Async task conversion

Question

I have a method which invokes a while loop with a condition defined as a specified time. The body of the loop must remain synchronous up to the very end, the last couple commands are a brutally long call into some other api. I know I can execute the body
of the loop synchronously over and over and queue the object it produces to be consumed by a parallel foreach as one option.
I do not want to exceed a defined threshold on the number of objects produced by the while loop, so one neat approach I saw was the second answer to http://stackoverflow.com/questions/22492383/throttling-asynchronous-tasks by
Noseratio.
I admit, I am new to async tasks and really not clear on the best approach to move out the small bit of code at the end of the loop into an async method. I assume I could run the loop entirely with the using context of a SemaphoreSlim and await
_semaphore.WaitAsync(); *after* the object is submitted for asynchronous completion so as not exceed the max number of tasks.
My confusion comes from the format of the new method containing the long waiting call I want moved out? I see so much literature on async/await/Task.FromResult etc?
In his second code block where he speaks of TPL Dataflow or Rx, why do I mostly see the pattern of a method with an async Task signature called from a method with an async void sig? Why not dispatch an asynchronous method directly and if needed, grab the
return if one needs to utilize the result?
Thanks!

Answer 1

Async and tasks is tricky.
It's easy to do simple stuff.  Quite easy to mess it up though.
When you try and do hard things then it can easily go wrong and be quite difficult to work out what's up.
I don't like the sound of putting ( what sounds like ) a very long call into a task this way.
If it's a very long call I would prefer async and callback to tasks.
I'd consider decoupling and putting it in a wcf or windows service.
If there are a load of these potentially then I might even decouple further by message queue so the "main" app and this processing can carry on at different speeds.
If there's a bunch of processing then windows workflow might be useful.
If there's a shed load of processing then putting it on a different machine and maybe even appfabric is something to consider.
That's probably well over the top though.
Hope that helps.
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