ZookeeperNet太难用，写了个RetryHelper来进行配套使用

迈不过友情╰ 2021-06-26 16:06 311阅读 0赞

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 = 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(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();
            }

运行：  
![在这里插入图片描述][20200710133912578.png]

[20200710133912578.png]: /images/20210626/cb214e4020e54c15bfa7d37f4d8d7d65.png