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带有权重的服务器SLB的实现
1）参考了网络上的算法，但是那个算法仅仅是用于展示“权重轮循”的意图，在真正的网络下，因为是并行的，所以不可能单纯一个简单的循环可以解决问题。
2）用lock的话性能显然有损失。
3）想了一阵，结合CAS和volatile等细粒度的锁的方式，一个真正可以用软件描述SLB带有权重的算法大概是这个样子（如下）：
using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading;namespace WBasedRobin{ /// <summary> /// 用于计算WeightRobin的数据结构 /// </summary> public class WeightedRobin { private readonly int _weight; private int _count; /// <summary> /// 命中次数（累加） /// </summary> public int ChoosenCount { get { return ++_count; } } /// <summary> /// 权重 /// </summary> public int Weight { get { return _weight; } } /// <summary> /// 输出当前的权重 /// </summary> public override string ToString() { return "Weight:" + Weight.ToString() + "\tCount:" + _count.ToString(); } /// <summary> /// 初始化每一个Server的内部值 /// </summary> public WeightedRobin(int weight, int count = 0) { _weight = weight; _count = count; } } public class WeightRobinRule { private List<WeightedRobin> _servers = null; private volatile int _index = -1; private volatile int _currentWeight = 0; private volatile bool _isServerChanging = false; private volatile int _maxWeight = 0; private volatile int _gcdWeight = 0; private int GetMaxWeight(IEnumerable<WeightedRobin> weights) { return weights.Max(w => w.Weight); } private int GetGCDWeight(int big, int small) { if (big < small) { big ^= small; small ^= big; big ^= small; } if (big % small == 0) { return small; } return GetGCDWeight(small, big % small); } private int GetTotalGCD() { int gcd = GetGCDWeight(_servers[0].Weight, _servers[1].Weight); for (int i = 2; i < _servers.Count; ++i) { gcd = GetGCDWeight(gcd, _servers[i].Weight); } return gcd; } /// <summary> /// 初始化权重服务器，至少2台服务器。 /// </summary> public WeightRobinRule(int totalServers = 2) { Random r = new Random(); _servers = new List<WeightedRobin>(totalServers); for (int i = 0; i < totalServers; i++) { _servers.Add(new WeightedRobin(r.Next(2, totalServers+1),0)); } _maxWeight = GetMaxWeight(_servers); _gcdWeight = GetTotalGCD(); } public void DoRolling() { int copyIndex = 0; int copyIndexNext = 0; int copycw = 0; //当服务器数量发生变化的时候，锁住该服务直到完毕。 reloop: while (_isServerChanging) ; for (;;) { //拷贝本地的index，用做同步 copyIndex = _index; //计算轮询的时候下一个的值 copyIndexNext = (copyIndex + 1) % _servers.Count; //同步作用 copycw = _currentWeight; //假定轮询后的Next=0，说明完成一轮轮询，权重减去最大公约数 if (copyIndexNext == 0) { copycw -= _gcdWeight; //如果权重已经扣完，重新从大的开始 if (copycw <= 0) { copycw = _maxWeight; } } //如果copyIndex和_index相同，说明是同一个线程抢到的，那么直接用本地的替换index进行替换 if (Interlocked.CompareExchange(ref _index, copyIndexNext, copyIndex) == copyIndex) { _currentWeight = copycw; try { //如果轮询的权重大于等于本地权重，选中它即可。 if (_servers[copyIndexNext].Weight >= copycw) { int t = _servers[copyIndexNext].ChoosenCount; break; } } //如果是Index溢出，那么说明服务器数量肯定发生变化了，所以跳过此次轮询，等下一轮，不处理。 catch (IndexOutOfRangeException) { goto reloop; } } } } /// <summary> /// 移除指定的服务器 /// </summary> public WeightedRobin RemoveByIndex(int index) { _isServerChanging = true; var removedServer = _servers[index]; _servers.RemoveAt(index); _gcdWeight = GetTotalGCD(); _maxWeight = GetMaxWeight(_servers); _isServerChanging = false; return removedServer; } /// <summary> /// 增加新的服务器 /// </summary> public void AddNewServer(int weight) { _isServerChanging = true; _servers.Add(new WeightedRobin(weight, 0)); _gcdWeight = GetTotalGCD(); _maxWeight = GetMaxWeight(_servers); _isServerChanging = false; } /// <summary> /// 格式化输出结果 /// </summary> public override string ToString() { StringBuilder sbu = new StringBuilder(10); foreach (WeightedRobin wr in _servers) { sbu.AppendLine(wr.ToString() + Environment.NewLine); } return sbu.ToString(); } }}
调用测试代码如下：
using System;using System.Threading;using System.Threading.Tasks;namespace WBasedRobin{ class Program { static Random r = new Random(); static void Rounding(WeightRobinRule wr) { wr.DoRolling(); } static void Main(string[] args) { WeightRobinRule wr = new WeightRobinRule(5); Timer t = new Timer((j) => { var removedS = wr.RemoveByIndex(0); Console.WriteLine("移除了服务器："+removedS); }, null, 2050, Timeout.Infinite); t = new Timer((o) => { wr.AddNewServer(6); Console.WriteLine("新增加服务器了。"); }, null, 3000, Timeout.Infinite); Parallel.For(1, 1001, (num) => { Thread.Sleep(r.Next(100, 500)); Rounding(wr); }); Console.WriteLine(wr); Console.ReadLine(); } }}
带有权重的服务器SLB的实现
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