fix: ordering keys publishing of last batch

google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/Publisher.java

@@ -371,6 +371,25 @@ private void publishAllWithoutInflight() {
     }
   }
 
+  /**
+   * Publish any outstanding batches if non-empty and there are no other batches in flight for
+   * orderingKey. This method sends buffered messages, but does not wait for the send operations to
+   * complete. To wait for messages to send, call {@code get} on the futures returned from {@code
+   * publish}.
+   */
+  private void publishAllWithoutInflightForKey(final String orderingKey) {
+    messagesBatchLock.lock();
+    try {
+      MessagesBatch batch = messagesBatches.get(orderingKey);
+      if (batch != null && !sequentialExecutor.hasTasksInflight(orderingKey)) {
+        publishOutstandingBatch(batch.popOutstandingBatch());
+        messagesBatches.remove(orderingKey);
+      }
+    } finally {
+      messagesBatchLock.unlock();
+    }
+  }
+
   private ApiFuture<PublishResponse> publishCall(OutstandingBatch outstandingBatch) {
     return publisherStub
         .publishCallable()
@@ -397,6 +416,11 @@ public void onSuccess(PublishResponse result) {
                             result.getMessageIdsCount(), outstandingBatch.size())));
               } else {
                 outstandingBatch.onSuccess(result.getMessageIdsList());
+                if (!activeAlarm.get()
+                    && outstandingBatch.orderingKey != null
+                    && !outstandingBatch.orderingKey.isEmpty()) {
+                  publishAllWithoutInflightForKey(outstandingBatch.orderingKey);
+                }
               }
             } finally {
               messagesWaiter.incrementPendingMessages(-outstandingBatch.size());

google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/SequentialExecutorService.java

@@ -216,8 +216,8 @@ public void run() {
                       // Step 5.1: on success
                       @Override
                       public void onSuccess(T msg) {
-                        future.set(msg);
                         callNextTaskAsync(key);
+                        future.set(msg);
                       }
 
                       // Step 5.2: on failure

google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/FakePublisherServiceImpl.java

@@ -24,7 +24,10 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
+import org.threeten.bp.Duration;
 
 /**
  * A fake implementation of {@link PublisherImplBase}, that can be used to test clients of a Cloud
@@ -36,6 +39,8 @@ class FakePublisherServiceImpl extends PublisherImplBase {
   private final LinkedBlockingQueue<Response> publishResponses = new LinkedBlockingQueue<>();
   private final AtomicInteger nextMessageId = new AtomicInteger(1);
   private boolean autoPublishResponse;
+  private ScheduledExecutorService executor = null;
+  private Duration responseDelay = Duration.ZERO;
 
   /** Class used to save the state of a possible response. */
   private static class Response {
@@ -74,7 +79,8 @@ public String toString() {
   }
 
   @Override
-  public void publish(PublishRequest request, StreamObserver<PublishResponse> responseObserver) {
+  public void publish(
+      PublishRequest request, final StreamObserver<PublishResponse> responseObserver) {
     requests.add(request);
     Response response;
     try {
@@ -90,6 +96,23 @@ public void publish(PublishRequest request, StreamObserver<PublishResponse> resp
     } catch (InterruptedException e) {
       throw new IllegalArgumentException(e);
     }
+    if (responseDelay == Duration.ZERO) {
+      sendResponse(response, responseObserver);
+    } else {
+      final Response responseToSend = response;
+      executor.schedule(
+          new Runnable() {
+            @Override
+            public void run() {
+              sendResponse(responseToSend, responseObserver);
+            }
+          },
+          responseDelay.toMillis(),
+          TimeUnit.MILLISECONDS);
+    }
+  }
+
+  private void sendResponse(Response response, StreamObserver<PublishResponse> responseObserver) {
     if (response.isError()) {
       responseObserver.onError(response.getError());
     } else {
@@ -107,6 +130,18 @@ public FakePublisherServiceImpl setAutoPublishResponse(boolean autoPublishRespon
     return this;
   }
 
+  /** Set an executor to use to delay publish responses. */
+  public FakePublisherServiceImpl setExecutor(ScheduledExecutorService executor) {
+    this.executor = executor;
+    return this;
+  }
+
+  /** Set an amount of time by which to delay publish responses. */
+  public FakePublisherServiceImpl setPublishResponseDelay(Duration responseDelay) {
+    this.responseDelay = responseDelay;
+    return this;
+  }
+
   public FakePublisherServiceImpl addPublishResponse(PublishResponse publishResponse) {
     publishResponses.add(new Response(publishResponse));
     return this;

google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/PublisherImplTest.java

@@ -308,6 +308,8 @@ public void testBatchedMessagesWithOrderingKeyByDuration() throws Exception {
             .setEnableMessageOrdering(true)
             .build();
     testPublisherServiceImpl.setAutoPublishResponse(true);
+    testPublisherServiceImpl.setExecutor(fakeExecutor);
+    testPublisherServiceImpl.setPublishResponseDelay(Duration.ofSeconds(300));
 
     // Publish two messages with ordering key, "OrderA", and other two messages with "OrderB".
     ApiFuture<String> publishFuture1 = sendTestMessageWithOrderingKey(publisher, "m1", "OrderA");
@@ -325,10 +327,23 @@ public void testBatchedMessagesWithOrderingKeyByDuration() throws Exception {
     // The timeout expires.
     fakeExecutor.advanceTime(Duration.ofSeconds(100));
 
+    // Publish one more message on "OrderA" while publishes are outstanding.
+    testPublisherServiceImpl.setPublishResponseDelay(Duration.ZERO);
+    ApiFuture<String> publishFuture5 = sendTestMessageWithOrderingKey(publisher, "m5", "OrderA");
+
+    // The second timeout expires.
+    fakeExecutor.advanceTime(Duration.ofSeconds(100));
+
+    // Publishing completes on the first four messages.
+    fakeExecutor.advanceTime(Duration.ofSeconds(200));
+
     // Verify that they were delivered in order per ordering key.
     assertTrue(Integer.parseInt(publishFuture1.get()) < Integer.parseInt(publishFuture3.get()));
     assertTrue(Integer.parseInt(publishFuture2.get()) < Integer.parseInt(publishFuture4.get()));
 
+    // Verify that they were delivered in order per ordering key.
+    assertTrue(Integer.parseInt(publishFuture3.get()) < Integer.parseInt(publishFuture5.get()));
+
     // Verify that every message within the same batch has the same ordering key.
     List<PublishRequest> requests = testPublisherServiceImpl.getCapturedRequests();
     for (PublishRequest request : requests) {