[GitHub] [dubbo] fsx379 edited a comment on issue #7897: 使用curator 订阅多注册中心（使用zookeeper）的问题讨论

[GitBox <gi...@apache.org>]

fsx379 edited a comment on issue #7897:
URL: https://github.com/apache/dubbo/issues/7897#issuecomment-894147835


   在CuratorZookeeperClient中，对于create/delete/getchildren/checkExists代码，调用client增删改查前，是否可以加入isConnected() 判断，如果没有连接成功，直接抛出一个异常，然后操作就结束了。
   （1）由于抛出了异常，上层 FailbackRegistry 捕获并定期重试create\delete 等;（参考zkClientWrapper写法）
   （2）client重试连接，交给curator框架自动重试；
   
   不知道这么改有什么风险
   
   ```
       @Override
       public void createPersistent(String path) {
           try {
               if(!this.isConnected()){
                   throw new IllegalStateException("Zookeeper is not connected yet!");
               }
               client.create().forPath(path);
           } catch (NodeExistsException e) {
           } catch (Exception e) {
               throw new IllegalStateException(e.getMessage(), e);
           }
       }
   
       public boolean checkExists(String path) {
           try {
               if(!this.isConnected()){
                   throw new IllegalStateException("Zookeeper is not connected yet!");
               }
               if (client.checkExists().forPath(path) != null) {
                   return true;
               }
           } catch (Exception e) {
           }
           return false;
       }
   ```
   
   第二，在类初始化过程中，在 client.start() 之后，增加 一个卡点，防止zk异步告知connected之前，就开始做create等操作，导致打印异常日志。
   
   ```
   public CuratorZookeeperClient(URL url) {
           super(url);
           try {
               int timeout = url.getParameter(Constants.TIMEOUT_KEY, 5000);
              ........
               client.start();
             //add check
               try{
                   listenableFutureTask = ListenableFutureTask.create(new Callable<Boolean>() {
                       @Override
                       public Boolean call(){
                           try {
                               if (client.checkExists().forPath("/dubbo") != null) {
                                   return true;
                               }
                           } catch (Exception e) {
                           }
                           return false;
                       }
                   });
                   listenableFutureTask.get(timeout, TimeUnit.MILLISECONDS);
               }catch (Exception e){}
           } catch (Exception e) {
               throw new IllegalStateException(e.getMessage(), e);
           }
       }
   ```


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