Invoke() is blocking

Question

From time to time my applications GUI stops redrawing. There a lot of threads that are firing all kinds of events (like timers or network data ready etc.). Also there are a lot of controls that are subscribing these events. Because of that, all the event handlers play the InvokeRequired/Invoke game. Now I figured out that when the GUI freezes a lot of threads are waiting for Invoke() to return. Looks like the message pump stopped pumping. The handlers look like this:

private void MyEventHandler( object sender, EventArgs e ) {     if ( InvokeRequired ) {         Invoke( new EventHandler( MyEventHandler ), sender, e );         return;     }      SetSomeStateVariable();     Invalidate(); } 

Any ideas?

Solution: BeginInvoke(). Looks like you should always use BeginInvoke() if you have lots of CrossThread-Events...

Thanks.

Thanks everybody.

EDIT: Looks like BeginInvoke() really solved it. No freezing until now.

Answer 1

Invoke waits until the event is handled in the GUI thread. If you want it to be asynchronous use BeginInvoke()

Answer 2

Deadlock perhaps? Do you make sure that the events are never fired while holding a lock?

Are you able to see this with a debugger attached? If so, make it freeze and then hit the "pause" button - and see what the UI thread is doing.

Note that if you are able to get away with BeginInvoke instead of Invoke, life is a bit easier as it won't block.

Also note that you don't need the "new EventHandler" bit - just

Invoke((EventHandler) MyEventHandler, sender, e); 

should be fine.