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 add a filter for the root window's
events.

In each of main_event_handler function, 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 in root window's
event filter function is always valid, but the problem
is that sometimes the window associated with the same
event in main_event_handler is found as invalid
(acutually is NULL).

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.

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)
{
                if (!GDK_IS_WINDOW(event->any.window))
                        g_message("In main_event_handler, event->any.window
didn't return \
                                           a valid window!\n");
                else
                        g_message("In main_event_handler, event->any.window
returned a valid window!\n");

}


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

{
                if (!GDK_IS_WINDOW(event->any.window))
                        g_message("In root_event_monitor, event->any.window
didn't return \
                                           a valid window!\n");
                else
                        g_message("In root_event_monitor, event->any.window
returned 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

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