c# - How does async-await not block?

Question

I gather that the async methods are good for IO work because they don't block the thread whilst they're being awaited, but how is this actually possible? I assume something has to be listening to trigger the task to complete, so does this mean that the blocking is just moved somewhere else?

Answer 1

No, the blocking is not moved anywhere else. BCL methods that return awaitable types use techniques such as overlapped I/O with I/O completion ports for a fully asynchronous experience.

I have a recent blog post that describes how this works all the way down to the physical device and back.