I understand threads but I like using async for certain things.

If I had a web service using threads, would I map each request to one thread in a thread pool? It seems like a waste of OS resources when the IO multiplexing can be done without OS threads.

> last time I checked a lot of crates.io is filled with async functions for stuff that doesn't actually block.

Like what? Even file I/O blocks for large files on slow devices, so something like async tarball handling has a use case.

It's best to write in the sans-IO style and then your threading or async can be a thin layer on top that drives a dumb state machine. But in practice I find that passable sans-IO code is harder to write than passable async. It makes a lot of sense for a deep indirect dependency like an HTTP library, but less sense for an app