Are a .NET Task thread's resources returned back to the pool temporarily if the thread is waiting on an async operation to finish?

Question

I have a TPL Task that does two things. First, it calls a web service. Second, it inserts some data into a database. I have up to 20 Tasks started at one time doing this sam

Answer 1

The answer is yes. Although technically it's not "waiting" for the async operation to complete (otherwise there would be no benefit to async). Under the hood there is a callback delegate that is run when the async operation completes, which is what allows your calling thread to proceed without blocking. It's the async/await magic that turns these 'continuations' into a linear looking piece of code.

Because you are using a threadpool thread, when it hits an await the thread will return to the threadpool. The thing to be careful with here is that the normal behaviour is when the awaited operation completes it will try to get back onto the thread that it was started on (now probably being used by another Task) so you may observe latency problems in getting the results back as threadpool threads are now tied up starting other tasks. Over time the threadpool will try to adjust the number of available threads to meet demand but you might find this doesn't happen quickly enough if you work comes in bursts. The result will be apparently poor performance as you may only have a small number of threads available.