zookeeper--ClientCnxn

之前完成的项目作用zookeeper用作服务发现，抽象出注册和监听功能，供其他项目使用。对zookeeper的一些细节作个记录吧。

我们知道通过Zookeeper对象实例实现对zookeeper服务的调用。首先的问题就是消息的发送和接受，以及事件的回调。这里我们把目光转向ClientCnxn

创建实例
public ClientCnxn(String chrootPath, HostProvider hostProvider, int sessionTimeout, ZooKeeper zooKeeper,
            ClientWatchManager watcher, ClientCnxnSocket clientCnxnSocket,
            long sessionId, byte[] sessionPasswd, boolean canBeReadOnly) {
    ....
    /**
    *   send线程完成发送request，接受response，生成event
    *   event线程派发event
    */
    sendThread = new SendThread(clientCnxnSocket);
    eventThread = new EventThread();
}

`SendThread线程`
public void run() {
    //最大心跳间隔
    final int MAX_SEND_PING_INTERVAL = 10000; 
    while (state.isAlive()) {
        try {
            //1、如果末连接，随机休眠1~1000，根据closing(用户请求)决定是跳出还是重连
            //2、如果需要登录，进行登录请求，根据结果生成事件
                if (zooKeeperSaslClient != null) {
                    。。。
                    if (sendAuthEvent == true) {
                        eventThread.queueEvent(new WatchedEvent(
                              Watcher.Event.EventType.None,
                              authState,null));
                    }
                }
            //3、如果waitTimeOut超时，抛出SessionTimeoutException
                if (to <= 0) {
                    throw new SessionTimeoutException(...);
                }
            //4、心跳
                sendPing()
            //5、如果是只读模式
                pingRwServer();
            //6、开始读、写IO
                clientCnxnSocket.doTransport(to, pendingQ, outgoingQ, ClientCnxn);
        } catch (Throwable e) {
            //发送Disconnected事件
            if (state.isAlive()) {
                eventThread.queueEvent(new WatchedEvent(
                    Event.EventType.None,
                    Event.KeeperState.Disconnected,
                    null));
             }
        }
    }
    //如果alive状态发送Disconnected事件
    if (state.isAlive()) {
        eventThread.queueEvent(new WatchedEvent(Event.EventType.None,
                Event.KeeperState.Disconnected, null));
    }
}

`SendThread线程`
void readResponse(ByteBuffer incomingBuffer) throws IOException {
    //心跳响应
    if (replyHdr.getXid() == -2) {
        // -2 is the xid for pings
        if (LOG.isDebugEnabled()) {
            LOG.debug("Got ping response for sessionid: 0x"
                    + Long.toHexString(sessionId)
                    + " after "
                    + ((System.nanoTime() - lastPingSentNs) / 1000000)
                    + "ms");
        }
        return;
    }
    //认证响应
    if (replyHdr.getXid() == -4) {
        // -4 is the xid for AuthPacket               
        if(replyHdr.getErr() == KeeperException.Code.AUTHFAILED.intValue()) {
            state = States.AUTH_FAILED;                    
            eventThread.queueEvent( new WatchedEvent(Watcher.Event.EventType.None, 
                    Watcher.Event.KeeperState.AuthFailed, null) );                                      
        }
        if (LOG.isDebugEnabled()) {
            LOG.debug("Got auth sessionid:0x"
                    + Long.toHexString(sessionId));
        }
        return;
    }
    //通知
    if (replyHdr.getXid() == -1) {
        // -1 means notification
        if (LOG.isDebugEnabled()) {
            LOG.debug("Got notification sessionid:0x"
                + Long.toHexString(sessionId));
        }
        WatcherEvent event = new WatcherEvent();
        event.deserialize(bbia, "response");

        // convert from a server path to a client path
        if (chrootPath != null) {
            String serverPath = event.getPath();
            if(serverPath.compareTo(chrootPath)==0)
                event.setPath("/");
            else if (serverPath.length() > chrootPath.length())
                event.setPath(serverPath.substring(chrootPath.length()));
            else {
                LOG.warn("Got server path " + event.getPath()
                        + " which is too short for chroot path "
                        + chrootPath);
            }
        }

        WatchedEvent we = new WatchedEvent(event);
        if (LOG.isDebugEnabled()) {
            LOG.debug("Got " + we + " for sessionid 0x"
                    + Long.toHexString(sessionId));
        }

        eventThread.queueEvent( we );
        return;
    }
    ...
    finishPacket(packet);
}

`EventThread`
public void run() {
   try {
      isRunning = true;
      while (true) {
         Object event = waitingEvents.take();
         if (event == eventOfDeath) {
            wasKilled = true;
         } else {
            processEvent(event);
         }
         if (wasKilled)
            synchronized (waitingEvents) {
               if (waitingEvents.isEmpty()) {
                  isRunning = false;
                  break;
               }
            }
      }
   } catch (InterruptedException e) {
      LOG.error("Event thread exiting due to interruption", e);
   }

    LOG.info("EventThread shut down");
}