App doesn't exit when main window is closed

Question

I keep having this problem, solving it, and then when I implement new code it comes back again. It's driving me crazy!

What I finally found was that if you instantiate a Window of any kind, even if you never call Show() or ShowDialog(), when you close your application, it will not terminate. So now I make sure to call Close() when appropriate, and the problem hasn't ever come back with all of the Windows that I've created.

I've implemented more new features that don't create windows (as far as I can tell!), yet now my app will not terminate again. Hitting pause in the VS IDE is useless, I think, because the threads don't have any context so I can't figure out what code caused the hanging.

Normally, I would expect that a thread executing in the background that hasn't exited (and wasn't set as a Background thread) would cause this behavior, but I am not creating any threads at this point.

Can anyone recommend a good tool (free or license required) that will help me quickly resolve these sorts of stupid problems? For now, I'm going to go back, comment out a ton of the new code, and then uncomment line by line until the problem reappears. Brute force is how I typically end up fixing these sorts of things, and would really appreciate a tool to make my life easier. :)

Answer 1

While it may not help in your particular case, Process Explorer is an excellent tool for looking inside running processes and seeing how many threads etc. there are.

Answer 2

You might get more information if you attached using both managed and unmanaged code. In Visual Studio 2008, you can change the mode in the Attach to Process form. Press the "Select..." button and specify debugging for both "Managed" and "Native".

(Before you do this, make sure your symbol path is setup. Go to Tools/Options, Debugging, Symbols. Enter http://msdl.microsoft.com/download/symbols in the list of symbol file locations. Cache the symbols locally in some directory.)

When you attach in both managed and unmanaged modes, you should get a larger call stack. I recommend right-clicking in the Call Stack debug window and choosing "Include Calls To/From Other Threads".

If your main thread shows System.Windows.Forms.Application.Run or ThreadContext.RunMessageLoop, then your UI thread's message pump is alive and still pumping messages. If, for some reason, it is transitioning to another thread, then it can't exit until it's done.

You can also see the full stack traces of the rest of the managed and unmanaged threads. You might want to look for a garbage collector thread and see what it's doing. Look for one that is has a stack with "GCHeap::FinalizerThreadStart" in it. That might be doing something.

There may also be a GID+ thread that's busy trying to do work.

Answer 3

It sounds like you may be having other issues with background threads that the other answers are addressing but with regard to WPF Windows, have you tried changing the ShutdownMode of your App class? You can also try forcing the app to quit by calling Shutdown explicitly:

Application.Current.Shutdown();

Answer 4

I don't mean to over-simplify things, but have you tried setting the owner of the dialog window to the MainWindow? This will force the dialog window to close when the MainWindow is closed. In other words, it would look like this:

dialog.Owner = Window.GetWindow(this);
// Or...
dialog.Owner = Application.Current.MainWindow;

This may not be an option for you, but I just wanted to throw it out there since your post didn't mention you didn't want to set the window's owner.