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本节开始，将对 ResourceManager 中一些常见行为进行剖析探索，看某些具体要害的行为，在 RM 中是如何流转的。本节将深刻源码探索「启动 ApplicationMaster」的具体流程。
一、整体流程
本大节介绍从应用程序提交到启动 ApplicationMaster 的整个过程，期间波及 Client、RMService、RMAppManager、RMApplmpl、RMAppAttemptImpl、RMNode、ResourceScheduler 等几个次要组件。当客户端调用 RPC 函数 ApplicationClientProtocol#submitApplication 后，ResourceManager 端的处理过程如下图所示。
二、具体流程剖析
接下来追随下面的流程图，咱们深刻源码具体分析每一步都是如何执行的：
最开始由客户端发动工作提交 submitApplication()，通过 ClientRMService 和 RMAppManager 发送 RMAppEventType.START 事件，之后交由 RMAppImpl 解决。
protected void submitApplication(
ApplicationSubmissionContext submissionContext, long submitTime,
String user) throws YarnException {ApplicationId applicationId = submissionContext.getApplicationId();
RMAppImpl application =
createAndPopulateNewRMApp(submissionContext, submitTime, user, false);
Credentials credentials = null;
try {credentials = parseCredentials(submissionContext);
if (UserGroupInformation.isSecurityEnabled()) {this.rmContext.getDelegationTokenRenewer()
.addApplicationAsync(applicationId, credentials,
submissionContext.getCancelTokensWhenComplete(),
application.getUser());
} else {
// Dispatcher is not yet started at this time, so these START events
// enqueued should be guaranteed to be first processed when dispatcher
// gets started.
// 这里发送 RMAppEventType.START 事件
this.rmContext.getDispatcher().getEventHandler()
.handle(new RMAppEvent(applicationId, RMAppEventType.START));
}RMAppImpl 这货色是个状态机，收到事件之后会本人转换状态并且解决相应的逻辑。
（状态机还不相熟的同学，可翻到我后面的文章进行学习《2-4 Yarn 根底库 – 状态机库》）
截取一部分状态转换代码：
private static final StateMachineFactory<RMAppImpl,
RMAppState,
RMAppEventType,
RMAppEvent> stateMachineFactory
= new StateMachineFactory<RMAppImpl,
RMAppState,
RMAppEventType,
RMAppEvent>(RMAppState.NEW)
// Transitions from NEW state
.addTransition(RMAppState.NEW, RMAppState.NEW,
RMAppEventType.NODE_UPDATE, new RMAppNodeUpdateTransition())
// 收到 RMAppEventType.START 事件
.addTransition(RMAppState.NEW, RMAppState.NEW_SAVING,
RMAppEventType.START, new RMAppNewlySavingTransition())
.addTransition(RMAppState.NEW, EnumSet.of(RMAppState.SUBMITTED,
RMAppState.ACCEPTED, RMAppState.FINISHED, RMAppState.FAILED,
RMAppState.KILLED, RMAppState.FINAL_SAVING),
RMAppEventType.RECOVER, new RMAppRecoveredTransition())
.addTransition(RMAppState.NEW, RMAppState.KILLED, RMAppEventType.KILL,
new AppKilledTransition())
.addTransition(RMAppState.NEW, RMAppState.FINAL_SAVING,
RMAppEventType.APP_REJECTED,
new FinalSavingTransition(new AppRejectedTransition(),
RMAppState.FAILED))一）RMAppImpl – START
收到 RMAppEventType.START 事件之后，会执行 RMAppNewlySavingTransition()。
private static final class RMAppNewlySavingTransition extends RMAppTransition {
@Override
public void transition(RMAppImpl app, RMAppEvent event) {
// If recovery is enabled then store the application information in a
// non-blocking call so make sure that RM has stored the information
// needed to restart the AM after RM restart without further client
