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|
use arraydeque::ArrayDeque;
use spin::Mutex;
use std::mem;
use std::sync::atomic::{AtomicUsize, Ordering};
use super::constants::INORDER_QUEUE_SIZE;
pub trait SequentialJob {
fn is_ready(&self) -> bool;
fn sequential_work(self);
}
pub trait ParallelJob: Sized + SequentialJob {
fn queue(&self) -> &Queue<Self>;
fn parallel_work(&self);
}
pub struct Queue<J: SequentialJob> {
contenders: AtomicUsize,
queue: Mutex<ArrayDeque<[J; INORDER_QUEUE_SIZE]>>,
#[cfg(debug)]
_flag: Mutex<()>,
}
impl<J: SequentialJob> Queue<J> {
pub fn new() -> Queue<J> {
Queue {
contenders: AtomicUsize::new(0),
queue: Mutex::new(ArrayDeque::new()),
#[cfg(debug)]
_flag: Mutex::new(()),
}
}
pub fn push(&self, job: J) -> bool {
self.queue.lock().push_back(job).is_ok()
}
pub fn consume(&self) {
// check if we are the first contender
let pos = self.contenders.fetch_add(1, Ordering::SeqCst);
if pos > 0 {
assert!(usize::max_value() > pos, "contenders overflow");
return;
}
// enter the critical section
let mut contenders = 1; // myself
while contenders > 0 {
// check soundness in debug builds
#[cfg(debug)]
let _flag = self
._flag
.try_lock()
.expect("contenders should ensure mutual exclusion");
// handle every ready element
loop {
let mut queue = self.queue.lock();
// check if front job is ready
match queue.front() {
None => break,
Some(job) => {
if job.is_ready() {
()
} else {
break;
}
}
};
// take the job out of the queue
let job = queue.pop_front().unwrap();
debug_assert!(job.is_ready());
mem::drop(queue);
// process element
job.sequential_work();
}
#[cfg(debug)]
mem::drop(_flag);
// decrease contenders
contenders = self.contenders.fetch_sub(contenders, Ordering::SeqCst) - contenders;
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::sync::Arc;
use std::thread;
use rand::thread_rng;
use rand::Rng;
struct TestJob {}
impl SequentialJob for TestJob {
fn is_ready(&self) -> bool {
true
}
fn sequential_work(self) {}
}
/* Fuzz the Queue */
#[test]
fn test_queue() {
fn hammer(queue: &Arc<Queue<TestJob>>) {
let mut rng = thread_rng();
for _ in 0..1_000_000 {
if rng.gen() {
queue.push(TestJob {});
} else {
queue.consume();
}
}
}
let queue = Arc::new(Queue::new());
// repeatedly apply operations randomly from concurrent threads
let other = {
let queue = queue.clone();
thread::spawn(move || hammer(&queue))
};
hammer(&queue);
// wait, consume and check empty
other.join().unwrap();
queue.consume();
assert_eq!(queue.queue.lock().len(), 0);
}
}
|
