sync: add `watch::Sender::borrow()`
@@ -322,6 +322,25 @@ impl<T> Sender<T> {
Ok(())
}
+ /// Returns a reference to the most recently sent value
+ ///
+ /// Outstanding borrows hold a read lock. This means that long lived borrows
+ /// could cause the send half to block. It is recommended to keep the borrow
+ /// as short lived as possible.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use tokio::sync::watch;
+ ///
+ /// let (tx, _) = watch::channel("hello");
+ /// assert_eq!(*tx.borrow(), "hello");
+ /// ```
+ pub fn borrow(&self) -> Ref<'_, T> {
+ let inner = self.shared.value.read().unwrap();
+ Ref { inner }
+ }
+
/// Checks if the channel has been closed. This happens when all receivers
/// have dropped.
///
@@ -430,4 +449,44 @@ mod tests {
send_thread.join().unwrap();
});
}
+
+ #[test]
+ fn watch_borrow() {
+ loom::model(|| {
+ let (send, mut recv) = crate::sync::watch::channel(0i32);
+
+ assert!(send.borrow().eq(&0));
+ assert!(recv.borrow().eq(&0));
+
+ send.send(1).unwrap();
+ assert!(send.borrow().eq(&1));
+
+ let send_thread = thread::spawn(move || {
+ send.send(2).unwrap();
+ send
+ });
+
+ recv.changed().now_or_never();
+
+ let send = send_thread.join().unwrap();
+ let recv_thread = thread::spawn(move || {
+ recv.changed().now_or_never();
+ recv.changed().now_or_never();
+ recv
+ });
+
+ send.send(3).unwrap();
+
+ let recv = recv_thread.join().unwrap();
+ assert!(recv.borrow().eq(&3));
+ assert!(send.borrow().eq(&3));
+
+ send.send(2).unwrap();
+
+ thread::spawn(move || {
+ assert!(recv.borrow().eq(&2));
+ });
+ assert!(send.borrow().eq(&2));
+ });
+ }
}
