zookeeper启动入口

　　最近正在研究zookeeper，一些心得记录一下，如有错误，还请大神指正。

zookeeper下载地址：http://zookeeper.apache.org/releases.html，百度一下就能找到，不过还是在这里列一下。

我认为学习一个东西，首先要理出一个头绪，否则感觉无从下手，这里我从启动开始研究，即从zkSever.sh入手。

if [ "x$JMXDISABLE" = "x" ]
then
    echo "JMX enabled by default" >&2
    # for some reason these two options are necessary on jdk6 on Ubuntu
    #   accord to the docs they are not necessary, but otw jconsole cannot
    #   do a local attach
    ZOOMAIN="-Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.local.only=$JMXLOCALONLY org.apache.zookeeper.server.quorum.QuorumPeerMain"
else
    echo "JMX disabled by user request" >&2
    ZOOMAIN="org.apache.zookeeper.server.quorum.QuorumPeerMain"
fi

　　从zkSever.sh可以看出，启动入口在QuorumPeerMain中，源码如下：

  // 入口函数
public static void main(String[] args)
  {
    QuorumPeerMain main = new QuorumPeerMain();
   //...1、启动初始化
      main.initializeAndRun(args);
   // ...
  }

  protected void initializeAndRun(String[] args)
    throws QuorumPeerConfig.ConfigException, IOException
  {
    // 2、加载配置文件
    QuorumPeerConfig config = new QuorumPeerConfig();
    if (args.length == 1) {
      // 解析配置文件
      config.parse(args[0]);
    }

    if ((args.length == 1) && (config.servers.size() > 0)) {
　　　　// 配置文件的信息加载至QuorumPeer
      runFromConfig(config);
    } else {
      LOG.warn("Either no config or no quorum defined in config, running  in standalone mode");

      ZooKeeperServerMain.main(args);
    }
  }

  public void runFromConfig(QuorumPeerConfig config) throws IOException {
    try {
      ManagedUtil.registerLog4jMBeans();
    } catch (JMException e) {
      LOG.warn("Unable to register log4j JMX control", e);
    }

    LOG.info("Starting quorum peer");
    try {
      NIOServerCnxn.Factory cnxnFactory = new NIOServerCnxn.Factory(config.getClientPortAddress(), config.getMaxClientCnxns());

      // 3、启动QuorumPeer
      this.quorumPeer = new QuorumPeer();
      this.quorumPeer.setClientPortAddress(config.getClientPortAddress());
      //...加载各种配置信息

      this.quorumPeer.start();
      this.quorumPeer.join();
    }
    catch (InterruptedException e) {
      LOG.warn("Quorum Peer interrupted", e);
    }
  }

　　可以看出，配置文件的解析由QuorumPeerConfig 类完成，其部分源码如下：

  public void parse(String path)
    throws QuorumPeerConfig.ConfigException
  {
    File configFile = new File(path);

    LOG.info("Reading configuration from: " + configFile);
    try
    {
      if (!configFile.exists()) {
        throw new IllegalArgumentException(configFile.toString() + " file is missing");
      }
     // 将配置信息加载如property文件
      Properties cfg = new Properties();
      FileInputStream in = new FileInputStream(configFile);
      try {
        cfg.load(in);
      } finally {
        in.close();
      }

      parseProperties(cfg);
    } catch (IOException e) {
      throw new ConfigException("Error processing " + path, e);
    } catch (IllegalArgumentException e) {
      throw new ConfigException("Error processing " + path, e);
    }
  }

  public void parseProperties(Properties zkProp)
    throws IOException, QuorumPeerConfig.ConfigException
  {
    int clientPort = 0;
    String clientPortAddress = null;
// 循环解析配置文件
    for (Map.Entry entry : zkProp.entrySet()) {
      String key = entry.getKey().toString().trim();
      String value = entry.getValue().toString().trim();
      if (key.equals("dataDir")) {
        this.dataDir = value;
      } else if (key.equals("dataLogDir")) {
        this.dataLogDir = value;
      } else if (key.equals("clientPort")) {
　　　　// 客户端连接的端口号
        clientPort = Integer.parseInt(value);
      } else if (key.equals("clientPortAddress")) {
        clientPortAddress = value.trim();
      } else if (key.equals("tickTime")) {
　　　　// 心跳时间
        this.tickTime = Integer.parseInt(value);
      } else if (key.equals("maxClientCnxns")) {
        this.maxClientCnxns = Integer.parseInt(value);
      } else if (key.equals("minSessionTimeout")) {
        this.minSessionTimeout = Integer.parseInt(value);
      } else if (key.equals("maxSessionTimeout")) {
        this.maxSessionTimeout = Integer.parseInt(value);
      } else if (key.equals("initLimit")) {
        this.initLimit = Integer.parseInt(value);
      } else if (key.equals("syncLimit")) {
        this.syncLimit = Integer.parseInt(value);
      } else if (key.equals("electionAlg")) {
　　　　// 选举算法的类型，默认算法为FastLeaderElection
        this.electionAlg = Integer.parseInt(value);
      } else if (key.equals("peerType")) {
        if (value.toLowerCase().equals("observer"))
          this.peerType = QuorumPeer.LearnerType.OBSERVER;
        else if (value.toLowerCase().equals("participant")) {
          this.peerType = QuorumPeer.LearnerType.PARTICIPANT;
        }
        else
          throw new ConfigException("Unrecognised peertype: " + value);
      }
      //...

　　回到QuorumPeerMain类的runFromConfig方法。此方法中，会将配置信息加载至QuorumPeer，并调用其start方法：

  public synchronized void start()
  {
    try {
      this.zkDb.loadDataBase();
    } catch (IOException ie) {
      LOG.fatal("Unable to load database on disk", ie);
      throw new RuntimeException("Unable to run quorum server ", ie);
    }
    this.cnxnFactory.start();
    startLeaderElection();
    super.start();
  }

　　在start方法中，会现价在硬盘中的数据，

 this.zkDb.loadDataBase();即ZKDatabase中

  public long loadDataBase()
    throws IOException
  {
    FileTxnSnapLog.PlayBackListener listener = new FileTxnSnapLog.PlayBackListener() {
      public void onTxnLoaded(TxnHeader hdr, Record txn) {
        Request r = new Request(null, 0L, hdr.getCxid(), hdr.getType(), null, null);

        r.txn = txn;
        r.hdr = hdr;
        r.zxid = hdr.getZxid();
        ZKDatabase.this.addCommittedProposal(r);
      }
    };
    long zxid = this.snapLog.restore(this.dataTree, this.sessionsWithTimeouts, listener);
    this.initialized = true;
    return zxid;
  }

　　然后开确定选类型，startLeaderElection

  public synchronized void startLeaderElection() {
    this.currentVote = new Vote(this.myid, getLastLoggedZxid());
    for (QuorumServer p : getView().values()) {
      if (p.id == this.myid) {
        this.myQuorumAddr = p.addr;
        break;
      }
    }
    if (this.myQuorumAddr == null) {
      throw new RuntimeException("My id " + this.myid + " not in the peer list");
    }
    if (this.electionType == 0) {
      try {
        this.udpSocket = new DatagramSocket(this.myQuorumAddr.getPort());
        this.responder = new ResponderThread();
        this.responder.start();
      } catch (SocketException e) {
        throw new RuntimeException(e);
      }
    }
    this.electionAlg = createElectionAlgorithm(this.electionType);//加载选举类型
}

　　然后启动run方法