YARN源码分析之ApplicationMaster启动流程之RM端

任何一个计算框架或者说一个服务要运行在yarn上，都需要一个master来对job进行管理，这个master就是ApplicationMaster。

ApplicationMaster是一个job的大脑，下面就以MapReduce为例，介绍下ApplicationMaster的启动流程。

首先client向RM提交一个application请求，RM创建一个application，然后再创建一个appattempt，后期的调度和任务的拆解都是对这个appattempt进行的，当appattempt的状态从ALLOCATED_SAVING变成ALLOCATED时，由AttemptStoredTransition.transition调用appAttempt.launchAttempt()进行启动，下面来看下具体代码:

// RMAppAttemptImpl.javaprivate void launchAttempt(){  // Send event to launch the AM Container  // 通过异步调度器得到该事件注册的handle (在ResourceManager中注册)  // AMLauncherEvent 对应的handle是ApplicationMasterLauncher  eventHandler.handle(new AMLauncherEvent(AMLauncherEventType.LAUNCH, this));}

AMLauncherEvent对应的handle是ApplicationMasterLauncher，事件类型是LAUNCH，在ApplicationMasterLauncher.handle中会调用launch(application)，代码如下:

private void launch(RMAppAttempt application) {  // 创建一个线程  Runnable launcher = createRunnableLauncher(application,       AMLauncherEventType.LAUNCH);  // 将线程放入阻塞队列中  masterEvents.add(launcher);}

只从这个方法来分析，首先创建了一个launcher线程，然后将其放入一个队列中，等待另一个线程从队列中取出进行操作，这是典型的生产者消费者模型。那么我们就来看下ApplicationMasterLauncher(ApplicationMasterLauncher是一个事件也是一个服务)关于这块代码的具体实现。

先看下createRunnableLauncher，

protected Runnable createRunnableLauncher(RMAppAttempt application,     AMLauncherEventType event) {  Runnable launcher =      new AMLauncher(context, application, event, getConfig());  return launcher;}

这里只是new了一个AMLauncher，AMLauncher实现了Runnable接口，是执行AM操作的线程，只执行launch和cleanup。

launcher线程创建之后add到阻塞队列masterEvents中，那么必然会有另一个线程来队列中take launcher，这个线程是LauncherThread类型的launcherHandlingThread，launcherHandlingThread将launcher取出丢给线程池去执行，代码如下:

private class LauncherThread extends Thread {  public LauncherThread() {    super("ApplicationMaster Launcher");  }  @Override  public void run() {    while (!this.isInterrupted()) {      Runnable toLaunch;      try {        // 从阻塞队列中取出         toLaunch = masterEvents.take();        // 交给线程池执行        // this.launcherPool = new ThreadPoolExecutor(10, 10, 1, TimeUnit.HOURS, new LinkedBlockingQueue<Runnable>());        launcherPool.execute(toLaunch);      } catch (InterruptedException e) {        LOG.warn(this.getClass().getName() + " interrupted. Returning.");        return;      }    }  }} 

放入线程池之后，launcher线程就开始执行，调用的是AMLauncher.run

public void run() {  switch (eventType) {  case LAUNCH:    try {      LOG.info("Launching master" + application.getAppAttemptId());      launch();      handler.handle(new RMAppAttemptEvent(application.getAppAttemptId(),          RMAppAttemptEventType.LAUNCHED));    } catch(Exception ie) {      String message = "Error launching " + application.getAppAttemptId()          + ". Got exception: " + StringUtils.stringifyException(ie);      LOG.info(message);      handler.handle(new RMAppAttemptLaunchFailedEvent(application          .getAppAttemptId(), message));    }    break;  case CLEANUP:    ...    break;  default:    LOG.warn("Received unknown event-type " + eventType + ". Ignoring.");    break;  }}

之前放入阻塞队列masterEvents的事件类型是LAUNCH，则此处调用launch()方法:

private void launch() throws IOException, YarnException {  // 得到对应node的rpc客户端  connect();  ContainerId masterContainerID = masterContainer.getId();  ApplicationSubmissionContext applicationContext =    application.getSubmissionContext();  LOG.info("Setting up container " + masterContainer      + " for AM " + application.getAppAttemptId());    ContainerLaunchContext launchContext =      createAMContainerLaunchContext(applicationContext, masterContainerID);  // 构建request  StartContainerRequest scRequest =      StartContainerRequest.newInstance(launchContext,        masterContainer.getContainerToken());  List<StartContainerRequest> list = new ArrayList<StartContainerRequest>();  list.add(scRequest);  StartContainersRequest allRequests =      StartContainersRequest.newInstance(list);  // 远程调用startContainers  StartContainersResponse response =      containerMgrProxy.startContainers(allRequests);  if (response.getFailedRequests() != null      && response.getFailedRequests().containsKey(masterContainerID)) {    Throwable t =        response.getFailedRequests().get(masterContainerID).deSerialize();    parseAndThrowException(t);  } else {    LOG.info("Done launching container " + masterContainer + " for AM "        + application.getAppAttemptId());  }}

AMLaunch.launch先在connect()中拿到对应node的rpc客户端containerMgrProxy，然后构造request，最后调用rpc函数startContainers()并返回response。

以上是RM端MRAppMaster的启动流程，下一篇将继续介绍nodemanager端端启动流程。