Re: GTK & threads

[Gregory Hosler <ghosler redhat com>]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Marshall Lake wrote:
> I posted this on gtk-list but in the hope of catching a wider audience ...
>
> I'm developing a program(s) which runs in the client/server environment.
> I'm using GTK, sockets, and threads.  (GTK and threads only on the
> client side.)  I don't have very much experience using threads and this
> is the first time I've tried to call GTK functions within a thread, and
> I'm having problems.  I've tried different ways of approaching the
> problem but can't seem to get anywhere.  I suspect there's something I
> don't understand about thread processing or I'm under some
> misconception. Maybe someone can help me?  Any help is much appreciated.

If I'm not mistaken, X isn't tread-safe, which may be the root cause of the
specific error message that you're seeing. The implication is that any call
which may invoke X should be done from the main thread. When an auxiliary thread
does need to do some drawing, one way to achieve that would be with a
g_idle_add(), which will get invoked by the main thread when there is nothing
else to do.

Hope this helps,

- -Greg

> I get the following errors when trying to run the code below (the errors
> show up when the program calls gtk_dialog_run() in the thread
> (Wait4Challenge()):
>
> src/xcb_io.c:242: process_responses: Assertion `(((long)
> (dpy->last_request_read) - (long) (dpy->request)) <= 0)' failed.
> Fatal IO error 0 (Success) on X server :0.0.
>
>
> void *
> Wait4Challenge () {
>       int wsock, x, port = 0, listensock, connected;
>       char buffer[5000], *msg[5], challenger[50];
>
>       listensock = -1;
>       for (x = 0; x < 5; x++)
>           msg[x] = NULL;
>
>       wsock = get_connection (SOCK_STREAM, port, &listensock);
>
>       connected = 1;
>       while (connected) {
>           GtkWidget *dialog;
>           int response;
>
>           if (sock_gets (wsock, &buffer[0], sizeof (buffer)) < 0) {
>               msg[0] = "There is a problem with the server.\n\n";
>               outMessage (msg);
>               connected = 0;
>           }
>
>           if (buffer[0] == 'R')
>               connected = 0;
>
>           if (buffer[0] != 'C')
>               continue;
>
>           strcpy (&challenger[0], &buffer[1]);
>
>           gdk_threads_enter ();
>
>           dialog = gtk_message_dialog_new (GTK_WINDOW (mainwin),
> GTK_DIALOG_DESTROY_WITH_PARENT, GTK_MESSAGE_QUESTION,
>                               GTK_BUTTONS_YES_NO, "%s has challenged you
> to a game.  Do you wish to play?", challenger);
>           gtk_window_set_title (GTK_WINDOW (dialog), "Play Challenger?");
>           response = gtk_dialog_run (GTK_DIALOG (dialog));
>           gtk_widget_destroy (dialog);
>
>           gdk_flush();
>           gdk_threads_leave ();
>
>           if (response == GTK_RESPONSE_YES) {
>               sock_puts (wsock, "OK\n");
>               connected = 0;
>           }
>           else {
>               sock_puts (wsock, "NO\n");
>               for (x = 0; x < 5; x++)
>                   msg[x] = NULL;
>               continue;
>           }
>       }
>
>       shutdown (wsock, SHUT_RDWR);
>       close (wsock);
>       return (NULL);
> }
>
> int
> main (int argc, char *argv[]) {
>       g_thread_init (NULL);
>       gdk_threads_init ();
>
>       gtk_init (&argc, &argv);
>
>       mainwin = gtk_window_new (GTK_WINDOW_TOPLEVEL);
>       gtk_widget_set_usize (mainwin, WINSIZEX, WINSIZEY);
>       gtk_widget_realize (mainwin);
>
>       gtk_widget_add_events (mainwin, GDK_BUTTON_PRESS_MASK);
>       gtk_signal_connect (GTK_OBJECT (mainwin), "delete_event",
> GTK_SIGNAL_FUNC (delete_event), 0);
>
>       gtk_widget_show_all (mainwin);
>
>       if (!g_thread_create (Wait4Challenge, NULL, FALSE, NULL))
>           syslog (LOG_INFO, "error trying to create new thread");
>
>       gdk_threads_enter ();
>
>       gtk_main ();
>
>       gdk_flush();
>       gdk_threads_leave ();
>
>       return 0;
> }


- --
+---------------------------------------------------------------------+

Please also check the log file at "/dev/null" for additional information.
                (from /var/log/Xorg.setup.log)

| Greg Hosler                                   ghosler redhat com    |
+---------------------------------------------------------------------+
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.9 (GNU/Linux)
Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org

iEYEARECAAYFAkpU99MACgkQ404fl/0CV/QP0gCdFjSI6ASkdRfr70QXpy5amjQn
z28AoKG55bgTe2t9dUERYc1G8wxPULaT
=DMvb
-----END PGP SIGNATURE-----