void SubTasksDone::clear() {

  {- -------------------------------------------
  (1) _tasks 配列を初期状態に戻す (全ての root 種別の処理が未処理状態)
      ---------------------------------------- -}

      for (int i = 0; i < _n_tasks; i++) {
        _tasks[i] = 0;
      }

  {- -------------------------------------------
  (1) 処理完了数も 0 に戻す
      ---------------------------------------- -}

      _threads_completed = 0;
    #ifdef ASSERT
      _claimed = 0;
    #endif
    }