A simple communication infrastructure providing typed exchange channels.

This crate is part of the timely dataflow system, used primarily for its inter-worker communication. It may be independently useful, but it is separated out mostly to make clear boundaries in the project.

Threads are spawned with an allocator::Generic, whose allocate method returns a pair of several send endpoints and one receive endpoint. Messages sent into a send endpoint will eventually be received by the corresponding worker, if it receives often enough. The point-to-point channels are each FIFO, but with no fairness guarantees.

To be communicated, a type must implement the Bytesable trait.

Channel endpoints also implement a lower-level push and pull interface (through the Push and Pull traits), which is used for more precise control of resources.

Examples

use timely_communication::{Allocate, Bytesable};

/// A wrapper that indicates `bincode` as the serialization/deserialization strategy.
pub struct Message {
    /// Text contents.
    pub payload: String,
}

impl Bytesable for Message {
    fn from_bytes(bytes: timely_bytes::arc::Bytes) -> Self {
        Message { payload: std::str::from_utf8(&bytes[..]).unwrap().to_string() }
    }

    fn length_in_bytes(&self) -> usize {
        self.payload.len()
    }

    fn into_bytes<W: ::std::io::Write>(&self, writer: &mut W) {
        writer.write_all(self.payload.as_bytes()).unwrap();
    }
}

// extract the configuration from user-supplied arguments, initialize the computation.
let config = timely_communication::Config::from_args(std::env::args()).unwrap();
let guards = timely_communication::initialize(config, |mut allocator| {

    println!("worker {} of {} started", allocator.index(), allocator.peers());

    // allocates a pair of senders list and one receiver.
    let (mut senders, mut receiver) = allocator.allocate(0);

    // send typed data along each channel
    for i in 0 .. allocator.peers() {
        senders[i].send(Message { payload: format!("hello, {}", i)});
        senders[i].done();
    }

    // no support for termination notification,
    // we have to count down ourselves.
    let mut received = 0;
    while received < allocator.peers() {

        allocator.receive();

        if let Some(message) = receiver.recv() {
            println!("worker {}: received: <{}>", allocator.index(), message.payload);
            received += 1;
        }

        allocator.release();
    }

    allocator.index()
});

// computation runs until guards are joined or dropped.
if let Ok(guards) = guards {
    for guard in guards.join() {
        println!("result: {:?}", guard);
    }
}
else { println!("error in computation"); }

This should produce output like:

worker 0 started
worker 1 started
worker 0: received: <hello, 0>
worker 1: received: <hello, 1>
worker 0: received: <hello, 0>
worker 1: received: <hello, 1>
result: Ok(0)
result: Ok(1)