Deadlock with select-send and select-recv

[ghost]

Code is worth more than a thousand words. :)

#[macro_use]
extern crate chan;
extern crate crossbeam;

fn main() {
    let (tx, rx) = chan::sync(0);

    // Good.
    crossbeam::scope(|s| {
        let (tx, rx) = (tx.clone(), rx.clone());
        s.spawn(move || tx.send(()));
        s.spawn(move || chan_select! { rx.recv() => {} });
    });

    // Good.
    crossbeam::scope(|s| {
        let (tx, rx) = (tx.clone(), rx.clone());
        s.spawn(move || chan_select! { tx.send(()) => {} });
        s.spawn(move || rx.recv());
    });

    // Deadlock.
    crossbeam::scope(|s| {
        let (tx, rx) = (tx.clone(), rx.clone());
        s.spawn(move || chan_select! { tx.send(()) => {} });
        s.spawn(move || chan_select! { rx.recv() => {} });
    });
}

[BurntSushi]

Interesting. Does this happen without using crossbeam? i.e., Does there exist a smaller example?

[ghost]

Yes. Here's the smallest example I've got:

#[macro_use]
extern crate chan;

use std::thread;

fn main() {
    let (tx, rx) = chan::sync(0);
    thread::spawn(move || chan_select! { tx.send(()) => {} });
    chan_select! { rx.recv() => {} }
}