async await performance?

Question

(Just a theoretical question - for non-gui apps)

Assuming I have this code with many awaits:

public async Task<T> ConsumeAsync()     {           await A();           await b();           await c();           await d();           //..     } 

Where each task can take a very short period of time ,

Question (again , theoretical)

There could be a situation where the overall time dealing with all those "releasing back threads" and "fetching threads back" ( red & green here :)

Is taking more time than a single thread which could done all the work with a small amount of delay ,

I mean , I wanted to be the most productive , but instead , since all those switches back and forth - I actually lost productivity.

Can such scenario occur ?

Answer 1

Yes, in theory. Not normally, in the real world.

In the common case, async is used for I/O-bound operations, and the overhead of thread management is undetectable in comparison to them. Most of the time, asynchronous operations either take a very long time (compared to thread management) or are already completed (e.g., a cache). Note that async has a "fast path" that kicks in if the operation is already completed, where it does not yield the thread.

For more information, see the Zen of Async and Async Performance.