// communication
LOG.info("Storing application with id" + app.applicationId);
app.rmContext.getStateStore().storeNewApplication(app);
}
} 跟上来会发现它收回 RMStateStoreEventType.STORE_APP 事件，去 RMStateStore 中找一下对应的事件处理。发现也是个状态机：
.addTransition(RMStateStoreState.ACTIVE,
EnumSet.of(RMStateStoreState.ACTIVE, RMStateStoreState.FENCED),
RMStateStoreEventType.STORE_APP, new StoreAppTransition()) 跟着 StoreAppTransition 看看做了啥（发送 RMAppEventType.APP_NEW_SAVED 事件）
private static class StoreAppTransition
implements MultipleArcTransition<RMStateStore, RMStateStoreEvent,
RMStateStoreState> {
@Override
public RMStateStoreState transition(RMStateStore store,
RMStateStoreEvent event) {if (!(event instanceof RMStateStoreAppEvent)) {
// should never happen
LOG.error("Illegal event type:" + event.getClass());
return RMStateStoreState.ACTIVE;
}
boolean isFenced = false;
ApplicationStateData appState =
((RMStateStoreAppEvent) event).getAppState();
ApplicationId appId =
appState.getApplicationSubmissionContext().getApplicationId();
LOG.info("Storing info for app:" + appId);
try {store.storeApplicationStateInternal(appId, appState);
// 这里发送了 RMAppEventType.APP_NEW_SAVED 事件
store.notifyApplication(new RMAppEvent(appId,
RMAppEventType.APP_NEW_SAVED));
} catch (Exception e) {LOG.error("Error storing app:" + appId, e);
isFenced = store.notifyStoreOperationFailedInternal(e);
}
return finalState(isFenced);
};
}二）RMAppImpl – APP_NEW_SAVED
咱们再回到 RMAppImpl，找到对应的状态转移逻辑。
// 刚刚咱们的状态是 NEW_SAVING，收到了 APP_NEW_SAVED 事件，执行 AddApplicationToSchedulerTransition() 后，转换为 SUBMITTED 状态
.addTransition(RMAppState.NEW_SAVING, RMAppState.SUBMITTED,
RMAppEventType.APP_NEW_SAVED, new AddApplicationToSchedulerTransition()) 在 AddApplicationToSchedulerTransition() 中会发送 SchedulerEventType.APP_ADDED 事件。之后 RMAppImpl 转换为 RMAppState.SUBMITTED 状态。SchedulerEventType.APP_ADDED 会被多个事件处理器捕捉解决：
1）ResourceSchedulerWrapper 事件处理器，仅记录
} else if (schedulerEvent.getType() == SchedulerEventType.APP_ADDED
&& schedulerEvent instanceof AppAddedSchedulerEvent) {
AppAddedSchedulerEvent appAddEvent =
(AppAddedSchedulerEvent) schedulerEvent;
String queueName = appAddEvent.getQueue();
appQueueMap.put(appAddEvent.getApplicationId(), queueName);
}2）各个 AbstractYarnScheduler 的实现类。以 CapacityScheduler 为例：
执行 addApplication()
case APP_ADDED:
{AppAddedSchedulerEvent appAddedEvent = (AppAddedSchedulerEvent) event;
String queueName = resolveReservationQueueName(appAddedEvent.getQueue(),
appAddedEvent.getApplicationId(), appAddedEvent.getReservationID(),
appAddedEvent.getIsAppRecovering());
if (queueName != null) {if (!appAddedEvent.getIsAppRecovering()) {addApplication(appAddedEvent.getApplicationId(), queueName,
appAddedEvent.getUser(), appAddedEvent.getApplicatonPriority());
} else {addApplicationOnRecovery(appAddedEvent.getApplicationId(), queueName,
appAddedEvent.getUser(), appAddedEvent.getApplicatonPriority());
}
}
} 在 addApplication() 中会提交 Application 并发送 RMAppEventType.APP_ACCEPTED 事件。
