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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();
else
updateTimer = 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。
@Override
public 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 recompute
now = 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Trigger
if(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 again
for (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 soon
if (!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;
}