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|
//! Slow down a stream by enforcing a delay between items.
use crate::time::{Delay, Duration, Instant};
use std::future::Future;
use std::marker::Unpin;
use std::pin::Pin;
use std::task::{self, Poll};
use futures_core::Stream;
use pin_project_lite::pin_project;
/// Slow down a stream by enforcing a delay between items.
/// They will be produced not more often than the specified interval.
///
/// # Example
///
/// Create a throttled stream.
/// ```rust,norun
/// use futures::stream::StreamExt;
/// use std::time::Duration;
/// use tokio::time::throttle;
///
/// # async fn dox() {
/// let mut item_stream = throttle(Duration::from_secs(2), futures::stream::repeat("one"));
///
/// loop {
/// // The string will be produced at most every 2 seconds
/// println!("{:?}", item_stream.next().await);
/// }
/// # }
/// ```
pub fn throttle<T>(duration: Duration, stream: T) -> Throttle<T>
where
T: Stream,
{
let delay = if duration == Duration::from_millis(0) {
None
} else {
Some(Delay::new_timeout(Instant::now() + duration, duration))
};
Throttle {
delay,
duration,
has_delayed: true,
stream,
}
}
pin_project! {
/// Stream for the [`throttle`](throttle) function.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Throttle<T> {
// `None` when duration is zero.
delay: Option<Delay>,
duration: Duration,
// Set to true when `delay` has returned ready, but `stream` hasn't.
has_delayed: bool,
// The stream to throttle
#[pin]
stream: T,
}
}
// XXX: are these safe if `T: !Unpin`?
impl<T: Unpin> Throttle<T> {
/// Acquires a reference to the underlying stream that this combinator is
/// pulling from.
pub fn get_ref(&self) -> &T {
&self.stream
}
/// Acquires a mutable reference to the underlying stream that this combinator
/// is pulling from.
///
/// Note that care must be taken to avoid tampering with the state of the stream
/// which may otherwise confuse this combinator.
pub fn get_mut(&mut self) -> &mut T {
&mut self.stream
}
/// Consumes this combinator, returning the underlying stream.
///
/// Note that this may discard intermediate state of this combinator, so care
/// should be taken to avoid losing resources when this is called.
pub fn into_inner(self) -> T {
self.stream
}
}
impl<T: Stream> Stream for Throttle<T> {
type Item = T::Item;
fn poll_next(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Option<Self::Item>> {
if !self.has_delayed && self.delay.is_some() {
ready!(Pin::new(self.as_mut()
.project().delay.as_mut().unwrap())
.poll(cx));
*self.as_mut().project().has_delayed = true;
}
let value = ready!(self
.as_mut()
.project().stream
.poll_next(cx));
if value.is_some() {
let dur = self.duration;
if let Some(ref mut delay) = self.as_mut().project().delay {
delay.reset(Instant::now() + dur);
}
*self.as_mut().project().has_delayed = false;
}
Poll::Ready(value)
}
}
|
