Crash when screen is lost

Hi.

We encounter this problem since we migrated from QT 5.9 to QT 5.12 :

• On Windows, for users connecting through RDP, going to sleepmode, or using Cintiq tablets (those are actually screens), our application would crash.
• This happens only on Windows
• If this is relevant, our application is using OpenGL contexts
• Unfortunately, I was not able to reproduce the case with a minimal Qt App (simple window with OGL Context), only with our full application which I cannot share.

We are not able to reproduce on every configurations, but I was able to reproduce on my system, erratically, using 2 monitors plugged in the same graphic card, and play with the Windows display settings (extended, clone, display only on 1, only on 2).

• Launching the software on display 1 while display mode is extended
• Changing the Window to the display 2
• Setting only on display 1 in Windows settings
• Or maybe the opposite, as I said this is erratic

I had the chance to debug the software and found 2 portions of code with suspicious behaviour:

• First, and assert isn't satisfied here :

  // qcoreapplication.cpp l.568
  
  void QCoreApplicationPrivate::checkReceiverThread(QObject *receiver)
  {
      QThread *currentThread = QThread::currentThread();
      QThread *thr = receiver->thread();
      Q_ASSERT_X(currentThread == thr || !thr, ...);
  

  But as this is an assert, that maybe not the root cause, plus it would not be hit in production, so I skipped to the end of the checkRecevierThread function in order to continue the execution flow

• Second, the creationContext of the QWindowsWindow gets uninitialized value

  // qwindowswindow.cpp l.1312
  
  void QWindowsWindow::initialize()
  {
      // Clear the creation context as the window can be found in QWindowsContext's map.
      QWindowCreationContextPtr creationContext =
          QWindowsContext::instance()->setWindowCreationContext(QWindowCreationContextPtr());

  Here, creationContext is sometimes uninitialized, leading creationContext->requestedGeometryIn to crash due to read access violation

• If I skip again to the end of the function when this happens, the application continue working as expected

Thank you for your help.