聊聊dubbo-go的failsafeCluster

序

本文主要研究一下dubbo-go的failsafeCluster

failsafeCluster

dubbo-go-v1.4.2/cluster/cluster_impl/failsafe_cluster.go

type failsafeCluster struct{}

const failsafe = "failsafe"

func init() {
    extension.SetCluster(failsafe, NewFailsafeCluster)
}

// NewFailsafeCluster ...
func NewFailsafeCluster() cluster.Cluster {
    return &failsafeCluster{}
}

func (cluster *failsafeCluster) Join(directory cluster.Directory) protocol.Invoker {
    return newFailsafeClusterInvoker(directory)
}

• failsafeCluster的join方法执行newFailsafeClusterInvoker

newFailsafeClusterInvoker

dubbo-go-v1.4.2/cluster/cluster_impl/failsafe_cluster_invoker.go

type failsafeClusterInvoker struct {
    baseClusterInvoker
}

func newFailsafeClusterInvoker(directory cluster.Directory) protocol.Invoker {
    return &failsafeClusterInvoker{
        baseClusterInvoker: newBaseClusterInvoker(directory),
    }
}

• newFailsafeClusterInvoker方法创建failsafeClusterInvoker

Invoke

dubbo-go-v1.4.2/cluster/cluster_impl/failsafe_cluster_invoker.go

func (invoker *failsafeClusterInvoker) Invoke(ctx context.Context, invocation protocol.Invocation) protocol.Result {
    invokers := invoker.directory.List(invocation)

    err := invoker.checkInvokers(invokers, invocation)
    if err != nil {
        return &protocol.RPCResult{}
    }

    url := invokers[0].GetUrl()
    methodName := invocation.MethodName()
    //Get the service loadbalance config
    lb := url.GetParam(constant.LOADBALANCE_KEY, constant.DEFAULT_LOADBALANCE)
    //Get the service method loadbalance config if have
    if v := url.GetMethodParam(methodName, constant.LOADBALANCE_KEY, ""); v != "" {
        lb = v
    }
    loadbalance := extension.GetLoadbalance(lb)

    invoked := make([]protocol.Invoker, 0)
    var result protocol.Result

    ivk := invoker.doSelect(loadbalance, invocation, invokers, invoked)
    //DO INVOKE
    result = ivk.Invoke(ctx, invocation)
    if result.Error() != nil {
        // ignore
        logger.Errorf("Failsafe ignore exception: %v.\n", result.Error().Error())
        return &protocol.RPCResult{}
    }
    return result
}

• Invoke方法先通过invoker.directory.List(invocation)获取invokers，之后通过invoker.doSelect(loadbalance, invocation, invokers, invoked)选择ivk，最后执行ivk.Invoke(ctx, invocation)，如果有error，则打印error，返回空结果

GetLoadbalance

dubbo-go-v1.4.2/common/extension/loadbalance.go

// GetLoadbalance ...
func GetLoadbalance(name string) cluster.LoadBalance {
    if loadbalances[name] == nil {
        panic("loadbalance for " + name + " is not existing, make sure you have import the package.")
    }

    return loadbalances[name]()
}

• GetLoadbalance方法根据执行的name获取cluster.LoadBalance，默认为randomLoadBalance

小结

failsafeCluster的join方法执行newFailsafeClusterInvoker；Invoke方法先通过invoker.directory.List(invocation)获取invokers，之后通过invoker.doSelect(loadbalance, invocation, invokers, invoked)选择ivk，最后执行ivk.Invoke(ctx, invocation)，如果有error，则打印error，返回空结果

与failfastCluster的区别就是针对error进行log，然后返回的始终的是没有err的