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use crossbeam_deque::{self as deque, Steal, Stealer, Worker};
use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
use std::sync::{Mutex, TryLockError};
use std::thread::yield_now;
use current_num_threads;
use iter::plumbing::{bridge_unindexed, Folder, UnindexedConsumer, UnindexedProducer};
use iter::ParallelIterator;
/// Conversion trait to convert an `Iterator` to a `ParallelIterator`.
///
/// This creates a "bridge" from a sequential iterator to a parallel one, by distributing its items
/// across the Rayon thread pool. This has the advantage of being able to parallelize just about
/// anything, but the resulting `ParallelIterator` can be less efficient than if you started with
/// `par_iter` instead. However, it can still be useful for iterators that are difficult to
/// parallelize by other means, like channels or file or network I/O.
///
/// The resulting iterator is not guaranteed to keep the order of the original iterator.
///
/// # Examples
///
/// To use this trait, take an existing `Iterator` and call `par_bridge` on it. After that, you can
/// use any of the `ParallelIterator` methods:
///
/// ```
/// use rayon::iter::ParallelBridge;
/// use rayon::prelude::ParallelIterator;
/// use std::sync::mpsc::channel;
///
/// let rx = {
/// let (tx, rx) = channel();
///
/// tx.send("one!");
/// tx.send("two!");
/// tx.send("three!");
///
/// rx
/// };
///
/// let mut output: Vec<&'static str> = rx.into_iter().par_bridge().collect();
/// output.sort_unstable();
///
/// assert_eq!(&*output, &["one!", "three!", "two!"]);
/// ```
pub trait ParallelBridge: Sized {
/// Create a bridge from this type to a `ParallelIterator`.
fn par_bridge(self) -> IterBridge<Self>;
}
impl<T: Iterator + Send> ParallelBridge for T
where
T::Item: Send,
{
fn par_bridge(self) -> IterBridge<Self> {
IterBridge { iter: self }
}
}
/// `IterBridge` is a parallel iterator that wraps a sequential iterator.
///
/// This type is created when using the `par_bridge` method on `ParallelBridge`. See the
/// [`ParallelBridge`] documentation for details.
///
/// [`ParallelBridge`]: trait.ParallelBridge.html
#[derive(Debug, Clone)]
pub struct IterBridge<Iter> {
iter: Iter,
}
impl<Iter: Iterator + Send> ParallelIterator for IterBridge<Iter>
where
Iter::Item: Send,
{
type Item = Iter::Item;
fn drive_unindexed<C>(self, consumer: C) -> C::Result
where
C: UnindexedConsumer<Self::Item>,
{
let split_count = AtomicUsize::new(current_num_threads());
let (worker, stealer) = deque::fifo();
let done = AtomicBool::new(false);
let iter = Mutex::new((self.iter, worker));
bridge_unindexed(
IterParallelProducer {
split_count: &split_count,
done: &done,
iter: &iter,
items: stealer,
},
consumer,
)
}
}
struct IterParallelProducer<'a, Iter: Iterator + 'a> {
split_count: &'a AtomicUsize,
done: &'a AtomicBool,
iter: &'a Mutex<(Iter, Worker<Iter::Item>)>,
items: Stealer<Iter::Item>,
}
// manual clone because T doesn't need to be Clone, but the derive assumes it should be
impl<'a, Iter: Iterator + 'a> Clone for IterParallelProducer<'a, Iter> {
fn clone(&self) -> Self {
IterParallelProducer {
split_count: self.split_count,
done: self.done,
iter: self.iter,
items: self.items.clone(),
}
}
}
impl<'a, Iter: Iterator + Send + 'a> UnindexedProducer for IterParallelProducer<'a, Iter>
where
Iter::Item: Send,
{
type Item = Iter::Item;
fn split(self) -> (Self, Option<Self>) {
let mut count = self.split_count.load(Ordering::SeqCst);
loop {
let done = self.done.load(Ordering::SeqCst);
match count.checked_sub(1) {
Some(new_count) if !done => {
let last_count =
self.split_count
.compare_and_swap(count, new_count, Ordering::SeqCst);
if last_count == count {
return (self.clone(), Some(self));
} else {
count = last_count;
}
}
_ => {
return (self, None);
}
}
}
}
fn fold_with<F>(self, mut folder: F) -> F
where
F: Folder<Self::Item>,
{
loop {
match self.items.steal() {
Steal::Data(it) => {
folder = folder.consume(it);
if folder.full() {
return folder;
}
}
Steal::Empty => {
if self.done.load(Ordering::SeqCst) {
// the iterator is out of items, no use in continuing
return folder;
} else {
// our cache is out of items, time to load more from the iterator
match self.iter.try_lock() {
Ok(mut guard) => {
let count = current_num_threads();
let count = (count * count) * 2;
let (ref mut iter, ref worker) = *guard;
// while worker.len() < count {
// FIXME the new deque doesn't let us count items. We can just
// push a number of items, but that doesn't consider active
// stealers elsewhere.
for _ in 0..count {
if let Some(it) = iter.next() {
worker.push(it);
} else {
self.done.store(true, Ordering::SeqCst);
break;
}
}
}
Err(TryLockError::WouldBlock) => {
// someone else has the mutex, just sit tight until it's ready
yield_now(); //TODO: use a thread=pool-aware yield? (#548)
}
Err(TryLockError::Poisoned(_)) => {
// any panics from other threads will have been caught by the pool,
// and will be re-thrown when joined - just exit
return folder;
}
}
}
}
Steal::Retry => (),
}
}
}
}