseFinalizeFunc) NULL, /* base finalize */
        (GClassInitFunc) gtk_icon_view_accessible_class_init,
        (GClassFinalizeFunc) NULL, /* class finalize */
        NULL, /* class data */
        0, /* instance size */
        0, /* nb preallocs */
        (GInstanceInitFunc) NULL, /* instance init */
        NULL /* value table */
      };
      static const GInterfaceInfo atk_component_info =
      {
        (GInterfaceInitFunc) atk_component_interface_init,
        (GInterfaceFinalizeFunc) NULL,
        NULL
      };
      static const GInterfaceInfo atk_selection_info = 
      {
        (GInterfaceInitFunc) gtk_icon_view_accessible_selection_interface_init,
        (GInterfaceFinalizeFunc) NULL,
        NULL
      };

      /*
       * Figure out the size of the class and instance
       * we are deriving from
       */
      AtkObjectFactory *factory;
      GType derived_type;
      GTypeQuery query;
      GType derived_atk_type;

      derived_type = g_type_parent (GTK_TYPE_ICON_VIEW);
      factory = atk_registry_get_factory (atk_get_default_registry (), 
                                          derived_type);
      derived_atk_type = atk_object_factory_get_accessible_type (factory);
      g_type_query (derived_atk_type, &query);
      tinfo.class_size = query.class_size;
      tinfo.instance_size = query.instance_size;
 
      type = g_type_register_static (derived_atk_type, 
                                     I_("GtkIconViewAccessible"), 
                                     &tinfo, 0);
      g_type_add_interface_static (type, ATK_TYPE_COMPONENT,
                                   &atk_component_info);
      g_type_add_interface_static (type, ATK_TYPE_SELECTION,
                                   &atk_selection_info);
    }
  return type;
}


There are two problems with it:
- it is not thread-safe (see bug 65041)
- it introduces unnecessary relocations, due to the use of the static GTypeInfo  and GInterfaceInfo structs

I therefore propose to introduce some convenience macros in the spirit of G_DEFINE_TYPE[_WITH_CODE], that will enable one to rewrite the above function to

ATK_DEFINE_TYPE_WITH_CODE
  (GtkIconViewAccesssible, gtk_icon_view_accessible,
   GTK_TYPE_ICON_VIEW,
   G_IMPLEMENT_INTERFACE (ATK_TYPE_COMPONENT, atk_component_interface_init)
   G_IMPLEMENT_INTERFACE (ATK_TYPE_SELECTION, gtk_icon_view_accessible_selection_interface_init))

and so get a thread-safe, relocation-less get_type function.