cros_async/
complete.rs

1// Copyright 2020 The ChromiumOS Authors
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5// Need non-snake case so the macro can re-use type names for variables.
6#![allow(non_snake_case)]
7
8use std::future::Future;
9use std::pin::Pin;
10use std::task::Context;
11use std::task::Poll;
12
13use futures::future::maybe_done;
14use futures::future::MaybeDone;
15use pin_utils::unsafe_pinned;
16
17// Macro-generate future combinators to allow for running different numbers of top-level futures in
18// this FutureList. Generates the implementation of `FutureList` for the completion types. For an
19// explicit example this is modeled after, see `UnitFutures`.
20macro_rules! generate {
21    ($(
22        $(#[$doc:meta])*
23        ($Complete:ident, <$($Fut:ident),*>),
24    )*) => ($(
25        #[must_use = "Combinations of futures don't do anything unless run in an executor."]
26        pub(crate) struct $Complete<$($Fut: Future),*> {
27            $($Fut: MaybeDone<$Fut>,)*
28        }
29
30        impl<$($Fut),*> $Complete<$($Fut),*>
31        where $(
32            $Fut: Future,
33        )*
34        {
35            // Safety:
36            // * No Drop impl
37            // * No Unpin impl
38            // * Not #[repr(packed)]
39            $(
40                unsafe_pinned!($Fut: MaybeDone<$Fut>);
41            )*
42
43            pub(crate) fn new($($Fut: $Fut),*) -> $Complete<$($Fut),*> {
44                $(
45                    let $Fut = maybe_done($Fut);
46                )*
47                $Complete {
48                    $($Fut),*
49                }
50            }
51        }
52
53        impl<$($Fut),*> Future for $Complete<$($Fut),*>
54        where $(
55            $Fut: Future,
56        )*
57        {
58            type Output = ($($Fut::Output),*);
59
60            fn poll(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
61                let mut complete = true;
62                $(
63                    complete &= self.as_mut().$Fut().poll(cx).is_ready();
64                )*
65
66                if complete {
67                    $(
68                        let $Fut = self.as_mut().$Fut().take_output().unwrap();
69                    )*
70                    Poll::Ready(($($Fut), *))
71                } else {
72                    Poll::Pending
73                }
74            }
75        }
76    )*)
77}
78
79generate! {
80    /// _Future for the [`complete2`] function.
81    (Complete2, <_Fut1, _Fut2>),
82
83    /// _Future for the [`complete3`] function.
84    (Complete3, <_Fut1, _Fut2, _Fut3>),
85
86    /// _Future for the [`complete4`] function.
87    (Complete4, <_Fut1, _Fut2, _Fut3, _Fut4>),
88
89    /// _Future for the [`complete5`] function.
90    (Complete5, <_Fut1, _Fut2, _Fut3, _Fut4, _Fut5>),
91}
cros_async/complete.rs

cros_async/
complete.rs
