*     r.run();
   *   }
   * }
   * }</pre>
   *
   * <p>This should be preferred to {@link #newDirectExecutorService()} because implementing the
   * {@link ExecutorService} subinterface necessitates significant performance overhead.
   *
   * @since 18.0
   */
  public static Executor directExecutor() {
    return DirectExecutor.INSTANCE;
  }

  /**