A runtime for writing reliable, asynchronous, and slim applications with the Rust programming language. It is:

• Fast: Tokio's zero-cost abstractions give you bare-metal performance.

• Reliable: Tokio leverages Rust's ownership, type system, and concurrency model to reduce bugs and ensure thread safety.

• Scalable: Tokio has a minimal footprint, and handles backpressure and cancellation naturally.

Website | Guides | API Docs

The API docs for the master branch are published here.

Tokio is an event-driven, non-blocking I/O platform for writing asynchronous applications with the Rust programming language. At a high level, it provides a few major components:

• A multithreaded, work-stealing based task scheduler.
• A reactor backed by the operating system's event queue (epoll, kqueue, IOCP, etc...).
• Asynchronous TCP and UDP sockets.

These components provide the runtime components necessary for building an asynchronous application.

A basic TCP echo server with Tokio:

extern crate tokio;

use tokio::prelude::*;
use tokio::io::copy;
use tokio::net::TcpListener;

fn main() {
    // Bind the server's socket.
    let addr = "127.0.0.1:12345".parse().unwrap();
    let listener = TcpListener::bind(&addr)
        .expect("unable to bind TCP listener");

    // Pull out a stream of sockets for incoming connections
    let server = listener.incoming()
        .map_err(|e| eprintln!("accept failed = {:?}", e))
        .for_each(|sock| {
            // Split up the reading and writing parts of the
            // socket.
            let (reader, writer) = sock.split();

            // A future that echos the data and returns how
            // many bytes were copied...
            let bytes_copied = copy(reader, writer);

            // ... after which we'll print what happened.
            let handle_conn = bytes_copied.map(|amt| {
                println!("wrote {:?} bytes", amt)
            }).map_err(|err| {
                eprintln!("IO error {:?}", err)
            });

            // Spawn the future as a concurrent task.
            tokio::spawn(handle_conn)
        });

    // Start the Tokio runtime
    tokio::run(server);
}

More examples can be found here.

The tokio crate, found at the root, is primarily intended for use by application developers. Library authors should depend on the sub crates, which have greater guarantees of stability.

The crates included as part of Tokio are:

• tokio-executor: Task execution related traits and utilities.

• tokio-io: Asynchronous I/O related traits and utilities.

• tokio-reactor: Event loop that drives I/O resources (like TCP and UDP sockets).

• tokio-threadpool: Schedules the execution of futures across a pool of threads.

This project is licensed under either of

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in tokio by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.