With a _NET_WM_PING message, a window manager can check if an
application still works or if it froze. The WM sends such a message to
the application window and the application sends the message back to the
root window.
Since change Ia04268b0 / commit d8090022f "Move the X11 system tray code
from widgets into XCB-plugin.", Qt selects StructureNotifyMask on the
root window. Due to this, we now also receive replies to _NET_WM_PING
and treat them like a _NET_WM_PING request.
This caused an endless loop as soon as any _NET_WM_PING was seen where
Qt would send a _NET_WM_PING to itself and handle it again and again.
Fix this by ignoring _NET_WM_PING messages that are sent to the root
window. According to EWMH, such messages can only be replies to
_NET_WM_PING and GTK does this, too.
Task-number: QTBUG-32957
Change-Id: I1b0aa682f99b17d633baacc14b18b3adca7a1aba
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
ac5c64fccd