Conflict between ports and tasks wanting to destroy channels

[brson]

Test case:

use std;
import std::task;

fn a() {
    fn doit() {
        fn b(c: chan[chan[int]]) {
            let p = port[int]();   
            task::send(c, chan(p));
        }
        let p = port[chan[int]]();
        spawn b(chan(p));
        task::recv(p);
    }
    let i = 0;
    while i < 100 {
        doit();
        i += 1;
    }
}

fn main() {
    while (true) {
        let t = spawn a();
        task::join(t);
    }
}

This eventually fail somewhere in the channel destruction path, either from trying to grab a lock that doesn't exist or double freeing memory. I believe it's because the port (on one thread) and the task sending to that port (on another thread) are both trying to destroy the same channel. Run with RUST_THREADS>1.

[eholk]

This is probably due to non-atomic ref counts on channels and ports. Now that I have the proxies and message queues out of the way, I'm planning to start working on handles, which should make these issues a lot easier to deal with.