queue.submitApplication(applicationId, user, queueName);
rmContext.getDispatcher().getEventHandler()
.handle(new RMAppEvent(applicationId, RMAppEventType.APP_ACCEPTED));三）RMAppImpl – APP_ACCEPTED（重点）
持续回到 RMAppImpl，执行 StartAppAttemptTransition()，创立 newAttempt，发送事件 RMAppAttemptEventType.START
.addTransition(RMAppState.SUBMITTED, RMAppState.ACCEPTED,
RMAppEventType.APP_ACCEPTED, new StartAppAttemptTransition()) private static final class StartAppAttemptTransition extends RMAppTransition {
@Override
public void transition(RMAppImpl app, RMAppEvent event) {app.createAndStartNewAttempt(false);
};
} private void
createAndStartNewAttempt(boolean transferStateFromPreviousAttempt) {createNewAttempt();
handler.handle(new RMAppStartAttemptEvent(currentAttempt.getAppAttemptId(),
transferStateFromPreviousAttempt));
} 在 RMAppAttemptImpl 中会捕捉这个事件，执行 AttemptStartedTransition()，其中会发送 SchedulerEventType.APP_ATTEMPT_ADDED 事件，由 AbstractYarnScheduler 实现类解决
.addTransition(RMAppAttemptState.NEW, RMAppAttemptState.SUBMITTED,
RMAppAttemptEventType.START, new AttemptStartedTransition()) 如在 CapacityScheduler 中由 addApplicationAttempt 解决，会提交 ApplicationAttempt，并发送 RMAppAttemptEventType.ATTEMPT_ADDED 事件
private synchronized void addApplicationAttempt() {
// 提交 attempt
queue.submitApplicationAttempt(attempt, application.getUser());
// 发送 RMAppAttemptEventType.ATTEMPT_ADDED 事件
rmContext.getDispatcher().getEventHandler().handle(
new RMAppAttemptEvent(applicationAttemptId,
RMAppAttemptEventType.ATTEMPT_ADDED));
}RMAppAttemptImpl 收到 event 后持续解决，在 ScheduleTransition 会 allocate am container 资源。
.addTransition(RMAppAttemptState.SUBMITTED,
EnumSet.of(RMAppAttemptState.LAUNCHED_UNMANAGED_SAVING,
RMAppAttemptState.SCHEDULED),
RMAppAttemptEventType.ATTEMPT_ADDED,
new ScheduleTransition()) // AM resource has been checked when submission
Allocation amContainerAllocation =
appAttempt.scheduler.allocate(
appAttempt.applicationAttemptId,
Collections.singletonList(appAttempt.amReq),
EMPTY_CONTAINER_RELEASE_LIST,
amBlacklist.getBlacklistAdditions(),
amBlacklist.getBlacklistRemovals(), null, null);ResourceScheduler 将资源返回给它之前，会向 RMContainerlmpl 发送一个 RMContainerEventType.ACQUIRED 事件。
在 RMContainerImpl 接到 RMContainerEventType.START，发送 RMAppAttemptEventType.CONTAINER_ALLOCATED 事件。
.addTransition(RMContainerState.NEW, RMContainerState.ALLOCATED,
RMContainerEventType.START, new ContainerStartedTransition()) private static final class ContainerStartedTransition extends
BaseTransition {
@Override
public void transition(RMContainerImpl container, RMContainerEvent event) {
container.eventHandler.handle(new RMAppAttemptEvent(container.appAttemptId, RMAppAttemptEventType.CONTAINER_ALLOCATED));
}
} 又回到 RMAppAttemptImpl 后续状态机，执行 AMContainerAllocatedTransition，在其中又一次为 am allocate，和上一个状态中 allocate 仅参数不同，没搞懂为啥。这里如果发现 allocate container 资源还是 0，会退回上一步，状态还是 RMAppAttemptState.SCHEDULED 期待再次获取资源。如果失常获取到了资源，就会转为 RMAppAttemptState.ALLOCATED_SAVING 状态。
.addTransition(RMAppAttemptState.SCHEDULED,
