Hadoop学习二十一：Hadoop-Hdfs DataNode 源码

一. DataNode类图

 

 

二. DateNode属性说明

•  DatanodeProtocol namenode：RPC代理类。RPC.getProxy(nameNodeAddress)得到远程NameNode代理类。后续的versionRequest()，register()，sendHeartbeat()，blockReceived()，blockReport()都是namenode的行为。
• org.apache.hadoop.ipc.Server ipcServer：RPC Server。conf里配置ipcAddr=0.0.0.0:50020，ipcServer = RPC.getServer(this, ipcAddr.getHostName()...)，此DataNode作为RPC Server提供远程服务，提供接口ClientDatanodeProtocol和InterDatanodeProtocol中定义的服务。
• HttpServer infoServer：a Jetty embedded server to answer http requests。
• DataStorage storage：参考http://zy19982004.iteye.com/admin/blogs/1878758。
• DatanodeRegistration dnRegistration：DatanodeRegistration class conatins all information the Namenode needs to identify and verify a Datanode when it contacts the Namenode.后续的sendHeartbeat()，blockReceived()，blockReport()方法第一个参数就是DatanodeRegistration 。
• FSDatasetInterface data：FSDataset的接口，管理着DataNode的所有block。参考http://zy19982004.iteye.com/admin/blogs/1880303。
• DataBlockScanner blockScanner：定时对数据块文件进行校验。
• DataXceiverServer dataXceiverServer：参考http://zy19982004.iteye.com/admin/blogs/1881117。
• LinkedList<Block> receivedBlockList：成功创建的新block。
• LinkedList<String> delHints：可以删掉该数据块的节点。DataXceiver.replaceBlock()和writeBlock成功后会调用DataNode.notifyNamenodeReceivedBlock()方法给这两个List add value.

  protected void notifyNamenodeReceivedBlock(Block block, String delHint) {
      synchronized (receivedBlockList) {
        synchronized (delHints) {
          receivedBlockList.add(block);
          delHints.add(delHint);
          receivedBlockList.notifyAll();
        }
      }
    }

   

三. 代码顺序阅读

1.  main()函数入口。

     public static void main(String args[]) {
       secureMain(args, null);
     }

2. secureMain()：初始化DataNode；加入线程里。

   public static void secureMain(String [] args, SecureResources resources) {
         DataNode datanode = createDataNode(args, null, resources);
         if (datanode != null)
           datanode.join();
         }

3. createDataNode()：初始化DataNode；启动该线程。

     public static DataNode createDataNode(String args[],
               Configuration conf, SecureResources resources) throws IOException {
       DataNode dn = instantiateDataNode(args, conf, resources);
       runDatanodeDaemon(dn);
       return dn;
     }

4. instantiateDataNode()：读取dataDirs；调用makeInstance()。makeInstance()：check dataDirs；new DateNode。new DataNode()：调用startDataNode()。

   public static DataNode instantiateDataNode(String args[],
                                         Configuration conf, 
                                         SecureResources resources) throws IOException {
           String[] dataDirs = conf.getStrings(DATA_DIR_KEY);
           return makeInstance(dataDirs, conf, resources);
     }
   
   public static DataNode makeInstance(String[] dataDirs, Configuration conf, 
         SecureResources resources) throws IOException {
         DiskChecker.checkDir(localFS, new Path(dir), dataDirPermission);
         return new DataNode(conf, dirs, resources);
     
     }
   
   DataNode(final Configuration conf,
              final AbstractList<File> dataDirs, SecureResources resources) throws IOException {
             startDataNode(conf, dataDirs, resources);
         }

5. startDataNode()：1.根据conf对象初始化各个ip port；2.初始化DataStorage；3.初始化DatanodeRegistration；4.初始化DatanodeProtocol；5.handshake() get version and id info from the name-node，实际调用namenode.versionRequest()；6.DataStorage.recoverTransitionRead(...)检查文件系统的状态并做恢复；7.初始化FSDatasetInterface；8.初始化DataBlockScanner；9.创建serverSocket，据此初始化DataXceiverServer；10.HttpServer，配置参数然后启动；11.初始化ipcServer；
6. 接3，runDatanodeDaemon()：注册DataNode；启动DataNode线程。

     public static void runDatanodeDaemon(DataNode dn) throws IOException {
       if (dn != null) {
         dn.register();
         dn.dataNodeThread = new Thread(dn, dnThreadName);
         dn.dataNodeThread.setDaemon(true); // needed for JUnit testing
         dn.dataNodeThread.start();
       }
     }
   
   private void register() throws IOException {
           dnRegistration = namenode.register(dnRegistration);
     } 

7. 进入run()：启动DataXceiverServer线程；启动ipcServer；startDistributedUpgradeIfNeeded() Start distributed upgrade if it should be initiated by the data-node；offerService()开始工作。

     public void run() {
       LOG.info(dnRegistration + "In DataNode.run, data = " + data);
   
       dataXceiverServer.start();
       ipcServer.start();
           
       while (shouldRun) {
           startDistributedUpgradeIfNeeded();
           offerService();
           }

8. offerService()：1.定期heartBeatInterval调用namenode.sendHeartbeat()发送DataNode信息的心跳，并执行带回的DatanodeCommand；2.一直调用namenode.blockReceived()向Namenode报告最近接收到的数据块、要删除的多余块副本；3.定期调用namenode.blockReport()发送block report 告诉NameNode此DataNode上的block信息，并执行带回的DatanodeCommand。4.启动blockScannerThread线程。

   public void offerService() throws Exception {
        
   
       while (shouldRun) {
   	      try {
   	        long startTime = now();
   	        if (startTime - lastHeartbeat > heartBeatInterval) {
   	          lastHeartbeat = startTime;
   	          1.DatanodeCommand[] cmds = namenode.sendHeartbeat(dnRegistration,
   	                                                       data.getCapacity(),
   	                                                       data.getDfsUsed(),
   	                                                       data.getRemaining(),
   	                                                       xmitsInProgress.get(),
   	                                                       getXceiverCount());
   	          processCommand(cmds)；
   	        }
   	            
   	        2.namenode.blockReceived(dnRegistration, blockArray, delHintArray);
                 blockReceived成功后删除receivedBlockListhe delHints里的数据	
   	        if (startTime - lastBlockReport > blockReportInterval) {
   	            3.DatanodeCommand cmd = namenode.blockReport(dnRegistration,
   	                    BlockListAsLongs.convertToArrayLongs(bReport));
   	            processCommand(cmd);
   	        }
   
                            blockScannerThread = new Daemon(blockScanner);
                            blockScannerThread.start();
   	    } // while (shouldRun)
       } // offerService
     }