[zookeeper] Zookeeper概述

1. Zookeeper客户端

Zookeeper
    |
    |--- ClientCnxn
    |           |
    |           |----SendThread  
    |           | 
    |           |----EventThread  
    |
    |--- ZkWatchManager

　　在客户端中，SendThread和EventThread均使用BlockingQueue方式进行异步处理。

2. Zookeeper服务端

   ZookeeperServer
        |
        |--- QuorumCnxManager
        |           |
        |           |---- RecvWorker
        |           |
        |           |---- SendWorker
        |
        |--- ZkWatcherManager
        |
        |--- RequestProcessors
        |
        |--- ZkDataBase(All in Memory)
                    |
                    |---- Load Data from Snapshot
                    |
                    |---- Sync Data from Leader
                    |
                    |---- Dump Data into disk

　　服务器中移除处理是通过阻塞队列完成。

3. 客户端与服务端交互