C# 实现 Nginx 平滑加权轮询算法

代码很简单，算法很经典！

1. 定义实体类

    public struct ServerConfig
    {
        //初始权重
        public int Weight {get;set;}

        //当前权重
        public int Current {get;set;}

        //服务名称
        public string Name {get;set;}
    }

2. 算法

    // 找出数组中当前权重最小的那个服务的index，并把那个服务的当前权重减去总权重。
    public static int NextServerIndex(ServerConfig[] serverConfigArray)
    {
        int index = -1;
        int totalWeight = 0;
        int size = serverConfigArray.Count();
        for(int i = 0; i< size; i++)
        {
            serverConfigArray[i].Current += serverConfigArray[i].Weight;
            totalWeight += serverConfigArray[i].Weight;
            if (index == -1 || serverConfigArray[index].Current < serverConfigArray[i].Current)
            {
                index = i;
            }
        }
        serverConfigArray[index].Current -= totalWeight;
        return index;
    }

3.调用

    public static void TestServerAssignment()
    {
        //构建三台服务器
        var servers = new ServerConfig[] {
            new ServerConfig{Name="A", Weight = 4},
            new ServerConfig{Name="B", Weight = 2},
            new ServerConfig{Name="C", Weight = 1}
        };
        int beUsedIndex = 0;
        int sum = servers.Sum(m => m.Weight); //总权重
        //模拟调用服务次数为总权重数
        for(int i=0; i<sum; i++)
        {
            beUsedIndex = NextServerIndex(servers);
            Console.WriteLine("Current Server is {0}, its weight is {1}", 
                    servers[beUsedIndex].Name, servers[beUsedIndex].Weight);
        }
    }

4.运行结果

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*** No matter how far you go, looking back is also necessary. ***

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