blob: be31c9e4de8539ba0c8871140f7dd31d81abd72c [file] [log] [blame]
use crate::stream::{Fuse, FuturesOrdered};
use futures_core::future::Future;
use futures_core::stream::Stream;
use futures_core::task::{LocalWaker, Poll};
use futures_sink::Sink;
use pin_utils::{unsafe_pinned, unsafe_unpinned};
use std::fmt;
use std::marker::Unpin;
use std::pin::Pin;
/// An adaptor for a stream of futures to execute the futures concurrently, if
/// possible.
///
/// This adaptor will buffer up a list of pending futures, and then return their
/// results in the order that they were pulled out of the original stream. This
/// is created by the `Stream::buffered` method.
#[must_use = "streams do nothing unless polled"]
pub struct Buffered<St: Stream>
where
St: Stream,
St::Item: Future,
{
stream: Fuse<St>,
in_progress_queue: FuturesOrdered<St::Item>,
max: usize,
}
impl<St> Unpin for Buffered<St>
where
St: Stream + Unpin,
St::Item: Future,
{}
impl<St> fmt::Debug for Buffered<St>
where
St: Stream + fmt::Debug,
St::Item: Future,
{
fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
fmt.debug_struct("Buffered")
.field("stream", &self.stream)
.field("in_progress_queue", &self.in_progress_queue)
.field("max", &self.max)
.finish()
}
}
impl<St> Buffered<St>
where
St: Stream,
St::Item: Future,
{
unsafe_pinned!(stream: Fuse<St>);
unsafe_unpinned!(in_progress_queue: FuturesOrdered<St::Item>);
pub(super) fn new(stream: St, n: usize) -> Buffered<St> {
Buffered {
stream: super::Fuse::new(stream),
in_progress_queue: FuturesOrdered::new(),
max: n,
}
}
/// Acquires a reference to the underlying stream that this combinator is
/// pulling from.
pub fn get_ref(&self) -> &St {
self.stream.get_ref()
}
/// Acquires a mutable reference to the underlying stream that this
/// combinator is pulling from.
///
/// Note that care must be taken to avoid tampering with the state of the
/// stream which may otherwise confuse this combinator.
pub fn get_mut(&mut self) -> &mut St {
self.stream.get_mut()
}
/// Acquires a mutable pinned reference to the underlying stream that this
/// combinator is pulling from.
///
/// Note that care must be taken to avoid tampering with the state of the
/// stream which may otherwise confuse this combinator.
#[allow(clippy::needless_lifetimes)] // https://github.com/rust-lang/rust/issues/52675
pub fn get_pin_mut<'a>(self: Pin<&'a mut Self>) -> Pin<&'a mut St> {
unsafe { Pin::map_unchecked_mut(self, |x| x.get_mut()) }
}
/// Consumes this combinator, returning the underlying stream.
///
/// Note that this may discard intermediate state of this combinator, so
/// care should be taken to avoid losing resources when this is called.
pub fn into_inner(self) -> St {
self.stream.into_inner()
}
}
impl<St> Stream for Buffered<St>
where
St: Stream,
St::Item: Future,
{
type Item = <St::Item as Future>::Output;
fn poll_next(
mut self: Pin<&mut Self>,
lw: &LocalWaker,
) -> Poll<Option<Self::Item>> {
// Try to spawn off as many futures as possible by filling up
// our in_progress_queue of futures.
while self.in_progress_queue.len() < self.max {
match self.as_mut().stream().poll_next(lw) {
Poll::Ready(Some(fut)) => self.as_mut().in_progress_queue().push(fut),
Poll::Ready(None) | Poll::Pending => break,
}
}
// Attempt to pull the next value from the in_progress_queue
let res = Pin::new(self.as_mut().in_progress_queue()).poll_next(lw);
if let Some(val) = ready!(res) {
return Poll::Ready(Some(val))
}
// If more values are still coming from the stream, we're not done yet
if self.stream.is_done() {
Poll::Ready(None)
} else {
Poll::Pending
}
}
}
// Forwarding impl of Sink from the underlying stream
impl<S> Sink for Buffered<S>
where
S: Stream + Sink,
S::Item: Future,
{
type SinkItem = S::SinkItem;
type SinkError = S::SinkError;
delegate_sink!(stream);
}