Implement Sync for Sender

CHANGELOG.md

@@ -15,6 +15,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 
 ## [Unreleased]
+### Added
+- Implement `Sync` for `Sender`. There is not a whole lot someone can do with a `&Sender`,
+  but this allows storing the sender in places that are overly conservative and require
+  a `Sync` bound on the content.
 
 
 ## [0.1.8] - 2024-06-13

src/lib.rs

@@ -227,6 +227,12 @@ pub struct Receiver<T> {
 }
 
 unsafe impl<T: Send> Send for Sender<T> {}
+
+// SAFETY: The only methods that assumes there is only a single reference to the sender
+// takes `self` by value, guaranteeing that there is only one reference to the sender at
+// the time it is called.
+unsafe impl<T: Sync> Sync for Sender<T> {}
+
 unsafe impl<T: Send> Send for Receiver<T> {}
 impl<T> Unpin for Receiver<T> {}