一、源码下载
下面是hadoop官方源码下载地址，我下载的是hadoop-3.2.4，那就一起来看下吧
二、上下文
在上一篇<Hadoop-MapReduce-MRAppMaster启动篇>中已经将到：MRAppMaster的启动，那么运行MapTask、ReduceTask的容器（YarnChild）是怎么启动的呢？接下来我们一起来看看
三、结论
MRJobConfig是一个MRJob的配置，里面包含了Map、Reduce、Combine类以及Job名称、用户名称、队列名称、MapTask数量、ReduceTask数量、工作目录，jar在本地的路径、任务超时时间、任务id、输入输出目录，每个任务的内存大小和cpu核数等等。
此外它里面还有一个属性，如下：
java
package org.apache.hadoop.mapreduce;
public interface MRJobConfig {
//......省略......
public static final String APPLICATION_MASTER_CLASS =
"org.apache.hadoop.mapreduce.v2.app.MRAppMaster";
public static final String MAPREDUCE_V2_CHILD_CLASS =
"org.apache.hadoop.mapred.YarnChild";
//......省略......
}MRAppMaster是MapReduce的ApplicationMaster实现，负责整个MapReduce作业的过程调度和状态协调
YarnChid是运行在每个容器中的进程，负责运行某一个MapTask或者ReduceTask，
有兴趣的同学可以看一个任务的Yarn日志，也可以看我的<Hadoop-MapReduce-跟着日志理解整体流程>一篇中的日志，就可以发现ApplicationMaster容器和MapTask、ReduceTask所在容器的的日志开头分别就是MRAppMaster和YarnChid
MRAppMaster的启动参数是在YARNRunner中配置的：
java
public class YARNRunner implements ClientProtocol {
private List<String> setupAMCommand(Configuration jobConf) {
List<String> vargs = new ArrayList<>(8);
vargs.add(MRApps.crossPlatformifyMREnv(jobConf, Environment.JAVA_HOME)
+ "/bin/java");
//......省略......
vargs.add(MRJobConfig.APPLICATION_MASTER_CLASS);
//......省略......
return vargs;
}
}YarnChid的启动参数是在MapReduceChildJVM中配置的：
java
public class MapReduceChildJVM {
public static List<String> getVMCommand(
InetSocketAddress taskAttemptListenerAddr, Task task,
JVMId jvmID) {
TaskAttemptID attemptID = task.getTaskID();
JobConf conf = task.conf;
Vector<String> vargs = new Vector<String>(8);
vargs.add(MRApps.crossPlatformifyMREnv(task.conf, Environment.JAVA_HOME)
+ "/bin/java");
//......省略......
vargs.add(YarnChild.class.getName()); // main of Child
//......省略......
return vargsFinal;
}
}YarnChid启动后会启动MapTask或者ReduceTask
四、调用细节（源码跟读）
1、MRAppMaster
MRAppMaster是Map Reduce应用程序母版。状态机被封装在Job接口的实现中。所有状态更改都通过作业界面进行。每个事件都会导致作业中的有限状态转换。
MR AppMaster是松散耦合服务的组合。服务之间通过事件进行交互。这些组件类似于Actors模型。该组件对接收到的事件进行操作，并将事件发送到其他组件。
这使它保持高度并发性，而不需要同步或只需要最少的同步。
事件由中央调度机制进行调度。所有组件都注册到Dispatcher。
使用AppContext在不同组件之间共享信息。
我们先从MRAppMaster的main方法开始捋
java
public static void main(String[] args) {
try {
mainStarted = true;
//设置默认异常处理
Thread.setDefaultUncaughtExceptionHandler(new YarnUncaughtExceptionHandler());
//获取容器相关信息：容器id、容器所在的NodeManager信息、应用提交时间
String containerIdStr =
System.getenv(Environment.CONTAINER_ID.name());
String nodeHostString = System.getenv(Environment.NM_HOST.name());
String nodePortString = System.getenv(Environment.NM_PORT.name());
String nodeHttpPortString =
System.getenv(Environment.NM_HTTP_PORT.name());
String appSubmitTimeStr =
System.getenv(ApplicationConstants.APP_SUBMIT_TIME_ENV);
//校验容器相关信息
validateInputParam(containerIdStr,
Environment.CONTAINER_ID.name());
validateInputParam(nodeHostString, Environment.NM_HOST.name());
validateInputParam(nodePortString, Environment.NM_PORT.name());
validateInputParam(nodeHttpPortString,
Environment.NM_HTTP_PORT.name());
validateInputParam(appSubmitTimeStr,
ApplicationConstants.APP_SUBMIT_TIME_ENV);
