googleapis
diff --git a/‎[refs]‎
Lines changed: 1 addition & 1 deletion b/‎[refs]‎
Lines changed: 1 addition & 1 deletion
diff --git a/‎branches/pubsub-ordering-keys/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/MessageDispatcher.java‎
Lines changed: 9 additions & 2 deletions b/‎branches/pubsub-ordering-keys/google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/MessageDispatcher.java‎
Lines changed: 9 additions & 2 deletions
@@ -155,7 +155,7 @@ refs/tags/v0.72.0: a7703f2593ba312c0b2dde6fdfd4f5c764bb55ac
 refs/tags/v0.73.0: 21241ea8be9439cc5764c4944cdce21d34ce4f9e
 refs/tags/v0.74.0: 9d1f733dbbf790de7b494418523b69c4a9a57638
 refs/heads/ignoretest: 23c412ae07af3d0ab1caa2d44d5bc5c0ccb8b31d
-refs/heads/pubsub-ordering-keys: 2fc4e551b5263fe1e902efdbc1fd01acf8e3b5e9
+refs/heads/pubsub-ordering-keys: e026c5ce0b76bc6ab55e50ca1a08e743cb2c76e4
 "refs/heads/update_mvn_badge": ae2d773814db0f71197ccf5a8612ee1d8056f8de
 refs/tags/v0.75.0: c3673089ae09a897c1b4cf7dfe167fe4f8ab32fb
 refs/tags/v0.76.0: 395b016826d3ddf9cb8b34919636df15a4dbd032
 
@@ -62,6 +62,7 @@ class MessageDispatcher {
   @InternalApi static final Duration PENDING_ACKS_SEND_DELAY = Duration.ofMillis(100);
 
   private final Executor executor;
+  private final SequentialExecutorService sequentialExecutor;
   private final ScheduledExecutorService systemExecutor;
   private final ApiClock clock;
 
@@ -205,6 +206,7 @@ void sendAckOperations(
     jobLock = new ReentrantLock();
     messagesWaiter = new MessageWaiter();
     this.clock = clock;
+    this.sequentialExecutor = new SequentialExecutorService(executor);
   }
 
   void start() {
@@ -349,7 +351,7 @@ public void nack() {
           }
         };
     ApiFutures.addCallback(response, ackHandler, MoreExecutors.directExecutor());
-    executor.execute(
+    Runnable deliverMessageTask =
         new Runnable() {
           @Override
           public void run() {
@@ -370,7 +372,12 @@ public void run() {
               response.setException(e);
             }
           }
-        });
+        };
+    if (message.getOrderingKey().isEmpty()) {
+      executor.execute(deliverMessageTask);
+    } else {
+      sequentialExecutor.submit(message.getOrderingKey(), deliverMessageTask);
+    }
   }
 
   /** Compute the ideal deadline, set subsequent modacks to this deadline, and return it. */