I meant higher-level concurrency. Threads are great and all, unless you're trying to write a network server.

Last I checked, there were no thread-safe async/await primitives, coroutines, standard event-loops/reactors built into the language or the stdlib, though I would be very happy if this turned out to the case.

To preempt: Mio is not an acceptable answer without multi-threaded reactor capabilities and compiler-supported primitives to make the callback interface pleasant.

I would also state that Mio makes me fear that Rust will suffer the same horrible fate as Python or Ruby in this department: tons of fragmented, incompatible implementations with no blessed one. I really want to use Rust, but this is a deal-breaker.