125 lines
3.4 KiB
Rust
125 lines
3.4 KiB
Rust
// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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use kinds::{Send, Sync};
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use sync::{Mutex, Condvar};
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/// A barrier enables multiple tasks to synchronize the beginning
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/// of some computation.
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///
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/// ```rust
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/// use std::sync::{Arc, Barrier};
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/// use std::thread::Thread;
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///
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/// let barrier = Arc::new(Barrier::new(10));
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/// for _ in range(0u, 10) {
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/// let c = barrier.clone();
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/// // The same messages will be printed together.
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/// // You will NOT see any interleaving.
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/// Thread::spawn(move|| {
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/// println!("before wait");
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/// c.wait();
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/// println!("after wait");
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/// }).detach();
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/// }
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/// ```
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pub struct Barrier {
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lock: Mutex<BarrierState>,
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cvar: Condvar,
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num_threads: uint,
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}
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unsafe impl Send for Barrier {}
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unsafe impl Sync for Barrier {}
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// The inner state of a double barrier
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struct BarrierState {
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count: uint,
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generation_id: uint,
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}
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unsafe impl Send for BarrierState {}
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unsafe impl Sync for BarrierState {}
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impl Barrier {
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/// Create a new barrier that can block a given number of threads.
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///
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/// A barrier will block `n`-1 threads which call `wait` and then wake up
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/// all threads at once when the `n`th thread calls `wait`.
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pub fn new(n: uint) -> Barrier {
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Barrier {
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lock: Mutex::new(BarrierState {
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count: 0,
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generation_id: 0,
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}),
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cvar: Condvar::new(),
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num_threads: n,
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}
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}
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/// Block the current thread until all threads has rendezvoused here.
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///
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/// Barriers are re-usable after all threads have rendezvoused once, and can
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/// be used continuously.
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pub fn wait(&self) {
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let mut lock = self.lock.lock();
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let local_gen = lock.generation_id;
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lock.count += 1;
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if lock.count < self.num_threads {
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// We need a while loop to guard against spurious wakeups.
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// http://en.wikipedia.org/wiki/Spurious_wakeup
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while local_gen == lock.generation_id &&
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lock.count < self.num_threads {
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self.cvar.wait(&lock);
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}
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} else {
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lock.count = 0;
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lock.generation_id += 1;
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self.cvar.notify_all();
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}
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}
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}
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#[cfg(test)]
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mod tests {
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use prelude::*;
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use sync::{Arc, Barrier};
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use comm::Empty;
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#[test]
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fn test_barrier() {
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let barrier = Arc::new(Barrier::new(10));
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let (tx, rx) = channel();
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for _ in range(0u, 9) {
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let c = barrier.clone();
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let tx = tx.clone();
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spawn(move|| {
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c.wait();
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tx.send(true);
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});
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}
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// At this point, all spawned tasks should be blocked,
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// so we shouldn't get anything from the port
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assert!(match rx.try_recv() {
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Err(Empty) => true,
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_ => false,
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});
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barrier.wait();
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// Now, the barrier is cleared and we should get data.
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for _ in range(0u, 9) {
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rx.recv();
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}
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}
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}
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