TaskTracker发送Heartbeat以及接受HeartbeatResponse

          我们通过在命令行输入start-all.sh启动hadoop服务，该脚本通过SSH运行各个节点上的TaskTracker类的main()来启动TaskTracker，它是作为一个单独的JVM来运行的。TaskTracker类实现了MapReduce模型中的TaskTracker的功能。TaskTracker的main函数如下： 

    main（）{ 

    TaskTracker tt = new  TaskTracker(); 

        tt. run(); 

.......

 }

 TaskTracker的run()方法主要调用了offerService()，其主要代码如下： 

while (running && !shuttingDown) {//TaskTracker运行期间一直执行，每隔一段时间就想JobTracker发送一次心跳包，并接受JobTracker发送的HeartbeatResponse

      try {

      //判断是否该发送下一个心跳包

        while (remaining > 0) {

...

        } 

        // TaskTracker 刚启动:

        // 1. 验证buildVersion

        // 2. 为TaskTracker创建一个System Directory

        if(justInited) {

          String jobTrackerBV = jobClient.getBuildVersion();

        ...

          systemDirectory = new Path(dir);

          systemFS = systemDirectory.getFileSystem(fConf);

        }

//每个一段时间检查一下TaskTrack的工作目录

        now = System.currentTimeMillis();

        if (now > (lastCheckDirsTime + diskHealthCheckInterval)) {

          localStorage.checkDirs();

          lastCheckDirsTime = now;

          int numFailures = localStorage.numFailures();

          // Re-init the task tracker if there were any new failures

          if (numFailures > lastNumFailures) {

            lastNumFailures = numFailures;

            return State.STALE;

          }

        }

         //发送心跳包，并向JobTracker请求Task

        HeartbeatResponse heartbeatResponse = transmitHeartBeat(now);

 ...

 //从心跳包的响应中获取它要执行的任务

        TaskTrackerAction[] actions = heartbeatResponse.getActions();

 

//将相应的Task放入到特定的Queue

 if (actions != null){ 

          for(TaskTrackerAction action: actions) {

//将要运行一个Task

            if (action instanceof LaunchTaskAction) {

              addToTaskQueue((LaunchTaskAction)action);

            } else if (action instanceof CommitTaskAction) {//

              CommitTaskAction commitAction = (CommitTaskAction)action;

              if (!commitResponses.contains(commitAction.getTaskID())) {

                LOG.info("Received commit task action for " + 

                          commitAction.getTaskID());

                commitResponses.add(commitAction.getTaskID());

              }

            } else {//待清理的Task

              tasksToCleanup.put(action);

            }

          }

        }

} 

转载于:https://www.cnblogs.com/yueliming/archive/2013/04/09/3009869.html