Any difference between “await Task.Run(); return;” and “return Task.Run()”?

Question

Is there any conceptual difference between the following two pieces of code:

async Task TestAsync() 
{
    await Task.Run(() => DoSomeWork());
}
         


        

Answer 1

The two examples do differ. When a method is marked with the async keyword, the compiler generates a state-machine behind the scenes. This is what is responsible for resuming continuations once an awaitable has been awaited.

In contrast, when a method is not marked with async you are losing the ability to await awaitables. (That is, within the method itself; the method can still be awaited by its caller.) However, by avoiding the async keyword, you are no longer generating the state-machine, which can add a fair bit of overhead (lifting locals to fields of the state-machine, additional objects to the GC).

In examples like this, if you are able to avoid async-await and return an awaitable directly, it should be done to improve the efficiency of the method.

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