聊聊dubbo-go的leastActiveLoadBalance

const (
    // LeastActive ...
    LeastActive = "leastactive"
)
​
func init() {
    extension.SetLoadbalance(LeastActive, NewLeastActiveLoadBalance)
}
​
type leastActiveLoadBalance struct {
}
​
// NewLeastActiveLoadBalance ...
func NewLeastActiveLoadBalance() cluster.LoadBalance {
    return &leastActiveLoadBalance{}
}

func (lb *leastActiveLoadBalance) Select(invokers []protocol.Invoker, invocation protocol.Invocation) protocol.Invoker {
    count := len(invokers)
    if count == 0 {
        return nil
    }
    if count == 1 {
        return invokers[0]
    }
​
    var (
        leastActive  int32                = -1 // The least active value of all invokers
        totalWeight  int64                     // The number of invokers having the same least active value (LEAST_ACTIVE)
        firstWeight  int64                     // Initial value, used for comparison
        leastCount   int                       // The number of invokers having the same least active value (LEAST_ACTIVE)
        leastIndexes = make([]int, count)      // The index of invokers having the same least active value (LEAST_ACTIVE)
        sameWeight   = true                    // Every invoker has the same weight value?
    )
​
    for i := 0; i < count; i++ {
        invoker := invokers[i]
        // Active number
        active := protocol.GetMethodStatus(invoker.GetUrl(), invocation.MethodName()).GetActive()
        // current weight (maybe in warmUp)
        weight := GetWeight(invoker, invocation)
        // There are smaller active services
        if leastActive == -1 || active < leastActive {
            leastActive = active
            leastIndexes[0] = i
            leastCount = 1 // next available leastIndex offset
            totalWeight = weight
            firstWeight = weight
            sameWeight = true
        } else if active == leastActive {
            leastIndexes[leastCount] = i
            totalWeight += weight
            leastCount++
​
            if sameWeight && (i > 0) && weight != firstWeight {
                sameWeight = false
            }
        }
    }
​
    if leastCount == 1 {
        return invokers[0]
    }
​
    if !sameWeight && totalWeight > 0 {
        offsetWeight := rand.Int63n(totalWeight) + 1
        for i := 0; i < leastCount; i++ {
            leastIndex := leastIndexes[i]
            offsetWeight -= GetWeight(invokers[i], invocation)
            if offsetWeight <= 0 {
                return invokers[leastIndex]
            }
        }
    }
​
    index := leastIndexes[rand.Intn(leastCount)]
    return invokers[index]
}

// GetWeight ...
func GetWeight(invoker protocol.Invoker, invocation protocol.Invocation) int64 {
    url := invoker.GetUrl()
    weight := url.GetMethodParamInt64(invocation.MethodName(), constant.WEIGHT_KEY, constant.DEFAULT_WEIGHT)
​
    if weight > 0 {
        //get service register time an do warm up time
        now := time.Now().Unix()
        timestamp := url.GetParamInt(constant.REMOTE_TIMESTAMP_KEY, now)
        if uptime := now - timestamp; uptime > 0 {
            warmup := url.GetParamInt(constant.WARMUP_KEY, constant.DEFAULT_WARMUP)
            if uptime < warmup {
                if ww := float64(uptime) / float64(warmup) / float64(weight); ww < 1 {
                    weight = 1
                } else if int64(ww) <= weight {
                    weight = int64(ww)
                }
            }
        }
    }
    return weight
}