virtual void work(unsigned int i, BoolObjectClosure& is_alive,
                    OopClosure& keep_alive,
                    VoidClosure& complete_gc)
  {

  {- -------------------------------------------
  (1) カレントスレッドの ID (WorkerThread::id()) に対応する DiscoveredList を引数として
      ReferenceProcessor::process_phase1() を呼び出すだけ.
      ---------------------------------------- -}

        Thread* thr = Thread::current();
        int refs_list_index = ((WorkerThread*)thr)->id();
        _ref_processor.process_phase1(_refs_lists[refs_list_index], _policy,
                                      &is_alive, &keep_alive, &complete_gc);
      }