如何正确等待调用Dispatcher.Invoke的多个线程在WPF应用程序中完成

I have a WPF application that kicks off 3 threads and needs to wait for them to finish. I have read many posts here that deal with this but none seem to address the situation where the thread code calls Dispatcher.Invoke or Dispatcher.BeginInvoke. If I use the thread's Join() method or a ManualResetEvent, the thread blocks on the Invoke call. Here's a simplified code snippet of an ugly solution that seems to work:I have a WPF application that kicks off 3 threa