How can a background thread hang the UI thread?

Question

I am using a background thread to initialize an instrument over USB. The UI hangs when I try to open the device. I would expect the background thread to pause when calling O

Answer 1

Consider using a BackgroundWorker for this task.

Answer 2

I would suggest you wrap the call to meter.open() in a separate method, and call that method from within the updateMeter() method using Invoke() or BeginInvoke() construct on the form or parent control. Doing this will marshal the action back on to the UI thread and should execute gracefully. I hope this helps.

Answer 3

Does meter require running in an STA? Is the call to Open() actually being marshalled back to the UI thread for this reason?

You can verify this is true by looking at the callstack of the hung UI thread in the debugger.

Answer 4

How long time does the instantiation of the FancyVoltmeter take? Could it be that it is not the Open method that causes the UI freeze, but creating the COM object (which is done on the UI thread)?

If that turns out to be the case, moving the creation of this object to happen on the new, separate worker thread should take care of the problem.

Edit: I saw now that you already found this out in your comment to Michael...