hadoop 2.6 源码 解读之Namenode启停

NameNode类入口

 public static void main(String argv[]) throws Exception {
    if (DFSUtil.parseHelpArgument(argv, NameNode.USAGE, System.out, true)) {
      System.exit(0);
    }

    try {
      StringUtils.startupShutdownMessage(NameNode.class, argv, LOG);
      NameNode namenode = createNameNode(argv, null);
      if (namenode != null) {
        namenode.join();
      }
    } catch (Throwable e) {
      LOG.fatal("Failed to start namenode.", e);
      terminate(1, e);
    }
  }

createNameNode

  public static NameNode createNameNode(String argv[], Configuration conf)
      throws IOException {

default: {
        DefaultMetricsSystem.initialize("NameNode");
        return new NameNode(conf);
      }
...

}

new NameNode 最终调用如下

  protected NameNode(Configuration conf, NamenodeRole role) 
      throws IOException { 
    this.conf = conf;
    this.role = role;
    setClientNamenodeAddress(conf);
    String nsId = getNameServiceId(conf);
    String namenodeId = HAUtil.getNameNodeId(conf, nsId);
    this.haEnabled = HAUtil.isHAEnabled(conf, nsId);
    state = createHAState(getStartupOption(conf));
    this.allowStaleStandbyReads = HAUtil.shouldAllowStandbyReads(conf);
    this.haContext = createHAContext();
    try {
      initializeGenericKeys(conf, nsId, namenodeId);
      initialize(conf);
      try {
        haContext.writeLock();
        state.prepareToEnterState(haContext);
        state.enterState(haContext);
      } finally {
        haContext.writeUnlock();
      }
    } catch (IOException e) {
      this.stop();
      throw e;
    } catch (HadoopIllegalArgumentException e) {
      this.stop();
      throw e;
    }
  }

initialize(conf)

  protected void initialize(Configuration conf) throws IOException {
    if (conf.get(HADOOP_USER_GROUP_METRICS_PERCENTILES_INTERVALS) == null) {
      String intervals = conf.get(DFS_METRICS_PERCENTILES_INTERVALS_KEY);
      if (intervals != null) {
        conf.set(HADOOP_USER_GROUP_METRICS_PERCENTILES_INTERVALS,
          intervals);
      }
    }

    UserGroupInformation.setConfiguration(conf);
    loginAsNameNodeUser(conf);

    NameNode.initMetrics(conf, this.getRole());
    StartupProgressMetrics.register(startupProgress);

//创建 并 启动 http 服务
    if (NamenodeRole.NAMENODE == role) {
      startHttpServer(conf);
    }

    this.spanReceiverHost = SpanReceiverHost.getInstance(conf);
//初始化FSNamesystem
    loadNamesystem(conf);
//创建RPC server
    rpcServer = createRpcServer(conf);
    if (clientNamenodeAddress == null) {
      // This is expected for MiniDFSCluster. Set it now using 
      // the RPC server's bind address.
      clientNamenodeAddress = 
          NetUtils.getHostPortString(rpcServer.getRpcAddress());
      LOG.info("Clients are to use " + clientNamenodeAddress + " to access"
          + " this namenode/service.");
    }
    if (NamenodeRole.NAMENODE == role) {
      httpServer.setNameNodeAddress(getNameNodeAddress());
      httpServer.setFSImage(getFSImage());
    }

    pauseMonitor = new JvmPauseMonitor(conf);
    pauseMonitor.start();
    metrics.getJvmMetrics().setPauseMonitor(pauseMonitor);
    //启动httpserver 及 RPCServer
    startCommonServices(conf);
  }

loadNamesystem(conf); 展开

 protected void loadNamesystem(Configuration conf) throws IOException {
    this.namesystem = FSNamesystem.loadFromDisk(conf);
  }

继续展开

  static FSNamesystem loadFromDisk(Configuration conf) throws IOException {

    checkConfiguration(conf);
    FSImage fsImage = new FSImage(conf,
        FSNamesystem.getNamespaceDirs(conf),
        FSNamesystem.getNamespaceEditsDirs(conf));
        // 创建对象
    FSNamesystem namesystem = new FSNamesystem(conf, fsImage, false);
    StartupOption startOpt = NameNode.getStartupOption(conf);
    if (startOpt == StartupOption.RECOVER) {
      namesystem.setSafeMode(SafeModeAction.SAFEMODE_ENTER);
    }

    long loadStart = now();
    try {
    //加载fsimage、 editlog
      namesystem.loadFSImage(startOpt);
    } catch (IOException ioe) {
      LOG.warn("Encountered exception loading fsimage", ioe);
      fsImage.close();
      throw ioe;
    }
    long timeTakenToLoadFSImage = now() - loadStart;
    LOG.info("Finished loading FSImage in " + timeTakenToLoadFSImage + " msecs");
    NameNodeMetrics nnMetrics = NameNode.getNameNodeMetrics();
    if (nnMetrics != null) {
      nnMetrics.setFsImageLoadTime((int) timeTakenToLoadFSImage);
    }
    return namesystem;
  }

FSNamesystem 负责实现 Namenode 的所有逻辑

NameNode停止

入口函数中

StringUtils.startupShutdownMessage(NameNode.class, argv, LOG);

该方法通过向JVM注册一个挂钩
Registers a new virtual-machine shutdown hook.。
虚拟机非正常退出，比如用户按下ctrl+c、OOM宕机、操作系统关闭(kill pid)等。会执行相应的方法体