fix(pubsub): Pop messages which count is 0 after unsubscribe

embassy-sync/src/pubsub/mod.rs

@@ -371,6 +371,20 @@ impl<T: Clone, const CAP: usize, const SUBS: usize, const PUBS: usize> PubSubSta
                 .iter_mut()
                 .skip(current_message_index)
                 .for_each(|(_, counter)| *counter -= 1);
+
+            let mut wake_publishers = false;
+            while let Some((_, count)) = self.queue.front() {
+                if *count == 0 {
+                    self.queue.pop_front().unwrap();
+                    wake_publishers = true;
+                } else {
+                    break;
+                }
+            }
+
+            if wake_publishers {
+                self.publisher_wakers.wake();
+            }
         }
     }
 
@@ -612,4 +626,37 @@ mod tests {
         sub1.next_message().await;
         assert_eq!(pub0.space(), 4);
     }
+
+    #[futures_test::test]
+    async fn empty_channel_when_last_subscriber_is_dropped() {
+        let channel = PubSubChannel::<NoopRawMutex, u32, 4, 4, 4>::new();
+
+        let pub0 = channel.publisher().unwrap();
+        let mut sub0 = channel.subscriber().unwrap();
+        let mut sub1 = channel.subscriber().unwrap();
+
+        assert_eq!(4, pub0.space());
+
+        pub0.publish(1).await;
+        pub0.publish(2).await;
+
+        assert_eq!(2, channel.space());
+
+        assert_eq!(1, sub0.try_next_message_pure().unwrap());
+        assert_eq!(2, sub0.try_next_message_pure().unwrap());
+
+        assert_eq!(2, channel.space());
+
+        drop(sub0);
+
+        assert_eq!(2, channel.space());
+
+        assert_eq!(1, sub1.try_next_message_pure().unwrap());
+
+        assert_eq!(3, channel.space());
+
+        drop(sub1);
+
+        assert_eq!(4, channel.space());
+    }
 }