Fix memory leak of MpMcQueue

Author: sosthene-nitrokey

CHANGELOG.md

@@ -31,6 +31,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Fixed the list of implemented data structures in the crate docs, by adding `Deque`,
   `HistoryBuffer` and `SortedLinkedList` to the list.
 - Fixed `MpMcQueue` with `mpmc_large` feature.
+- Fix missing `Drop` for `MpMcQueue`
 
 ## [v0.8.0] - 2023-11-07
 

src/mpmc.rs

@@ -194,6 +194,13 @@ impl<T, const N: usize> Default for MpMcQueue<T, N> {
     }
 }
 
+impl<T, const N: usize> Drop for MpMcQueue<T, N> {
+    fn drop(&mut self) {
+        // drop all contents currently in the queue
+        while self.dequeue().is_some() {}
+    }
+}
+
 unsafe impl<T, const N: usize> Sync for MpMcQueue<T, N> where T: Send {}
 
 struct Cell<T> {
@@ -306,6 +313,18 @@ mod tests {
     // Ensure a `MpMcQueue` containing `!Send` values stays `!Send` itself.
     assert_not_impl_any!(MpMcQueue<*const (), 4>: Send);
 
+    #[test]
+    fn memory_leak() {
+        droppable!();
+
+        let q = Q2::new();
+        q.enqueue(Droppable::new()).unwrap_or_else(|_| panic!());
+        q.enqueue(Droppable::new()).unwrap_or_else(|_| panic!());
+        drop(q);
+
+        assert_eq!(Droppable::count(), 0);
+    }
+
     #[test]
     fn sanity() {
         let q = Q2::new();