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A fast, low-level IO library for Rust focusing on non-blocking APIs, event notification, and other useful utilities for building high performance IO apps.


  • Fast - minimal overhead over the equivalent OS facilities (epoll, kqueue, etc...)
  • Zero allocations
  • A scalable readiness-based API, similar to epoll on Linux
  • Design to allow for stack allocated buffers when possible (avoid double buffering).
  • Provide utilities such as a timers, a notification channel, buffer abstractions, and a slab.


Using mio starts by creating an EventLoop, which handles receiving events from the OS and dispatching them to a supplied Handler.


use mio::*;
use mio::net::{SockAddr};
use mio::net::tcp::{TcpSocket, TcpAcceptor};

// Setup some tokens to allow us to identify which event is
// for which socket.
const SERVER: Token = Token(0);
const CLIENT: Token = Token(1);

let addr = SockAddr::parse("").unwrap();

// Setup the server socket
let server = TcpSocket::v4().unwrap()

// Create an event loop
let mut event_loop = EventLoop::<(), ()>::new().unwrap();

// Start listening for incoming connections
event_loop.register(&server, SERVER).unwrap();

// Setup the client socket
let sock = TcpSocket::v4().unwrap();

// Connect to the server

// Register the socket
event_loop.register(&sock, CLIENT).unwrap();

// Define a handler to process the events
struct MyHandler(TcpAcceptor);

impl Handler<(), ()> for MyHandler {
    fn readable(&mut self, event_loop: &mut EventLoop<(), ()>, token: Token, _: ReadHint) {
        match token {
            SERVER => {
                let MyHandler(ref mut server) = *self;
                // Accept and drop the socket immediately, this will close
                // the socket and notify the client of the EOF.
                let _ = server.accept();
            CLIENT => {
                // The server just shuts down the socket, let's just
                // shutdown the event loop
            _ => panic!("unexpected token"),

// Start handling events
let _ =;