ContainerId containerId = ContainerId.fromString(containerIdStr);
//根据containerId 获取ApplicationAttemptId
//ContainerId：表示集群中容器的全局唯一标识符
//ApplicationAttemptId：表示ApplicationMaster对给定ApplicationId的特定尝试,由于ApplicationMaster的临时故障，如硬件故障、连接问题等，在计划应用程序的节点上，可能需要多次尝试才能运行应用程序。
ApplicationAttemptId applicationAttemptId =
containerId.getApplicationAttemptId();
if (applicationAttemptId != null) {
CallerContext.setCurrent(new CallerContext.Builder(
"mr_appmaster_" + applicationAttemptId.toString()).build());
}
long appSubmitTime = Long.parseLong(appSubmitTimeStr);
//构建MRAppMaster
MRAppMaster appMaster =
new MRAppMaster(applicationAttemptId, containerId, nodeHostString,
Integer.parseInt(nodePortString),
Integer.parseInt(nodeHttpPortString), appSubmitTime);
//在JVM正常关闭期间接收到AND信号时运行的关闭挂钩。
ShutdownHookManager.get().addShutdownHook(
new MRAppMasterShutdownHook(appMaster), SHUTDOWN_HOOK_PRIORITY);
//构建 map/reduce 作业配置
JobConf conf = new JobConf(new YarnConfiguration());
//添加配置资源（启动MRAppMaster 时配置过）
conf.addResource(new Path(MRJobConfig.JOB_CONF_FILE));
MRWebAppUtil.initialize(conf);
//记录系统属性
String systemPropsToLog = MRApps.getSystemPropertiesToLog(conf);
if (systemPropsToLog != null) {
LOG.info(systemPropsToLog);
}
String jobUserName = System
.getenv(ApplicationConstants.Environment.USER.name());
conf.set(MRJobConfig.USER_NAME, jobUserName);
//初始化并启动该作业的AppMaster
initAndStartAppMaster(appMaster, conf, jobUserName);
} catch (Throwable t) {
LOG.error("Error starting MRAppMaster", t);
ExitUtil.terminate(1, t);
}
}下面我们接着看initAndStartAppMaster()
java
protected static void initAndStartAppMaster(final MRAppMaster appMaster,
final JobConf conf, String jobUserName) throws IOException,
InterruptedException {
//设置UGI的静态配置
UserGroupInformation.setConfiguration(conf);
// MAPREDUCE-6565: 需要设置SecurityUtil的配置。
SecurityUtil.setConfiguration(conf);
//安全框架已经将令牌加载到当前的UGI中，只需使用它们
Credentials credentials =
UserGroupInformation.getCurrentUser().getCredentials();
LOG.info("Executing with tokens: {}", credentials.getAllTokens());
//使用登录名创建用户。它旨在用于RPC中的远程用户，因为它没有任何凭据。
UserGroupInformation appMasterUgi = UserGroupInformation
.createRemoteUser(jobUserName);
//将给定的凭据添加到此用户。
appMasterUgi.addCredentials(credentials);
//现在删除AM->RM令牌，这样任务就没有它了
Iterator<Token<?>> iter = credentials.getAllTokens().iterator();
while (iter.hasNext()) {
Token<?> token = iter.next();
if (token.getKind().equals(AMRMTokenIdentifier.KIND_NAME)) {
iter.remove();
}
}
//将所有凭据从一个凭据对象复制到另一个。现有的机密和令牌将被覆盖。
conf.getCredentials().addAll(credentials);
appMasterUgi.doAs(new PrivilegedExceptionAction<Object>() {
@Override
public Object run() throws Exception {
//服务所需的所有初始化代码。
//在特定服务实例的生命周期中，此方法只会被调用一次。
//有兴趣的同学可以进去看看，我这里大致总结下它做了什么：
// 1、创建作业类加载器
// 2、获得作业所需的令牌，并将其放入UGI
// 3、创建事件调度程序接口。它根据事件类型将事件分派给已注册的事件处理程序。
// 4、将事件调度程序添加到管理的服务列表
// 5、创建尝试任务完成监控（如果任务尝试在FINISHING状态下停留的时间过长，则此类会生成TA_TIMED_OUT。）
// 6、将尝试任务完成监控添加到管理的服务列表
// 7、根据尝试任务创建心的jobid
// 8、判断是用新API还是旧API
// 9、获取该作业输出格式的输出提交器。它负责确保正确提交输出。
// 10、检查该作业在HDFS上的临时目录是否存在
// 11、构建用于处理来自JobClient的请求的服务
// 12、创建用于处理输出提交的服务并添加到管理的服务列表
