1 files changed, 112 insertions, 0 deletions
diff --git a/tokio/src/time/interval.rs b/tokio/src/time/interval.rs
new file mode 100644
index 00000000..f517b23f
--- /dev/null
+++ b/tokio/src/time/interval.rs
@@ -0,0 +1,112 @@
+use crate::time::{clock, Delay};
+
+use futures_core::ready;
+use futures_util::future::poll_fn;
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{self, Poll};
+use std::time::{Duration, Instant};
+
+/// A stream representing notifications at fixed interval
+#[derive(Debug)]
+pub struct Interval {
+    /// Future that completes the next time the `Interval` yields a value.
+    delay: Delay,
+
+    /// The duration between values yielded by `Interval`.
+    duration: Duration,
+}
+
+impl Interval {
+    /// Create a new `Interval` that starts at `at` and yields every `duration`
+    /// interval after that.
+    ///
+    /// Note that when it starts, it produces item too.
+    ///
+    /// The `duration` argument must be a non-zero duration.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if `duration` is zero.
+    pub fn new(at: Instant, duration: Duration) -> Interval {
+        assert!(
+            duration > Duration::new(0, 0),
+            "`duration` must be non-zero."
+        );
+
+        Interval::new_with_delay(Delay::new(at), duration)
+    }
+
+    /// Creates new `Interval` that yields with interval of `duration`.
+    ///
+    /// The function is shortcut for `Interval::new(tokio::time::clock::now() + duration, duration)`.
+    ///
+    /// The `duration` argument must be a non-zero duration.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if `duration` is zero.
+    pub fn new_interval(duration: Duration) -> Interval {
+        Interval::new(clock::now() + duration, duration)
+    }
+
+    pub(crate) fn new_with_delay(delay: Delay, duration: Duration) -> Interval {
+        Interval { delay, duration }
+    }
+
+    #[doc(hidden)] // TODO: remove
+    pub fn poll_next(&mut self, cx: &mut task::Context<'_>) -> Poll<Option<Instant>> {
+        // Wait for the delay to be done
+        ready!(Pin::new(&mut self.delay).poll(cx));
+
+        // Get the `now` by looking at the `delay` deadline
+        let now = self.delay.deadline();
+
+        // The next interval value is `duration` after the one that just
+        // yielded.
+        let next = now + self.duration;
+        self.delay.reset(next);
+
+        // Return the current instant
+        Poll::Ready(Some(now))
+    }
+
+    /// Completes when the next instant in the interval has been reached.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::time::Interval;
+    ///
+    /// use std::time::Duration;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let mut interval = Interval::new_interval(Duration::from_millis(10));
+    ///
+    ///     interval.next().await;
+    ///     interval.next().await;
+    ///     interval.next().await;
+    ///
+    ///     // approximately 30ms have elapsed.
+    /// }
+    /// ```
+    #[allow(clippy::should_implement_trait)] // TODO: rename (tokio-rs/tokio#1261)
+    pub async fn next(&mut self) -> Option<Instant> {
+        poll_fn(|cx| self.poll_next(cx)).await
+    }
+}
+
+impl futures_core::FusedStream for Interval {
+    fn is_terminated(&self) -> bool {
+        false
+    }
+}
+
+impl futures_core::Stream for Interval {
+    type Item = Instant;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Option<Self::Item>> {
+        Interval::poll_next(self.get_mut(), cx)
+    }
+}