Client: Don't always recreate frame callbacks

The main QWaylandWindow method that is executed when handling updates is
QWaylandWindow::handleUpdate(). This method always, unconditionally queues
a frame callback, regardless of whether any other one is already queued.

On some circumstances, e.g. when a window is hidden or completely obscured
by other windows, it stops receiving frame callbacks from the compositor.
However, QWaylandWindow would continue to request for them, which eventually
fills up the Wayland socket, and causes the application to crash.

This can be avoided by checking if the platform window is already waiting
for a frame callback, before queueing another one.

In QWaylandWindow::handleUpdate(), check if mWaitingForFrameCallback is true
before queueing frame callbacks, and early return if that's the case.

The XDG-shell test needed to be updated for this: The mock compositor is
not responding to any frame callbacks, so the window will be unexposed,
no longer get paint events and therefore not trigger any commit. This
worked by accident before because we were issuing updates quickly enough
to reset the timer before it had a chance to unexpose the window. The
easiest fix is just to disable the dependency on frame callbacks in
this test, since that is clearly not what it's testing.

Task-number: QTBUG-81504
Change-Id: Ieacb05c7d5a5fcf662243d9177ebcc308cb9ca84
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Georges Basile Stavracas Neto <gbsneto@gnome.org>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

2 files changed, 6 insertions, 0 deletions

diff --git a/src/client/qwaylandwindow.cpp b/src/client/qwaylandwindow.cpp
index a708afce..d83d5169 100644
--- a/src/client/qwaylandwindow.cpp
+++ b/src/client/qwaylandwindow.cpp
@@ -1357,6 +1357,10 @@ void QWaylandWindow::requestUpdate()
 void QWaylandWindow::handleUpdate()
 {
     qCDebug(lcWaylandBackingstore) << "handleUpdate" << QThread::currentThread();
+
+    if (mWaitingForFrameCallback)
+        return;
+
     // TODO: Should sync subsurfaces avoid requesting frame callbacks?
     QReadLocker lock(&mSurfaceLock);
     if (!mSurface)
diff --git a/tests/auto/client/xdgshell/tst_xdgshell.cpp b/tests/auto/client/xdgshell/tst_xdgshell.cpp
index 1d2a2014..962093c7 100644
--- a/tests/auto/client/xdgshell/tst_xdgshell.cpp
+++ b/tests/auto/client/xdgshell/tst_xdgshell.cpp
@@ -138,6 +138,7 @@ void tst_xdgshell::configureSize()
 
 void tst_xdgshell::configureStates()
 {
+    QVERIFY(qputenv("QT_WAYLAND_FRAME_CALLBACK_TIMEOUT", "0"));
     QRasterWindow window;
     window.resize(64, 48);
     window.show();
@@ -186,6 +187,7 @@ void tst_xdgshell::configureStates()
     QCOMPARE(window.windowStates(), Qt::WindowNoState);
     QCOMPARE(window.frameGeometry().size(), windowedSize);
 //    QCOMPARE(window.frameGeometry().topLeft(), QPoint()); // TODO: this doesn't currently work when window decorations are enabled
+    QVERIFY(qunsetenv("QT_WAYLAND_FRAME_CALLBACK_TIMEOUT"));
 }
 
 void tst_xdgshell::popup()