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

//!
//! `Interval` stream backed by the Tokio `Interval` stream.
//!

#![allow(dead_code)]

use crate::channel::Channel;
use futures::{task::AtomicWaker, Stream};
use instant::Duration;
use std::{
    pin::Pin,
    sync::{
        atomic::{AtomicBool, Ordering},
        Arc, Mutex,
    },
    task::{Context, Poll},
};

struct Inner {
    ready: AtomicBool,
    period: Mutex<Duration>,
    waker: AtomicWaker,
    shutdown_ctl: Channel,
    period_ctl: Channel<Duration>,
}

///
/// `Interval` stream used by the `interval()` function to provide a
/// a time interval stream. The stream is backed by tokio interval
/// stream on native platforms and by by the JavaScript `setInterval()`
/// and `clearInterval()` APIs in WASM32 environment.
///
/// This Interval stream has an advantage of having `Send` and `Sync` markers.
///
/// Please note that the `Interval` fires upon creation to mimic
/// the tokio-backed Interval stream available on the native target.
///
#[derive(Clone)]
pub struct Interval {
    inner: Arc<Inner>,
}

impl Interval {
    /// Create a new `Interval` stream that will resolve each given duration.
    pub fn new(duration: Duration) -> Self {
        let inner = Arc::new(Inner {
            ready: AtomicBool::new(false),
            waker: AtomicWaker::new(),
            period: Mutex::new(duration),
            shutdown_ctl: Channel::oneshot(),
            period_ctl: Channel::unbounded(),
        });

        let inner_ = inner.clone();

        crate::task::spawn(async move {
            let mut current_period = *inner_.period.lock().unwrap();

            'outer: loop {
                let mut interval = tokio::time::interval(current_period);

                'inner: loop {
                    tokio::select! {
                        _ = interval.tick() => {
                            inner_.ready.store(true, Ordering::SeqCst);
                            inner_.waker.wake();
                        },
                        new_period = inner_.period_ctl.recv() => {
                            if let Ok(new_period) = new_period {
                                current_period = new_period;
                            } else {
                                // if the duration channel is closed, we stop the interval
                                break 'outer;
                            }
                            break 'inner;
                        },
                        _ = inner_.shutdown_ctl.recv() => {
                            break 'outer;
                        },
                    }
                }
            }
        });

        Interval { inner }
    }

    #[inline]
    fn change_period(&self, period: Duration) {
        self.inner
            .period_ctl
            .try_send(period)
            .expect("Interval::change_period() unable to send period signal");
    }

    #[inline]
    fn shutdown(&self) {
        self.inner
            .shutdown_ctl
            .try_send(())
            .expect("Interval::shutdown() unable to send shutdown signal");
    }

    /// Cancel the current timeout.
    pub fn cancel(&self) {
        self.shutdown();
    }
}

impl Stream for Interval {
    type Item = ();

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        match self.inner.ready.load(Ordering::SeqCst) {
            true => {
                self.inner.ready.store(false, Ordering::SeqCst);
                Poll::Ready(Some(()))
            }
            false => {
                self.inner.waker.register(cx.waker());
                if self.inner.ready.load(Ordering::SeqCst) {
                    self.inner.ready.store(false, Ordering::SeqCst);
                    Poll::Ready(Some(()))
                } else {
                    Poll::Pending
                }
            }
        }
    }
}

impl Drop for Interval {
    fn drop(&mut self) {
        self.shutdown();
    }
}

/// `async interval()` function backed by the JavaScript `createInterval()`
pub fn interval(duration: Duration) -> Interval {
    Interval::new(duration)
}