Zookeeper源码解析之Server启动

本篇讲述Zookeeper Server启动过程。Zookeeper的源码可以在Github中下载，地址是：https://github.com/apache/zookeeper/。不过是用ivy构建，所以有兴趣的话，可以安装ivy来构建Zookeeper。

Zookeeper的启动类：org.apache.zookeeper.server.quorum.QuorumPeerMain

通过Main函数启动：

 

public static void main(String[] args) {
        QuorumPeerMain main = new QuorumPeerMain();
        try {
            //初始化并运行
            main.initializeAndRun(args);
        } catch (IllegalArgumentException e) {
            LOG.error("Invalid arguments, exiting abnormally", e);
            LOG.info(USAGE);
            System.err.println(USAGE);
            System.exit(2);
        } catch (ConfigException e) {
            LOG.error("Invalid config, exiting abnormally", e);
            System.err.println("Invalid config, exiting abnormally");
            System.exit(2);
        } catch (Exception e) {
            LOG.error("Unexpected exception, exiting abnormally", e);
            System.exit(1);
        }
        LOG.info("Exiting normally");
        System.exit(0);
    }

 

 

初始化并运行：

    protected void initializeAndRun(String[] args)
        throws ConfigException, IOException
    {
        //加载配置文件实现类
        QuorumPeerConfig config = new QuorumPeerConfig();
        if (args.length == 1) {
            config.parse(args[0]);
        }

        //启动并调度清理任务，主要的配置是：autopurge.snapRetainCount（保留日志和快照文件的数量），清理任务的频率：autopurge.purgeInterval（单位:小时）
        DatadirCleanupManager purgeMgr = new DatadirCleanupManager(config
                .getDataDir(), config.getDataLogDir(), config
                .getSnapRetainCount(), config.getPurgeInterval());
        purgeMgr.start();

        if (args.length == 1 && config.servers.size() > 0) {
            //根据配置文件运行Zookeeper
            runFromConfig(config);
        } else {
            LOG.warn("Either no config or no quorum defined in config, running "
                    + " in standalone mode");
            // there is only server in the quorum -- run as standalone
            //单机模式下运行Zookeeper
            ZooKeeperServerMain.main(args);
        }
    }

根据配置文件运行：

 

 

    public void runFromConfig(QuorumPeerConfig config) throws IOException {
      try {
          //注册JMX
          ManagedUtil.registerLog4jMBeans();
      } catch (JMException e) {
          LOG.warn("Unable to register log4j JMX control", e);
      }
  
      LOG.info("Starting quorum peer");
      try {
          ServerCnxnFactory cnxnFactory = ServerCnxnFactory.createFactory();
          cnxnFactory.configure(config.getClientPortAddress(),
                                config.getMaxClientCnxns());
          //实例化QuorumPeer
          quorumPeer = new QuorumPeer();
          //服务监听端口
          quorumPeer.setClientPortAddress(config.getClientPortAddress());
          //日志和快照存放路径
          quorumPeer.setTxnFactory(new FileTxnSnapLog(
                      new File(config.getDataLogDir()),
                      new File(config.getDataDir())));
          //Server Map
          quorumPeer.setQuorumPeers(config.getServers());
          //选举算法
          quorumPeer.setElectionType(config.getElectionAlg());
          //服务器ID
          quorumPeer.setMyid(config.getServerId());
          //时间单元
          quorumPeer.setTickTime(config.getTickTime());
          //最大和最小超时时间
          quorumPeer.setMinSessionTimeout(config.getMinSessionTimeout());
          quorumPeer.setMaxSessionTimeout(config.getMaxSessionTimeout());
          //交互的时间限制
          quorumPeer.setInitLimit(config.getInitLimit());
          quorumPeer.setSyncLimit(config.getSyncLimit());
          quorumPeer.setQuorumVerifier(config.getQuorumVerifier());
          //连接工厂，默认NIOServerCnxnFactory
          quorumPeer.setCnxnFactory(cnxnFactory);
          quorumPeer.setZKDatabase(new ZKDatabase(quorumPeer.getTxnFactory()));
          quorumPeer.setLearnerType(config.getPeerType());
          quorumPeer.setSyncEnabled(config.getSyncEnabled());
          quorumPeer.setQuorumListenOnAllIPs(config.getQuorumListenOnAllIPs());
          //启动  
          quorumPeer.start();
          quorumPeer.join();
      } catch (InterruptedException e) {
          // warn, but generally this is ok
          LOG.warn("Quorum Peer interrupted", e);
      }
    }
}

