[mutter/wip/carlosg/x11-services-initialization-fix: 1/2] core: Ensure stack tracker gets synchronized once

[Carlos Garnacho <carlosg src gnome org>]

commit e68d4b4f09b66673da9dc8303aa0a0920333052e
Author: Carlos Garnacho <carlosg gnome org>
Date:   Wed Sep 11 17:56:47 2019 +0200

    core: Ensure stack tracker gets synchronized once
    
    For "reasons", we may need to emit ::x11-display-opened twice, one
    at the right time so MetaStackTracker captures xserver state at a
    time we don't have in flight requests for our own windows, another
    at a time the upper layers might be aware of it.
    
    Protect the stack tracker against such double initialization if it
    ever happened.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/792

 src/core/stack-tracker.c | 8 ++++++++
 1 file changed, 8 insertions(+)
---
diff --git a/src/core/stack-tracker.c b/src/core/stack-tracker.c
index 5a2956c00..eb89848c9 100644
--- a/src/core/stack-tracker.c
+++ b/src/core/stack-tracker.c
@@ -169,6 +169,8 @@ struct _MetaStackTracker
    * stack up with our best guess before a frame is drawn.
    */
   guint sync_stack_later;
+
+  gboolean synchronized_with_xserver;
 };
 
 static void
@@ -492,6 +494,10 @@ query_xserver_stack (MetaDisplay      *display,
   guint n_children;
   guint i, old_len;
 
+  if (tracker->synchronized_with_xserver)
+    return;
+
+  tracker->synchronized_with_xserver = TRUE;
   tracker->xserver_serial = XNextRequest (x11_display->xdisplay);
 
   XQueryTree (x11_display->xdisplay,
@@ -542,6 +548,8 @@ drop_x11_windows (MetaDisplay      *display,
 
       l = next;
     }
+
+  tracker->synchronized_with_xserver = FALSE;
 }
 
 MetaStackTracker *