Exposing AutoExecutor and CallbackExecutor directly

google-cloud-clients/google-cloud-pubsub/src/main/java/com/google/cloud/pubsub/v1/MessageDispatcher.java

@@ -62,7 +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 SequentialExecutorService.AutoExecutor sequentialExecutor;
   private final ScheduledExecutorService systemExecutor;
   private final ApiClock clock;
 
@@ -206,7 +206,7 @@ void sendAckOperations(
     jobLock = new ReentrantLock();
     messagesWaiter = new MessageWaiter();
     this.clock = clock;
-    this.sequentialExecutor = new SequentialExecutorService(executor);
+    this.sequentialExecutor = new SequentialExecutorService.AutoExecutor(executor);
   }
 
   void start() {

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

@@ -99,7 +99,7 @@ public class Publisher {
   private final PublisherStub publisherStub;
 
   private final ScheduledExecutorService executor;
-  private final SequentialExecutorService sequentialExecutor;
+  private final SequentialExecutorService.CallbackExecutor sequentialExecutor;
   private final AtomicBoolean shutdown;
   private final List<AutoCloseable> closeables;
   private final MessageWaiter messagesWaiter;
@@ -127,7 +127,7 @@ private Publisher(Builder builder) throws IOException {
     messagesBatchLock = new ReentrantLock();
     activeAlarm = new AtomicBoolean(false);
     executor = builder.executorProvider.getExecutor();
-    sequentialExecutor = new SequentialExecutorService(executor);
+    sequentialExecutor = new SequentialExecutorService.CallbackExecutor(executor);
     if (builder.executorProvider.shouldAutoClose()) {
       closeables =
           Collections.<AutoCloseable>singletonList(new ExecutorAsBackgroundResource(executor));

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

@@ -42,36 +42,18 @@ interface CancellableRunnable extends Runnable {
  * be run in parallel.
  */
 final class SequentialExecutorService {
-  private static final Logger logger = Logger.getLogger(SequentialExecutorService.class.getName());
 
-  private final CallbackExecutor callbackExecutor;
-  private final AutoExecutor autoExecutor;
-
-  SequentialExecutorService(Executor executor) {
-    this.callbackExecutor = new CallbackExecutor(executor);
-    this.autoExecutor = new AutoExecutor(executor);
-  }
-
-  /**
-   * Runs asynchronous {@code Callable} tasks sequentially. If one of the tasks fails, other tasks
-   * with the same key that have not been executed will be cancelled.
-   */
-  <T> ApiFuture<T> submit(final String key, final Callable<ApiFuture<T>> callable) {
-    return callbackExecutor.submit(key, callable);
-  }
-
-  /** Runs synchronous {@code Runnable} tasks sequentially. */
-  void submit(String key, Runnable runnable) {
-    autoExecutor.execute(key, runnable);
+  // This class is not directly usable.
+  private SequentialExecutorService() {
   }
 
   /**
-   * Internal implementation of SequentialExecutorService. Takes a serial stream of string keys and
+   * This Executor takes a serial stream of string keys and
    * {@code Runnable} tasks, and runs the tasks with the same key sequentially. Tasks with the same
    * key will be run only when its predecessor has been completed while tasks with different keys
    * can be run in parallel.
    */
-  abstract static class SequentialExecutor {
+  private abstract static class SequentialExecutor {
     // Maps keys to tasks.
     protected final Map<String, Deque<Runnable>> tasksByKey;
     protected final Executor executor;
@@ -81,7 +63,7 @@ private SequentialExecutor(Executor executor) {
       this.tasksByKey = new HashMap<>();
     }
 
-    void execute(final String key, Runnable task) {
+    protected void execute(final String key, Runnable task) {
       Deque<Runnable> newTasks;
       synchronized (tasksByKey) {
         newTasks = tasksByKey.get(key);
@@ -110,11 +92,16 @@ protected void invokeCallback(final Deque<Runnable> tasks) {
     }
   }
 
-  private static class AutoExecutor extends SequentialExecutor {
+  static class AutoExecutor extends SequentialExecutor {
     AutoExecutor(Executor executor) {
       super(executor);
     }
 
