Add mark_unchanged method to watch::Receiver

tokio/src/sync/watch.rs

@@ -669,6 +669,22 @@ impl<T> Receiver<T> {
  self.version.decrement();
  }
 
+ /// Marks the state as unchanged.
+ ///
+ /// The current value can will be considered seen by the receiver.
+ ///
+ /// After invoking this method [`has_changed()`](Self::has_changed)
+ /// *MAY* return `false` and [`changed()`](Self::changed) *MAY* not return
+ /// immediately. This is because a new value could be sent before
+ /// this method returns.
+ ///
+ /// This is useful if you are not interested in the current value
+ /// visible in the receiver.
+ pub fn mark_unchanged(&mut self) {
+ let current_version = self.shared.state.load().version();
+ self.version = current_version;
+ }
+
  /// Waits for a change notification, then marks the newest value as seen.
  ///
  /// If the newest value in the channel has not yet been marked seen when

tokio/tests/sync_watch.rs

@@ -102,6 +102,39 @@ fn rx_mark_changed() {
  assert_eq!(*rx.borrow(), "two");
 }
 
+#[test]
+fn rx_mark_unchanged() {
+ let (tx, mut rx) = watch::channel("one");
+
+ let mut rx2 = rx.clone();
+
+ {
+ assert!(!rx.has_changed().unwrap());
+
+ rx.mark_changed();
+ assert!(rx.has_changed().unwrap());
+
+ rx.mark_unchanged();
+ assert!(!rx.has_changed().unwrap());
+
+ let mut t = spawn(rx.changed());
+ assert_pending!(t.poll());
+ }
+
+ {
+ assert!(!rx2.has_changed().unwrap());
+
+ tx.send("two").unwrap();
+ assert!(rx2.has_changed().unwrap());
+
+ rx2.mark_unchanged();
+ assert!(!rx2.has_changed().unwrap());
+ assert_eq!(*rx2.borrow_and_update(), "two");
+ }
+
+ assert_eq!(*rx.borrow(), "two");
+}
+
 #[test]
 fn multi_rx() {
  let (tx, mut rx1) = watch::channel("one");