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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};
pub enum SelectResult<F: Future> {
Pending(F),
Finished(F::Output),
}
// Macro-generate future combinators to allow for running different numbers of top-level futures in
// this FutureList. Generates the implementation of `FutureList` for the select types. For an
// explicit example this is modeled after, see `UnitFutures`.
macro_rules! generate {
($(
$(#[$doc:meta])*
($Select:ident, <$($Fut:ident),*>),
)*) => ($(
#[must_use = "Combinations of futures don't do anything unless run in an executor."]
paste::item! {
pub(crate) struct $Select<$($Fut: Future + Unpin),*> {
added_futures: UnitFutures,
$($Fut: MaybeDone<$Fut>,)*
$([<$Fut _state>]: FutureState,)*
}
}
impl<$($Fut: Future + Unpin),*> $Select<$($Fut),*> {
paste::item! {
pub(crate) fn new($($Fut: $Fut),*) -> $Select<$($Fut),*> {
$Select {
added_futures: UnitFutures::new(),
$($Fut: maybe_done($Fut),)*
$([<$Fut _state>]: FutureState::new(),)*
}
}
}
}
impl<$($Fut: Future + Unpin),*> FutureList for $Select<$($Fut),*> {
type Output = ($(SelectResult<$Fut>),*);
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 = false;
$(
let $Fut = Pin::new(&mut self.$Fut);
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.$Fut.poll_unpin(&mut ctx).is_ready();
}
)*
if complete {
Some(($(
match std::mem::replace(&mut self.$Fut, MaybeDone::Gone) {
MaybeDone::Future(f) => SelectResult::Pending(f),
MaybeDone::Done(o) => SelectResult::Finished(o),
MaybeDone::Gone=>unreachable!(),
}
), *))
} 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 [`select2`] function.
(Select2, <_Fut1, _Fut2>),
/// _Future for the [`select3`] function.
(Select3, <_Fut1, _Fut2, _Fut3>),
/// _Future for the [`select4`] function.
(Select4, <_Fut1, _Fut2, _Fut3, _Fut4>),
/// _Future for the [`select5`] function.
(Select5, <_Fut1, _Fut2, _Fut3, _Fut4, _Fut5>),
/// _Future for the [`select6`] function.
(Select6, <_Fut1, _Fut2, _Fut3, _Fut4, _Fut5, _Fut6>),
}
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