Reduce server grabs during window creation

Remove some obvious server grabs from the window creation codepath,
also ones that are taken at startup.

During startup, there is no need to grab: we install the event handlers
before querying for the already-existing windows, so there is no danger
that we will 'lose' some window. We might try to create a window twice
(if it comes back in the original query and then we get an event for it)
but the code is already protected against such conditions.

When windows are created later, we also do not need grabs, we just need
appropriate error checking as the window may be destroyed at any time
(or it may have already been destroyed).

The stack tracker is unaffected here - as it listens to CreateNotify and
DestroyNotify events and responds directly, the internal stack
representation will always be consistent even if the window goes away while
we are processing MapRequest or similar.

https://bugzilla.gnome.org/show_bug.cgi?id=721345

3 files changed, 5 insertions, 12 deletions

diff --git a/src/core/display.c b/src/core/display.c
index 9455331a0..edb122d36 100644
--- a/src/core/display.c
+++ b/src/core/display.c
@@ -918,8 +918,6 @@ meta_display_open (void)
 
   enable_compositor (the_display);
    
-  meta_display_grab (the_display);
-  
   /* Now manage all existing windows */
   tmp = the_display->screens;
   while (tmp != NULL)
@@ -971,8 +969,6 @@ meta_display_open (void)
 
   meta_idle_monitor_init_dbus ();
 
-  meta_display_ungrab (the_display);
-
   /* Done opening new display */
   the_display->display_opening = FALSE;
 
diff --git a/src/core/screen.c b/src/core/screen.c
index efd6f4101..1143f554c 100644
--- a/src/core/screen.c
+++ b/src/core/screen.c
@@ -887,8 +887,6 @@ meta_screen_manage_all_windows (MetaScreen *screen)
   Window *children;
   int n_children, i;
 
-  meta_display_grab (screen->display);
-
   if (screen->guard_window == None)
     screen->guard_window = create_guard_window (screen->display->xdisplay,
                                                 screen);
@@ -907,8 +905,6 @@ meta_screen_manage_all_windows (MetaScreen *screen)
 
   g_free (children);
   meta_stack_thaw (screen->stack);
-
-  meta_display_ungrab (screen->display);
 }
 
 /**
diff --git a/src/core/window.c b/src/core/window.c
index 05f7dcfa2..a2f04aa27 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -792,11 +792,14 @@ meta_window_new (MetaDisplay   *display,
       return NULL;
     }
 
-  /* Grab server */
-  meta_display_grab (display);
   meta_error_trap_push (display); /* Push a trap over all of window
                                    * creation, to reduce XSync() calls
                                    */
+  /*
+   * This function executes without any server grabs held. This means that
+   * the window could have already gone away, or could go away at any point,
+   * so we must be careful with X error handling.
+   */
 
   if (!XGetWindowAttributes (display->xdisplay, xwindow, &attrs))
     {
@@ -1437,7 +1440,6 @@ meta_window_new (MetaDisplay   *display,
     unminimize_window_and_all_transient_parents (window);
 
   meta_error_trap_pop (display); /* pop the XSync()-reducing trap */
-  meta_display_ungrab (display);
 
   window->constructing = FALSE;
 
@@ -1453,7 +1455,6 @@ meta_window_new (MetaDisplay   *display,
 
 error:
   meta_error_trap_pop (display);
-  meta_display_ungrab (display);
   return NULL;
 }