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use crate::TaskPool;
mod adapters;
pub use adapters::*;
/// [`ParallelIterator`] closely emulates the `std::iter::Iterator`
/// interface. However, it uses `bevy_task` to compute batches in parallel.
///
/// Note that the overhead of [`ParallelIterator`] is high relative to some
/// workloads. In particular, if the batch size is too small or task being
/// run in parallel is inexpensive, *a [`ParallelIterator`] could take longer
/// than a normal [`Iterator`]*. Therefore, you should profile your code before
/// using [`ParallelIterator`].
pub trait ParallelIterator<BatchIter>
where
BatchIter: Iterator + Send,
Self: Sized + Send,
{
/// Returns the next batch of items for processing.
///
/// Each batch is an iterator with items of the same type as the
/// [`ParallelIterator`]. Returns `None` when there are no batches left.
fn next_batch(&mut self) -> Option<BatchIter>;
/// Returns the bounds on the remaining number of items in the
/// parallel iterator.
///
/// See [`Iterator::size_hint()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.size_hint)
fn size_hint(&self) -> (usize, Option<usize>) {
(0, None)
}
/// Consumes the parallel iterator and returns the number of items.
///
/// See [`Iterator::count()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.count)
fn count(mut self, pool: &TaskPool) -> usize {
pool.scope(|s| {
while let Some(batch) = self.next_batch() {
s.spawn(async move { batch.count() });
}
})
.iter()
.sum()
}
/// Consumes the parallel iterator and returns the last item.
///
/// See [`Iterator::last()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.last)
fn last(mut self, _pool: &TaskPool) -> Option<BatchIter::Item> {
let mut last_item = None;
while let Some(batch) = self.next_batch() {
last_item = batch.last();
}
last_item
}
/// Consumes the parallel iterator and returns the nth item.
///
/// See [`Iterator::nth()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.nth)
// TODO: Optimize with size_hint on each batch
fn nth(mut self, _pool: &TaskPool, n: usize) -> Option<BatchIter::Item> {
let mut i = 0;
while let Some(batch) = self.next_batch() {
for item in batch {
if i == n {
return Some(item);
}
i += 1;
}
}
None
}
/// Takes two parallel iterators and returns a parallel iterators over
/// both in sequence.
///
/// See [`Iterator::chain()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.chain)
// TODO: Use IntoParallelIterator for U
fn chain<U>(self, other: U) -> Chain<Self, U>
where
U: ParallelIterator<BatchIter>,
{
Chain {
left: self,
right: other,
left_in_progress: true,
}
}
/// Takes a closure and creates a parallel iterator which calls that
/// closure on each item.
///
/// See [`Iterator::map()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.map)
fn map<T, F>(self, f: F) -> Map<Self, F>
where
F: FnMut(BatchIter::Item) -> T + Send + Clone,
{
Map { iter: self, f }
}
/// Calls a closure on each item of a parallel iterator.
///
/// See [`Iterator::for_each()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.for_each)
fn for_each<F>(mut self, pool: &TaskPool, f: F)
where
F: FnMut(BatchIter::Item) + Send + Clone + Sync,
{
pool.scope(|s| {
while let Some(batch) = self.next_batch() {
let newf = f.clone();
s.spawn(async move {
batch.for_each(newf);
});
}
});
}
/// Creates a parallel iterator which uses a closure to determine
/// if an element should be yielded.
///
/// See [`Iterator::filter()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.filter)
fn filter<F>(self, predicate: F) -> Filter<Self, F>
where
F: FnMut(&BatchIter::Item) -> bool,
{
Filter {
iter: self,
predicate,
}
}
/// Creates a parallel iterator that both filters and maps.
///
/// See [`Iterator::filter_map()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.filter_map)
fn filter_map<R, F>(self, f: F) -> FilterMap<Self, F>
where
F: FnMut(BatchIter::Item) -> Option<R>,
{
FilterMap { iter: self, f }
}
/// Creates a parallel iterator that works like map, but flattens
/// nested structure.
///
/// See [`Iterator::flat_map()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.flat_map)
fn flat_map<U, F>(self, f: F) -> FlatMap<Self, F>
where
F: FnMut(BatchIter::Item) -> U,
U: IntoIterator,
{
FlatMap { iter: self, f }
}
/// Creates a parallel iterator that flattens nested structure.
///
/// See [`Iterator::flatten()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.flatten)
fn flatten(self) -> Flatten<Self>
where
BatchIter::Item: IntoIterator,
{
Flatten { iter: self }
}
/// Creates a parallel iterator which ends after the first None.
///
/// See [`Iterator::fuse()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.fuse)
fn fuse(self) -> Fuse<Self> {
Fuse { iter: Some(self) }
}
/// Does something with each item of a parallel iterator, passing
/// the value on.
