Async all the way down?

Question

Trying to understand the new async/await pattern, I have one question which I can\'t find an answer to, namely if I should decorate my methods with async, if I intend to cal

Answer 1

Both versions work effectively the same, the only difference is that when you use await here, you get some performance penalty (because the state machine must be set up and a continuation will most likely be used).

So, it comes down to a tradeoff: Do you want your methods to be somewhat more efficient at the cost of being slightly less readable? Or are you willing to sacrifice performance for readability?

Usually, I would advise you to go for readability first and only focus on performance if profiling tells you it's worth it. But in this case, I think the increase in readability is small, so I would probably not use await.

Also note that your class C still doesn't go far enough: foo1() also doesn't need await.

Answer 2

The async in the signature is there to allow the compiler to create the state-machine rewriting of the contained code that is necessary to implement the await semantics in the general case.

Your example is exactly the special case where you do not need that rewriting: The asynchronous operation is the last thing happening within a method. That kind of method is already possible and valid in .NET4.0. This compatibility might be one reason to avoid async when you do not need it.