// 13、处理来自RM的抢占请求
// 14、创建用于处理对TaskUmplicalProtocol的请求的服务并添加到管理的服务列表
// 15、创建用于记录作业历史事件的服务，并注册到事件调度程序中
// 16、创建该作业的事件调度服务并注册到事件调度程序中
// 17、创建投机者组件事件调度服务并注册到事件调度程序中（任务尝试的状态更新将发送到此组件）并注册到事件调度程序
// 18、启动临时目录清理程序
// 19、构建从ResourceManager分配容器的服务（如果是uber模式，则是伪造容器）并注册到事件调度程序
// 20、构建通过NodeManager启动分配容器的相应服务并注册到事件调度程序
// 21、最后添加JobHistoryEventHandler并添加到管理的服务列表
appMaster.init(conf);
//启动该作业的AppMaster
appMaster.start();
if(appMaster.errorHappenedShutDown) {
throw new IOException("Was asked to shut down.");
}
return null;
}
});
}下面我们接着看appMaster.start()，它最终还是会调用本类的serviceStart()
java
protected void serviceStart() throws Exception {
amInfos = new LinkedList<AMInfo>();
//因为作业有失败重试功能，假如这一次是重试作业旧需要覆盖上一次的Task并清理上一次的临时目录和输出
completedTasksFromPreviousRun = new HashMap<TaskId, TaskInfo>();
processRecovery();
cleanUpPreviousJobOutput();
//当前AM生成的当前AMInfo（里面有AppAttemptId、开始时间、所在容器id、所在NodeManager域名和端口）
AMInfo amInfo =
MRBuilderUtils.newAMInfo(appAttemptID, startTime, containerID, nmHost,
nmPort, nmHttpPort);
//创建并初始化（但不启动）单例job。
//并将job完成事件和处理程序注册到事件调度程序中
job = createJob(getConfig(), forcedState, shutDownMessage);
//为所有以前的AM发送一个MR AM启动的事件。
for (AMInfo info : amInfos) {
dispatcher.getEventHandler().handle(
new JobHistoryEvent(job.getID(), new AMStartedEvent(info
.getAppAttemptId(), info.getStartTime(), info.getContainerId(),
info.getNodeManagerHost(), info.getNodeManagerPort(), info
.getNodeManagerHttpPort(), appSubmitTime)));
}
//为此AM发送一个MR AM启动的事件。
dispatcher.getEventHandler().handle(
new JobHistoryEvent(job.getID(), new AMStartedEvent(amInfo
.getAppAttemptId(), amInfo.getStartTime(), amInfo.getContainerId(),
amInfo.getNodeManagerHost(), amInfo.getNodeManagerPort(), amInfo
.getNodeManagerHttpPort(), this.forcedState == null ? null
: this.forcedState.toString(), appSubmitTime)));
amInfos.add(amInfo);
//metrics system（度量系统）初始化并启动
DefaultMetricsSystem.initialize("MRAppMaster");
boolean initFailed = false;
if (!errorHappenedShutDown) {
// create a job event for job initialization
JobEvent initJobEvent = new JobEvent(job.getID(), JobEventType.JOB_INIT);
// Send init to the job (this does NOT trigger job execution)
// This is a synchronous call, not an event through dispatcher. We want
// job-init to be done completely here.
jobEventDispatcher.handle(initJobEvent);
// If job is still not initialized, an error happened during
// initialization. Must complete starting all of the services so failure
// events can be processed.
initFailed = (((JobImpl)job).getInternalState() != JobStateInternal.INITED);
// JobImpl's InitTransition is done (call above is synchronous), so the
// "uber-decision" (MR-1220) has been made. Query job and switch to
// ubermode if appropriate (by registering different container-allocator
// and container-launcher services/event-handlers).
if (job.isUber()) {
speculatorEventDispatcher.disableSpeculation();
LOG.info("MRAppMaster uberizing job " + job.getID()
+ " in local container (\"uber-AM\") on node "
+ nmHost + ":" + nmPort + ".");
} else {
// send init to speculator only for non-uber jobs.
