code: func (t *TimeoutWheel) Start() {
  	t.lockAllBuckets()
  	defer t.unlockAllBuckets()
  
  	for t.state != stopped {
  		switch t.state {
  		case stopping:
  			t.unlockAllBuckets()
  			<-t.done
  			t.lockAllBuckets()
  		case running:
  			panic("Tried to start a running TimeoutWheel")
  		}
  	}
  
  	t.state = running
  	t.done = make(chan struct{})
  	t.calloutCh = make(chan timeoutList)
  
  	go t.doTick()
  	go t.doExpired()
  }
docs: // Start starts a stopped timeout wheel. Subsequent calls to Start panic.