EnumSet.of(RMAppAttemptState.ALLOCATED_SAVING,
RMAppAttemptState.SCHEDULED),
RMAppAttemptEventType.CONTAINER_ALLOCATED,
new AMContainerAllocatedTransition()) Allocation amContainerAllocation =
appAttempt.scheduler.allocate(appAttempt.applicationAttemptId,
EMPTY_CONTAINER_REQUEST_LIST, EMPTY_CONTAINER_RELEASE_LIST, null,
null, null, null); 日志记录实现后，RMStateStore 向 RMAppAttemptImpl 发送 RMAppAttemptEventType.ATTEMPT_NEW_SAVED 事件。RMAppAttemptImpl 后续向 ApplicationMasterLauncher 发 送 AMLauncherEventType.LAUNCH 事件（理论执行是在 AMLauncher 中），并将状态从 ALLOCATED_SAVING 转移为 ALLOCATED。
.addTransition(RMAppAttemptState.ALLOCATED_SAVING,
RMAppAttemptState.ALLOCATED,
RMAppAttemptEventType.ATTEMPT_NEW_SAVED, new AttemptStoredTransition())ApplicationMasterLauncher 收到 AMLauncherEventType.LAUNCH 事件后，会将该事件放到事件队列中，期待 AMLauncher 线程池中的线程解决该事件。它将与对应的 NodeManager 通信，启动 ApplicationMaster，一旦胜利启动后，将向 RMAppAttemptImpl 发送 RMAppAttemptEventType.LAUNCHED 事件。
public void run() {switch (eventType) {
case LAUNCH:
try {LOG.info("Launching master" + application.getAppAttemptId());
launch();
handler.handle(new RMAppAttemptEvent(application.getAppAttemptId(),
RMAppAttemptEventType.LAUNCHED));RMAppAttemptImpl 收到 RMAppAttemptEventType.LAUNCHED 事件后，会向 AMLivelinessMonitor 注册，以监控运行状态。RMAppAttemptImpl 状态从 ALLOCATED 转移为 LAUNCHED。
之后，NodeManager 通过心跳机制汇报 ApplicationMaster 所在 Container 曾经胜利启动，收到该信息后，ResourceScheduler 将发送一个 RMContainerEventType.LAUNCHED 事件，RMContainerImpl 收到该事件后，会从 ContainerAllocationExpirer 监控列表中移除。
启动的 ApplicationMaster 通过 RPC 函数 ApplicationMasterProtocol#registerApplicationMaster 向 ResourceManager 注册，ResourceManager 中的 ApplicationMasterService 服务接管到该申请后，发送 RMAppAttemptEventType.REGISTERED 事件。
// ApplicationMasterService#registerApplicationMaster
LOG.info("AM registration" + applicationAttemptId);
this.rmContext
.getDispatcher()
.getEventHandler()
.handle(
// 这里发送 RMAppAttemptEventType.REGISTERED 事件
new RMAppAttemptRegistrationEvent(applicationAttemptId, request
.getHost(), request.getRpcPort(), request.getTrackingUrl()));RMAppAttemptImpl 收到该事件后，首先保留该 ApplicationMaster 的根本信息（比方所在 host、启用的 RPC 端口号等），而后向 RMApplmpl 发送一个 RMAppEventType.ATTEMPT_REGISTERED 事件。RMAppAttemptImpl 状态从 LAUNCHED 转移为 RUNNING。
.addTransition(RMAppAttemptState.LAUNCHED, RMAppAttemptState.RUNNING,
RMAppAttemptEventType.REGISTERED, REGISTERED_TRANSITION)// AMRegisteredTransition
appAttempt.eventHandler.handle(new RMAppEvent(appAttempt
.getAppAttemptId().getApplicationId(),
RMAppEventType.ATTEMPT_REGISTERED));四）RMAppImpl – ATTEMPT_REGISTERED
RMAppImpl 收到 RMAppEventType.ATTEMPT_REGISTERED 事件后，将状态从 ACCEPTED 转换为 RUNNING。
.addTransition(RMAppState.ACCEPTED, RMAppState.RUNNING,
RMAppEventType.ATTEMPT_REGISTERED, new RMAppStateUpdateTransition(YarnApplicationState.RUNNING))到这里，启动 ApplicationMaster 的整体流程剖析结束！
三、总结
本篇文章剖析了从应用程序提交到启动 ApplicationMaster 的整个过程，剖析具体过程看的可能会有些繁琐。但只有抓住外围实质，就很容易捋分明。重点就是事件处理和状态机，这两个部件了解分明，就很容易看明确程序的流转。
理论逻辑无非就是几个服务之间相互发送对应的事件，接管到事件后会执行启动服务、记录日志、监控状态，而后再发送个新的事件。
自身不难，但须要耐下心来一点点去梳理。
