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use core::fmt;
use core::future::Future;
use core::iter::FromIterator;
use core::mem;
use core::pin::Pin;
use core::task::{Context, Poll};
use alloc::boxed::Box;
use alloc::vec::Vec;
use super::{MaybeDone, assert_future};
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) })
}
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub struct JoinAll<F>
where
F: Future,
{
elems: Pin<Box<[MaybeDone<F>]>>,
}
impl<F> fmt::Debug for JoinAll<F>
where
F: Future + fmt::Debug,
F::Output: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("JoinAll")
.field("elems", &self.elems)
.finish()
}
}
pub fn join_all<I>(i: 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() })
}
impl<F> Future for JoinAll<F>
where
F: Future,
{
type Output = Vec<F::Output>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let mut all_done = true;
for elem in iter_pin_mut(self.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
}
}
}
impl<F: Future> FromIterator<F> for JoinAll<F> {
fn from_iter<T: IntoIterator<Item = F>>(iter: T) -> Self {
join_all(iter)
}
}