WorkQueue implementation

[mgax]

A simple worker queue.

Example

use std::task;

// Create the queue
let (queue, dispatcher) = WorkQueue::<int, int>();

// Spawn a dispatcher thread
task::spawn(proc() { dispatcher.run(); });

// Spawn 10 workers
for _ in range(0, 10) {
    let worker = queue.worker();
    task::spawn(proc() { worker.run(|arg| arg + 2); });
}

// Execute jobs on the queue
let answers: ~[int] =
    range(0, 1000)
    .map(|n| queue.push(n))
    .map(|rv| rv.recv())
    .collect();
assert_eq!(answers, range(2, 1002).collect());

// The dispatcher and workers are shut down when `queue` goes out ouf scope

Jobs can be queued from other tasks:

let proxy = queue.proxy();
assert!(task::try(proc() {
    assert_eq!(proxy.push(5).recv(), 7);
}).is_ok());

[jdm]

cc @pcwalton

[thestinger]

In my opinion, we should have something like the Thread Building Blocks task graphs, although it would be much easier to just do a tree to start with. The building blocks for work stealing are there after all.

[brson]

We need to not take this step lightly. Rust is almost powerful enough now to express a lot of cool stuff and there are multiple competing work stealing implementations in development. This subject is probably RFC worthy.

[sinistersnare]

Shouldn't this say 2014?

[mgax]

Whoops, I blindly copied that from another file. Fixed.

[nikomatsakis]

On Mon, Mar 31, 2014 at 12:58:56PM -0700, Brian Anderson wrote:

We need to not take this step lightly. Rust is almost powerful
enough now to express a lot of cool stuff and there are multiple
competing work stealing implementations in development. This subject
is probably RFC worthy.

+1

[alexcrichton]

Thank you for this work, I think it's great that there's effort behind adding a work queue!

I agree with @brson though, that this is a broad enough topic that it warrants an RFC. Work queues have many flavors to them, and I think that an RFC is necessary to discuss the tradeoffs and discuss design for the one inside of libsync. I would recommend starting by gathering more knowledge about existing work queues in Rust and see how they play into this design. I would be more than willing to talk about the "work queue" in libgreen, and I'm sure @pcwalton would love to talk about the work queue work that he's done in Servo.

Our RFC process is documented at the rfcs repo.