async-std 0.99.12: async/.await is ready!

Today marks the release of Rust 1.39, with a finally ready async/.await feature.

In our announcement blog post, we communicated our intent to ship async-std on the release day of this feature. We will miss this deadline by a few days, but give you a short roadmap here.

The delay is caused by the futures-rs library, which we depend on, making their final release yesterday. We highly respect futures-rs timeline, the time was well spent in release polish and we congratulate the team to their release! Still, this means that we will release async-std a little later, to also give ourselves time for quality control and release polish. The current release date is Monday, November 11th.

Today, we will release async-std 0.99.12, a final point release for you to play around with the new async/.await feature.

The best way to try futures-rs

async-std is an easy to use, well-documented library that provides an interface very close to Rust’s standard library. It provides implementations of all important I/O types like TcpListener, File and others. It is compatible with all libraries that are using futures-rs as their library interface.

In practice, that means that async_std::stream::Stream can be used anywhere a futures::stream::Stream is expected and all I/O types can be used anywhere AsyncRead and AsyncWrite are expected.

async-std provides a book to learn the finer details and background, which we will keep continuously expanding. It supplements the official async book.

On top of that, async-std makes spawning tasks as easy as possible. For example, async-std unifies blocking and non-blocking tasks in the async_std::task module under an interface similar to std::thread::JoinHandle.

use async_std::task;
use std::thread;
use std::time::Duration;

fn main() {
    task::block_on(async {
        let mut tasks: Vec<task::JoinHandle<()>> = vec![];
        let task = task::spawn(async {
        let blocking = task::spawn_blocking(|| {
        for task in tasks {

Note: This examples still needs the unstable feature of the library.

The JoinHandle makes it easy to spawn tasks and retrieve their results in a uniform fashion. Also, every spawned task is stored within a single allocation, making this process quick and efficient.

See the task module for more details.

Current Status

async-std has been mainly focused on stabilising and trying out its interface over the last couple of months. We have used the time to gather confidence in our concept of the port of Rust’s std to the async world.

A lot of time has been spent in proper integration into the current futures library, so that you can use both the direct async-std interface and the futures-rs common traits to interact with async-std.

We have moved a number of newer features under the feature flag unstable, which acts as a stability gate similar to the #![feature(…)] attribute used in nightly versions of Rust’s standard library. One of those features is a very fast implementation of MPMC (Multiple Sender Multiple Receiver) channels, which will cover most usecases people might have. We’re still taking feedback on their interface.

We feel confident about the release and the stability promises it brings. The 1.0 version covers all important parts to build an async system.

Meet us at RustFest!

Finally, meet us all at the async/.await special edition of RustFest! We’ll be around the whole weekend, including the impl Days! We’re happy to assist you in making your library run on top of async-std or help you on your first contribution to async-std or related libraries.