ZookeeperNet太難用，寫了個RetryHelper來進行配套使用

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普通的zk用法，如下寫法：

zk.Exists("/aaa", true);zk.Create(...);

 

但是由於這些API會拋Zookeeper的Exception，比如ConnectionLossException, NoNodeException等，所以必須配合一堆try/catch的機制來catch錯誤，catch後再處理...

寫起來很麻煩

 

因此寫了個RetryHelper來封裝上面這個try/catch行為，用起來也比較方便，如下：

RetryHelper helper=RetryHelper.Make();helper.CreateNodeStructure = () => { Console.WriteLine("CreateNodeStructure"); };helper.FixConnectionLossAction = () => { Console.WriteLine("FixConnectionLossAction");};helper.IfErrorThen = () => { Console.WriteLine("IfErrorThen"); };helper.Execute(() =>{     this.zk.GetChildren(...);});

 

上面的意思是如果在Execute中，如果報錯了，則會看報錯的是哪種類型，如果是ConnectionLoss則執行FixConnectionLossAction委託，如果是NoNode則執行建立節點的委託

也就是將最常見的2個zookeeper動作給結構化了：建立節點目錄結構以及串連丟失時的重新串連動作 

 

RetryHelper代碼：

public class RetryHelper    {        private int retryDelay = 500;        private long signal = 0;        public Action IfErrorThen;        public Action CreateNodeStructure;        public Action FixConnectionLossAction;        public static RetryHelper Make()        {            return new RetryHelper();        }        public void Execute(Action action)        {            while (true)            {                try                {                    action();                    break;                }                catch (ZooKeeperNet.KeeperException.NoNodeException ex)                {                    //create node structure                    Console.WriteLine("retry helper NoNodeException: " + ex.Message);                    if (CreateNodeStructure != null)                        RetryHelper.Make().Execute(CreateNodeStructure);                    continue;                }                catch (ZooKeeperNet.KeeperException.ConnectionLossException ex)                {                    Console.WriteLine("retry helper ConnectionLossException: " + ex.Message);                    long attempSignal = Interlocked.Read(ref signal);                    while (Interlocked.Read(ref signal) > 0)                        Thread.Sleep(retryDelay);                    if (attempSignal == 0)                    {                        Interlocked.Increment(ref signal);                        if (FixConnectionLossAction != null)                            RetryHelper.Make().Execute(FixConnectionLossAction);                        Interlocked.Decrement(ref signal);                    }                    continue;                }                catch (Exception ex)                {                    Console.WriteLine("retry helper catch: " + ex.Message);                    Thread.Sleep(retryDelay);                    if (IfErrorThen != null)                        IfErrorThen();                    continue;                }            }        }    }

 

仔細看上面代碼的朋友肯定也注意到裡面catch connectionloss exception的代碼塊中使用了Interlocked，這是因為：在多線程系統俠，如果zk串連丟失了，由於多個地方都在嘗試zk操作，所以會導致並發性的進入catch loss connection exception代碼處理塊，如果此時不加判斷的處理所有並發請求，則會出現串連多次到zk，嚴重影響效能；因此，這裡的代碼實際上意圖是將多次串連請求合并為一次串連。此處特別感謝我同事的code review，哈哈。

下面是個測試並發消除的demo，為了讓結果清晰，我把RetryHelper的catch中的Console.WriteLine注釋了

static void Main(string[] args)        {            RetryHelper helper=RetryHelper.Make();            helper.CreateNodeStructure = () => { Console.WriteLine("CreateNodeStructure"); };            helper.FixConnectionLossAction = () =>             {                 Console.WriteLine(Thread.CurrentThread.ManagedThreadId+" FixConnectionLossAction BEGIN "+DateTime.Now.ToString());                Thread.Sleep(2000);                Console.WriteLine(Thread.CurrentThread.ManagedThreadId + " FixConnectionLossAction END " + DateTime.Now.ToString());            };            helper.IfErrorThen = () => { Console.WriteLine("IfErrorThen"); };            var tasks=new List<Task>();            for (int i = 0; i < 10; i++)            {                var task = new Task(() => {                    helper.Execute(() =>                    {                        throw new ZooKeeperNet.KeeperException.ConnectionLossException();                    });                });                tasks.Add(task);            }            tasks.ForEach(t=>t.Start());            Task.WaitAll(tasks.ToArray());            Console.ReadKey();        }

 

運行：

 

 

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