// This won't yet start as dispatcher isn't started yet.
dispatcher.getEventHandler().handle(
new SpeculatorEvent(job.getID(), clock.getTime()));
LOG.info("MRAppMaster launching normal, non-uberized, multi-container "
+ "job " + job.getID() + ".");
}
// Start ClientService here, since it's not initialized if
// errorHappenedShutDown is true
clientService.start();
}
//启动所有组件
super.serviceStart();
//最终设置作业类加载器
MRApps.setClassLoader(jobClassLoader, getConfig());
if (initFailed) {
JobEvent initFailedEvent = new JobEvent(job.getID(), JobEventType.JOB_INIT_FAILED);
jobEventDispatcher.handle(initFailedEvent);
} else {
//所有组件都已启动后，启动作业
startJobs();
}
}下面我们接着看startJobs()，可以覆盖此项以实例化多个作业并创建工作流
java
protected void startJobs() {
/** 创建一个作业启动事件（JobEventType.JOB_START）来启动 */
JobEvent startJobEvent = new JobStartEvent(job.getID(),
recoveredJobStartTime);
/** 发送作业启动事件。这将触发作业执行 */
dispatcher.getEventHandler().handle(startJobEvent);
}下面我们看下JobEventType.JOB_START事件的处理，作业启动事件和处理程序在JobImpl中。
2、JobImpl
JobImpl是作业界面的实施。维护作业的状态机。读和写调用使用ReadWriteLock实现并发。
关于作业的状态有NEW、INITED、SETUP、RUNNING、KILL_WAIT、COMMITTING、SUCCEEDED、FAIL_WAIT、FAIL_ABORT、KILL_ABORT、FAILED、KILLED、INTERNAL_ERROR、AM_REBOOT等，有兴趣的同学可以跟读下每个状态的转换细节，这里不一一跟读了，
java
protected static final
StateMachineFactory<JobImpl, JobStateInternal, JobEventType, JobEvent>
stateMachineFactory
= new StateMachineFactory<JobImpl, JobStateInternal, JobEventType, JobEvent>
(JobStateInternal.NEW)
// Transitions from NEW state
// Transitions from INITED state
.addTransition(JobStateInternal.INITED, JobStateInternal.SETUP,
JobEventType.JOB_START,
new StartTransition())
// Transitions from SETUP state
.addTransition(JobStateInternal.SETUP, JobStateInternal.RUNNING,
JobEventType.JOB_SETUP_COMPLETED,
new SetupCompletedTransition())
// Transitions from RUNNING state
// Transitions from KILL_WAIT state.
// Transitions from COMMITTING state
// Transitions from SUCCEEDED state
// Transitions from FAIL_WAIT state
//Transitions from FAIL_ABORT state
// Transitions from KILL_ABORT state
// Transitions from FAILED state
// Transitions from KILLED state
// No transitions from INTERNAL_ERROR state. Ignore all.
// No transitions from AM_REBOOT state. Ignore all.
// create the topology tables
.installTopology();以下是JobEventType.JOB_START事件的处理程序
java
public static class StartTransition
implements SingleArcTransition<JobImpl, JobEvent> {
/**
* 这个转换在事件调度器线程中执行，尽管它是在MRAppMaster的startJobs（）方法中触发的。
*/
@Override
public void transition(JobImpl job, JobEvent event) {
JobStartEvent jse = (JobStartEvent) event;
if (jse.getRecoveredJobStartTime() != -1L) {
job.startTime = jse.getRecoveredJobStartTime();
} else {
job.startTime = job.clock.getTime();
}
JobInitedEvent jie =
new JobInitedEvent(job.oldJobId,
job.startTime,
job.numMapTasks, job.numReduceTasks,
job.getState().toString(),
job.isUber());
job.eventHandler.handle(new JobHistoryEvent(job.jobId, jie));
JobInfoChangeEvent jice = new JobInfoChangeEvent(job.oldJobId,
job.appSubmitTime, job.startTime);
job.eventHandler.handle(new JobHistoryEvent(job.jobId, jice));
job.metrics.runningJob(job);
//CommitterEventType.JOB_SETUP事件处理
job.eventHandler.handle(new CommitterJobSetupEvent(
job.jobId, job.jobContext));
}
}JOB_SETUP事件是由CommitterEventHandler处理
3、CommitterEventHandler
CommitterEventHandler负责处理JOB_SETUP、JOB_COMMIT、JOB_ABORT、TASK_ABORT事件
java
public class CommitterEventHandler extends AbstractService
implements EventHandler<CommitterEvent> {
public void run() {
LOG.info("Processing the event " + event.toString());
switch (event.getType()) {
case JOB_SETUP:
handleJobSetup((CommitterJobSetupEvent) event);
break;
case JOB_COMMIT:
handleJobCommit((CommitterJobCommitEvent) event);
break;
case JOB_ABORT:
handleJobAbort((CommitterJobAbortEvent) event);
break;