///
/// See [`Iterator::inspect()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.inspect)
fn inspect<F>(self, f: F) -> Inspect<Self, F>
where
F: FnMut(&BatchIter::Item),
{
Inspect { iter: self, f }
}
/// Borrows a parallel iterator, rather than consuming it.
///
/// See [`Iterator::by_ref()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.by_ref)
fn by_ref(&mut self) -> &mut Self {
self
}
/// Transforms a parallel iterator into a collection.
///
/// See [`Iterator::collect()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.collect)
// TODO: Investigate optimizations for less copying
fn collect<C>(mut self, pool: &TaskPool) -> C
where
C: FromIterator<BatchIter::Item>,
BatchIter::Item: Send + 'static,
{
pool.scope(|s| {
while let Some(batch) = self.next_batch() {
s.spawn(async move { batch.collect::<Vec<_>>() });
}
})
.into_iter()
.flatten()
.collect()
}
/// Consumes a parallel iterator, creating two collections from it.
///
/// See [`Iterator::partition()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.partition)
// TODO: Investigate optimizations for less copying
fn partition<C, F>(mut self, pool: &TaskPool, f: F) -> (C, C)
where
C: Default + Extend<BatchIter::Item> + Send,
F: FnMut(&BatchIter::Item) -> bool + Send + Sync + Clone,
BatchIter::Item: Send + 'static,
{
let (mut a, mut b) = <(C, C)>::default();
pool.scope(|s| {
while let Some(batch) = self.next_batch() {
let newf = f.clone();
s.spawn(async move { batch.partition::<Vec<_>, F>(newf) });
}
})
.into_iter()
.for_each(|(c, d)| {
a.extend(c);
b.extend(d);
});
(a, b)
}
/// Repeatedly applies a function to items of each batch of a parallel
/// iterator, producing a Vec of final values.
///
/// *Note that this folds each batch independently and returns a Vec of
/// results (in batch order).*
///
/// See [`Iterator::fold()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.fold)
fn fold<C, F, D>(mut self, pool: &TaskPool, init: C, f: F) -> Vec<C>
where
F: FnMut(C, BatchIter::Item) -> C + Send + Sync + Clone,
C: Clone + Send + Sync + 'static,
{
pool.scope(|s| {
while let Some(batch) = self.next_batch() {
let newf = f.clone();
let newi = init.clone();
s.spawn(async move { batch.fold(newi, newf) });
}
})
}
/// Tests if every element of the parallel iterator matches a predicate.
///
/// *Note that all is **not** short circuiting.*
///
/// See [`Iterator::all()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.all)
fn all<F>(mut self, pool: &TaskPool, f: F) -> bool
where
F: FnMut(BatchIter::Item) -> bool + Send + Sync + Clone,
{
pool.scope(|s| {
while let Some(mut batch) = self.next_batch() {
let newf = f.clone();
s.spawn(async move { batch.all(newf) });
}
})
.into_iter()
.all(std::convert::identity)
}
/// Tests if any element of the parallel iterator matches a predicate.
///
/// *Note that any is **not** short circuiting.*
///
/// See [`Iterator::any()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.any)
fn any<F>(mut self, pool: &TaskPool, f: F) -> bool
where
F: FnMut(BatchIter::Item) -> bool + Send + Sync + Clone,
{
pool.scope(|s| {
while let Some(mut batch) = self.next_batch() {
let newf = f.clone();
s.spawn(async move { batch.any(newf) });
}
})
.into_iter()
.any(std::convert::identity)
}
/// Searches for an element in a parallel iterator, returning its index.
///
/// *Note that position consumes the whole iterator.*
///
/// See [`Iterator::position()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.position)
// TODO: Investigate optimizations for less copying
fn position<F>(mut self, pool: &TaskPool, f: F) -> Option<usize>
where
F: FnMut(BatchIter::Item) -> bool + Send + Sync + Clone,
{
let poses = pool.scope(|s| {
while let Some(batch) = self.next_batch() {
let mut newf = f.clone();
s.spawn(async move {
let mut len = 0;
let mut pos = None;
for item in batch {
if pos.is_none() && newf(item) {
pos = Some(len);
}
len += 1;
}
(len, pos)
});
}
});
let mut start = 0;
for (len, pos) in poses {
if let Some(pos) = pos {
return Some(start + pos);
}
start += len;
}
None
}
/// Returns the maximum item of a parallel iterator.
///
/// See [`Iterator::max()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.max)
fn max(mut self, pool: &TaskPool) -> Option<BatchIter::Item>
where
BatchIter::Item: Ord + Send + 'static,
{
pool.scope(|s| {
while let Some(batch) = self.next_batch() {
s.spawn(async move { batch.max() });
}
})
.into_iter()
.flatten()
.max()
}
/// Returns the minimum item of a parallel iterator.
