聊聊dubbo-go的roundRobinLoadBalance

序

本文主要研究一下dubbo-go的roundRobinLoadBalance

roundRobinLoadBalance

dubbo-go-v1.4.2/cluster/loadbalance/round_robin.go

const (
	// RoundRobin ...
	RoundRobin = "roundrobin"

	// COMPLETE ...
	COMPLETE = 0
	// UPDATING ...
	UPDATING = 1
)

var (
	methodWeightMap sync.Map          // [string]invokers
	state           = int32(COMPLETE) // update lock acquired ?
	recyclePeriod   = 60 * time.Second.Nanoseconds()
)

func init() {
	extension.SetLoadbalance(RoundRobin, NewRoundRobinLoadBalance)
}

type roundRobinLoadBalance struct{}

// NewRoundRobinLoadBalance ...
func NewRoundRobinLoadBalance() cluster.LoadBalance {
	return &roundRobinLoadBalance{}
}

• roundRobinLoadBalance的NewRoundRobinLoadBalance方法创建了roundRobinLoadBalance

Select

dubbo-go-v1.4.2/cluster/loadbalance/round_robin.go

func (lb *roundRobinLoadBalance) Select(invokers []protocol.Invoker, invocation protocol.Invocation) protocol.Invoker {
	count := len(invokers)
	if count == 0 {
		return nil
	}
	if count == 1 {
		return invokers[0]
	}

	key := invokers[0].GetUrl().Path + "." + invocation.MethodName()
	cache, _ := methodWeightMap.LoadOrStore(key, &cachedInvokers{})
	cachedInvokers := cache.(*cachedInvokers)

	var (
		clean               = false
		totalWeight         = int64(0)
		maxCurrentWeight    = int64(math.MinInt64)
		now                 = time.Now()
		selectedInvoker     protocol.Invoker
		selectedWeightRobin *weightedRoundRobin
	)

	for _, invoker := range invokers {
		var weight = GetWeight(invoker, invocation)
		if weight < 0 {
			weight = 0
		}

		identifier := invoker.GetUrl().Key()
		loaded, found := cachedInvokers.LoadOrStore(identifier, &weightedRoundRobin{weight: weight})
		weightRobin := loaded.(*weightedRoundRobin)
		if !found {
			clean = true
		}

		if weightRobin.Weight() != weight {
			weightRobin.setWeight(weight)
		}

		currentWeight := weightRobin.increaseCurrent()
		weightRobin.lastUpdate = &now

		if currentWeight > maxCurrentWeight {
			maxCurrentWeight = currentWeight
			selectedInvoker = invoker
			selectedWeightRobin = weightRobin
		}
		totalWeight += weight
	}

	cleanIfRequired(clean, cachedInvokers, &now)

	if selectedWeightRobin != nil {
		selectedWeightRobin.Current(totalWeight)
		return selectedInvoker
	}

	// should never happen
	return invokers[0]
}

• Select方法遍历invokers，通过weightRobin.increaseCurrent()作为currentWeight，若currentWeight大于maxCurrentWeight则更新maxCurrentWeight，设置selectedInvoker为当前invoker，设置selectedWeightRobin为当前weightRobin；之后对于selectedWeightRobin不为nil的执行selectedWeightRobin.Current(totalWeight)，返回selectedInvoker

小结

roundRobinLoadBalance的NewRoundRobinLoadBalance方法创建了roundRobinLoadBalance；其Select方法遍历invokers，通过weightRobin.increaseCurrent()作为currentWeight，若currentWeight大于maxCurrentWeight则更新maxCurrentWeight，设置selectedInvoker为当前invoker，设置selectedWeightRobin为当前weightRobin

doc

• round_robin

来源：oschina

链接：https://my.oschina.net/go4it/blog/4492843