case TASK_ABORT:
handleTaskAbort((CommitterTaskAbortEvent) event);
break;
default:
throw new YarnRuntimeException("Unexpected committer event "
+ event.toString());
}
}
//处理JOB_SETUP事件
protected void handleJobSetup(CommitterJobSetupEvent event) {
try {
committer.setupJob(event.getJobContext());
//现在job的状态为JobEventType.JOB_SETUP_COMPLETED
context.getEventHandler().handle(
new JobSetupCompletedEvent(event.getJobID()));
} catch (Exception e) {
LOG.warn("Job setup failed", e);
context.getEventHandler().handle(new JobSetupFailedEvent(
event.getJobID(), StringUtils.stringifyException(e)));
}
}
}4、再回JobImpl
JobEventType.JOB_SETUP_COMPLETED的处理程序为SetupCompletedTransition()，在第2步中有。
java
private static class SetupCompletedTransition
implements SingleArcTransition<JobImpl, JobEvent> {
@Override
public void transition(JobImpl job, JobEvent event) {
job.setupProgress = 1.0f;
//调度MapTask
job.scheduleTasks(job.mapTasks, job.numReduceTasks == 0);
//调度ReduceTask
job.scheduleTasks(job.reduceTasks, true);
//如果没有任务，只需过渡到已完成的工作状态
if (job.numReduceTasks == 0 && job.numMapTasks == 0) {
job.eventHandler.handle(new JobEvent(job.jobId,
JobEventType.JOB_COMPLETED));
}
}
}
protected void scheduleTasks(Set<TaskId> taskIDs,
boolean recoverTaskOutput) {
for (TaskId taskID : taskIDs) {
TaskInfo taskInfo = completedTasksFromPreviousRun.remove(taskID);
if (taskInfo != null) {
//如果是重试任务需要覆盖
eventHandler.handle(new TaskRecoverEvent(taskID, taskInfo,
committer, recoverTaskOutput));
} else {
//新任务，需要做任务调度处理，我们看这块的逻辑
eventHandler.handle(new TaskEvent(taskID, TaskEventType.T_SCHEDULE));
}
}
}5、TaskImpl
TaskImpl是任务接口的实现，维护任务的状态机。任务的状态有NEW、SCHEDULED、RUNNING、KILL_WAIT、SUCCEEDED、FAILED
java
private static final StateMachineFactory
<TaskImpl, TaskStateInternal, TaskEventType, TaskEvent>
stateMachineFactory
= new StateMachineFactory<TaskImpl, TaskStateInternal, TaskEventType, TaskEvent>
(TaskStateInternal.NEW)
// 定义Task的状态机
// Transitions from NEW state
.addTransition(TaskStateInternal.NEW, TaskStateInternal.SCHEDULED,
TaskEventType.T_SCHEDULE, new InitialScheduleTransition())
// Transitions from SCHEDULED state
//启动第一次尝试时，任务状态设置为RUNNING
// Transitions from RUNNING state
// Transitions from KILL_WAIT state
// Transitions from SUCCEEDED state
// Transitions from FAILED state
// create the topology tables
.installTopology();可以看到处理事件调用的是InitialScheduleTransition()
java
private static class InitialScheduleTransition
implements SingleArcTransition<TaskImpl, TaskEvent> {
@Override
public void transition(TaskImpl task, TaskEvent event) {
task.addAndScheduleAttempt(Avataar.VIRGIN);
task.scheduledTime = task.clock.getTime();
task.sendTaskStartedEvent();
}
}
private void addAndScheduleAttempt(Avataar avataar, boolean reschedule) {
TaskAttempt attempt = addAttempt(avataar);
inProgressAttempts.add(attempt.getID());
//schedule the nextAttemptNumber
if (failedAttempts.size() > 0 || reschedule) {
eventHandler.handle(new TaskAttemptEvent(attempt.getID(),
TaskAttemptEventType.TA_RESCHEDULE));
} else {
//将任务状态变成TaskAttemptEventType.TA_SCHEDULE)
eventHandler.handle(new TaskAttemptEvent(attempt.getID(),
TaskAttemptEventType.TA_SCHEDULE));
}
}
private void sendTaskStartedEvent() {
launchTime = getLaunchTime();
//创建事件以记录任务的开始
TaskStartedEvent tse = new TaskStartedEvent(
TypeConverter.fromYarn(taskId), launchTime,
TypeConverter.fromYarn(taskId.getTaskType()),
getSplitsAsString());
eventHandler
.handle(new JobHistoryEvent(taskId.getJobId(), tse));
historyTaskStartGenerated = true;
}
public static org.apache.hadoop.mapreduce.TaskType fromYarn(
TaskType taskType) {
switch (taskType) {
case MAP:
return org.apache.hadoop.mapreduce.TaskType.MAP;
case REDUCE:
return org.apache.hadoop.mapreduce.TaskType.REDUCE;
default:
throw new YarnRuntimeException("Unrecognized task type: " + taskType);
