WaitAll for multiple handles on a STA thread is not supported

Question

1. Why do I get this error message? \"WaitAll for multiple handles on a STA thread is not supported.\"
2. Should I use [MTAThreadAttribute] attribut? Update

Answer 1

Use one ManualResetEvent and wait on it. Also maintain a TaskCount variable that is set to the number of worker threads you start, use Interlocked.Decrement in the worker thread code as the very last action of the worker and signal the event if the counter reaches zero,e.g.

// other worker actions...
if (Interlocked.Decrement(ref taskCount) == 0)
   doneEvent.Set();