+    /** Runs synchronous {@code Runnable} tasks sequentially. */
+    void submit(String key, Runnable task)  {
+      super.execute(key, task);
+    }
+
     @Override
     protected void execute(final String key, final Deque<Runnable> tasks) {
       executor.execute(
@@ -142,12 +129,21 @@ private void invokeCallbackAndExecuteNext(final String key, final Deque<Runnable
     }
   }
 
-  private static class CallbackExecutor extends SequentialExecutor {
+  /**
+   * Runs asynchronous {@code Callable} tasks sequentially for the same key. If one of the tasks fails, other tasks
+   * with the same key that have not been executed will be cancelled.
+   */
+  static class CallbackExecutor extends SequentialExecutor {
+    private static final Logger logger = Logger.getLogger(SequentialExecutorService.SequentialExecutor.class.getName());
+
     CallbackExecutor(Executor executor) {
       super(executor);
     }
 
     /**
+     * Runs asynchronous {@code Callable} tasks sequentially. If one of the tasks fails, other tasks
+     * with the same key that have not been executed will be cancelled.
+     * <p>
      * This method does the following in a chain:
      *
      * <ol>

google-cloud-clients/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/SequentialExecutorServiceTest.java

@@ -71,8 +71,8 @@ public void finish() {
 
   @Test
   public void testExecutorRunsNextTaskWhenPrevResponseReceived() throws Exception {
-    SequentialExecutorService sequentialExecutorService =
-        new SequentialExecutorService(executorProvider.getExecutor());
+    SequentialExecutorService.CallbackExecutor sequentialExecutorService =
+        new SequentialExecutorService.CallbackExecutor(executorProvider.getExecutor());
     AsyncTaskCallable callable1 = new AsyncTaskCallable();
     AsyncTaskCallable callable2 = new AsyncTaskCallable();
     AsyncTaskCallable callable3 = new AsyncTaskCallable();
@@ -97,8 +97,8 @@ public void testExecutorRunsNextTaskWhenPrevResponseReceived() throws Exception
 
   @Test
   public void testExecutorRunsDifferentKeySimultaneously() throws Exception {
-    SequentialExecutorService sequentialExecutorService =
-        new SequentialExecutorService(executorProvider.getExecutor());
+    SequentialExecutorService.CallbackExecutor sequentialExecutorService =
+        new SequentialExecutorService.CallbackExecutor(executorProvider.getExecutor());
     AsyncTaskCallable callable1 = new AsyncTaskCallable();
     AsyncTaskCallable callable2 = new AsyncTaskCallable();
     AsyncTaskCallable callable3 = new AsyncTaskCallable();
@@ -126,8 +126,8 @@ public void testExecutorRunsDifferentKeySimultaneously() throws Exception {
 
   @Test
   public void testExecutorCancelsAllTasksWhenOneFailed() throws Exception {
-    SequentialExecutorService sequentialExecutorService =
-        new SequentialExecutorService(executorProvider.getExecutor());
+    SequentialExecutorService.CallbackExecutor sequentialExecutorService =
+        new SequentialExecutorService.CallbackExecutor(executorProvider.getExecutor());
     AsyncTaskCallable callable1 = new AsyncTaskCallable();
     AsyncTaskCallable callable2 = new AsyncTaskCallable();
     AsyncTaskCallable callable3 = new AsyncTaskCallable();
@@ -207,8 +207,8 @@ public void run() {
   public void SequentialExecutorRunsTasksAutomatically() throws Exception {
     int numKeys = 100;
     int numTasks = 100;
-    SequentialExecutorService sequentialExecutor =
-        new SequentialExecutorService(executorProvider.getExecutor());
+    SequentialExecutorService.AutoExecutor sequentialExecutor =
+        new SequentialExecutorService.AutoExecutor(executorProvider.getExecutor());
     CountDownLatch remainingTasksCount = new CountDownLatch(numKeys * numTasks);
     // Maps keys to lists of started and completed tasks.
     Map<String, LinkedHashSet<Integer>> startedTasks = new HashMap<>();