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
use pin_project_lite::pin_project;
use futures_core::stream::Stream;
use std::pin::Pin;
use std::task::{Context, Poll};
pin_project! {
/// Filter out all items after the first for a specified time.
///
/// This `struct` is created by the [`throttle`] method on [`StreamExt`]. See its
/// documentation for more.
///
/// [`throttle`]: crate::stream::StreamExt::throttle
/// [`StreamExt`]: crate::stream::StreamExt
#[derive(Debug)]
#[must_use = "streams do nothing unless polled or .awaited"]
pub struct Throttle<S: Stream, I> {
#[pin]
stream: S,
#[pin]
interval: I,
state: State,
budget: usize,
}
}
impl<S: Stream, I> Throttle<S, I> {
pub(crate) fn new(stream: S, interval: I) -> Self {
Self {
state: State::Streaming(0),
stream,
interval,
budget: 1,
}
}
}
#[derive(Debug)]
enum State {
/// The underlying stream is yielding items.
Streaming(usize),
/// All timers have completed and all data has been yielded.
StreamDone,
/// The closing `Ready(None)` has been yielded.
AllDone,
}
impl<S: Stream, I: Stream> Stream for Throttle<S, I> {
type Item = S::Item;
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
let mut this = self.project();
let mut slot = None;
match this.state {
// The underlying stream is yielding items.
State::Streaming(count) => {
// Poll the underlying stream until we get to `Poll::Pending`.
loop {
match this.stream.as_mut().poll_next(cx) {
Poll::Ready(Some(value)) => {
if count < this.budget {
slot = Some(value);
*count += 1;
}
}
Poll::Ready(None) => {
*this.state = State::StreamDone;
break;
}
Poll::Pending => break,
}
}
// After the stream, always poll the interval timer.
let _ = this
.interval
.as_mut()
.poll_next(cx)
.map(move |_| match this.state {
State::Streaming(count) => *count = 0, // reset the counter
State::StreamDone => cx.waker().wake_by_ref(),
State::AllDone => {}
});
match slot {
Some(item) => Poll::Ready(Some(item)),
None => Poll::Pending,
}
}
// All streams have completed and all data has been yielded.
State::StreamDone => {
*this.state = State::AllDone;
Poll::Ready(None)
}
// The closing `Ready(None)` has been yielded.
State::AllDone => panic!("stream polled after completion"),
}
}
}
#[cfg(test)]
mod test {
use crate::prelude::*;
use crate::time::Duration;
use futures_lite::prelude::*;
#[test]
fn smoke() {
async_io::block_on(async {
let interval = Duration::from_millis(100);
let throttle = Duration::from_millis(300);
let take = 4;
let expected = 2;
let mut counter = 0;
crate::stream::interval(interval)
.take(take)
.throttle(throttle)
.for_each(|_| counter += 1)
.await;
assert_eq!(counter, expected);
})
}
}