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// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! A concurrent queue that supports multiple producers and a
//! single consumer.
use container::Container;
use kinds::Send;
use vec::OwnedVector;
use cell::Cell;
use option::*;
use unstable::sync::{UnsafeArc, LittleLock};
use clone::Clone;
pub struct MessageQueue<T> {
priv state: UnsafeArc<State<T>>
}
struct State<T> {
count: uint,
queue: ~[T],
lock: LittleLock
}
impl<T: Send> MessageQueue<T> {
pub fn new() -> MessageQueue<T> {
MessageQueue {
state: UnsafeArc::new(State {
count: 0,
queue: ~[],
lock: LittleLock::new()
})
}
}
pub fn push(&mut self, value: T) {
unsafe {
let value = Cell::new(value);
let state = self.state.get();
do (*state).lock.lock {
(*state).count += 1;
(*state).queue.push(value.take());
}
}
}
pub fn pop(&mut self) -> Option<T> {
unsafe {
let state = self.state.get();
do (*state).lock.lock {
if !(*state).queue.is_empty() {
(*state).count += 1;
Some((*state).queue.shift())
} else {
None
}
}
}
}
/// A pop that may sometimes miss enqueued elements, but is much faster
/// to give up without doing any synchronization
pub fn casual_pop(&mut self) -> Option<T> {
unsafe {
let state = self.state.get();
// NB: Unsynchronized check
if (*state).count == 0 { return None; }
do (*state).lock.lock {
if !(*state).queue.is_empty() {
(*state).count += 1;
Some((*state).queue.shift())
} else {
None
}
}
}
}
}
impl<T: Send> Clone for MessageQueue<T> {
fn clone(&self) -> MessageQueue<T> {
MessageQueue {
state: self.state.clone()
}
}
}
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