MetaDisplay: remove meta_display_grab()/ungrab()

Now that we have two connections to the X server, the idea of a
ref-counted server grab that might be held across extended portions
of code is very dangerous since we might try to use the backend
connection while the frontend connection is grabbed.

Replace the only usage (which was local) with direct
XGrabServer/XUngrabServer usage and remove the meta_display_grab()
API.

https://bugzilla.gnome.org/show_bug.cgi?id=733068

src/core/display-private.h

@@ -146,8 +146,6 @@ struct _MetaDisplay
   GHashTable *xids;
   GHashTable *wayland_windows;
 
-  int server_grab_count;
-
   /* serials of leave/unmap events that may
    * correspond to an enter event we should
    * ignore
@@ -314,8 +312,6 @@ struct _MetaDisplayClass
 gboolean      meta_display_open                (void);
 void          meta_display_close               (MetaDisplay *display,
                                                 guint32      timestamp);
-void          meta_display_grab                (MetaDisplay *display);
-void          meta_display_ungrab              (MetaDisplay *display);
 
 void          meta_display_unmanage_windows_for_screen (MetaDisplay *display,
                                                         MetaScreen  *screen,

src/core/display.c

@@ -512,7 +512,6 @@ meta_display_open (void)
    */
   the_display->name = g_strdup (XDisplayName (NULL));
   the_display->xdisplay = xdisplay;
-  the_display->server_grab_count = 0;
   the_display->display_opening = TRUE;
 
   the_display->pending_pings = NULL;
@@ -1076,50 +1075,6 @@ meta_display_close (MetaDisplay *display,
   meta_quit (META_EXIT_SUCCESS);
 }
 
-/* Grab/ungrab routines taken from fvwm.
- * Calling this function will cause X to ignore all other clients until
- * you ungrab. This may not be quite as bad as it sounds, yet there is
- * agreement that avoiding server grabs except when they are clearly needed
- * is a good thing.
- *
- * If you do use such grabs, please clearly explain the necessity for their
- * usage in a comment. Try to keep their scope extremely limited. In
- * particular, try to avoid emitting any signals or notifications while
- * a grab is active (if the signal receiver tries to block on an X request
- * from another client at this point, you will have a deadlock).
- */
-void
-meta_display_grab (MetaDisplay *display)
-{
-  if (display->server_grab_count == 0)
-    {
-      XGrabServer (display->xdisplay);
-    }
-  display->server_grab_count += 1;
-  meta_verbose ("Grabbing display, grab count now %d\n",
-                display->server_grab_count);
-}
-
-void
-meta_display_ungrab (MetaDisplay *display)
-{
-  if (display->server_grab_count == 0)
-    meta_bug ("Ungrabbed non-grabbed server\n");
-
-  display->server_grab_count -= 1;
-  if (display->server_grab_count == 0)
-    {
-      /* FIXME we want to purge all pending "queued" stuff
-       * at this point, such as window hide/show
-       */
-      XUngrabServer (display->xdisplay);
-      XFlush (display->xdisplay);
-    }
-
-  meta_verbose ("Ungrabbing display, grab count now %d\n",
-                display->server_grab_count);
-}
-
 /**
  * meta_display_for_x_display:
  * @xdisplay: An X display
@@ -1554,7 +1509,7 @@ request_xserver_input_focus_change (MetaDisplay *display,
    * we know which is which by making two requests that the server will
    * process at the same time.
    */
-  meta_display_grab (display);
+  XGrabServer (display->xdisplay);
 
   serial = XNextRequest (display->xdisplay);
 
@@ -1567,7 +1522,8 @@ request_xserver_input_focus_change (MetaDisplay *display,
                    display->atom__MUTTER_FOCUS_SET,
                    XA_STRING, 8, PropModeAppend, NULL, 0);
 
-  meta_display_ungrab (display);
+  XUngrabServer (display->xdisplay);
+  XFlush (display->xdisplay);
 
   meta_display_update_focus_window (display,
                                     meta_window,