code: protected void updateThrottle()
    {
      long now = CurrentTime.getCurrentTimeActual();
      
      if (_throttleTimestamp + _throttlePeriod < now) {
        _throttleTimestamp = now;
        _throttleCount = 1;
        _isThrottle = false;
        
        return;
      }
      
      _throttleCount++;
      
      if (_throttleCount < _throttleLimit) {
        return;
      }
      
      /*
      System.out.println("THROTTLE: " + _throttleCount + " " + this
                         + " idle:" + getIdleCount());
                         */
      
      if (! _isThrottle) {
        _isThrottle = true;
        
        if (_throttleSleep > 0 || log.isLoggable(Level.FINE)) {
          String msg = (this + " " + _throttleCount
                        + " threads created in " + _throttlePeriod + "ms"
                        + " sleep=" + _throttleSleep + "ms");
        
          onThrottle(msg);
        }
      }
      
      if (_throttleSleep > 0) {
        try {
          Thread.sleep(_throttleSleep);
        } catch (Exception e) {
        }
      }
    }
docs: Throttle the thread creation, so only 100 threads/sec (default) can
  be created.