futures_util/future/
join_all.rs

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
//! Definition of the `JoinAll` combinator, waiting for all of a list of futures
//! to finish.

use std::prelude::v1::*;

use std::fmt;
use std::mem;
use std::iter::FromIterator;

use futures_core::{Future, IntoFuture, Poll, Async};
use futures_core::task;

#[derive(Debug)]
enum ElemState<F> where F: Future {
    Pending(F),
    Done(F::Item),
}

/// A future which takes a list of futures and resolves with a vector of the
/// completed values.
///
/// This future is created with the `join_all` method.
#[must_use = "futures do nothing unless polled"]
pub struct JoinAll<F>
    where F: Future,
{
    elems: Vec<ElemState<F>>,
}

impl<F> fmt::Debug for JoinAll<F>
    where F: Future + fmt::Debug,
          F::Item: fmt::Debug,
{
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        fmt.debug_struct("JoinAll")
            .field("elems", &self.elems)
            .finish()
    }
}

/// Creates a future which represents a collection of the results of the futures
/// given.
///
/// 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.
///
/// # Examples
///
/// ```
/// # extern crate futures;
/// use futures::prelude::*;
/// use futures::future::{join_all, ok, err};
///
/// # fn main() {
/// #
/// let f = join_all(vec![
///     ok::<u32, u32>(1),
///     ok::<u32, u32>(2),
///     ok::<u32, u32>(3),
/// ]);
/// let f = f.map(|x| {
///     assert_eq!(x, [1, 2, 3]);
/// });
///
/// let f = join_all(vec![
///     Box::new(ok::<u32, u32>(1)),
///     Box::new(err::<u32, u32>(2)),
///     Box::new(ok::<u32, u32>(3)),
/// ]);
/// let f = f.then(|x| {
///     assert_eq!(x, Err(2));
///     x
/// });
/// # }
/// ```
pub fn join_all<I>(i: I) -> JoinAll<<I::Item as IntoFuture>::Future>
    where I: IntoIterator,
          I::Item: IntoFuture,
{
    let elems = i.into_iter().map(|f| {
        ElemState::Pending(f.into_future())
    }).collect();
    JoinAll { elems }
}

impl<F> Future for JoinAll<F>
    where F: Future,
{
    type Item = Vec<F::Item>;
    type Error = F::Error;


    fn poll(&mut self, cx: &mut task::Context) -> Poll<Self::Item, Self::Error> {
        let mut all_done = true;

        for idx in 0 .. self.elems.len() {
            let done_val = match self.elems[idx] {
                ElemState::Pending(ref mut t) => {
                    match t.poll(cx) {
                        Ok(Async::Ready(v)) => Ok(v),
                        Ok(Async::Pending) => {
                            all_done = false;
                            continue
                        }
                        Err(e) => Err(e),
                    }
                }
                ElemState::Done(ref mut _v) => continue,
            };

            match done_val {
                Ok(v) => self.elems[idx] = ElemState::Done(v),
                Err(e) => {
                    // On completion drop all our associated resources
                    // ASAP.
                    self.elems = Vec::new();
                    return Err(e)
                }
            }
        }

        if all_done {
            let elems = mem::replace(&mut self.elems, Vec::new());
            let result = elems.into_iter().map(|e| {
                match e {
                    ElemState::Done(t) => t,
                    _ => unreachable!(),
                }
            }).collect();
            Ok(Async::Ready(result))
        } else {
            Ok(Async::Pending)
        }
    }
}

impl<F: IntoFuture> FromIterator<F> for JoinAll<F::Future> {
    fn from_iter<T: IntoIterator<Item=F>>(iter: T) -> Self {
        join_all(iter)
    }
}