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lock-free queue for scheduler message queue
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/* Multi-producer/single-consumer queue | ||
* Copyright (c) 2010-2011 Dmitry Vyukov. All rights reserved. | ||
* Redistribution and use in source and binary forms, with or without | ||
* modification, are permitted provided that the following conditions are met: | ||
* | ||
* 1. Redistributions of source code must retain the above copyright notice, | ||
* this list of conditions and the following disclaimer. | ||
* | ||
* 2. Redistributions in binary form must reproduce the above copyright | ||
* notice, this list of conditions and the following disclaimer in the | ||
* documentation and/or other materials provided with the distribution. | ||
* | ||
* THIS SOFTWARE IS PROVIDED BY DMITRY VYUKOV "AS IS" AND ANY EXPRESS OR IMPLIED | ||
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF | ||
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT | ||
* SHALL DMITRY VYUKOV OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, | ||
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT | ||
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR | ||
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF | ||
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE | ||
* OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF | ||
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | ||
* | ||
* The views and conclusions contained in the software and documentation are | ||
* those of the authors and should not be interpreted as representing official | ||
* policies, either expressed or implied, of Dmitry Vyukov. | ||
*/ | ||
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//! A mostly lock-free multi-producer, single consumer queue. | ||
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use unstable::sync::UnsafeArc; | ||
use unstable::atomics::{AtomicPtr,Relaxed,Release,Acquire}; | ||
use ptr::{mut_null, to_mut_unsafe_ptr}; | ||
use cast; | ||
use option::*; | ||
use clone::Clone; | ||
use default::Default; | ||
use kinds::Send; | ||
use fmt; | ||
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struct Node<T> { | ||
next: AtomicPtr<Node<T>>, | ||
value: Option<T>, | ||
} | ||
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impl<T> Node<T> { | ||
fn new(value: T) -> Node<T> { | ||
Node{next: AtomicPtr::new(mut_null()), value: Some(value)} | ||
} | ||
} | ||
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impl<T> Default for Node<T> { | ||
fn default() -> Node<T> { | ||
Node{next: AtomicPtr::new(mut_null()), value: None} | ||
} | ||
} | ||
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struct State<T> { | ||
stub: Node<T>, | ||
head: AtomicPtr<Node<T>>, | ||
tail: *mut Node<T>, | ||
} | ||
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struct Queue<T> { | ||
priv state: UnsafeArc<State<T>>, | ||
} | ||
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impl<T: Send> Clone for Queue<T> { | ||
fn clone(&self) -> Queue<T> { | ||
Queue { | ||
state: self.state.clone() | ||
} | ||
} | ||
} | ||
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impl<T: Send> fmt::Default for Queue<T> { | ||
fn fmt(value: &Queue<T>, f: &mut fmt::Formatter) { | ||
write!(f.buf, "Queue({})", value.state.get()); | ||
} | ||
} | ||
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impl<T: Send> Queue<T> { | ||
pub fn new() -> Queue<T> { | ||
let mut q = Queue{state: UnsafeArc::new(State { | ||
stub: Default::default(), | ||
head: AtomicPtr::new(mut_null()), | ||
tail: mut_null(), | ||
})}; | ||
let stub = q.get_stub_unsafe(); | ||
q.get_head().store(stub, Relaxed); | ||
q.set_tail(stub); | ||
q | ||
} | ||
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pub fn push(&mut self, value: T) { | ||
unsafe { | ||
let node = cast::transmute(~Node::new(value)); | ||
self.push_node(node); | ||
} | ||
} | ||
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fn push_node(&mut self, node: *mut Node<T>) { | ||
unsafe { | ||
(*node).next.store(mut_null(), Release); | ||
let prev = (*self.state.get()).head.swap(node, Relaxed); | ||
(*prev).next.store(node, Release); | ||
} | ||
} | ||
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fn get_stub_unsafe(&mut self) -> *mut Node<T> { | ||
unsafe { to_mut_unsafe_ptr(&mut (*self.state.get()).stub) } | ||
} | ||
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fn get_head(&mut self) -> &mut AtomicPtr<Node<T>> { | ||
unsafe { &mut (*self.state.get()).head } | ||
} | ||
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fn get_tail(&mut self) -> *mut Node<T> { | ||
unsafe { (*self.state.get()).tail } | ||
} | ||
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fn set_tail(&mut self, tail: *mut Node<T>) { | ||
unsafe { (*self.state.get()).tail = tail } | ||
} | ||
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pub fn casual_pop(&mut self) -> Option<T> { | ||
self.pop() | ||
} | ||
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pub fn pop(&mut self) -> Option<T> { | ||
unsafe { | ||
let mut tail = self.get_tail(); | ||
let mut next = (*tail).next.load(Acquire); | ||
let stub = self.get_stub_unsafe(); | ||
if tail == stub { | ||
if mut_null() == next { | ||
return None | ||
} | ||
self.set_tail(next); | ||
tail = next; | ||
next = (*next).next.load(Acquire); | ||
} | ||
if next != mut_null() { | ||
let tail: ~Node<T> = cast::transmute(tail); | ||
self.set_tail(next); | ||
return tail.value | ||
} | ||
let head = self.get_head().load(Relaxed); | ||
if tail != head { | ||
return None | ||
} | ||
self.push_node(stub); | ||
next = (*tail).next.load(Acquire); | ||
if next != mut_null() { | ||
let tail: ~Node<T> = cast::transmute(tail); | ||
self.set_tail(next); | ||
return tail.value | ||
} | ||
} | ||
None | ||
} | ||
} | ||
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#[cfg(test)] | ||
mod tests { | ||
use prelude::*; | ||
use option::*; | ||
use task; | ||
use comm; | ||
use fmt; | ||
use super::Queue; | ||
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#[test] | ||
fn test() { | ||
let nthreads = 8u; | ||
let nmsgs = 1000u; | ||
let mut q = Queue::new(); | ||
assert_eq!(None, q.pop()); | ||
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for _ in range(0, nthreads) { | ||
let (port, chan) = comm::stream(); | ||
chan.send(q.clone()); | ||
do task::spawn_sched(task::SingleThreaded) { | ||
let mut q = port.recv(); | ||
for i in range(0, nmsgs) { | ||
q.push(i); | ||
} | ||
} | ||
} | ||
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let mut i = 0u; | ||
loop { | ||
match q.pop() { | ||
None => {}, | ||
Some(_) => { | ||
i += 1; | ||
if i == nthreads*nmsgs { break } | ||
} | ||
} | ||
} | ||
} | ||
} | ||
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