}

    void stop() {
      stopLatch.countDown();
    }

    boolean isRunning() {
      return running;
    }
  }

  private static final class TestCallable implements AsyncCallable<@Nullable Void> {

    private final ListenableFuture<@Nullable Void> future;
    private boolean called = false;

    private TestCallable(ListenableFuture<@Nullable Void> future) {
      this.future = future;

    }

    void stop() {
      stopLatch.countDown();
    }

    boolean isRunning() {
      return running;
    }
  }

  private static final class TestCallable implements AsyncCallable<@Nullable Void> {

    private final ListenableFuture<@Nullable Void> future;
    private boolean called = false;

    private TestCallable(ListenableFuture<@Nullable Void> future) {
      this.future = future;

     */
    public final <V extends @Nullable Object> ClosingFuture<V> callAsync(
        AsyncCombiningCallable<V> combiningCallable, Executor executor) {
      AsyncCallable<V> asyncCallable =
          new AsyncCallable<V>() {
            @Override
            public ListenableFuture<V> call() throws Exception {
              return new Peeker(inputs).callAsync(combiningCallable, closeables);
            }