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

use super::task::Task;
use super::FuturesUnordered;
use core::marker::PhantomData;
use core::pin::Pin;
use core::ptr;
use core::sync::atomic::Ordering::Relaxed;

/// Mutable iterator over all futures in the unordered set.
#[derive(Debug)]
pub struct IterPinMut<'a, Fut> {
    pub(super) task: *const Task<Fut>,
    pub(super) len: usize,
    pub(super) _marker: PhantomData<&'a mut FuturesUnordered<Fut>>,
}

/// Mutable iterator over all futures in the unordered set.
#[derive(Debug)]
pub struct IterMut<'a, Fut: Unpin>(pub(super) IterPinMut<'a, Fut>);

/// Immutable iterator over all futures in the unordered set.
#[derive(Debug)]
pub struct IterPinRef<'a, Fut> {
    pub(super) task: *const Task<Fut>,
    pub(super) len: usize,
    pub(super) pending_next_all: *mut Task<Fut>,
    pub(super) _marker: PhantomData<&'a FuturesUnordered<Fut>>,
}

/// Immutable iterator over all the futures in the unordered set.
#[derive(Debug)]
pub struct Iter<'a, Fut: Unpin>(pub(super) IterPinRef<'a, Fut>);

/// Owned iterator over all futures in the unordered set.
#[derive(Debug)]
pub struct IntoIter<Fut: Unpin> {
    pub(super) len: usize,
    pub(super) inner: FuturesUnordered<Fut>,
}

impl<Fut: Unpin> Iterator for IntoIter<Fut> {
    type Item = Fut;

    fn next(&mut self) -> Option<Self::Item> {
        // `head_all` can be accessed directly and we don't need to spin on
        // `Task::next_all` since we have exclusive access to the set.
        let task = self.inner.head_all.get_mut();

        if (*task).is_null() {
            return None;
        }

        unsafe {
            // Moving out of the future is safe because it is `Unpin`
            let future = (*(**task).future.get()).take().unwrap();

            // Mutable access to a previously shared `FuturesUnordered` implies
            // that the other threads already released the object before the
            // current thread acquired it, so relaxed ordering can be used and
            // valid `next_all` checks can be skipped.
            let next = (**task).next_all.load(Relaxed);
            *task = next;
            if !task.is_null() {
                *(**task).prev_all.get() = ptr::null_mut();
            }
            self.len -= 1;
            Some(future)
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        (self.len, Some(self.len))
    }
}

impl<Fut: Unpin> ExactSizeIterator for IntoIter<Fut> {}

impl<'a, Fut> Iterator for IterPinMut<'a, Fut> {
    type Item = Pin<&'a mut Fut>;

    fn next(&mut self) -> Option<Self::Item> {
        if self.task.is_null() {
            return None;
        }

        unsafe {
            let future = (*(*self.task).future.get()).as_mut().unwrap();

            // Mutable access to a previously shared `FuturesUnordered` implies
            // that the other threads already released the object before the
            // current thread acquired it, so relaxed ordering can be used and
            // valid `next_all` checks can be skipped.
            let next = (*self.task).next_all.load(Relaxed);
            self.task = next;
            self.len -= 1;
            Some(Pin::new_unchecked(future))
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        (self.len, Some(self.len))
    }
}

impl<Fut> ExactSizeIterator for IterPinMut<'_, Fut> {}

impl<'a, Fut: Unpin> Iterator for IterMut<'a, Fut> {
    type Item = &'a mut Fut;

    fn next(&mut self) -> Option<Self::Item> {
        self.0.next().map(Pin::get_mut)
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.0.size_hint()
    }
}

impl<Fut: Unpin> ExactSizeIterator for IterMut<'_, Fut> {}

impl<'a, Fut> Iterator for IterPinRef<'a, Fut> {
    type Item = Pin<&'a Fut>;

    fn next(&mut self) -> Option<Self::Item> {
        if self.task.is_null() {
            return None;
        }

        unsafe {
            let future = (*(*self.task).future.get()).as_ref().unwrap();

            // Relaxed ordering can be used since acquire ordering when
            // `head_all` was initially read for this iterator implies acquire
            // ordering for all previously inserted nodes (and we don't need to
            // read `len_all` again for any other nodes).
            let next = (*self.task).spin_next_all(self.pending_next_all, Relaxed);
            self.task = next;
            self.len -= 1;
            Some(Pin::new_unchecked(future))
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        (self.len, Some(self.len))
    }
}

impl<Fut> ExactSizeIterator for IterPinRef<'_, Fut> {}

impl<'a, Fut: Unpin> Iterator for Iter<'a, Fut> {
    type Item = &'a Fut;

    fn next(&mut self) -> Option<Self::Item> {
        self.0.next().map(Pin::get_ref)
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        self.0.size_hint()
    }
}

impl<Fut: Unpin> ExactSizeIterator for Iter<'_, Fut> {}

// SAFETY: we do nothing thread-local and there is no interior mutability,
// so the usual structural `Send`/`Sync` apply.
unsafe impl<Fut: Send> Send for IterPinRef<'_, Fut> {}
unsafe impl<Fut: Sync> Sync for IterPinRef<'_, Fut> {}

unsafe impl<Fut: Send> Send for IterPinMut<'_, Fut> {}
unsafe impl<Fut: Sync> Sync for IterPinMut<'_, Fut> {}

unsafe impl<Fut: Send + Unpin> Send for IntoIter<Fut> {}
unsafe impl<Fut: Sync + Unpin> Sync for IntoIter<Fut> {}