Crate tokio_core [] [src]

Future-powered I/O at the core of Tokio

This crate uses the futures crate to provide an event loop ("reactor core") which can be used to drive I/O like TCP and UDP, spawned future tasks, and other events like channels/timeouts. All asynchronous I/O is powered by the mio crate.

The concrete types provided in this crate are relatively bare bones but are intended to be the essential foundation for further projects needing an event loop. In this crate you'll find:

  • TCP, both streams and listeners
  • UDP sockets
  • Message queues
  • Timeouts

More functionality is likely to be added over time, but otherwise the crate is intended to be flexible, with the PollEvented type accepting any type that implements mio::Evented. For example, the tokio-uds crate uses PollEvented to provide support for Unix domain sockets.

Some other important tasks covered by this crate are:

  • The ability to spawn futures into an event loop. The Handle and Pinned types have a spawn method which allows executing a future on an event loop. The Pinned::spawn method crucially does not require the future itself to be Send.

  • The Io trait serves as an abstraction for future crates to build on top of. This packages up Read and Write functionality as well as the ability to poll for readiness on both ends.

  • All I/O is futures-aware. If any action in this crate returns "not ready" or "would block", then the current future task is scheduled to receive a notification when it would otherwise make progress.


A simple TCP echo server:

extern crate futures;
extern crate tokio_core;

use std::env;
use std::net::SocketAddr;

use futures::Future;
use futures::stream::Stream;
use tokio_core::io::{copy, Io};
use tokio_core::net::TcpListener;
use tokio_core::reactor::Core;

fn main() {
    let addr = env::args().nth(1).unwrap_or("".to_string());
    let addr = addr.parse::<SocketAddr>().unwrap();

    // Create the event loop that will drive this server
    let mut l = Core::new().unwrap();
    let handle = l.handle();

    // Create a TCP listener which will listen for incoming connections
    let socket = TcpListener::bind(&addr, &handle).unwrap();

    // Once we've got the TCP listener, inform that we have it
    println!("Listening on: {}", addr);

    // Pull out the stream of incoming connections and then for each new
    // one spin up a new task copying data.
    // We use the `io::copy` future to copy all data from the
    // reading half onto the writing half.
    let done = socket.incoming().for_each(|(socket, addr)| {
        let pair = futures::lazy(|| Ok(socket.split()));
        let amt = pair.and_then(|(reader, writer)| copy(reader, writer));

        // Once all that is done we print out how much we wrote, and then
        // critically we *spawn* this future which allows it to run
        // concurrently with other connections.
        handle.spawn(amt.then(move |result| {
            println!("wrote {:?} bytes to {}", result, addr);


    // Execute our server (modeled as a future) and wait for it to
    // complete.;


channel [Deprecated]

In-memory evented channels.


I/O conveniences when working with primitives in tokio-core


TCP/UDP bindings for tokio-core


The core reactor driving all I/O



A convenience macro for working with io::Result<T> from the Read and Write traits.