三）Yarn 状态机类
在 Yarn 中提供了一个工厂类 StateMachineFactory 来帮助定义状态机。如何使用，我们直接写个 demo。
二、案例 demo
在上一篇文章《Yarn 服务库和事件库》案例基础上进行扩展，增加状态机库的内容。如果还不了解服务库和事件库的同学，建议先学习下上一篇文章。案例已上传至 github，有帮助可以点个 ⭐️https://github.com/Simon-Ace/hadoop-yarn-study-demo/tree/master/state-demo
一）状态机实现状态机实现，可以直接嵌入到上篇文章中的 AsyncDispatcher使用。这里仅给出状态机JobStateMachine以及各种事件处理的代码。完整的代码项目执行，请到 github demo 中查看。
import com.shuofxz.event.JobEvent;import com.shuofxz.event.JobEventType;import org.apache.hadoop.yarn.event.EventHandler;import org.apache.hadoop.yarn.state.;import java.util.EnumSet;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReadWriteLock;import java.util.concurrent.locks.ReentrantReadWriteLock;/ 可参考 Yarn 中实现的状态机对象： ResourceManager 中的 RMAppImpl、RMApp- AttemptImpl、RMContainerImpl 和 RMNodeImpl， NodeManager 中 的 ApplicationImpl、 ContainerImpl 和 LocalizedResource， MRAppMaster 中的 JobImpl、TaskImpl 和 TaskAttemptImpl 等 /@SuppressWarnings({"rawtypes", "unchecked"})public class JobStateMachine implements EventHandler<JobEvent> { private final String jobID; private EventHandler eventHandler; private final Lock writeLock; private final Lock readLock; // 定义状态机 protected static final StateMachineFactory<JobStateMachine, JobStateInternal, JobEventType, JobEvent> stateMachineFactory = new StateMachineFactory<JobStateMachine, JobStateInternal, JobEventType, JobEvent>(JobStateInternal.NEW) .addTransition(JobStateInternal.NEW, JobStateInternal.INITED, JobEventType.JOB_INIT, new InitTransition()) .addTransition(JobStateInternal.INITED, JobStateInternal.SETUP, JobEventType.JOB_START, new StartTransition()) .addTransition(JobStateInternal.SETUP, JobStateInternal.RUNNING, JobEventType.JOB_SETUP_COMPLETED, new SetupCompletedTransition()) .addTransition(JobStateInternal.RUNNING, EnumSet.of(JobStateInternal.KILLED, JobStateInternal.SUCCEEDED), JobEventType.JOB_COMPLETED, new JobTasksCompletedTransition()) .installTopology(); private final StateMachine<JobStateInternal, JobEventType, JobEvent> stateMachine; public JobStateMachine(String jobID, EventHandler eventHandler) { this.jobID = jobID; // 多线程异步处理，state 有可能被同时读写，使用读写锁来避免竞争 ReadWriteLock readWriteLock = new ReentrantReadWriteLock(); this.readLock = readWriteLock.readLock(); this.writeLock = readWriteLock.writeLock(); this.eventHandler = eventHandler; stateMachine = stateMachineFactory.make(this); } protected StateMachine<JobStateInternal, JobEventType, JobEvent> getStateMachine() { return stateMachine; } public static class InitTransition implements SingleArcTransition<JobStateMachine, JobEvent> { @Override public void transition(JobStateMachine jobStateMachine, JobEvent jobEvent) { System.out.println("Receiving event " + jobEvent); // do something... // 完成后发送新的 Event —— JOB_START jobStateMachine.eventHandler.handle(new JobEvent(jobStateMachine.jobID, JobEventType.JOB_START)); } } public static class StartTransition implements SingleArcTransition<JobStateMachine, JobEvent> { @Override public void transition(JobStateMachine jobStateMachine, JobEvent jobEvent) { System.out.println("Receiving event " + jobEvent); jobStateMachine.eventHandler.handle(new JobEvent(jobStateMachine.jobID, JobEventType.JOB_SETUP_COMPLETED)); } } public static class SetupCompletedTransition implements SingleArcTransition<JobStateMachine, JobEvent> { @Override public void transition(JobStateMachine jobStateMachine, JobEvent jobEvent) { System.out.println("Receiving event " + jobEvent); jobStateMachine.eventHandler.handle(new JobEvent(jobStateMachine.jobID, JobEventType.JOB_COMPLETED)); } } public static class JobTasksCompletedTransition implements MultipleArcTransition<JobStateMachine, JobEvent, JobStateInternal> { @Override public JobStateInternal transition(JobStateMachine jobStateMachine, JobEvent jobEvent) { System.out.println("Receiving event " + jobEvent); // 这是多结果状态部分，因此需要人为制定后续状态 // 这里整个流程结束，设置一下对应的状态 boolean flag = true; if (flag) { return JobStateInternal.SUCCEEDED; } else { return JobStateInternal.KILLED; } } } @Override public void handle(JobEvent jobEvent) { try { // 注意这里为了避免静态条件，使用了读写锁 writeLock.lock(); JobStateInternal oldState = getInternalState(); try { getStateMachine().doTransition(jobEvent.getType(), jobEvent); } catch (InvalidStateTransitionException e) { System.out.println("Can't handle this event at current state!"); } if (oldState != getInternalState()) { System.out.println("Job Transitioned from " + oldState + " to " + getInternalState()); } } finally { writeLock.unlock(); } } public JobStateInternal getInternalState() { readLock.lock(); try { return getStateMachine().getCurrentState(); } finally { readLock.unlock(); } } public enum JobStateInternal { NEW, SETUP, INITED, RUNNING, SUCCEEDED, KILLED }}二）状态机可视化
hadoop 中提供了状态机可视化的工具类 VisualizeStateMachine.java，可以拷贝到我们的工程中使用。根据提示，运行需要三个参数：
Usage: %s <GraphName> <class[,class[,...]]> <OutputFile>%n
运行后会在项目根目录生成图文件 jsm.gv。需要使用 graphviz工具将 gv 文件转换成 png 文件：
# linux 安装yum install graphviz# mac 安装brew install graphviz
转换：
dot -Tpng jsm.gv > jsm.png三）如果不用状态机库
【思考】如果不用状态机，代码结构会是什么样呢？下面这样的代码，如果要增加或修改逻辑可能就是很痛苦的一件事情了。
// 一堆的函数调用// 一堆的 if 嵌套// 或者 switch case三、总结
本节对 Yarn 状态机库进行了介绍。实际使用时会结合事件库、服务库一同使用。状态机库的使用帮助代码结构更加的清晰，新增状态处理逻辑只需要增加一个状态类别，或者增加一个方法处理对应类型的事件即可。将整个处理逻辑进行了拆分，便于编写和维护。
