A barrier enables multiple tasks to synchronize the beginning of some computation.

use sync::{Arc, Barrier};

let barrier = Arc::new(Barrier::new(10));
for _ in range(0, 10) {
    let c = barrier.clone();
    // The same messages will be printed together.
    // You will NOT see any interleaving.
    spawn(proc() {
        println!("before wait");
        c.wait();
        println!("after wait");
    });
}