dubbo-go中roundRobinLoadBalance的作用是什么

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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

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