output: #fixed code
                                void startRebalancingTimer(long period, HelixManager manager) {
      if (period != _timerPeriod) {
        logger.info("Controller starting timer at period " + period);
        if (_rebalanceTimer != null) {
          _rebalanceTimer.cancel();
        }
        _rebalanceTimer = new Timer(true);
        _timerPeriod = period;
        _rebalanceTimer
            .scheduleAtFixedRate(new RebalanceTask(manager), _timerPeriod, _timerPeriod);
      } else {
        logger.info("Controller already has timer at period " + _timerPeriod);
      }
    }
input: #vulnerable code 
                                void stopRebalancingTimer() {
      if (_rebalanceTimer != null) {
        _rebalanceTimer.cancel();
        _rebalanceTimer = null;
      }
      _timerPeriod = Integer.MAX_VALUE;
    } 
                              #location 6 
                              #vulnerability type THREAD_SAFETY_VIOLATION