*
 * <p>If the values corresponding to a single key should be ordered according to a {@link
 * java.util.Comparator} (or the natural order), see the {@link SortedSetMultimap} subinterface.
 *
 * <p>Since the value collections are sets, the behavior of a {@code SetMultimap} is not specified
 * if key or value objects already present in the multimap change in a manner that affects

   *     r.run();
   *   }
   * }
   * }
   *
   * <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;
  }

  /**