* Attempt at fixing hang on exit by ending the WindowNotificationManager notification loop, so that the Thread running it can exit. * explicitly apply the NotificationManager template to allow the notification loop to begin * NotificationHelper - remove explicity call to ApplyTemplate(). Change to ManualResetEventSlim so we can cancel the Wait on it. * add a timeout to AudioRenderSystem.Stop()'s waiting for the termination signal, log a warning if this timeout occurs, and continue execution * NotifiationHelper - cancel first, the CompleteAdding() * Remove AudioRenderSystem._terminationEvent, redundant * NotificationHelper - use host.Closing event to trigger cancellation instead of _notifationManager.DetachedFromLogicalTree * Change NotificationHelper to use an explicit Thread for background work. Wait on the cancellationToken's WaitHandle so the Thread doesn't have to deal with async. Wrap foreach in try/catch (OperationCanceledException) to swallow the escaping exception from the GetConsumingEnumerable(). * adjust formatting of AsyncWorkQueue constructor to use object initializers consistently * use AsyncWorkQueue to do everything I added in SetNotificationManager() * Revert "use AsyncWorkQueue to do everything I added in SetNotificationManager()" This reverts commit f0e78366b8776ec8e2fef8ab023c0db1833155d3. * use AsyncWorkQueue to handle the Thread-related changes previously made to NotificationHelper.SetNotificationHelper(). Wrap it in Lazy<T> and force instantiation in the TemplateApplied event handler to accomodate for the fact that AsyncWorkQueue starts immediately, and the notification dispatch loop was being delayed by _templateAppliedEvent. * impl changes suggested by AcK77 * impl changes suggested by AcK77 (more)