上一篇博客Quartz任务调度框架--简介与示例（一）中我们已经简介和示例代码对quartz有了初步的认识，这篇博客我们通过追踪quartz的定时任务执行流程来加深对quartz的了解。

1、运行活动线程

（1）Quartz_Worker-*线程是quartz的线程池初始化的线程数目，在配置文件中可以进行配置

（2）Timer-0是Timer定时任务，作用不是很大，主要是保活

（3）Quartz_QuartzSchedulerThread线程，quartz中最重要的线程，此线程用来计算定时任务，将定时任务提交到线程池进行执行等操作。

2、流程解析

在Quartz初始化时需要创建调度器工厂，并根据调度器工厂获取调度器

//1.创建Scheduler的工厂
SchedulerFactory sf = new StdSchedulerFactory();
//2.从工厂中获取调度器实例
Scheduler scheduler = sf.getScheduler();

在初始化调度器Scheduler时会初始化QuartzSchedulerThread线程，在scheduler调用start方法时会启动QuartzSchedulerThread线程。

 public QuartzScheduler(QuartzSchedulerResources resources, long idleWaitTime, @Deprecated long dbRetryInterval)throws SchedulerException {this.resources = resources;if (resources.getJobStore() instanceof JobListener) {addInternalJobListener((JobListener)resources.getJobStore());}//初始化QuartzSchedulerThread线程this.schedThread = new QuartzSchedulerThread(this, resources);ThreadExecutor schedThreadExecutor = resources.getThreadExecutor();schedThreadExecutor.execute(this.schedThread);if (idleWaitTime > 0) {this.schedThread.setIdleWaitTime(idleWaitTime);}jobMgr = new ExecutingJobsManager();addInternalJobListener(jobMgr);errLogger = new ErrorLogger();addInternalSchedulerListener(errLogger);signaler = new SchedulerSignalerImpl(this, this.schedThread);if(shouldRunUpdateCheck()) updateTimer = scheduleUpdateCheck();elseupdateTimer = null;getLog().info("Quartz Scheduler v." + getVersion() + " created.");}

