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|
//! [`PollAll`]
use futures::FutureExt as _;
use smallvec::{SmallVec, smallvec};
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};
/// The future type in a [`PollAll`].
type BoxedFut<'a, T> = Pin<Box<dyn Future<Output = T> + Send + 'a>>;
/// Helper for driving multiple futures in lockstep.
///
/// When `.await`ed, a [`PollAll`] will unconditionally poll *all* of its
/// underlying futures, in the order they were [`push`](PollAll::push)ed,
/// until one or more of them resolves.
/// Any remaining unresolved futures will be dropped.
/// An empty `PollAll` will resolve immediately, yielding an empty list.
///
/// `PollAll` resolves to an *ordered* list of results, obtained from polling
/// the futures in insertion order. Because some of the futures may not
/// get a chance to resolve, the number of results will always
/// be less than or equal to the number of inserted futures.
///
/// Because `PollAll` drives the futures in lockstep,
/// if one future becomes ready, all of the futures will get polled,
/// even if they didn't generate a wakeup notification.
///
/// ### Invariants
///
/// All of the futures inserted into this set **must** be cancellation safe.
#[derive(Default)]
pub(crate) struct PollAll<'a, const N: usize, T> {
/// The futures to drive in lockstep.
inner: SmallVec<[BoxedFut<'a, T>; N]>,
}
impl<'a, const N: usize, T> PollAll<'a, N, T> {
/// Create an empty [`PollAll`].
pub(crate) fn new() -> Self {
Self { inner: smallvec![] }
}
/// Add a future to this [`PollAll`].
pub(crate) fn push<S: Future<Output = T> + Send + 'a>(&mut self, item: S) {
self.inner.push(Box::pin(item));
}
}
impl<'a, const N: usize, T> Future for PollAll<'a, N, T> {
type Output = SmallVec<[T; N]>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let mut results = smallvec![];
if self.inner.is_empty() {
// Nothing to do.
return Poll::Ready(results);
}
for fut in self.inner.iter_mut() {
match fut.poll_unpin(cx) {
Poll::Ready(res) => results.push(res),
Poll::Pending => continue,
}
}
if results.is_empty() {
return Poll::Pending;
}
Poll::Ready(results)
}
}
#[cfg(test)]
mod test {
// @@ begin test lint list maintained by maint/add_warning @@
#![allow(clippy::bool_assert_comparison)]
#![allow(clippy::clone_on_copy)]
#![allow(clippy::dbg_macro)]
#![allow(clippy::mixed_attributes_style)]
#![allow(clippy::print_stderr)]
#![allow(clippy::print_stdout)]
#![allow(clippy::single_char_pattern)]
#![allow(clippy::unwrap_used)]
#![allow(clippy::unchecked_time_subtraction)]
#![allow(clippy::useless_vec)]
#![allow(clippy::needless_pass_by_value)]
#![allow(clippy::string_slice)] // See arti#2571
//! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
use super::*;
use tor_rtmock::MockRuntime;
use std::sync::Arc;
use std::sync::atomic::{AtomicUsize, Ordering};
/// Dummy smallvec capacity.
const RES_COUNT: usize = 5;
/// A wrapper over a future, that counts how many times it is polled.
struct PollCounter<F> {
/// The poll count, shared with the caller.
count: Arc<AtomicUsize>,
/// The underlying future.
inner: F,
}
/// A future that resolves after a fixed number of calls to `poll()`.
struct ResolveAfter {
/// The number of poll() calls until this future resolves
resolve_after: usize,
/// The number of times poll() was called on this.
poll_count: usize,
}
impl ResolveAfter {
fn new(resolve_after: usize) -> Self {
Self {
resolve_after,
poll_count: 0,
}
}
}
impl<F> PollCounter<F> {
fn new(inner: F) -> (Self, Arc<AtomicUsize>) {
let count = Arc::new(AtomicUsize::new(0));
let poll_counter = Self {
count: Arc::clone(&count),
inner,
};
(poll_counter, count)
}
}
impl<F: Future + Unpin> Future for PollCounter<F> {
type Output = F::Output;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let _ = self.count.fetch_add(1, Ordering::Relaxed);
self.inner.poll_unpin(cx)
}
}
impl Future for ResolveAfter {
type Output = usize;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
self.poll_count += 1;
if self.poll_count == self.resolve_after {
Poll::Ready(self.resolve_after)
} else if self.poll_count > self.resolve_after {
panic!("future polled after completion?!");
} else {
// Immediately wake the waker
cx.waker().wake_by_ref();
Poll::Pending
}
}
}
#[test]
fn poll_none() {
MockRuntime::test_with_various(|_| async move {
assert!(PollAll::<RES_COUNT, ()>::new().await.is_empty());
});
}
#[test]
fn poll_multiple() {
MockRuntime::test_with_various(|_| async move {
let mut poll_all = PollAll::<RES_COUNT, usize>::new();
let (never_fut, never_count) = PollCounter::new(futures::future::pending::<usize>());
poll_all.push(never_fut);
let (futures, counters): (Vec<_>, Vec<_>) = [
PollCounter::new(ResolveAfter::new(5)),
PollCounter::new(ResolveAfter::new(5)),
// These won't get a chance to resolve
PollCounter::new(ResolveAfter::new(8)),
PollCounter::new(ResolveAfter::new(9)),
]
.into_iter()
.unzip();
for fut in futures {
poll_all.push(fut);
}
let res = poll_all.await;
assert_eq!(&res[..], &[5, 5]);
// All futures were polled 5 times.
assert_eq!(never_count.load(Ordering::Relaxed), 5);
for counter in counters {
assert_eq!(counter.load(Ordering::Relaxed), 5);
}
});
}
}
|
