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// Copyright 2020 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Need non-snake case so the macro can re-use type names for variables.
#![allow(non_snake_case)]
use std::future::Future;
use std::pin::Pin;
use std::task::Context;
use futures::future::{maybe_done, FutureExt, MaybeDone};
use crate::executor::{FutureList, FutureState, UnitFutures};
// Macro-generate future combinators to allow for running different numbers of top-level futures in
// this FutureList. Generates the implementation of `FutureList` for the completion types. For an
// explicit example this is modeled after, see `UnitFutures`.
macro_rules! generate {
($(
$(#[$doc:meta])*
($Complete:ident, <$($Fut:ident),*>),
)*) => ($(
#[must_use = "Combinations of futures don't do anything unless run in an executor."]
paste::item! {
pub(crate) struct $Complete<$($Fut: Future + Unpin),*> {
added_futures: UnitFutures,
$($Fut: MaybeDone<$Fut>,)*
$([<$Fut _state>]: FutureState,)*
}
}
impl<$($Fut: Future + Unpin),*> $Complete<$($Fut),*> {
paste::item! {
pub(crate) fn new($($Fut: $Fut),*) -> $Complete<$($Fut),*> {
$Complete {
added_futures: UnitFutures::new(),
$($Fut: maybe_done($Fut),)*
$([<$Fut _state>]: FutureState::new(),)*
}
}
}
}
impl<$($Fut: Future + Unpin),*> FutureList for $Complete<$($Fut),*> {
type Output = ($($Fut::Output),*);
fn futures_mut(&mut self) -> &mut UnitFutures {
&mut self.added_futures
}
paste::item! {
fn poll_results(&mut self) -> Option<Self::Output> {
let _ = self.added_futures.poll_results();
let mut complete = true;
$(
if self.[<$Fut _state>].needs_poll.replace(false) {
let mut ctx = Context::from_waker(&self.[<$Fut _state>].waker);
// The future impls `Unpin`, use `poll_unpin` to avoid wrapping it in
// `Pin` to call `poll`.
complete &= self.$Fut.poll_unpin(&mut ctx).is_ready();
}
)*
if complete {
$(
let $Fut = Pin::new(&mut self.$Fut);
)*
Some(($($Fut.take_output().unwrap()), *))
} else {
None
}
}
fn any_ready(&self) -> bool {
let mut ready = self.added_futures.any_ready();
$(
ready |= self.[<$Fut _state>].needs_poll.get();
)*
ready
}
}
}
)*)
}
generate! {
/// _Future for the [`complete2`] function.
(Complete2, <_Fut1, _Fut2>),
/// _Future for the [`complete3`] function.
(Complete3, <_Fut1, _Fut2, _Fut3>),
/// _Future for the [`complete4`] function.
(Complete4, <_Fut1, _Fut2, _Fut3, _Fut4>),
/// _Future for the [`complete5`] function.
(Complete5, <_Fut1, _Fut2, _Fut3, _Fut4, _Fut5>),
}
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