Async and await - difference between console, Windows Forms and ASP.NET

Question

I have been educating myself on async / await use and I think I understood under-the-hood concept. However, most of Channel 9 tutorials, MSDN articles and Stack overflow ans

Answer 1

Since, in UI thread based application, the UI thread is always available (unless the process is stopped explicitly or by Windows), so the ThreadPool thread responsible for executing the code after "await" in any async method, will guarantee to find the UI thread to post the results back (if any).

This is slightly confused. There's no indication that a ThreadPool thread will be required at all.

It's up to the awaitable implementation to determine where to run the continuation, but normally the current synchronization context is used to work out where to run it:

• In a console application, there is no synchronization context, so a thread pool thread is used for the continuation.
• In a Windows Forms application, when you're running on the UI thread the synchronization context is one which will execute code on the UI thread... so the continuation executes there (unless you use ConfigureAwait, etc...)
• In an ASP.NET application, there's a synchronization context specific to ASP.NET itself.

See Stephen Cleary's MSDN article for more details.

It's not clear what you mean by your later question about having to call Wait or Result in ASP.NET or a console app... in both scenarios it may be required, but equally it may not be. It depends on what you're doing really. Don't forget that even a console app can start its own threads and do all kinds of other things - you can write an HTTP server in a console app, for example...