code: func (sq *servingQueue) threadCountLoop() {
  	var threadCountTarget int
  	for {
  		for threadCountTarget > sq.threadCount {
  			sq.wg.Add(1)
  			go sq.threadController()
  			sq.threadCount++
  		}
  		if threadCountTarget < sq.threadCount {
  			select {
  			case threadCountTarget = <-sq.setThreadsCh:
  			case sq.stopThreadCh <- struct{}{}:
  				sq.threadCount--
  			case <-sq.quit:
  				sq.wg.Done()
  				return
  			}
  		} else {
  			select {
  			case threadCountTarget = <-sq.setThreadsCh:
  			case <-sq.quit:
  				sq.wg.Done()
  				return
  			}
  		}
  	}
  }
docs: // threadCountLoop is an event loop running in a goroutine. It adjusts the number
  // of active thread controller goroutines.