Zero-cost futures in Rust · Aaron Turon
One of the key gaps in Rust’s ecosystem has been a strong story for fast and productive asynchronous I/O. We have solid foundations, like the mio library, but they’re very low level: you have to wire up state machines and juggle callbacks directly.
We’ve wanted something higher level, with better ergonomics, but also better composability, supporting an ecosystem of asynchronous abstractions that all work together. This story might sound familiar: it’s the same goal that’s led to the introduction of futures (aka promises) in many languages, with some supporting async/await sugar on top.
A major tenet of Rust is the ability to build zero-cost abstractions, and that leads to one additional goal for our async I/O story: ideally, an abstraction like futures should compile down to something equivalent to the state-machine-and-callback-juggling code we’re writing today (with no additional runtime overhead).
Over the past couple of months, Alex Crichton and I have developed a zero-cost futures library for Rust, one that we believe achieves these goals. (Thanks to Carl Lerche, Yehuda Katz, and Nicholas Matsakis for insights along the way.)
