Client: Make handleUpdate aware of exposure changes

The wl_surface can be destroyed whilst a render is happening. Calling
wl_surface::frame after the window is reset can crash as wl_surface is
null.

Fixes: QTBUG-77747
Change-Id: I139a9b234cb6acba81d6c1d5fa58629904a25053
Reviewed-by: Paul Olav Tvete <paul.tvete@qt.io>

src/plugins/platforms/wayland/qwaylandwindow.cpp

@@ -210,6 +210,8 @@ void QWaylandWindow::initWindow()
 
 void QWaylandWindow::initializeWlSurface()
 {
+    Q_ASSERT(!isInitialized());
+    QWriteLocker lock(&mSurfaceLock);
     init(mDisplay->createSurface(static_cast<QtWayland::wl_surface *>(this)));
 }
 
@@ -245,8 +247,10 @@ void QWaylandWindow::reset(bool sendDestroyEvent)
     mShellSurface = nullptr;
     delete mSubSurfaceWindow;
     mSubSurfaceWindow = nullptr;
-    if (isInitialized())
+    if (isInitialized()) {
+        QWriteLocker lock(&mSurfaceLock);
         destroy();
+    }
     mScreens.clear();
 
     if (mFrameCallback) {
@@ -1147,6 +1151,9 @@ void QWaylandWindow::requestUpdate()
 void QWaylandWindow::handleUpdate()
 {
     // TODO: Should sync subsurfaces avoid requesting frame callbacks?
+    QReadLocker lock(&mSurfaceLock);
+    if (!isInitialized())
+        return;
 
     if (mFrameCallback) {
         wl_callback_destroy(mFrameCallback);

src/plugins/platforms/wayland/qwaylandwindow_p.h

@@ -53,6 +53,8 @@
 
 #include <QtCore/QWaitCondition>
 #include <QtCore/QMutex>
+#include <QtCore/QReadWriteLock>
+
 #include <QtGui/QIcon>
 #include <QtCore/QVariant>
 #include <QtCore/QLoggingCategory>
@@ -272,6 +274,8 @@ private:
     static QMutex mFrameSyncMutex;
     static QWaylandWindow *mMouseGrab;
 
+    QReadWriteLock mSurfaceLock;
+
     friend class QWaylandSubSurface;
 };