diff options
Diffstat (limited to 'src/future/join_all.rs')
-rw-r--r-- | src/future/join_all.rs | 95 |
1 files changed, 73 insertions, 22 deletions
diff --git a/src/future/join_all.rs b/src/future/join_all.rs index 427e71c..2e52ac1 100644 --- a/src/future/join_all.rs +++ b/src/future/join_all.rs @@ -12,6 +12,9 @@ use core::task::{Context, Poll}; use super::{assert_future, MaybeDone}; +#[cfg(not(futures_no_atomic_cas))] +use crate::stream::{Collect, FuturesOrdered, StreamExt}; + fn iter_pin_mut<T>(slice: Pin<&mut [T]>) -> impl Iterator<Item = Pin<&mut T>> { // Safety: `std` _could_ make this unsound if it were to decide Pin's // invariants aren't required to transmit through slices. Otherwise this has @@ -19,13 +22,29 @@ fn iter_pin_mut<T>(slice: Pin<&mut [T]>) -> impl Iterator<Item = Pin<&mut T>> { unsafe { slice.get_unchecked_mut() }.iter_mut().map(|t| unsafe { Pin::new_unchecked(t) }) } -/// Future for the [`join_all`] function. #[must_use = "futures do nothing unless you `.await` or poll them"] +/// Future for the [`join_all`] function. pub struct JoinAll<F> where F: Future, { - elems: Pin<Box<[MaybeDone<F>]>>, + kind: JoinAllKind<F>, +} + +#[cfg(not(futures_no_atomic_cas))] +const SMALL: usize = 30; + +pub(crate) enum JoinAllKind<F> +where + F: Future, +{ + Small { + elems: Pin<Box<[MaybeDone<F>]>>, + }, + #[cfg(not(futures_no_atomic_cas))] + Big { + fut: Collect<FuturesOrdered<F>, Vec<F::Output>>, + }, } impl<F> fmt::Debug for JoinAll<F> @@ -34,7 +53,13 @@ where F::Output: fmt::Debug, { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - f.debug_struct("JoinAll").field("elems", &self.elems).finish() + match self.kind { + JoinAllKind::Small { ref elems } => { + f.debug_struct("JoinAll").field("elems", elems).finish() + } + #[cfg(not(futures_no_atomic_cas))] + JoinAllKind::Big { ref fut, .. } => fmt::Debug::fmt(fut, f), + } } } @@ -50,10 +75,9 @@ where /// /// # See Also /// -/// This is purposefully a very simple API for basic use-cases. In a lot of -/// cases you will want to use the more powerful -/// [`FuturesOrdered`][crate::stream::FuturesOrdered] APIs, or, if order does -/// not matter, [`FuturesUnordered`][crate::stream::FuturesUnordered]. +/// `join_all` will switch to the more powerful [`FuturesOrdered`] for performance +/// reasons if the number of futures is large. You may want to look into using it or +/// it's counterpart [`FuturesUnordered`][crate::stream::FuturesUnordered] directly. /// /// Some examples for additional functionality provided by these are: /// @@ -75,13 +99,33 @@ where /// assert_eq!(join_all(futures).await, [1, 2, 3]); /// # }); /// ``` -pub fn join_all<I>(i: I) -> JoinAll<I::Item> +pub fn join_all<I>(iter: I) -> JoinAll<I::Item> where I: IntoIterator, I::Item: Future, { - let elems: Box<[_]> = i.into_iter().map(MaybeDone::Future).collect(); - assert_future::<Vec<<I::Item as Future>::Output>, _>(JoinAll { elems: elems.into() }) + #[cfg(futures_no_atomic_cas)] + { + let elems = iter.into_iter().map(MaybeDone::Future).collect::<Box<[_]>>().into(); + let kind = JoinAllKind::Small { elems }; + assert_future::<Vec<<I::Item as Future>::Output>, _>(JoinAll { kind }) + } + #[cfg(not(futures_no_atomic_cas))] + { + let iter = iter.into_iter(); + let kind = match iter.size_hint().1 { + None => JoinAllKind::Big { fut: iter.collect::<FuturesOrdered<_>>().collect() }, + Some(max) => { + if max <= SMALL { + let elems = iter.map(MaybeDone::Future).collect::<Box<[_]>>().into(); + JoinAllKind::Small { elems } + } else { + JoinAllKind::Big { fut: iter.collect::<FuturesOrdered<_>>().collect() } + } + } + }; + assert_future::<Vec<<I::Item as Future>::Output>, _>(JoinAll { kind }) + } } impl<F> Future for JoinAll<F> @@ -91,20 +135,27 @@ where type Output = Vec<F::Output>; fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { - let mut all_done = true; + match &mut self.kind { + JoinAllKind::Small { elems } => { + let mut all_done = true; - for elem in iter_pin_mut(self.elems.as_mut()) { - if elem.poll(cx).is_pending() { - all_done = false; - } - } + for elem in iter_pin_mut(elems.as_mut()) { + if elem.poll(cx).is_pending() { + all_done = false; + } + } - if all_done { - let mut elems = mem::replace(&mut self.elems, Box::pin([])); - let result = iter_pin_mut(elems.as_mut()).map(|e| e.take_output().unwrap()).collect(); - Poll::Ready(result) - } else { - Poll::Pending + if all_done { + let mut elems = mem::replace(elems, Box::pin([])); + let result = + iter_pin_mut(elems.as_mut()).map(|e| e.take_output().unwrap()).collect(); + Poll::Ready(result) + } else { + Poll::Pending + } + } + #[cfg(not(futures_no_atomic_cas))] + JoinAllKind::Big { fut } => Pin::new(fut).poll(cx), } } } |