按权重值轮训算法

    /// <summary>
    /// 轮训算法
    /// </summary>
    public class WeightBalance
    {
        private static readonly object LockObject = new object();
        private WeightBalance() { }
        static WeightBalance()
        {
            Instance = new WeightBalance();
        }
        public static WeightBalance Instance
        {
            get;
            private set;
        }

        public T Next<T>(List<T> list) where T : IWeightItem
        {
            if (list == null || !list.Any())
            {
                throw new ArgumentNullException(nameof(list));
            }
            if (list.Count == 1)
            {
                return list.First();
            }
            lock (LockObject)
            {
                int total = list.Sum(i => i.Weight);
                int maxIndex = 0;
                int maxValue = 0;
                int weight = 0;
                for (int i = 0; i < list.Count; i++)
                {
                    if (list[i].Attach != 0)
                    {
                        weight = list[i].Attach;
                    }
                    else
                    {
                        weight = list[i].Weight;
                        list[i].Attach = weight;
                    }
                    if (i == 0)
                    {
                        maxValue = weight;
                    }
                    else if (weight > maxValue)
                    {
                            maxIndex = i;
                            maxValue = weight;
                    }
                }

                list[maxIndex].Attach = list[maxIndex].Attach - total;
                return list[maxIndex];
            }
        }
    }

    /// <summary>
    /// 被轮询的实体要实现此接口
    /// </summary>
    public interface IWeightItem
    {
        /// <summary>
        /// 权重值
        /// </summary>
        int Weight { get; set; }
        /// <summary>
        /// 附加值
        /// </summary>
        int Attach { get; set; }
    }

    class Program
    {
        static void Main(string[] args)
        {
            var connectionList = new List<SlaveConnection>{
            new SlaveConnection{ ConnectionString="server=.;Database=2;",Weight=2},
            new SlaveConnection{ ConnectionString="server=.;Database=5;",Weight=5},
            new SlaveConnection{ ConnectionString="server=.;Database=1;",Weight=1},
            new SlaveConnection{ ConnectionString="server=.;Database=3;",Weight=3},
            new SlaveConnection{ ConnectionString="server=.;Database=4;",Weight=4},
            };
            for (int i = 0; i < 30; i++)
            {
                Console.WriteLine(WeightBalance.Instance.Next(connectionList).ConnectionString);
            }
            Console.ReadKey();

        }
    }
    public class SlaveConnection : IWeightItem
    {
        public string ConnectionString { get; set; }

        public int Weight { get; set; }

        public int Attach { get; set; }

    }