}
}6、TaskAttemptImpl
TaskAttemptImpl是尝试任务的实现，因为有失败重试机制，因此每一次在容器中运行的任务都先称为尝试任务，当尝试任务运行成功后，对应的任务也会标记为成功。
TaskAttemptImpl维护尝试任务的状态机。任务的状态有NEW、UNASSIGNED、ASSIGNED、RUNNING、SUCCESS_FINISHING_CONTAINER、FAIL_FINISHING_CONTAINER、COMMIT_PENDING、SUCCESS_CONTAINER_CLEANUP、FAIL_CONTAINER_CLEANUP、KILL_CONTAINER_CLEANUP、FAIL_TASK_CLEANUP、KILL_TASK_CLEANUP、SUCCEEDED、FAILED、KILLED
java
private static final StateMachineFactory
<TaskAttemptImpl, TaskAttemptStateInternal, TaskAttemptEventType, TaskAttemptEvent>
stateMachineFactory
= new StateMachineFactory
<TaskAttemptImpl, TaskAttemptStateInternal, TaskAttemptEventType, TaskAttemptEvent>
(TaskAttemptStateInternal.NEW)
// Transitions from the NEW state.
.addTransition(TaskAttemptStateInternal.NEW, TaskAttemptStateInternal.UNASSIGNED,
TaskAttemptEventType.TA_SCHEDULE, new RequestContainerTransition(false))
// Transitions from the UNASSIGNED state.
.addTransition(TaskAttemptStateInternal.UNASSIGNED,
TaskAttemptStateInternal.ASSIGNED, TaskAttemptEventType.TA_ASSIGNED,
new ContainerAssignedTransition())
// Transitions from the ASSIGNED state.
// Transitions from RUNNING state.
// Transitions from SUCCESS_FINISHING_CONTAINER state
// Transitions from COMMIT_PENDING state
// Transitions from SUCCESS_CONTAINER_CLEANUP state
// kill and cleanup the container
// Transitions from FAIL_CONTAINER_CLEANUP state.
// Transitions from KILL_CONTAINER_CLEANUP
// Transitions from FAIL_TASK_CLEANUP
// run the task cleanup
// Transitions from KILL_TASK_CLEANUP
// Transitions from SUCCEEDED
// Transitions from FAILED state
// Transitions from KILLED state
// create the topology tables
.installTopology();可以看到处理TaskAttemptEventType.TA_SCHEDULE事件的逻辑是RequestContainerTransition()
java
static class RequestContainerTransition implements
SingleArcTransition<TaskAttemptImpl, TaskAttemptEvent> {
private final boolean rescheduled;
public RequestContainerTransition(boolean rescheduled) {
this.rescheduled = rescheduled;
}
@SuppressWarnings("unchecked")
@Override
public void transition(TaskAttemptImpl taskAttempt,
TaskAttemptEvent event) {
//告诉任何投机者我们正在请求一个容器
taskAttempt.eventHandler.handle
(new SpeculatorEvent(taskAttempt.getID().getTaskId(), +1));
//申请容器
if (rescheduled) {
taskAttempt.eventHandler.handle(
ContainerRequestEvent.createContainerRequestEventForFailedContainer(
taskAttempt.attemptId,
taskAttempt.resourceCapability));
} else {
//处理ContainerAllocator.EventType.CONTAINER_REQ事件
taskAttempt.eventHandler.handle(new ContainerRequestEvent(
taskAttempt.attemptId, taskAttempt.resourceCapability,
taskAttempt.dataLocalHosts.toArray(
new String[taskAttempt.dataLocalHosts.size()]),
taskAttempt.dataLocalRacks.toArray(
new String[taskAttempt.dataLocalRacks.size()])));
}
}
}7、LocalContainerAllocator
LocalContainerAllocator负责在本地分配容器。不分配真正的容器；而是为所有请求发送一个已分配的事件。也处理ContainerAllocator.EventType.CONTAINER_REQ事件
java
public void handle(ContainerAllocatorEvent event) {
if (event.getType() == ContainerAllocator.EventType.CONTAINER_REQ) {
LOG.info("Processing the event " + event.toString());
//分配与AM相同的容器ID
ContainerId cID =
ContainerId.newContainerId(getContext().getApplicationAttemptId(),
this.containerId.getContainerId());
Container container = recordFactory.newRecordInstance(Container.class);
container.setId(cID);
NodeId nodeId = NodeId.newInstance(this.nmHost, this.nmPort);
container.setResource(Resource.newInstance(0, 0));
container.setNodeId(nodeId);
container.setContainerToken(null);
container.setNodeHttpAddress(this.nmHost + ":" + this.nmHttpPort);
//将容器分配的事件发送到任务尝试
if (event.getAttemptID().getTaskId().getTaskType() == TaskType.MAP) {
JobCounterUpdateEvent jce =
new JobCounterUpdateEvent(event.getAttemptID().getTaskId()
.getJobId());
// TODO Setting OTHER_LOCAL_MAP for now.
