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

use std::collections::VecDeque;
use std::fmt;
use std::marker::PhantomData;
use std::marker::Unpin;
use std::ops::{Deref, DerefMut};
use std::pin::Pin;
use std::sync::Arc;
use std::sync::Mutex;
use std::task::{Context, Poll};
use std::sync::atomic::{AtomicBool, Ordering};

use futures::Stream;
use futures::task::AtomicWaker;
use pin_project_lite::pin_project;

use super::Waker;

pin_project! {
    #[must_use = "streams do nothing unless polled"]
    pub struct QueueStream<Q, Item, F> {
        #[pin]
        q: Q,
        #[pin]
        f: F,
        recv_task: Arc<AtomicWaker>,
        parked_queue: Arc<Mutex<VecDeque<std::task::Waker>>>,
        closed: Arc<AtomicBool>,
        _item: PhantomData<Item>,
    }
}

unsafe impl<Q, Item, F> Sync for QueueStream<Q, Item, F> {}

unsafe impl<Q, Item, F> Send for QueueStream<Q, Item, F> {}

impl<Q, Item, F> Clone for QueueStream<Q, Item, F>
    where
        Q: Clone,
        F: Clone,
{
    #[inline]
    fn clone(&self) -> Self {
        Self {
            q: self.q.clone(),
            f: self.f.clone(),
            recv_task: self.recv_task.clone(),
            parked_queue: self.parked_queue.clone(),
            closed: self.closed.clone(),
            _item: PhantomData,
        }
    }
}

impl<Q, Item, F> fmt::Debug for QueueStream<Q, Item, F>
    where
        Q: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("QueueStream")
            .field("queue", &self.q)
            .finish()
    }
}

impl<Q: Unpin, Item, F> QueueStream<Q, Item, F> {
    #[inline]
    pub(super) fn new(q: Q, f: F) -> Self {
        Self {
            q,
            f,
            recv_task: Arc::new(AtomicWaker::new()),
            parked_queue: Arc::new(Mutex::new(VecDeque::default())),
            closed: Arc::new(AtomicBool::new(false)),
            _item: PhantomData,
        }
    }

    #[inline]
    pub fn is_closed(&self) -> bool {
        self.closed.load(Ordering::SeqCst)
    }
}

impl<Q, Item, F> Waker for QueueStream<Q, Item, F> {
    #[inline]
    fn rx_wake(&self) {
        self.recv_task.wake()
    }

    #[inline]
    fn tx_park(&self, w: std::task::Waker) {
        self.parked_queue.lock().unwrap().push_back(w);
    }

    #[inline]
    fn close_channel(&self) {
        self.closed.store(true, Ordering::SeqCst);
        self.rx_wake();
    }
}

impl<Q, Item, F> Stream for QueueStream<Q, Item, F>
    where
        Q: Unpin,
        F: Fn(Pin<&mut Q>, &mut Context<'_>) -> Poll<Option<Item>>,
{
    type Item = Item;

    fn poll_next(self: Pin<&mut Self>, ctx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        let mut this = self.project();
        let f = this.f.as_mut();
        match f(this.q.as_mut(), ctx) {
            Poll::Ready(msg) => {
                if let Some(w) = this.parked_queue.lock().unwrap().pop_front() {
                    w.wake();
                }
                Poll::Ready(msg)
            }
            Poll::Pending => {
                if this.closed.load(Ordering::SeqCst) {
                    Poll::Ready(None)
                }else {
                    this.recv_task.register(ctx.waker());
                    f(this.q.as_mut(), ctx)
                }
            }
        }
    }
}

impl<Q, Item, F> Deref for QueueStream<Q, Item, F> {
    type Target = Q;
    #[inline]
    fn deref(&self) -> &Self::Target {
        &self.q
    }
}

impl<Q, Item, F> DerefMut for QueueStream<Q, Item, F> {
    #[inline]
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.q
    }
}