///
/// See [`Iterator::min()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.min)
fn min(mut self, pool: &TaskPool) -> Option<BatchIter::Item>
where
BatchIter::Item: Ord + Send + 'static,
{
pool.scope(|s| {
while let Some(batch) = self.next_batch() {
s.spawn(async move { batch.min() });
}
})
.into_iter()
.flatten()
.min()
}
/// Returns the item that gives the maximum value from the specified function.
///
/// See [`Iterator::max_by_key()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.max_by_key)
fn max_by_key<R, F>(mut self, pool: &TaskPool, f: F) -> Option<BatchIter::Item>
where
R: Ord,
F: FnMut(&BatchIter::Item) -> R + Send + Sync + Clone,
BatchIter::Item: Send + 'static,
{
pool.scope(|s| {
while let Some(batch) = self.next_batch() {
let newf = f.clone();
s.spawn(async move { batch.max_by_key(newf) });
}
})
.into_iter()
.flatten()
.max_by_key(f)
}
/// Returns the item that gives the maximum value with respect to the specified comparison
/// function.
///
/// See [`Iterator::max_by()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.max_by)
fn max_by<F>(mut self, pool: &TaskPool, f: F) -> Option<BatchIter::Item>
where
F: FnMut(&BatchIter::Item, &BatchIter::Item) -> std::cmp::Ordering + Send + Sync + Clone,
BatchIter::Item: Send + 'static,
{
pool.scope(|s| {
while let Some(batch) = self.next_batch() {
let newf = f.clone();
s.spawn(async move { batch.max_by(newf) });
}
})
.into_iter()
.flatten()
.max_by(f)
}
/// Returns the item that gives the minimum value from the specified function.
///
/// See [`Iterator::min_by_key()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.min_by_key)
fn min_by_key<R, F>(mut self, pool: &TaskPool, f: F) -> Option<BatchIter::Item>
where
R: Ord,
F: FnMut(&BatchIter::Item) -> R + Send + Sync + Clone,
BatchIter::Item: Send + 'static,
{
pool.scope(|s| {
while let Some(batch) = self.next_batch() {
let newf = f.clone();
s.spawn(async move { batch.min_by_key(newf) });
}
})
.into_iter()
.flatten()
.min_by_key(f)
}
/// Returns the item that gives the minimum value with respect to the specified comparison
/// function.
///
/// See [`Iterator::min_by()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.min_by)
fn min_by<F>(mut self, pool: &TaskPool, f: F) -> Option<BatchIter::Item>
where
F: FnMut(&BatchIter::Item, &BatchIter::Item) -> std::cmp::Ordering + Send + Sync + Clone,
BatchIter::Item: Send + 'static,
{
pool.scope(|s| {
while let Some(batch) = self.next_batch() {
let newf = f.clone();
s.spawn(async move { batch.min_by(newf) });
}
})
.into_iter()
.flatten()
.min_by(f)
}
/// Creates a parallel iterator which copies all of its items.
///
/// See [`Iterator::copied()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.copied)
fn copied<'a, T>(self) -> Copied<Self>
where
Self: ParallelIterator<BatchIter>,
T: 'a + Copy,
{
Copied { iter: self }
}
/// Creates a parallel iterator which clones all of its items.
///
/// See [`Iterator::cloned()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.cloned)
fn cloned<'a, T>(self) -> Cloned<Self>
where
Self: ParallelIterator<BatchIter>,
T: 'a + Copy,
{
Cloned { iter: self }
}
/// Repeats a parallel iterator endlessly.
///
/// See [`Iterator::cycle()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.cycle)
fn cycle(self) -> Cycle<Self>
where
Self: Clone,
{
Cycle {
iter: self,
curr: None,
}
}
/// Sums the items of a parallel iterator.
///
/// See [`Iterator::sum()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.sum)
fn sum<S, R>(mut self, pool: &TaskPool) -> R
where
S: std::iter::Sum<BatchIter::Item> + Send + 'static,
R: std::iter::Sum<S>,
{
pool.scope(|s| {
while let Some(batch) = self.next_batch() {
s.spawn(async move { batch.sum() });
}
})
.into_iter()
.sum()
}
/// Multiplies all the items of a parallel iterator.
///
/// See [`Iterator::product()`](https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.product)
fn product<S, R>(mut self, pool: &TaskPool) -> R
where
S: std::iter::Product<BatchIter::Item> + Send + 'static,
R: std::iter::Product<S>,
{
pool.scope(|s| {
while let Some(batch) = self.next_batch() {
s.spawn(async move { batch.product() });
}
})
.into_iter()
.product()
}
}