[pcwalton]

If you want to use epoll directly in Rust, go right ahead. Nothing is stopping you. You don't have to switch to C++ to use epoll.

It's pretty clear that most people don't want to write and maintain that kind of code, though—that's what async/await is for. Personally, I hate writing state machines.

[jnordwick]

They're not very well done. Rust kind of skipped the whole non-blocking thing and went straight to tokio, then had to backtrack a little to mio+tokio, then when mio is only half way jupmed to async/await. (mio was originall tokio rolled into it - it was the whole thing and you had to use mios sockets and mios timers on the mio event loop - tokio was then split out - metal io, it was not - this was because there wasnt a non-blocking interface in rust yet).

Async is deinitely a distraction. Rust should have stabilized other pieces more before jumping to yet another paradigm. It is gaining this collection of half-implemented things. I'm guessing generators are going to the the next move before async/await is even in the print book.

Rust has moved from zero-cost abstraction to "an fairly efficient implemention of everything you can think of".

[pcwalton]

Rust didn't implement async/await for fun. The team implemented it because it was perhaps the #1 requested feature from users, including me.

You can see it here on HN. What's the #1 comment that always appears on Rust async threads? Invariably it's "why not just use goroutines? That kind of code is so much easier to write!" Now for various reasons M:N threading like in Go doesn't work in Rust. What does work, and offers most of the ergonomics of threads/goroutines, is async/await. That's why the team has prioritized it.

There are people who care less about ergonomics than optimizing every CPU cycle for socket servers. For those people, the focus on getting the ergonomics right before microoptimization of mio and tokio might be frustrating to see. But the overwhelming majority of users just want easy-to-use async I/O. Async/await is an enormous improvement in readability and maintainability over hand-written state machines. Rust would be doing a disservice to its users if it focused on microoptimization of tokio instead.

[saghm]

> Rust kind of skipped the whole non-blocking thing and went straight to tokio, then had to backtrack a little to mio+tokio, then when mio is only half way jupmed to async/await.

Not sure exactly what you mean here; mio predates tokio by a couple years, and has been possible to use standalone since before tokio ever became a thing.

[devit]

Early versions of mio had a bunch of non-essential things like a timer wheel built-in, that were later removed.

[rapsey]

What does tokio have to do with that?

[SomeOldThrow]

This strikes me as needlessly hostile without contributing anything.