async_std/future/future/
race.rs

1use std::future::Future;
2use std::pin::Pin;
3
4use crate::future::MaybeDone;
5use pin_project_lite::pin_project;
6
7use crate::task::{Context, Poll};
8
9pin_project! {
10    #[allow(missing_docs)]
11    #[allow(missing_debug_implementations)]
12    pub struct Race<L, R>
13    where
14        L: Future,
15        R: Future<Output = L::Output>
16    {
17        #[pin] left: MaybeDone<L>,
18        #[pin] right: MaybeDone<R>,
19    }
20}
21
22impl<L, R> Race<L, R>
23where
24    L: Future,
25    R: Future<Output = L::Output>,
26{
27    pub(crate) fn new(left: L, right: R) -> Self {
28        Self {
29            left: MaybeDone::new(left),
30            right: MaybeDone::new(right),
31        }
32    }
33}
34
35impl<L, R> Future for Race<L, R>
36where
37    L: Future,
38    R: Future<Output = L::Output>,
39{
40    type Output = L::Output;
41
42    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
43        let this = self.project();
44
45        let mut left = this.left;
46        if Future::poll(Pin::new(&mut left), cx).is_ready() {
47            return Poll::Ready(left.take().unwrap());
48        }
49
50        let mut right = this.right;
51        if Future::poll(Pin::new(&mut right), cx).is_ready() {
52            return Poll::Ready(right.take().unwrap());
53        }
54
55        Poll::Pending
56    }
57}
async_std/future/future/race.rs

async_std/future/future/
race.rs
