inline void ObjectMonitor::AddWaiter(ObjectWaiter* node) {

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

      assert(node != NULL, "should not dequeue NULL node");
      assert(node->_prev == NULL, "node already in list");
      assert(node->_next == NULL, "node already in list");

  {- -------------------------------------------
  (1) 引数で渡された ObjectWaiter (以下の node) を, 
      待ちキュー(_WaitSet) の末尾に追加する.
      ---------------------------------------- -}

      // put node at end of queue (circular doubly linked list)
      if (_WaitSet == NULL) {
        _WaitSet = node;
        node->_prev = node;
        node->_next = node;
      } else {
        ObjectWaiter* head = _WaitSet ;
        ObjectWaiter* tail = head->_prev;
        assert(tail->_next == head, "invariant check");
        tail->_next = node;
        head->_prev = node;
        node->_next = head;
        node->_prev = tail;
      }
    }