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Diffstat (limited to 'third_party/rust/futures-util/src/future/try_join_all.rs')
| -rw-r--r-- | third_party/rust/futures-util/src/future/try_join_all.rs | 200 |
1 files changed, 200 insertions, 0 deletions
diff --git a/third_party/rust/futures-util/src/future/try_join_all.rs b/third_party/rust/futures-util/src/future/try_join_all.rs new file mode 100644 index 0000000000..506f450657 --- /dev/null +++ b/third_party/rust/futures-util/src/future/try_join_all.rs @@ -0,0 +1,200 @@ +//! Definition of the `TryJoinAll` combinator, waiting for all of a list of +//! futures to finish with either success or error. + +use alloc::boxed::Box; +use alloc::vec::Vec; +use core::fmt; +use core::future::Future; +use core::iter::FromIterator; +use core::mem; +use core::pin::Pin; +use core::task::{Context, Poll}; + +use super::{assert_future, join_all, IntoFuture, TryFuture, TryMaybeDone}; + +#[cfg(not(futures_no_atomic_cas))] +use crate::stream::{FuturesOrdered, TryCollect, TryStreamExt}; +use crate::TryFutureExt; + +enum FinalState<E = ()> { + Pending, + AllDone, + Error(E), +} + +/// Future for the [`try_join_all`] function. +#[must_use = "futures do nothing unless you `.await` or poll them"] +pub struct TryJoinAll<F> +where + F: TryFuture, +{ + kind: TryJoinAllKind<F>, +} + +enum TryJoinAllKind<F> +where + F: TryFuture, +{ + Small { + elems: Pin<Box<[TryMaybeDone<IntoFuture<F>>]>>, + }, + #[cfg(not(futures_no_atomic_cas))] + Big { + fut: TryCollect<FuturesOrdered<IntoFuture<F>>, Vec<F::Ok>>, + }, +} + +impl<F> fmt::Debug for TryJoinAll<F> +where + F: TryFuture + fmt::Debug, + F::Ok: fmt::Debug, + F::Error: fmt::Debug, + F::Output: fmt::Debug, +{ + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + match self.kind { + TryJoinAllKind::Small { ref elems } => { + f.debug_struct("TryJoinAll").field("elems", elems).finish() + } + #[cfg(not(futures_no_atomic_cas))] + TryJoinAllKind::Big { ref fut, .. } => fmt::Debug::fmt(fut, f), + } + } +} + +/// Creates a future which represents either a collection of the results of the +/// futures given or an error. +/// +/// The returned future will drive execution for all of its underlying futures, +/// collecting the results into a destination `Vec<T>` in the same order as they +/// were provided. +/// +/// If any future returns an error then all other futures will be canceled and +/// an error will be returned immediately. If all futures complete successfully, +/// however, then the returned future will succeed with a `Vec` of all the +/// successful results. +/// +/// This function is only available when the `std` or `alloc` feature of this +/// library is activated, and it is activated by default. +/// +/// # See Also +/// +/// `try_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: +/// +/// * Adding new futures to the set even after it has been started. +/// +/// * Only polling the specific futures that have been woken. In cases where +/// you have a lot of futures this will result in much more efficient polling. +/// +/// +/// # Examples +/// +/// ``` +/// # futures::executor::block_on(async { +/// use futures::future::{self, try_join_all}; +/// +/// let futures = vec![ +/// future::ok::<u32, u32>(1), +/// future::ok::<u32, u32>(2), +/// future::ok::<u32, u32>(3), +/// ]; +/// +/// assert_eq!(try_join_all(futures).await, Ok(vec![1, 2, 3])); +/// +/// let futures = vec![ +/// future::ok::<u32, u32>(1), +/// future::err::<u32, u32>(2), +/// future::ok::<u32, u32>(3), +/// ]; +/// +/// assert_eq!(try_join_all(futures).await, Err(2)); +/// # }); +/// ``` +pub fn try_join_all<I>(iter: I) -> TryJoinAll<I::Item> +where + I: IntoIterator, + I::Item: TryFuture, +{ + let iter = iter.into_iter().map(TryFutureExt::into_future); + + #[cfg(futures_no_atomic_cas)] + { + let kind = TryJoinAllKind::Small { + elems: iter.map(TryMaybeDone::Future).collect::<Box<[_]>>().into(), + }; + + assert_future::<Result<Vec<<I::Item as TryFuture>::Ok>, <I::Item as TryFuture>::Error>, _>( + TryJoinAll { kind }, + ) + } + + #[cfg(not(futures_no_atomic_cas))] + { + let kind = match iter.size_hint().1 { + Some(max) if max <= join_all::SMALL => TryJoinAllKind::Small { + elems: iter.map(TryMaybeDone::Future).collect::<Box<[_]>>().into(), + }, + _ => TryJoinAllKind::Big { fut: iter.collect::<FuturesOrdered<_>>().try_collect() }, + }; + + assert_future::<Result<Vec<<I::Item as TryFuture>::Ok>, <I::Item as TryFuture>::Error>, _>( + TryJoinAll { kind }, + ) + } +} + +impl<F> Future for TryJoinAll<F> +where + F: TryFuture, +{ + type Output = Result<Vec<F::Ok>, F::Error>; + + fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { + match &mut self.kind { + TryJoinAllKind::Small { elems } => { + let mut state = FinalState::AllDone; + + for elem in join_all::iter_pin_mut(elems.as_mut()) { + match elem.try_poll(cx) { + Poll::Pending => state = FinalState::Pending, + Poll::Ready(Ok(())) => {} + Poll::Ready(Err(e)) => { + state = FinalState::Error(e); + break; + } + } + } + + match state { + FinalState::Pending => Poll::Pending, + FinalState::AllDone => { + let mut elems = mem::replace(elems, Box::pin([])); + let results = join_all::iter_pin_mut(elems.as_mut()) + .map(|e| e.take_output().unwrap()) + .collect(); + Poll::Ready(Ok(results)) + } + FinalState::Error(e) => { + let _ = mem::replace(elems, Box::pin([])); + Poll::Ready(Err(e)) + } + } + } + #[cfg(not(futures_no_atomic_cas))] + TryJoinAllKind::Big { fut } => Pin::new(fut).poll(cx), + } + } +} + +impl<F> FromIterator<F> for TryJoinAll<F> +where + F: TryFuture, +{ + fn from_iter<T: IntoIterator<Item = F>>(iter: T) -> Self { + try_join_all(iter) + } +} |