Question

I’m writing a game that uses WPF for its interface, and Direct3D11 for rendering the world. The rendering happens on its own thread but it needs to make use of a D3DImage in the window, so I need to use a SynchronizationContext to switch to the UI thread when rendering. When the game first starts up I make a DispatcherSynchronizationContext from the Application.Current.Dispatcher. Some time after this happens, a window is created and then is stored in Application.Current.MainWindow. When its time to render I have to switch to the context like so:

async {
    ...
    do! Async.SwitchToContext state.Context
    //render stuff

}

Everything is fine up until the main window closes. Once that happens my handler for Application.Exit runs, which tells all subsystems to shut down and then waits for their responses. The problem is the render thread hangs either on the next Async.SwitchToContext, or if the switch already happened just before the window closed then it hangs sometime during the actual rendering, so it can never respond to the shutdown request.

The DispatcherSynchronizationContext doesn’t become null, and both the value of DSC’s HasShutdownStarted and HasShutdownFinished are false. I’m not getting any exception either. The application is still running, it won’t exit until it gets a response from all the subsystems.

What is happening at this point in the program? The application is still running, so its dispatcher should still be there, so I should still be able to switch to its context. There is no change in the SynchronizationContext before and after the window closes that would lead me to believe its no longer valid, so I have no idea how to check if its safe to switch or not.

Answer 1

^{(Reposting from comments)}

For your value of Application.Current.ShutdownMode, the behavior you’re seeing is expected — because you have no other window open other than your main window, when your main window is closed, (quoting the docs)

Windows Presentation Foundation (WPF) implicitly calls Shutdown when the last window in an application closes.

And of course, invoking Shutdown (directly or indirectly) explicitly terminates the process.

If you want your process to remain alive even after all windows are closed, you must assign the value ShutdownMode.OnExplicitShutdown to Application.Current.ShutdownMode:

The lifetime of some applications may not be dependent on when the main window or last window is closed, or may not be dependent on windows at all. For these scenarios you need to set the ShutdownMode property to OnExplicitShutdown, which requires an explicit Shutdown method call to stop the application. Otherwise, the application continues running in the background.

Sounds like your exact scenario to me. ;-]