 

启动：

 

    @Override
    public synchronized void start() {
        //日志文件和快照文件
        loadDataBase();
        //启动连接工厂，主要用于处理Client的请求
        cnxnFactory.start();
        //初始化选举，主要是开始Leader的选举
        startLeaderElection();
        //启动
        super.start();
    }

 

loadDataBase过程，恢复epoch数：

 

    private void loadDataBase() {
        File updating = new File(getTxnFactory().getSnapDir(),
                                 UPDATING_EPOCH_FILENAME);
		try {
            //从文件中恢复db
            zkDb.loadDataBase();

            //从最新的zxid恢复epoch变量，zxid64位，前32位是epoch值，后32位是zxid
            long lastProcessedZxid = zkDb.getDataTree().lastProcessedZxid;
    		long epochOfZxid = ZxidUtils.getEpochFromZxid(lastProcessedZxid);
            try {
            	currentEpoch = readLongFromFile(CURRENT_EPOCH_FILENAME);
                if (epochOfZxid > currentEpoch && updating.exists()) {
                    LOG.info("{} found. The server was terminated after " +
                             "taking a snapshot but before updating current " +
                             "epoch. Setting current epoch to {}.",
                             UPDATING_EPOCH_FILENAME, epochOfZxid);
                    setCurrentEpoch(epochOfZxid);
                    if (!updating.delete()) {
                        throw new IOException("Failed to delete " +
                                              updating.toString());
                    }
                }
            } catch(FileNotFoundException e) {
            	// pick a reasonable epoch number
            	// this should only happen once when moving to a
            	// new code version
            	currentEpoch = epochOfZxid;
            	LOG.info(CURRENT_EPOCH_FILENAME
            	        + " not found! Creating with a reasonable default of {}. This should only happen when you are upgrading your installation",
            	        currentEpoch);
            	writeLongToFile(CURRENT_EPOCH_FILENAME, currentEpoch);
            }
            if (epochOfZxid > currentEpoch) {
            	throw new IOException("The current epoch, " + ZxidUtils.zxidToString(currentEpoch) + ", is older than the last zxid, " + lastProcessedZxid);
            }
            try {
            	acceptedEpoch = readLongFromFile(ACCEPTED_EPOCH_FILENAME);
            } catch(FileNotFoundException e) {
            	// pick a reasonable epoch number
            	// this should only happen once when moving to a
            	// new code version
            	acceptedEpoch = epochOfZxid;
            	LOG.info(ACCEPTED_EPOCH_FILENAME
            	        + " not found! Creating with a reasonable default of {}. This should only happen when you are upgrading your installation",
            	        acceptedEpoch);
            	writeLongToFile(ACCEPTED_EPOCH_FILENAME, acceptedEpoch);
            }
            if (acceptedEpoch < currentEpoch) {
            	throw new IOException("The current epoch, " + ZxidUtils.zxidToString(currentEpoch) + " is less than the accepted epoch, " + ZxidUtils.zxidToString(acceptedEpoch));
            }
        } catch(IOException ie) {
            LOG.error("Unable to load database on disk", ie);
            throw new RuntimeException("Unable to run quorum server ", ie);
        }
	}

初始化选举

 

 

    synchronized public void startLeaderElection() {
    	try {
                //初始化投票实例，投票的对象是自己
    		currentVote = new Vote(myid, getLastLoggedZxid(), getCurrentEpoch());
    	} catch(IOException e) {
    		RuntimeException re = new RuntimeException(e.getMessage());
    		re.setStackTrace(e.getStackTrace());
    		throw re;
    	}
        //从配置中拿自己的选举地址
        for (QuorumServer p : getView().values()) {
            if (p.id == myid) {
                myQuorumAddr = p.addr;
                break;
            }
        }
        if (myQuorumAddr == null) {
            throw new RuntimeException("My id " + myid + " not in the peer list");
        }
        if (electionType == 0) {
            try {
                udpSocket = new DatagramSocket(myQuorumAddr.getPort());
                responder = new ResponderThread();
                responder.start();
            } catch (SocketException e) {
                throw new RuntimeException(e);
            }
        }
        //根据配置文件，初始化选举实例。默认是FastLeaderElection
        this.electionAlg = createElectionAlgorithm(electionType);
    }

server启动完成，就等待client去连接了。server启动核心功能就是从snapshot和log文件中恢复datatree，其核心就是zxid。