1use crate::stream::{FuturesUnordered, StreamExt};
2use core::fmt;
3use core::mem;
4use core::num::NonZeroUsize;
5use core::pin::Pin;
6use futures_core::future::{FusedFuture, Future};
7use futures_core::stream::TryStream;
8use futures_core::task::{Context, Poll};
9use pin_project_lite::pin_project;
10
11pin_project! {
12 /// Future for the
13 /// [`try_for_each_concurrent`](super::TryStreamExt::try_for_each_concurrent)
14 /// method.
15 #[must_use = "futures do nothing unless you `.await` or poll them"]
16 pub struct TryForEachConcurrent<St, Fut, F> {
17 #[pin]
18 stream: Option<St>,
19 f: F,
20 futures: FuturesUnordered<Fut>,
21 limit: Option<NonZeroUsize>,
22 }
23}
24
25impl<St, Fut, F> fmt::Debug for TryForEachConcurrent<St, Fut, F>
26where
27 St: fmt::Debug,
28 Fut: fmt::Debug,
29{
30 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
31 f&mut DebugStruct<'_, '_>.debug_struct("TryForEachConcurrent")
32 .field("stream", &self.stream)
33 .field("futures", &self.futures)
34 .field(name:"limit", &self.limit)
35 .finish()
36 }
37}
38
39impl<St, Fut, F> FusedFuture for TryForEachConcurrent<St, Fut, F>
40where
41 St: TryStream,
42 F: FnMut(St::Ok) -> Fut,
43 Fut: Future<Output = Result<(), St::Error>>,
44{
45 fn is_terminated(&self) -> bool {
46 self.stream.is_none() && self.futures.is_empty()
47 }
48}
49
50impl<St, Fut, F> TryForEachConcurrent<St, Fut, F>
51where
52 St: TryStream,
53 F: FnMut(St::Ok) -> Fut,
54 Fut: Future<Output = Result<(), St::Error>>,
55{
56 pub(super) fn new(stream: St, limit: Option<usize>, f: F) -> Self {
57 Self {
58 stream: Some(stream),
59 // Note: `limit` = 0 gets ignored.
60 limit: limit.and_then(NonZeroUsize::new),
61 f,
62 futures: FuturesUnordered::new(),
63 }
64 }
65}
66
67impl<St, Fut, F> Future for TryForEachConcurrent<St, Fut, F>
68where
69 St: TryStream,
70 F: FnMut(St::Ok) -> Fut,
71 Fut: Future<Output = Result<(), St::Error>>,
72{
73 type Output = Result<(), St::Error>;
74
75 fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
76 let mut this = self.project();
77 loop {
78 let mut made_progress_this_iter = false;
79
80 // Check if we've already created a number of futures greater than `limit`
81 if this.limit.map(|limit| limit.get() > this.futures.len()).unwrap_or(true) {
82 let poll_res = match this.stream.as_mut().as_pin_mut() {
83 Some(stream) => stream.try_poll_next(cx),
84 None => Poll::Ready(None),
85 };
86
87 let elem = match poll_res {
88 Poll::Ready(Some(Ok(elem))) => {
89 made_progress_this_iter = true;
90 Some(elem)
91 }
92 Poll::Ready(None) => {
93 this.stream.set(None);
94 None
95 }
96 Poll::Pending => None,
97 Poll::Ready(Some(Err(e))) => {
98 // Empty the stream and futures so that we know
99 // the future has completed.
100 this.stream.set(None);
101 drop(mem::replace(this.futures, FuturesUnordered::new()));
102 return Poll::Ready(Err(e));
103 }
104 };
105
106 if let Some(elem) = elem {
107 this.futures.push((this.f)(elem));
108 }
109 }
110
111 match this.futures.poll_next_unpin(cx) {
112 Poll::Ready(Some(Ok(()))) => made_progress_this_iter = true,
113 Poll::Ready(None) => {
114 if this.stream.is_none() {
115 return Poll::Ready(Ok(()));
116 }
117 }
118 Poll::Pending => {}
119 Poll::Ready(Some(Err(e))) => {
120 // Empty the stream and futures so that we know
121 // the future has completed.
122 this.stream.set(None);
123 drop(mem::replace(this.futures, FuturesUnordered::new()));
124 return Poll::Ready(Err(e));
125 }
126 }
127
128 if !made_progress_this_iter {
129 return Poll::Pending;
130 }
131 }
132 }
133}
134