Window associated with GdkEvent is invalid sometimes

[Siddharth Uppal <siddharthuppal yahoo co in>]

Hi,

I have written a simple module for use with Gtk
applications. In my module, I set up my own main event
handler, and also add a filter for the root window's
events.

In both main_event_handler funciton, and root
window's filter function, when I receive a GdkEvent, I
simply check whether the window associated with the
event (event->any.window) is valid, using
GDK_IS_WINDOW().

The window associated with the event received in root
window's event filter function is always valid, but
the problem is that sometimes the window associated
with the same event when received in
main_event_handler is found as invalid (actually is
NULL). I've noted that this happends only when the
GdkEventType of the event is GDK_NOTHING.

I feel there is some kind of a race condition
somewhere. I would appreciate if someone could suggest
some solution or a suitable way around the problem. 

I am using Gtk+-2.0.

I shall provide further information as required.

Here's the code of my GTK module:

--code start "my_module.c"--
#include <gdk/gdkx.h>
#include <gdk/gdk.h>
#include <gmodule.h>
#include <gtk/gtk.h>


// Global variables
static GModule  *g_module = NULL;


static void
gdk_root_add_watch (guint         events,
		    GdkFilterFunc function,
		    gpointer      data)
{
  GdkWindow *root;

  g_return_if_fail (function != NULL);

  root = gdk_window_lookup (GDK_ROOT_WINDOW ());

  gdk_window_set_events (root, events |
gdk_window_get_events (root));
  gdk_window_add_filter (root, function, data);
}


static void
main_event_handler (GdkEvent *event,
		    gpointer  data)
{
  g_message("In main_event_handler got an event of
type '%d'\n", event->type);

  if (GDK_IS_WINDOW(event->any.window))
  	g_message("In main_event_handler event->any.window
returned a valid window\n");
  else
	g_message("In main_event_handler event->any.window
DIDN'T return a valid window\n");
}


static GdkFilterReturn
root_event_monitor (GdkXEvent *gdkxevent,
		    GdkEvent  *event,
		    gpointer ptr)

{
  g_message("In root_event_monitor got an event of
type '%d'\n", event->type);
  if (GDK_IS_WINDOW(event->any.window))
  	g_message("In root_event_monitor event->any.window
returned a valid window\n");
  else
	g_message("In root_event_monitor event->any.window
DIDN'T return a valid window\n");

  return FALSE;
}


void
events_init (void)
{
  static gboolean initialized = FALSE;

  if (!initialized)
    {
      initialized = TRUE;

      gdk_event_handler_set (main_event_handler, NULL,
NULL);
      gdk_root_add_watch (GDK_POINTER_MOTION_MASK,
root_event_monitor, NULL);
    }
}


G_MODULE_EXPORT const gchar* g_module_check_init
(GModule *module);
const gchar*
g_module_check_init (GModule *module)
{
  GModule *main_module;
  gchar *version_check = NULL;

  main_module = g_module_open (NULL, 0);
  if (!main_module)
    return "no main handle";
  if (!g_module_symbol (main_module,
"gtk_major_version", (gpointer*) &version_check) &&
version_check)
    return "no gtk library?";

  version_check = gtk_check_version
(GTK_MAJOR_VERSION,
				     GTK_MINOR_VERSION,
				     GTK_MICRO_VERSION - GTK_INTERFACE_AGE);

  if (version_check)
    return version_check;

  g_module = module;

  /* make ourselves resident */
  g_module_open (g_module_name (module),
G_MODULE_BIND_LAZY);

  return NULL;
}


G_MODULE_EXPORT void gtk_module_init (gint *argc,
gchar ***argv);
void
gtk_module_init (int    *argc, char ***argvp)
{
		events_init();
}


static gboolean
quit_loop (gpointer data)
{
  gtk_main_quit ();

  return FALSE;
}

--code end "my_module.c"--

I built the module in the following manner:

libtool --mode=compile gcc -c -fPIC `pkg-config
--cflags gtk+-2.0` my_module.c

libtool --mode=link gcc -rpath /usr/local/lib -o
libmy_module.la my_module.lo

libtool --mode=install cp libmy_module.la
/usr/local/lib

And, I invoke a GTK 2.0 application to load my module,
in the following manner:

LD_LIBRARY_PATH="/usr/local/lib"
GTK_MODULES=$GTK_MODULES:my_module
LD_PRELOAD=/usr/local/lib/libmy_module.so 
export GTK_MODULES LD_LIBRARY_PATH LD_PRELOAD
some_gtk_2.0_program

Thanks,
Siddharth

=====
Siddharth Uppal
Scientist 'B'
Artificial Intelligence and Neural Networks Division (AI & NN)
Center for Artificial Intelligence and Robotics (CAIR)
Defense R&D Organisation (DRDO)
High Grounds
Bangalore - 560093
India

Office: (+91) (080) 2265496 Extn. 225
Mobile: (+91) 9880055780 

Blog: http://upster.blogspot.com

----------------------------------------------------

43rd Law of Computing: 
Anything that can go wr 

ERROR: Segmentation violation -- Core dumped

----------------------------------------------------

________________________________________________________________________
Yahoo! India Insurance Special: Be informed on the best policies, services, tools and more. 
Go to: http://in.insurance.yahoo.com/licspecial/index.html