blob: f36c66a5d39aed048d0bcc57385cf7e09d6737dd [file] [log] [blame]
//! Slow down a stream by enforcing a delay between items.
use crate::Stream;
use tokio::time::{Duration, Instant, Sleep};
use std::future::Future;
use std::marker::Unpin;
use std::pin::Pin;
use std::task::{self, Poll};
use pin_project_lite::pin_project;
pub(super) fn throttle<T>(duration: Duration, stream: T) -> Throttle<T>
T: Stream,
Throttle {
delay: tokio::time::sleep_until(Instant::now() + duration),
has_delayed: true,
pin_project! {
/// Stream for the [`throttle`](throttle) function. This object is `!Unpin`. If you need it to
/// implement `Unpin` you can pin your throttle like this: `Box::pin(your_throttle)`.
#[must_use = "streams do nothing unless polled"]
pub struct Throttle<T> {
delay: Sleep,
duration: Duration,
// Set to true when `delay` has returned ready, but `stream` hasn't.
has_delayed: bool,
// The stream to throttle
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 {
/// 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 {
/// 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 {
impl<T: Stream> Stream for Throttle<T> {
type Item = T::Item;
fn poll_next(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Option<Self::Item>> {
let mut me = self.project();
let dur = *me.duration;
if !*me.has_delayed && !is_zero(dur) {
*me.has_delayed = true;
let value = ready!(;
if value.is_some() {
if !is_zero(dur) {
me.delay.reset(Instant::now() + dur);
*me.has_delayed = false;
fn is_zero(dur: Duration) -> bool {
dur == Duration::from_millis(0)