Adds new function interval_range

Cargo.toml

@@ -14,3 +14,4 @@ Timer facilities for Tokio
 [dependencies]
 futures = "0.1"
 slab = "0.3.0"
+rand = "0.3"

src/interval.rs

@@ -4,23 +4,58 @@ use {Sleep, TimerError};
 
 use std::time::Duration;
 
-/// A stream representing notifications at fixed interval
+use rand::{thread_rng, Rng};
+
+/// A stream representing notifications at given interval
 ///
 /// Intervals are created through `Timer::interval`.
 #[derive(Debug)]
 pub struct Interval {
     sleep: Sleep,
-    duration: Duration,
+    min_duration: Duration,
+    max_duration: Duration,
 }
 
 /// Create a new interval
-pub fn new(sleep: Sleep, dur: Duration) -> Interval {
+pub fn new(sleep: Sleep, min_dur: Duration, max_dur: Duration) -> Interval {
     Interval {
         sleep: sleep,
-        duration: dur,
+        min_duration: min_dur,
+        max_duration: max_dur,
     }
 }
 
+const NANOS_PER_SEC: u32 = 1_000_000_000;
+
+/// Returns the next duration for an interval
+/// If `min` and `max` are equal, the duration is fixed.
+/// If `min` and `max` are not equal, a duration in the range [`min`, `max`] is returned.
+///
+/// # Panics
+///
+/// Panics if `max < min`.
+pub(crate) fn next_duration(min: Duration, max: Duration) -> Duration {
+    let mut rng = thread_rng();
+
+    let secs = if min.as_secs() == max.as_secs() {
+        min.as_secs()
+    } else {
+        rng.gen_range(min.as_secs(), max.as_secs() + 1)
+    };
+
+    let nsecs = if min.subsec_nanos() == max.subsec_nanos() {
+        min.subsec_nanos()
+    } else if secs == min.as_secs() {
+        rng.gen_range(min.subsec_nanos(), NANOS_PER_SEC)
+    } else if secs == max.as_secs() {
+        rng.gen_range(0, max.subsec_nanos() + 1)
+    } else {
+        rng.gen_range(0, NANOS_PER_SEC)
+    };
+
+    Duration::new(secs, nsecs)
+}
+
 impl Stream for Interval {
     type Item = ();
     type Error = TimerError;
@@ -29,7 +64,7 @@ impl Stream for Interval {
         let _ = try_ready!(self.sleep.poll());
 
         // Reset the timeout
-        self.sleep = self.sleep.timer().sleep(self.duration);
+        self.sleep = self.sleep.timer().sleep(next_duration(self.min_duration, self.max_duration));
 
         Ok(Async::Ready(Some(())))
     }

src/lib.rs

@@ -90,6 +90,7 @@
 #[macro_use]
 extern crate futures;
 extern crate slab;
+extern crate rand;
 
 mod interval;
 mod mpmc;

src/timer.rs

@@ -112,7 +112,7 @@ impl Timer {
     /// Creates a new interval which will fire at `dur` time into the future,
     /// and will repeat every `dur` interval after
     pub fn interval(&self, dur: Duration) -> Interval {
-        interval::new(self.sleep(dur), dur)
+        interval::new(self.sleep(dur), dur, dur)
     }
 
     /// Creates a new interval which will fire at the time specified by `at`,
@@ -126,7 +126,17 @@ impl Timer {
             self.sleep(Duration::from_millis(0))
         };
 
-        interval::new(sleep, dur)
+        interval::new(sleep, dur, dur)
+    }
+
+    /// Creates a new interval which will fire at a time in the range [`min`, `max`] into the
+    /// future, and will repeat every time with a new interval in the range [`min`, `max`] after.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `max < min`.
+    pub fn interval_range(&self, min: Duration, max: Duration) -> Interval {
+        interval::new(self.sleep(interval::next_duration(min, max)), min, max)
     }
 }