Source code
Revision control
Copy as Markdown
Other Tools
//! 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)
}
}