From ce7bd6955f85baf53b3e1091974be70c6cf88b49 Mon Sep 17 00:00:00 2001
From: Rasmus Melchior Jacobsen <rmja@laesoe.org>
Date: Tue, 21 Mar 2023 13:25:49 +0100
Subject: [PATCH] perf(pubsub): Skip clone on last message

---
 embassy-sync/src/pubsub/mod.rs | 32 ++++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/embassy-sync/src/pubsub/mod.rs b/embassy-sync/src/pubsub/mod.rs
index 5989e86e..59e701c5 100644
--- a/embassy-sync/src/pubsub/mod.rs
+++ b/embassy-sync/src/pubsub/mod.rs
@@ -322,12 +322,15 @@ impl<T: Clone, const CAP: usize, const SUBS: usize, const PUBS: usize> PubSubSta
 
         // We're reading this item, so decrement the counter
         queue_item.1 -= 1;
-        let message = queue_item.0.clone();
 
-        if current_message_index == 0 && queue_item.1 == 0 {
-            self.queue.pop_front();
+        let message = if current_message_index == 0 && queue_item.1 == 0 {
+            let (message, _) = self.queue.pop_front().unwrap();
             self.publisher_wakers.wake();
-        }
+            // Return pop'd message without clone
+            message
+        } else {
+            queue_item.0.clone()
+        };
 
         Some(WaitResult::Message(message))
     }
@@ -659,4 +662,25 @@ mod tests {
 
         assert_eq!(4, channel.space());
     }
+
+    struct CloneCallCounter(usize);
+
+    impl Clone for CloneCallCounter {
+        fn clone(&self) -> Self {
+            Self(self.0 + 1)
+        }
+    }
+
+    #[futures_test::test]
+    async fn skip_clone_for_last_message() {
+        let channel = PubSubChannel::<NoopRawMutex, CloneCallCounter, 1, 2, 1>::new();
+        let pub0 = channel.publisher().unwrap();
+        let mut sub0 = channel.subscriber().unwrap();
+        let mut sub1 = channel.subscriber().unwrap();
+
+        pub0.publish(CloneCallCounter(0)).await;
+
+        assert_eq!(1, sub0.try_next_message_pure().unwrap().0);
+        assert_eq!(0, sub1.try_next_message_pure().unwrap().0);
+    }
 }