Merge branch 'add-is_cosed_method'

CHANGELOG.md

@@ -15,6 +15,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 
 ## [Unreleased]
+### Added
+* Add `is_closed` method to the `Sender`.
 
 
 ## [0.1.6] - 2023-09-14

src/lib.rs

@@ -312,6 +312,21 @@ impl<T> Sender<T> {
         }
     }
 
+    /// Returns true if the associated [`Receiver`] has been dropped.
+    ///
+    /// If true is returned, a future call to send is guaranteed to return an error.
+    pub fn is_closed(&self) -> bool {
+        // SAFETY: The channel exists on the heap for the entire duration of this method and we
+        // only ever acquire shared references to it. Note that if the receiver disconnects it
+        // does not free the channel.
+        let channel = unsafe { self.channel_ptr.as_ref() };
+
+        // ORDERING: We *chose* a Relaxed ordering here as it sufficient to
+        // enforce the method's contract: "if true is returned, a future
+        // call to send is guaranteed to return an error."
+        channel.state.load(Relaxed) == DISCONNECTED
+    }
+
     /// Consumes the Sender, returning a raw pointer to the channel on the heap.
     ///
     /// This is intended to simplify using oneshot channels with some FFI code. The only safe thing

tests/sync.rs

@@ -343,3 +343,13 @@ fn send_error_drops_message_correctly_on_into_inner() {
         assert_eq!(counter.count(), 1);
     });
 }
+
+#[test]
+fn dropping_receiver_disconnects_sender() {
+    maybe_loom_model(|| {
+        let (sender, receiver) = oneshot::channel::<()>();
+        assert!(!sender.is_closed());
+        drop(receiver);
+        assert!(sender.is_closed());
+    });
+}