NOTE: Tokio's master branch is currently in the process of moving to std::future::Future, for v0.1.x based tokio releases please check out the v0.1.x branch.

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.

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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:

#![feature(async_await)]

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

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let addr = "127.0.0.1:8080".parse()?;
    let mut listener = TcpListener::bind(&addr).unwrap();

    loop {
        let (mut socket, _) = listener.accept().await?;

        tokio::spawn(async move {
            let mut buf = [0; 1024];

            // In a loop, read data from the socket and write the data back.
            loop {
                let n = match socket.read(&mut buf).await {
                    // socket closed
                    Ok(n) if n == 0 => return,
                    Ok(n) => n,
                    Err(e) => {
                        println!("failed to read from socket; err = {:?}", e);
                        return;
                    }
                };

                // Write the data back
                if let Err(e) = socket.write_all(&buf[0..n]).await {
                    println!("failed to write to socket; err = {:?}", e);
                    return;
                }
            }
        });
    }
}

More examples can be found here. Note that the master branch is currently being updated to use async / await. The examples are not fully ported. Examples for stable Tokio can be found here.

First, see if the answer to your question can be found in the Guides or the API documentation. If the answer is not there, there is an active community in the Tokio Gitter channel. We would be happy to try to answer your question. Last, if that doesn't work, try opening an issue with the question.

🎈 Thanks for your help improving the project! We are so happy to have you! We have a contributing guide to help you get involved in the Tokio project.

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-current-thread: Schedule the execution of futures on the current thread.

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

• tokio-fs: Filesystem (and standard in / out) APIs.

• tokio-codec: Utilities for encoding and decoding protocol frames.

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

• tokio-macros: Macros for usage with Tokio.

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

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

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

• tokio-timer: Time related APIs.

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

• tokio-uds: Unix Domain Socket bindings for use with tokio-io and tokio-reactor.

In addition to the crates in this repository, the Tokio project also maintains several other libraries, including:

• tracing (formerly tokio-trace): A framework for application-level tracing and async-aware diagnostics.

• mio: A low-level, cross-platform abstraction over OS I/O APIs that powers tokio.

• bytes: Utilities for working with bytes, including efficient byte buffers.

Tokio is built against the latest stable, nightly, and beta Rust releases. The minimum version supported is the stable release from three months before the current stable release version. For example, if the latest stable Rust is 1.29, the minimum version supported is 1.26. The current Tokio version is not guaranteed to build on Rust versions earlier than the minimum supported version.

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.