jce.addCounterUpdate(JobCounter.OTHER_LOCAL_MAPS, 1);
eventHandler.handle(jce);
}
//此时处理TaskAttemptEventType.TA_ASSIGNED事件
eventHandler.handle(new TaskAttemptContainerAssignedEvent(
event.getAttemptID(), container, applicationACLs));
}
}8、再回TaskAttemptImpl
第6步已经写了TaskAttemptEventType.TA_ASSIGNED事件的处理逻辑：new ContainerAssignedTransition()
java
private static class ContainerAssignedTransition implements
SingleArcTransition<TaskAttemptImpl, TaskAttemptEvent> {
@SuppressWarnings({ "unchecked" })
@Override
public void transition(final TaskAttemptImpl taskAttempt,
TaskAttemptEvent event) {
final TaskAttemptContainerAssignedEvent cEvent =
(TaskAttemptContainerAssignedEvent) event;
Container container = cEvent.getContainer();
taskAttempt.container = container;
//这是真正的Task
taskAttempt.remoteTask = taskAttempt.createRemoteTask();
taskAttempt.jvmID =
new WrappedJvmID(taskAttempt.remoteTask.getTaskID().getJobID(),
taskAttempt.remoteTask.isMapTask(),
taskAttempt.container.getId().getContainerId());
taskAttempt.taskAttemptListener.registerPendingTask(
taskAttempt.remoteTask, taskAttempt.jvmID);
taskAttempt.computeRackAndLocality();
//启动容器
//为给定的Task尝试创建要启动的容器对象
ContainerLaunchContext launchContext = createContainerLaunchContext(
cEvent.getApplicationACLs(), taskAttempt.conf, taskAttempt.jobToken,
taskAttempt.remoteTask, taskAttempt.oldJobId, taskAttempt.jvmID,
taskAttempt.taskAttemptListener, taskAttempt.credentials);
taskAttempt.eventHandler
.handle(new ContainerRemoteLaunchEvent(taskAttempt.attemptId,
launchContext, container, taskAttempt.remoteTask));
// 向投机者发送我们的容器需求得到满足的事件
taskAttempt.eventHandler.handle
(new SpeculatorEvent(taskAttempt.getID().getTaskId(), -1));
}
}
static ContainerLaunchContext createContainerLaunchContext(
Map<ApplicationAccessType, String> applicationACLs,
Configuration conf, Token<JobTokenIdentifier> jobToken, Task remoteTask,
final org.apache.hadoop.mapred.JobID oldJobId,
WrappedJvmID jvmID,
TaskAttemptListener taskAttemptListener,
Credentials credentials) {
synchronized (commonContainerSpecLock) {
if (commonContainerSpec == null) {
commonContainerSpec = createCommonContainerLaunchContext(
applicationACLs, conf, jobToken, oldJobId, credentials);
}
}
//填写通用规范中缺少的每个容器所需的字段
boolean userClassesTakesPrecedence =
conf.getBoolean(MRJobConfig.MAPREDUCE_JOB_USER_CLASSPATH_FIRST, false);
//通过从公共环境克隆来设置环境。
Map<String, String> env = commonContainerSpec.getEnvironment();
Map<String, String> myEnv = new HashMap<String, String>(env.size());
myEnv.putAll(env);
if (userClassesTakesPrecedence) {
myEnv.put(Environment.CLASSPATH_PREPEND_DISTCACHE.name(), "true");
}
MapReduceChildJVM.setVMEnv(myEnv, remoteTask);
//设置启动命令 这里会调用MapReduceChildJVM的getVMCommand()
List<String> commands = MapReduceChildJVM.getVMCommand(
taskAttemptListener.getAddress(), remoteTask, jvmID);
//复制ByteBuffers以供多个容器访问。
Map<String, ByteBuffer> myServiceData = new HashMap<String, ByteBuffer>();
for (Entry<String, ByteBuffer> entry : commonContainerSpec
.getServiceData().entrySet()) {
myServiceData.put(entry.getKey(), entry.getValue().duplicate());
}
//构建实际的容器
ContainerLaunchContext container = ContainerLaunchContext.newInstance(
commonContainerSpec.getLocalResources(), myEnv, commands,
myServiceData, commonContainerSpec.getTokens().duplicate(),
applicationACLs);
return container;
}9、MapReduceChildJVM
这里就会加载YarnChild，启动运行MapTask、ReduceTask的容器
java
public static List<String> getVMCommand(
InetSocketAddress taskAttemptListenerAddr, Task task,
JVMId jvmID) {
TaskAttemptID attemptID = task.getTaskID();
JobConf conf = task.conf;
Vector<String> vargs = new Vector<String>(8);
vargs.add(MRApps.crossPlatformifyMREnv(task.conf, Environment.JAVA_HOME)
+ "/bin/java");
// Add child (task) java-vm options.
