futures_util/stream/try_stream/
try_buffer_unordered.rs

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1use crate::future::{IntoFuture, TryFutureExt};
2use crate::stream::{Fuse, FuturesUnordered, IntoStream, StreamExt};
3use core::pin::Pin;
4use futures_core::future::TryFuture;
5use futures_core::stream::{Stream, TryStream};
6use futures_core::task::{Context, Poll};
7#[cfg(feature = "sink")]
8use futures_sink::Sink;
9use pin_project_lite::pin_project;
10
11pin_project! {
12    /// Stream for the
13    /// [`try_buffer_unordered`](super::TryStreamExt::try_buffer_unordered) method.
14    #[derive(Debug)]
15    #[must_use = "streams do nothing unless polled"]
16    pub struct TryBufferUnordered<St>
17        where St: TryStream
18    {
19        #[pin]
20        stream: Fuse<IntoStream<St>>,
21        in_progress_queue: FuturesUnordered<IntoFuture<St::Ok>>,
22        max: usize,
23    }
24}
25
26impl<St> TryBufferUnordered<St>
27where
28    St: TryStream,
29    St::Ok: TryFuture,
30{
31    pub(super) fn new(stream: St, n: usize) -> Self {
32        Self {
33            stream: IntoStream::new(stream).fuse(),
34            in_progress_queue: FuturesUnordered::new(),
35            max: n,
36        }
37    }
38
39    delegate_access_inner!(stream, St, (. .));
40}
41
42impl<St> Stream for TryBufferUnordered<St>
43where
44    St: TryStream,
45    St::Ok: TryFuture<Error = St::Error>,
46{
47    type Item = Result<<St::Ok as TryFuture>::Ok, St::Error>;
48
49    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
50        let mut this = self.project();
51
52        // First up, try to spawn off as many futures as possible by filling up
53        // our queue of futures. Propagate errors from the stream immediately.
54        while this.in_progress_queue.len() < *this.max {
55            match this.stream.as_mut().poll_next(cx)? {
56                Poll::Ready(Some(fut)) => this.in_progress_queue.push(fut.into_future()),
57                Poll::Ready(None) | Poll::Pending => break,
58            }
59        }
60
61        // Attempt to pull the next value from the in_progress_queue
62        match this.in_progress_queue.poll_next_unpin(cx) {
63            x @ Poll::Pending | x @ Poll::Ready(Some(_)) => return x,
64            Poll::Ready(None) => {}
65        }
66
67        // If more values are still coming from the stream, we're not done yet
68        if this.stream.is_done() {
69            Poll::Ready(None)
70        } else {
71            Poll::Pending
72        }
73    }
74}
75
76// Forwarding impl of Sink from the underlying stream
77#[cfg(feature = "sink")]
78impl<S, Item, E> Sink<Item> for TryBufferUnordered<S>
79where
80    S: TryStream + Sink<Item, Error = E>,
81    S::Ok: TryFuture<Error = E>,
82{
83    type Error = E;
84
85    delegate_sink!(stream, Item);
86}
futures_util/stream/try_stream/try_buffer_unordered.rs

futures_util/stream/try_stream/
try_buffer_unordered.rs
