code: func (r *Runner) init() {
  	r.initOnce.Do(func() {
  		r.workC = make(chan WorkItem)
  		r.dispatchFinishedC = make(chan struct{})
  
  		go r.dispatchLoop(r.Sustained, r.Maximum)
  	})
  }
docs: // init initializes the starting state of the Runner. It must be called at the
  // beginning of all exported methods.