<T> Iterable<T> view(T root, TreeTraverser<T> viewer) {
        return viewer.postOrderTraversal(root);
      }
    },
    BREADTH_FIRST {
      @Override
      <T> Iterable<T> view(T root, TreeTraverser<T> viewer) {
        return viewer.breadthFirstTraversal(root);
      }
    };

    abstract <T> Iterable<T> view(T root, TreeTraverser<T> viewer);
  }

  private Iterable<BinaryNode> view;

    RateLimiter rateLimiter = new SmoothWarmingUp(stopwatch, warmupPeriod, unit, coldFactor);
    rateLimiter.setRate(permitsPerSecond);
    return rateLimiter;
  }

  /**
   * The underlying timer; used both to measure elapsed time and sleep as necessary. A separate
   * object to facilitate testing.
   */
  private final SleepingStopwatch stopwatch;

      <T> Iterable<T> view(T root, TreeTraverser<T> viewer) {
        return viewer.postOrderTraversal(root);
      }
    },
    BREADTH_FIRST {
      @Override
      <T> Iterable<T> view(T root, TreeTraverser<T> viewer) {
        return viewer.breadthFirstTraversal(root);
      }
    };

    abstract <T> Iterable<T> view(T root, TreeTraverser<T> viewer);
  }

  private Iterable<BinaryNode> view;

      producer.beganProducing.await();

      // make sure we time out
      Stopwatch timer = Stopwatch.createStarted();

      int drained = drain(q, newArrayList(), 2, 10, MILLISECONDS, interruptibly);
      assertThat(drained).isAtMost(1);

      assertThat(timer.elapsed(MILLISECONDS)).isAtLeast(10L);

    assertThat(startupTimes).hasSize(2);
    assertThat(startupTimes.get(a)).isAtLeast(150);
    // Service b startup takes at least 353 millis, but starting the timer is delayed by at least
    // 150 milliseconds. so in a perfect world the timing would be 353-150=203ms, but since either
    // of our sleep calls can be arbitrarily delayed we should just assert that there is a time

     */
    ServiceManagerState(ImmutableCollection<Service> services) {
      this.numberOfServices = services.size();
      servicesByState.putAll(NEW, services);
    }

    /**
     * Attempts to start the timer immediately prior to the service being started via {@link
     * Service#startAsync()}.
     */
    void tryStartTiming(Service service) {
      monitor.enter();
      try {

        setState(finalState);
        return true;
      }

      /**
       * Blocks until the task is complete or the timeout expires. Throws a {@link TimeoutException}
       * if the timer expires, otherwise behaves like {@link #get()}.
       */
      V get(long nanos)
          throws TimeoutException, CancellationException, ExecutionException, InterruptedException {

        setState(finalState);
        return true;
      }

      /**
       * Blocks until the task is complete or the timeout expires. Throws a {@link TimeoutException}
       * if the timer expires, otherwise behaves like {@link #get()}.
       */
      V get(long nanos)
          throws TimeoutException, CancellationException, ExecutionException, InterruptedException {

    Future<?> localTimer = timer;
    // Try to cancel the timer as an optimization.
    // timer may be null if this call to run was by the timer task since there is no happens-before
    // edge between the assignment to timer and an execution of the timer task.
    if (localTimer != null) {
      localTimer.cancel(false);
    }

    delegateRef = null;
    timer = null;
  }

      producer.beganProducing.await();

      // make sure we time out
      Stopwatch timer = Stopwatch.createStarted();

      int drained = drain(q, newArrayList(), 2, 10, MILLISECONDS, interruptibly);
      assertThat(drained).isAtMost(1);

      assertThat(timer.elapsed(MILLISECONDS)).isAtLeast(10L);