Even though I want to render 100 thumbnails asynchronously, I don't
want them all being "worked on" at once.
Or do you? Keep in mind that async tasks are much lighter weight than threads and that the thread pool that runs these tasks is cooperative (with regards that last point, if you haven’t watched WWDC 2021 Session 10254 Swift concurrency: Behind the scenes you should). So, it might be OK to use a lot of tasks, depending on your exact requirements. Specifically:
-
Is your rendering entirely CPU bound? If not, using tasks isn’t wise, because you’re holding down a cooperative thread waiting on I/O.
Note Keep in mind that I/O could include “talking to the GPU” (-:
-
Is rendering each thumbnail reasonably fast? If not, you may want to insert a yield to avoid hogging the cooperative thread for too long.
If the current task model isn’t suitable then, yeah, things get more complex. Long term I suspect that the answer will lie in a custom executor (see Support custom executors in Swift concurrency). In the absence of that, I think you’ll end up needing to use one of the existing primitives for your core concurrency.
One thing to keep in mind here is that you can still model this as an async function for the benefit of your clients. withCheckedContinuation is your friend (-: (see SE-0300 Continuations for interfacing async tasks with synchronous code).
Share and Enjoy
Quinn “The Eskimo!” @ DTS @ Apple