[mutter] display: Only send one ping to a window at a time

[Jonas Ådahl <jadahl src gnome org>]

commit e51279dcf036bfde3a95a020132050c771a79f1b
Author: Jonas Dreßler <verdre v0yd nl>
Date:   Wed Jan 22 15:59:29 2020 +0100

    display: Only send one ping to a window at a time
    
    If a window already is being pinged, it doesn't make sense to send more
    pings to the window, instead we should just wait for that answer or
    timeout until we send a new one.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/891

 src/core/display.c | 8 ++++++++
 1 file changed, 8 insertions(+)
---
diff --git a/src/core/display.c b/src/core/display.c
index eb0377ad3..f4d4c2090 100644
--- a/src/core/display.c
+++ b/src/core/display.c
@@ -2081,6 +2081,14 @@ meta_display_ping_window (MetaWindow *window,
     {
       MetaPingData *ping_data = l->data;
 
+      if (window == ping_data->window)
+        {
+          meta_topic (META_DEBUG_PING,
+                      "Window %s already is being pinged with serial %u\n",
+                      window->desc, ping_data->serial);
+          return;
+        }
+
       if (serial == ping_data->serial)
         {
           meta_warning ("Ping serial %u was reused for window %s, "