With Rust's switch to 1:1 threading (soon to be not even optional AFAIK), how will this affect the concurrency capabilities of Rust-based web servers, and servers in general?
Various people are working on async IO solutions; but it likely won't fall into the stdlib from what I can tell.
I'm currently working on a rust abstraction for epoll and kqueue to eventually be paired with a multithreaded event loop/reactor. Lots of stuff to reimplement.
No windows support yet, but planned.
They're gonna get yanked out of the core distribution too and won't be integrated in the stdlib IO anymore, so it's fair to say that Rust is switching to 1:1 threading.
The decision was made around https://github.com/rust-lang/rfcs/pull/230 but I'm not sure whether there's any important prior discussion not linked from there, the topic has been kicked around for a bit.
That said, with a 1:1 threading model, you can still build good abstractions for asynchronous I/O onto those threads. Erlang is kind of like this in that it spawns as many threads as you have cores (unless you tell it otherwise) and uses a thread for async I/O via epoll/kqueue.