tokio 0.1.5

An event-driven, non-blocking I/O platform for writing asynchronous I/O backed applications.


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. MIT licensed Travis Build Status Appveyor Build Status

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 = "".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 =|amt| {
                println!("wrote {:?} bytes", amt)
            }).map_err(|err| {
                eprintln!("IO error {:?}", err)

            // Spawn the future as a concurrent task.

    // Start the Tokio runtime

More examples can be found here.

Project layout

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.

  • tokio-tcp: TCP bindings for use with tokio-io and tokio-reactor.

  • tokio-udp: UDP bindings for use with tokio-io and tokio-reactor.


This project is licensed under the MIT license.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in Tokio by you, shall be licensed as MIT, without any additional terms or conditions.