1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137

//! 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, TryFuture, TryMaybeDone};

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
    // the same safety as a normal field pin projection.
    unsafe { slice.get_unchecked_mut() }.iter_mut().map(|t| unsafe { Pin::new_unchecked(t) })
}

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,
{
    elems: Pin<Box<[TryMaybeDone<F>]>>,
}

impl<F> fmt::Debug for TryJoinAll<F>
where
    F: TryFuture + fmt::Debug,
    F::Ok: fmt::Debug,
    F::Error: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("TryJoinAll").field("elems", &self.elems).finish()
    }
}

/// 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.
///
/// # 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>(i: I) -> TryJoinAll<I::Item>
where
    I: IntoIterator,
    I::Item: TryFuture,
{
    let elems: Box<[_]> = i.into_iter().map(TryMaybeDone::Future).collect();
    assert_future::<Result<Vec<<I::Item as TryFuture>::Ok>, <I::Item as TryFuture>::Error>, _>(
        TryJoinAll { elems: elems.into() },
    )
}

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> {
        let mut state = FinalState::AllDone;

        for elem in iter_pin_mut(self.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(&mut self.elems, Box::pin([]));
                let results =
                    iter_pin_mut(elems.as_mut()).map(|e| e.take_output().unwrap()).collect();
                Poll::Ready(Ok(results))
            }
            FinalState::Error(e) => {
                let _ = mem::replace(&mut self.elems, Box::pin([]));
                Poll::Ready(Err(e))
            }
        }
    }
}

impl<F: TryFuture> FromIterator<F> for TryJoinAll<F> {
    fn from_iter<T: IntoIterator<Item = F>>(iter: T) -> Self {
        try_join_all(iter)
    }
}