在线程QuartzSchedulerThread的run方法中做了如下处理操作

（1）线程是永久运行的，当quartz暂停时，线程会阻塞一段时间

（2）在执行定时之前首先会检查线程池中可执行线程数，当可执行线程数小于0时不执行定时任务

（3）从数据库或缓存中获取某一段时间内（30秒）要执行的任务

（4）根据任务处理器获取要执行的任务

（5）将任务创建JobRunShell，并初始化Job接口的实现类

（6）将JobRunShell添加到线程池中去运行

（7）当线程任务是持久化到数据库中时，这中间包含了一些数据库事物及锁相关的处理操作，完成集群及分布式相关的处理操作。

    @Overridepublic void run() {boolean lastAcquireFailed = false;while (!halted.get()) {try {// check if we're supposed to pause...//检查我们是否应该暂停...synchronized (sigLock) {while (paused && !halted.get()) {try {// wait until togglePause(false) is called...//等待直到togglePause（false）被调用...  sigLock.wait(1000L);} catch (InterruptedException ignore) {}}if (halted.get()) {break;}}//2.1获取可用线程的数量int availThreadCount = qsRsrcs.getThreadPool().blockForAvailableThreads();//将永远是true，由于blockForAvailableThreads的语义...if(availThreadCount > 0) { // will always be true, due to semantics of blockForAvailableThreads...List<OperableTrigger> triggers = null;//定义触发器集合long now = System.currentTimeMillis();//获取当前的时间clearSignaledSchedulingChange();try {//2.2 从jobStore中获取下次要触发的触发器集合//idleWaitTime == 30L * 1000L; 当调度程序发现没有当前触发器要触发，它应该等待多长时间再检查...triggers = qsRsrcs.getJobStore().acquireNextTriggers(now + idleWaitTime, Math.min(availThreadCount, qsRsrcs.getMaxBatchSize()), qsRsrcs.getBatchTimeWindow());lastAcquireFailed = false;if (log.isDebugEnabled()) log.debug("batch acquisition of " + (triggers == null ? 0 : triggers.size()) + " triggers");} catch (JobPersistenceException jpe) {if(!lastAcquireFailed) {qs.notifySchedulerListenersError("An error occurred while scanning for the next triggers to fire.",jpe);}lastAcquireFailed = true;continue;} catch (RuntimeException e) {if(!lastAcquireFailed) {getLog().error("quartzSchedulerThreadLoop: RuntimeException "+e.getMessage(), e);}lastAcquireFailed = true;continue;}//判断返回的触发器存在if (triggers != null && !triggers.isEmpty()) {now = System.currentTimeMillis();long triggerTime = triggers.get(0).getNextFireTime().getTime();//若有没有触发的Trigger，下次触发时间 next_fire_time 这个会在启动的时候有个默认的misfire机制，如上一篇中分析的 。setNextFireTime(); 即start（）启动时候的当前时间。long timeUntilTrigger = triggerTime - now;while(timeUntilTrigger > 2) {//这里为什么是2 ？？？不懂？？？synchronized (sigLock) {if (halted.get()) {break;}if (!isCandidateNewTimeEarlierWithinReason(triggerTime, false)) {try {// we could have blocked a long while// on 'synchronize', so we must recomputenow = System.currentTimeMillis();timeUntilTrigger = triggerTime - now;if(timeUntilTrigger >= 1)sigLock.wait(timeUntilTrigger);} catch (InterruptedException ignore) {}}}if(releaseIfScheduleChangedSignificantly(triggers, triggerTime)) {break;}now = System.currentTimeMillis();timeUntilTrigger = triggerTime - now;}// this happens if releaseIfScheduleChangedSignificantly decided to release triggers//这种情况发生，如果releaseIfScheduleChangedSignificantly 决定 释放Triggerif(triggers.isEmpty())continue;// set triggers to 'executing'//将触发器设置为“正在执行”List<TriggerFiredResult> bndles = new ArrayList<TriggerFiredResult>();boolean goAhead = true;synchronized(sigLock) {goAhead = !halted.get();}if(goAhead) {try {//2.3 通知JobStore调度程序现在正在触发其先前已获取（保留）的给定触发器（执行其关联的作业）。List<TriggerFiredResult> res = qsRsrcs.getJobStore().triggersFired(triggers);if(res != null)bndles = res;  //下面的2.3方法返回的数据赋值到bndles} catch (SchedulerException se) {qs.notifySchedulerListenersError("An error occurred while firing triggers '"+ triggers + "'", se);//QTZ-179 : a problem occurred interacting with the triggers from the db//we release them and loop againfor (int i = 0; i < triggers.size(); i++) {qsRsrcs.getJobStore().releaseAcquiredTrigger(triggers.get(i));}continue;}}//循环List<TriggerFiredResult> bndles 集合，获取TriggerFiredResult和TriggerFiredBundle等 for (int i = 0; i < bndles.size(); i++) {TriggerFiredResult result =  bndles.get(i);TriggerFiredBundle bndle =  result.getTriggerFiredBundle();Exception exception = result.getException();if (exception instanceof RuntimeException) {getLog().error("RuntimeException while firing trigger " + triggers.get(i), exception);qsRsrcs.getJobStore().releaseAcquiredTrigger(triggers.get(i));continue;}// it's possible to get 'null' if the triggers was paused,// blocked, or other similar occurrences that prevent it being// fired at this time...  or if the scheduler was shutdown (halted)
//如果触发器被暂停，阻塞或其他类似的事件阻止它在这时被触发，或者如果调度器被关闭（暂停），则可以获得'null'if (bndle == null) {qsRsrcs.getJobStore().releaseAcquiredTrigger(triggers.get(i));continue;}JobRunShell shell = null;try {//创建 JobRunShell ，并初始化shell = qsRsrcs.getJobRunShellFactory().createJobRunShell(bndle);shell.initialize(qs);} catch (SchedulerException se) {qsRsrcs.getJobStore().triggeredJobComplete(triggers.get(i), bndle.getJobDetail(), CompletedExecutionInstruction.SET_ALL_JOB_TRIGGERS_ERROR);continue;}if (qsRsrcs.getThreadPool().runInThread(shell) == false) {// this case should never happen, as it is indicative of the// scheduler being shutdown or a bug in the thread pool or// a thread pool being used concurrently - which the docs// say not to do...
//这种情况不应该发生，因为它表示调度程序正在关闭或线程池或线程池中并发使用的错误 - 文档说不要这样做...getLog().error("ThreadPool.runInThread() return false!");qsRsrcs.getJobStore().triggeredJobComplete(triggers.get(i), bndle.getJobDetail(), CompletedExecutionInstruction.SET_ALL_JOB_TRIGGERS_ERROR);}}continue; // while (!halted)}} else { // if(availThreadCount > 0)// should never happen, if threadPool.blockForAvailableThreads() follows contract////应该永远不会发生，如果threadPool.blockForAvailableThreads（）遵循约定continue; // while (!halted)}long now = System.currentTimeMillis();long waitTime = now + getRandomizedIdleWaitTime();long timeUntilContinue = waitTime - now;//idleWaitTime  == 30L * 1000L;  idleWaitVariablness ==  7 * 1000;              //计算getRandomizedIdleWaitTime()的值 : idleWaitTime - random.nextInt(idleWaitVariablness);synchronized(sigLock) {try {if(!halted.get()) {// QTZ-336 A job might have been completed in the mean time and we might have// missed the scheduled changed signal by not waiting for the notify() yet// Check that before waiting for too long in case this very job needs to be// scheduled very soonif (!isScheduleChanged()) {sigLock.wait(timeUntilContinue);}}} catch (InterruptedException ignore) {}}} catch(RuntimeException re) {getLog().error("Runtime error occurred in main trigger firing loop.", re);}} // while (!halted)// drop references to scheduler stuff to aid garbage collection...//删除对调度程序内容的引用以帮助垃圾回收...qs = null;qsRsrcs = null;}

 

整个quartz对任务调度的时序大致如下:

 

 

 

引用：

https://www.jianshu.com/p/5625d595a49a