1）參考了網絡上的算法，但是那個算法僅僅是用于展示“權重輪循”的意圖，在真正的網絡下，因為是并行的，所以不可能單純一個簡單的循環可以解決問題。

2）用lock的話性能顯然有損失。

3）想了一陣，結合CAS和volatile等細粒度的鎖的方式，一個真正可以用軟件描述SLB帶有權重的算法大概是這個樣子（如下）：

using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading;namespace WBasedRobin {/// <summary>/// 用于計算WeightRobin的數據結構/// </summary>public class WeightedRobin{private readonly int _weight;private int _count;/// <summary>/// 命中次數（累加）/// </summary>public int ChoosenCount{get{return ++_count;}}/// <summary>/// 權重/// </summary>public int Weight{get{return _weight;}}/// <summary>/// 輸出當前的權重/// </summary>public override string ToString(){return "Weight:" + Weight.ToString() + "\tCount:" + _count.ToString();}/// <summary>/// 初始化每一個Server的內部值/// </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>/// 初始化權重服務器，至少2臺服務器。/// </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;//當服務器數量發生變化的時候，鎖住該服務直到完畢。reloop: while (_isServerChanging) ;for (;;){//拷貝本地的index，用做同步copyIndex = _index;//計算輪詢的時候下一個的值copyIndexNext = (copyIndex + 1) % _servers.Count;//同步作用copycw = _currentWeight;//假定輪詢后的Next=0，說明完成一輪輪詢，權重減去最大公約數if (copyIndexNext == 0){copycw -= _gcdWeight;//如果權重已經扣完，重新從大的開始if (copycw <= 0){copycw = _maxWeight;}}//如果copyIndex和_index相同，說明是同一個線程搶到的，那么直接用本地的替換index進行替換if (Interlocked.CompareExchange(ref _index, copyIndexNext, copyIndex) == copyIndex){_currentWeight = copycw;try{//如果輪詢的權重大于等于本地權重，選中它即可。if (_servers[copyIndexNext].Weight >= copycw){int t = _servers[copyIndexNext].ChoosenCount;break;}}//如果是Index溢出，那么說明服務器數量肯定發生變化了，所以跳過此次輪詢，等下一輪，不處理。catch (IndexOutOfRangeException){goto reloop;}}}}/// <summary>/// 移除指定的服務器/// </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>/// 增加新的服務器/// </summary>public void AddNewServer(int weight){_isServerChanging = true;_servers.Add(new WeightedRobin(weight, 0));_gcdWeight = GetTotalGCD();_maxWeight = GetMaxWeight(_servers);_isServerChanging = false;}/// <summary>/// 格式化輸出結果/// </summary>public override string ToString(){StringBuilder sbu = new StringBuilder(10);foreach (WeightedRobin wr in _servers){sbu.AppendLine(wr.ToString() + Environment.NewLine);}return sbu.ToString();}} }

調用測試代碼如下：

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("移除了服務器："+removedS); }, null, 2050, Timeout.Infinite);t = new Timer((o) => { wr.AddNewServer(6); Console.WriteLine("新增加服務器了。"); }, null, 3000, Timeout.Infinite);Parallel.For(1, 1001, (num) => {Thread.Sleep(r.Next(100, 500));Rounding(wr);});Console.WriteLine(wr);Console.ReadLine();}} }

轉載于:https://www.cnblogs.com/ServiceboyNew/p/7156449.html

總結

以上是生活随笔為你收集整理的带有权重的服务器SLB的实现的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。