What is "naturally asynchronous" or "pure asynchronous"?

Question

In a lot of discussions about C#'s async/await, I see people mention the term "naturally asynchronous" or "pure asynchronous". What exactly do these terms mean?

What are some examples of a "naturally asynchronous" operation and why is it called so?

What are some examples of a "non-naturally asynchronous" operation, and why?

Answer 1

It's almost always I/O.

Naturally asynchronous operations are operations that don't require the CPU, like sending data over the network or reading data from the hard drive. They don't require any computations so the CPU can do other tasks while they run.

There are also logical operations that don't require a thread, for example waiting for a timeout to expire, or wait on synchronization constructs (e.g. AsyncLock)

Operations that are asynchronous but not naturally asynchronous are CPU operations being executed on a background thread. These are useful for responsiveness (e.g. For UI apps) but don't improve performance or scalability as they still require the same amount of resources.

So you have:

Naturally asynchronous operations running asynchronously:

await Task.Delay(1000);

Naturally asynchronous operations running synchronously:

Thread.Sleep(1000);

Naturally synchronous operations running asynchronously:

await Task.Run(() => CalculateSquareRoot(5));

Naturally synchronous operations running synchronously:

CalculateSquareRoot(5);