Im trying to understand when to use async and when it can improve performance.
I know it’s most-powerful in replacing otherwise-blocking IO operations like file IO, http calls, database operations, etc., but I was wondering if there’s any point beyond that (at least as far as performance is concerned).
A specific example might be large memory copies (shifting a large vector or otherwise copying lots of data). This is a synchronous operation that might take a while as far as the rest of the program is concerned. Can this example take advantage of async/await in order to do other things while we wait for the copy, or must the thread wait for the memory copy before it continues to execute?
If not this direct example, maybe another synch operation that can be improved via async/await?
Async/await does not give you any parallelism, only concurrency. That means that any sync operation using async/await to divide the work will just run one part after the other, not faster than without async/await and in fact slower because it adds overhead.
You can only get parallelism via threads, and you are limited to the number of cores you have in your system.
Some async runtimes do run the code in parallel, using multiple threads, so you will get some parallelism (and therefore speed) if you'll use them correctly; but this just adds overhead over using threads directly, or using a library such as rayon that avoids async/await and parallelizes the code using threads only.
If you're not I/O bound, don't use async/await. You have nothing to gain.