* {@link Runnable}s that close them submitted to each one's closing {@link Executor}.
   */
  @VisibleForTesting
  CountDownLatch whenClosedCountDown() {
    try {
      return state.closeables.whenClosedCountDown();
    } finally {
      reachabilityFence(this);
    }
  }

  /** The status of a {@link CloseableList}. */
  enum Status {