Fix potential crash when a window is released

There can be a race condition when a window is released. A crash
happens very rarely in the windowitem2 QML test case (~1%), but could
be seen more often in more complex code.
Because, both window->deleteLater() and isBeingDisplayedChanged are
processed asynchronously, the former might run before the latter and
hence the window might already be destructed when used in the
isBeingDisplayedChanged handler.

Cherry-picked from 5.15: 520d102

Change-Id: Iddb687f057666ef3d34feb6472d3ba2171093d91
Reviewed-by: Robert Griebl <robert.griebl@qt.io>

1 files changed, 8 insertions, 4 deletions

diff --git a/src/window-lib/windowmanager.cpp b/src/window-lib/windowmanager.cpp
index 97a3b68c..b361609a 100644
--- a/src/window-lib/windowmanager.cpp
+++ b/src/window-lib/windowmanager.cpp
@@ -633,10 +633,14 @@ void WindowManager::setupWindow(Window *window)
             emit windowPropertyChanged(win, name, value);
     });
 
-    connect(window, &Window::isBeingDisplayedChanged, this, [this, window]() {
-        if (window->contentState() == Window::NoSurface && !window->isBeingDisplayed()) {
-            removeWindow(window);
-            releaseWindow(window);
+    // In very rare cases window->deleteLater() is processed before the isBeingDisplayedChanged
+    // handler below, i.e. the window destructor runs before the handler.
+    QPointer<Window> guardedWindow = window;
+    connect(window, &Window::isBeingDisplayedChanged, this, [this, guardedWindow]() {
+        if (!guardedWindow.isNull() && guardedWindow->contentState() == Window::NoSurface
+            && !guardedWindow->isBeingDisplayed()) {
+            removeWindow(guardedWindow);
+            releaseWindow(guardedWindow);
         }
     }, Qt::QueuedConnection);