TaskCompletionSource - Trying to understand threadless async work

Question

I\'m trying to understand the purpose of TaskCompletionSource and its relation to async/threadless work. I think I have the general idea but I want to make sure

Answer 1

TaskCompletionSource is used to create Task objects that don't execute code.

They're used quite a bit by Microsoft's new async APIs - any time there's I/O-based asynchronous operations (or other non-CPU-based asynchronous operations, like a timeout). Also, any async Task method you write will use TCS to complete its returned Task.

I have a blog post Creating Tasks that discusses different ways to create Task instances. It's written from an async/await perspective (not a TPL perspective), but it still applies here.

Also see Stephen Toub's excellent posts:

• The Nature of TaskCompletionSource
• Mechanisms for Creating Tasks
• await anything; (using TaskCompletionSource to await anything).
• Using Tasks to implement the APM Pattern (creating Begin/End using TaskCompletionSource).