bool parMark(HeapWord* addr) {

  {- -------------------------------------------
  (1) (assert)
      ---------------------------------------- -}

        assert(_bmStartWord <= addr && addr < (_bmStartWord + _bmWordSize),
               "outside underlying space?");

  {- -------------------------------------------
  (1) BitMap::par_set_bit() でビットを立て, 結果をリターン
      ---------------------------------------- -}

        return _bm.par_at_put(heapWordToOffset(addr), true);
      }