[mutter/wayland] Reduce server grabs during window creation

[Daniel Drake <dsd src gnome org>]

commit 577624adefc73d8f724a9e7319ac8087d9bae825
Author: Daniel Drake <drake endlessm com>
Date:   Mon Dec 30 13:01:28 2013 -0600

    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.
    
    Now that there are no grabs we don't have to worry about explicitly calling
    display_notify_window after grabs have been dropped. Fold that into
    meta_window_new_shared().
    
    https://bugzilla.gnome.org/show_bug.cgi?id=721345

 src/core/display.c |    4 ----
 src/core/screen.c  |    4 ----
 src/core/window.c  |   39 ++++++++++++---------------------------
 3 files changed, 12 insertions(+), 35 deletions(-)
---
diff --git a/src/core/display.c b/src/core/display.c
index eced287..2313c88 100644
--- a/src/core/display.c
+++ b/src/core/display.c
@@ -825,8 +825,6 @@ 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)
@@ -894,8 +892,6 @@ 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 2fc9bfe..9394125 100644
--- a/src/core/screen.c
+++ b/src/core/screen.c
@@ -887,8 +887,6 @@ meta_screen_manage_all_windows (MetaScreen *screen)
   MetaStackWindow *children;
   int n_children, i;
 
-  meta_display_grab (screen->display);
-
   if (screen->guard_window == None)
     screen->guard_window =
       meta_screen_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 db34afe..5739367 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -1329,12 +1329,6 @@ meta_window_new_shared (MetaDisplay         *display,
 
   window->constructing = FALSE;
 
-  return window;
-}
-
-static void
-display_notify_window (MetaDisplay *display, MetaWindow *window)
-{
   meta_display_notify_window_created (display, window);
 
   if (window->wm_state_demands_attention)
@@ -1342,6 +1336,8 @@ display_notify_window (MetaDisplay *display, MetaWindow *window)
 
   if (window->wm_hints_urgent)
     g_signal_emit_by_name (window->display, "window-marked-urgent", window);
+
+  return window;
 }
 
 MetaWindow *
@@ -1376,15 +1372,12 @@ meta_window_new_for_wayland (MetaDisplay        *display,
   attrs.override_redirect = 0;
   attrs.screen = scr->xscreen;
 
-  /* XXX: Note: In the Wayland case we currently still grab the
-   * xserver and trap X errors while creating a MetaWindow because we
-   * will still be making various redundant X requests (passing a
-   * window xid of None) until we thoroughly audit all the code to
-   * make sure it knows about non X based clients...
+  /* XXX: Note: In the Wayland case we currently still trap X errors while
+   * creating a MetaWindow because we will still be making various redundant
+   * X requests (passing a window xid of None) until we thoroughly audit all
+   * the code to make sure it knows about non X based clients...
    */
 
-  /* Grab server */
-  meta_display_grab (display);
   meta_error_trap_push (display); /* Push a trap over all of window
                                    * creation, to reduce XSync() calls
                                    */
@@ -1400,14 +1393,12 @@ meta_window_new_for_wayland (MetaDisplay        *display,
                                    &attrs);
 
   meta_error_trap_pop (display); /* pop the XSync()-reducing trap */
-  meta_display_ungrab (display);
 
   /* XXX: Maybe this could be called in meta_window_new_shared() but
    * before splitting the X11 specific code out it came after the
-   * meta_display_ungrab() and we wanted to minimize the risk of
+   * meta_error_trap_pop() and we wanted to minimize the risk of
    * breaking something.
    */
-  display_notify_window (window->display, window);
 
   return window;
 }
@@ -1434,11 +1425,14 @@ 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))
     {
@@ -1581,20 +1575,11 @@ meta_window_new (MetaDisplay       *display,
                                    &attrs);
 
   meta_error_trap_pop (display); /* pop the XSync()-reducing trap */
-  meta_display_ungrab (display);
-
-  /* XXX: Maybe this could be called in meta_window_new_shared() but
-   * before splitting the X11 specific code out it came after the
-   * meta_display_ungrab() and we wanted to minimize the risk of
-   * breaking something.
-   */
-  display_notify_window (display, window);
 
   return window;
 
 error:
   meta_error_trap_pop (display);
-  meta_display_ungrab (display);
   return NULL;
 }