tokio-io-pool

This crate provides a thread pool for executing I/O-heavy futures.

The standard Runtime provided by tokio uses a thread-pool to allow concurrent execution of compute-heavy futures. However, it (currently) uses only a single I/O reactor to drive all network and file activity. While this trade-off works well for many asynchronous applications, it is not a great fit for high-performance I/O bound applications that are bottlenecked primarily by system calls.

This crate provides an alternative implementation of a futures-based thread pool. It spawns a pool of threads that each runs a tokio::runtime::current_thread::Runtime (and thus each have an I/O reactor of their own), and spawns futures onto the pool by assigning the future to threads round-robin. Once a future has been spawned onto a thread, it, and any child futures it may produce through tokio::spawn, remain under the control of that same thread.

Be aware that this pool does not support the blocking function since it is not supported by the underlying current_thread::Runtime. Hopefully this will be rectified down the line.

There is some discussion around trying to merge this pool into tokio proper; that effort is tracked in tokio-rs/tokio#486.

Examples

extern crate tokio_io_pool;
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_io_pool::run(server);
}