Control.Invoke is hanging

Question

I\'ve seen a ton of post regarding the problem of control.Invoke hanging applications but they mostly seemed to be restricted to those running on .NET 1.1. I\'ve also seen

Answer 1

You are using Thread.Join to let the UI thread pause until the other thread is done. At the same time you use Control.Invoke to let the UI thread do some action. This won't work because the UI thread is waiting for the other thread to finish.

I would suggest you either remove the Thread.Join call or do your action in the UI thread if you want it to wait for the action to finish.

Answer 2

There's only one reason a Control.Invoke() call would hang. Or a BeginInvoke() call not executing its target, same thing. It happens when the main thread of the program, the UI thread, is not idle and busy doing something else.

What the "something else" could be is all over the map. The worst thing you could do have the main thread wait for the worker thread to complete. That's a guaranteed deadlock if you use Invoke().

The condition is very easy to diagnose, use Debug + Break All and Debug + Windows + Threads. Double-click the Main thread and look at the Call Stack window. The top of the stack trace should say "Managed to Native Transition", the one below it should be FPushMessageLoop(). If you see something else then you've found the code that causes the deadlock.