blob: 2e6f9242d8d0617fd8392c1ac78af88decb546f9 [file] [log] [blame]
use crate::stream::{FuturesUnordered, StreamExt};
use core::marker::Unpin;
use core::pin::Pin;
use core::num::NonZeroUsize;
use futures_core::future::{FusedFuture, Future};
use futures_core::stream::Stream;
use futures_core::task::{LocalWaker, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
/// A stream combinator which executes a unit closure over each item on a
/// stream concurrently.
///
/// This structure is returned by the
/// [`StreamExt::for_each_concurrent`](super::StreamExt::for_each_concurrent)
/// method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct ForEachConcurrent<St, Fut, F> {
stream: Option<St>,
f: F,
futures: FuturesUnordered<Fut>,
limit: Option<NonZeroUsize>,
}
impl<St, Fut, F> Unpin for ForEachConcurrent<St, Fut, F>
where St: Unpin,
Fut: Unpin,
{}
impl<St, Fut, F> ForEachConcurrent<St, Fut, F>
where St: Stream,
F: FnMut(St::Item) -> Fut,
Fut: Future<Output = ()>,
{
unsafe_pinned!(stream: Option<St>);
unsafe_unpinned!(f: F);
unsafe_unpinned!(futures: FuturesUnordered<Fut>);
unsafe_unpinned!(limit: Option<NonZeroUsize>);
pub(super) fn new(stream: St, limit: Option<usize>, f: F) -> ForEachConcurrent<St, Fut, F> {
ForEachConcurrent {
stream: Some(stream),
// Note: `limit` = 0 gets ignored.
limit: limit.and_then(NonZeroUsize::new),
f,
futures: FuturesUnordered::new(),
}
}
}
impl<St, Fut, F> FusedFuture for ForEachConcurrent<St, Fut, F> {
fn is_terminated(&self) -> bool {
self.stream.is_none() && self.futures.is_empty()
}
}
impl<St, Fut, F> Future for ForEachConcurrent<St, Fut, F>
where St: Stream,
F: FnMut(St::Item) -> Fut,
Fut: Future<Output = ()>,
{
type Output = ();
fn poll(mut self: Pin<&mut Self>, lw: &LocalWaker) -> Poll<()> {
loop {
let mut made_progress_this_iter = false;
// Try and pull an item from the stream
let current_len = self.futures.len();
// Check if we've already created a number of futures greater than `limit`
if self.limit.map(|limit| limit.get() > current_len).unwrap_or(true) {
let mut stream_completed = false;
let elem = if let Some(stream) = self.as_mut().stream().as_pin_mut() {
match stream.poll_next(lw) {
Poll::Ready(Some(elem)) => {
made_progress_this_iter = true;
Some(elem)
},
Poll::Ready(None) => {
stream_completed = true;
None
}
Poll::Pending => None,
}
} else {
None
};
if stream_completed {
self.as_mut().stream().set(None);
}
if let Some(elem) = elem {
let next_future = (self.as_mut().f())(elem);
self.as_mut().futures().push(next_future);
}
}
match self.as_mut().futures().poll_next_unpin(lw) {
Poll::Ready(Some(())) => made_progress_this_iter = true,
Poll::Ready(None) => {
if self.as_mut().stream().is_none() {
return Poll::Ready(())
}
},
Poll::Pending => {}
}
if !made_progress_this_iter {
return Poll::Pending;
}
}
}
}