mapreduce源码分析之HeartBeat机制

三．再次回到JobTracker看看心跳机制是怎么回复的，哈哈。。。

当TaskTracker将heartbeat通过RPC发送到JobTracker时，会触发JobTracker的heartbeat()方法，具体见下面（我只是将流程分析了一下，其他的都是一些辅助类，以后慢慢看罗！）：

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/**

*Theperiodicheartbeatmechanismbetweenthe{@linkTaskTracker}and

*the{@linkJobTracker}.

*

*The{@linkJobTracker}processesthestatusinformationsentbythe

*{@linkTaskTracker}andrespondswithinstructionstostart/stop

*tasks or jobs, and also 'reset' instructions during contingencies.

*/

publicsynchronizedHeartbeatResponseheartbeat(TaskTrackerStatusstatus,

booleanrestarted,

booleaninitialContact,

booleanacceptNewTasks,

shortresponseId)

throwsIOException{

。。。

StringtrackerName = status.getTrackerName();

。。。

shortnewResponseId=(short)(responseId+1);

。。。

//Initializetheresponsetobesentfortheheartbeat

HeartbeatResponseresponse=newHeartbeatResponse(newResponseId,null);

List<TaskTrackerAction>actions

=newArrayList<TaskTrackerAction>();

//如果tasktracker向一个jobtracker请求一个task运行

if(acceptNewTasks){

TaskTrackerStatustaskTrackerStatus = getTaskTracker(trackerName);

if(taskTrackerStatus==null){

LOG.warn("Unknowntasktrackerpolling;ignoring:"+trackerName);

}else{

//setup和Cleanup的task优先级最搞，下面这个方法是returns//cleanuptasksfirst,thensetuptasks.

List<Task> tasks

=getSetupAndCleanupTasks(taskTrackerStatus);

if(tasks==null){

//采用默认的任务调度器分配任务

tasks= taskScheduler.assignTasks(taskTrackerStatus);

}

if(tasks!=null){

for(Tasktask:tasks){

//这个是将task放入一个队列中，该队列能监控该任务，如果完成之后长时间还存在就杀死它

expireLaunchingTasks.addNewTask(task.getTaskID());

LOG.debug(trackerName+"->LaunchTask:"+task.getTaskID());

//将任务放到Action列表里面，返回给TaskTracker

actions.add(newLaunchTaskAction(task));

}

}

}

}

。。。

//calculate next heartbeat interval and put in heartbeat response

intnextInterval=getNextHeartbeatInterval();

response.setHeartbeatInterval(nextInterval);

response.setActions(

actions.toArray(newTaskTrackerAction[actions.size()]));

。。。

returnresponse;

}