ZookeeperNet太难用，写了个RetryHelper来进行配套使用

普通的zk用法，如下写法：

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

zk.Create(...);

但是由于这些API会抛Zookeeper的Exception，比如ConnectionLossException, NoNodeException等，所以必须配合一堆try/catch的机制来catch错误，catch后再处理...

写起来很麻烦

因此写了个RetryHelper来封装上面这个try/catch行为，用起来也比较方便，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，如果报错了，则会看报错的是哪种类型，如果是ConnectionLoss则执行FixConnectionLossAction委托，如果是NoNode则执行建立节点的委托

也就是将最常见的2个zookeeper动作给结构化了：建立节点目录结构以及连接丢失时的重新连接动作

RetryHelper代码：

public class RetryHelper

    {

        private int retryDelay = ;

        private long signal = ;

        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) > )

                        Thread.Sleep(retryDelay);

                    if (attempSignal == )

                    {

                        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;

                }

            }

        }

    }

仔细看上面代码的朋友肯定也注意到里面catch connectionloss exception的代码块中使用了Interlocked，这是因为：在多线程系统侠，如果zk连接丢失了，由于多个地方都在尝试zk操作，所以会导致并发性的进入catch loss connection exception代码处理块，如果此时不加判断的处理所有并发请求，则会出现连接多次到zk，严重影响性能；因此，这里的代码实际上意图是将多次连接请求合并为一次连接。此处特别感谢我同事的code review，哈哈。

下面是个测试并发消除的demo，为了让结果清晰，我把RetryHelper的catch中的Console.WriteLine注释了

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();

                Console.WriteLine(Thread.CurrentThread.ManagedThreadId + " FixConnectionLossAction END " + DateTime.Now.ToString());

            };

            helper.IfErrorThen = () => { Console.WriteLine("IfErrorThen"); };

            var tasks=new List<Task>();

            for (int i = ; i < ; 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();

        }

运行：

code download

巴特西

ZookeeperNet太难用，写了个RetryHelper来进行配套使用

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