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|
//! Slow down a stream by enforcing a delay between items.
use crate::time::{clock, Delay};
use futures_core::ready;
use futures_core::Stream;
use std::{
future::Future,
marker::Unpin,
pin::Pin,
task::{self, Poll},
time::Duration,
};
/// Slow down a stream by enforcing a delay between items.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Throttle<T> {
delay: Delay,
/// Set to true when `delay` has returned ready, but `stream` hasn't.
has_delayed: bool,
stream: T,
}
impl<T> Throttle<T> {
/// Slow down a stream by enforcing a delay between items.
pub fn new(stream: T, duration: Duration) -> Self {
Self {
delay: Delay::new_timeout(clock::now() + duration, duration),
has_delayed: true,
stream,
}
}
}
// 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>> {
unsafe {
if !self.has_delayed {
ready!(self.as_mut().map_unchecked_mut(|me| &mut me.delay).poll(cx));
self.as_mut().get_unchecked_mut().has_delayed = true;
}
let value = ready!(self
.as_mut()
.map_unchecked_mut(|me| &mut me.stream)
.poll_next(cx));
if value.is_some() {
self.as_mut().get_unchecked_mut().delay.reset_timeout();
self.as_mut().get_unchecked_mut().has_delayed = false;
}
Poll::Ready(value)
}
}
}
|
