* 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)
