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
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
//! 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_attr(target_os = "none", cfg(target_has_atomic = "ptr"))]
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_attr(target_os = "none", cfg(target_has_atomic = "ptr"))]
    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_attr(target_os = "none", cfg(target_has_atomic = "ptr"))]
            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(target_os = "none")]
    #[cfg_attr(target_os = "none", cfg(not(target_has_atomic = "ptr")))]
    {
        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_attr(target_os = "none", cfg(target_has_atomic = "ptr"))]
    {
        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_attr(target_os = "none", cfg(target_has_atomic = "ptr"))]
            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)
    }
}