#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);
    }
  }
#vulnerable code 
                              void stopRebalancingTimer() {
    if (_rebalanceTimer != null) {
      _rebalanceTimer.cancel();
      _rebalanceTimer = null;
    }
    _timerPeriod = Integer.MAX_VALUE;
  } 
                            #location 3 
                            #vulnerability type THREAD_SAFETY_VIOLATION