//
// The following symbols if present in mapred.{map|reduce}.child.java.opts
// value are replaced:
// + @taskid@ is interpolated with value of TaskID.
// Other occurrences of @ will not be altered.
//
// Example with multiple arguments and substitutions, showing
// jvm GC logging, and start of a passwordless JVM JMX agent so can
// connect with jconsole and the likes to watch child memory, threads
// and get thread dumps.
//
// <property>
// <name>mapred.map.child.java.opts</name>
// <value>-Xmx 512M -verbose:gc -Xloggc:/tmp/@taskid@.gc \
// -Dcom.sun.management.jmxremote.authenticate=false \
// -Dcom.sun.management.jmxremote.ssl=false \
// </value>
// </property>
//
// <property>
// <name>mapred.reduce.child.java.opts</name>
// <value>-Xmx 1024M -verbose:gc -Xloggc:/tmp/@taskid@.gc \
// -Dcom.sun.management.jmxremote.authenticate=false \
// -Dcom.sun.management.jmxremote.ssl=false \
// </value>
// </property>
//
String javaOpts = getChildJavaOpts(conf, task.isMapTask());
javaOpts = javaOpts.replace("@taskid@", attemptID.toString());
String [] javaOptsSplit = javaOpts.split(" ");
for (int i = 0; i < javaOptsSplit.length; i++) {
vargs.add(javaOptsSplit[i]);
}
Path childTmpDir = new Path(MRApps.crossPlatformifyMREnv(conf, Environment.PWD),
YarnConfiguration.DEFAULT_CONTAINER_TEMP_DIR);
vargs.add("-Djava.io.tmpdir=" + childTmpDir);
MRApps.addLog4jSystemProperties(task, vargs, conf);
if (conf.getProfileEnabled()) {
if (conf.getProfileTaskRange(task.isMapTask()
).isIncluded(task.getPartition())) {
final String profileParams = conf.get(task.isMapTask()
? MRJobConfig.TASK_MAP_PROFILE_PARAMS
: MRJobConfig.TASK_REDUCE_PROFILE_PARAMS, conf.getProfileParams());
vargs.add(String.format(profileParams,
getTaskLogFile(TaskLog.LogName.PROFILE)));
}
}
//添加主类及其参数
vargs.add(YarnChild.class.getName()); // main of Child
//传递TaskAttemptListener的地址
vargs.add(taskAttemptListenerAddr.getAddress().getHostAddress());
vargs.add(Integer.toString(taskAttemptListenerAddr.getPort()));
vargs.add(attemptID.toString()); //传递任务标识符
//最后添加jvm ID
vargs.add(String.valueOf(jvmID.getId()));
vargs.add("1>" + getTaskLogFile(TaskLog.LogName.STDOUT));
vargs.add("2>" + getTaskLogFile(TaskLog.LogName.STDERR));
//最终命令
StringBuilder mergedCommand = new StringBuilder();
for (CharSequence str : vargs) {
mergedCommand.append(str).append(" ");
}
Vector<String> vargsFinal = new Vector<String>(1);
vargsFinal.add(mergedCommand.toString());
return vargsFinal;
}五、总结
1、MRAppMaster启动
2、初始化并启动job
3、处理各种job状态
4、启动Task
5、处理各种Task事件
6、启动尝试任务
7、处理各种尝试任务事件
8、在尝试任务的TaskAttemptEventType.TA_SCHEDULE事件处理时申请容器
9、调用java命令配置主类YarnChild启动容器运行MapTask或者ReduceTask