void PSRefProcTaskProxy::do_it(GCTaskManager* manager, uint which)
{

  {- -------------------------------------------
  (1) コンストラクタ引数で渡された AbstractRefProcTaskExecutor::ProcessTask オブジェクトに対して, 
      AbstractRefProcTaskExecutor::ProcessTask::work() を呼び出すだけ.
      ---------------------------------------- -}

      PSPromotionManager* promotion_manager =
        PSPromotionManager::gc_thread_promotion_manager(which);
      assert(promotion_manager != NULL, "sanity check");
      PSKeepAliveClosure keep_alive(promotion_manager);
      PSEvacuateFollowersClosure evac_followers(promotion_manager);
      PSIsAliveClosure is_alive;
      _rp_task.work(_work_id, is_alive, keep_alive, evac_followers);
    }