Question

I would like to know how is the best way to implement my own async method. I have read this article and it says that is not a good idea to wrapper a sync method into a task and use it as async method, because this way use other thread and use more resources, that is what we want to avoid with use async.

In the article use TaskCompletionSource, but I don’t know exactly how to use it. Which is the purpose of TaskCompletionSource?

Answer 1

The best resource for writing async method is the Task-based Asynchronous Pattern (TAP) document by Stephen Toub. Much of the information in that document is now part of the official MSDN documentation.

If you want a shorter (but still thorough) tutorial, I recommend my own async/await intro blog post, and there are several other tutorials out there. Once you have learned a bit about async, the next good resource is the official async/await FAQ.

There are also tons of great async videos on Channel9. Many (most?) of them discuss async when it was still a CTP, but very few design changes were made when it went into production.

To answer your specific question, TaskCompletionSource is used to create a Task wrapper around an existing asynchronous operation (e.g., an I/O operation, timer, or event). You can’t execute code in a Task created by TaskCompletionSource; you should use Task.Run to execute code in a Task.