本章阅读收获:可了解Quartz框架中的正式开始运行部分源码
继上节内容
在上一节内容中，我们讲到了schedule调取器的start的方法，但是对于具体job是如何运行的，我们还没有揭开它神秘的面纱，下面跟着我一步步来。
回忆杀
不知大家是否还记得，领略Quartz源码架构之美——源码实弹之Scheduler(五)中讲到的
qs = new QuartzScheduler(rsrcs, idleWaitTime, dbFailureRetry);
这行代码是否大家还记得。
我们深入进去给大家继续看下
/**
* 初始化QuartzScheduler类
*/
public QuartzScheduler(QuartzSchedulerResources resources, long idleWaitTime, @Deprecated long dbRetryInterval)
throws SchedulerException {
this.resources = resources;
if (resources.getJobStore() instanceof JobListener) {
addInternalJobListener((JobListener)resources.getJobStore());
}
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);
getLog().info("Quartz Scheduler v." + getVersion() + " created.");
}
划重点：
//创建调度线程
this.schedThread = new QuartzSchedulerThread(this, resources);
ThreadExecutor schedThreadExecutor = resources.getThreadExecutor();
schedThreadExecutor.execute(this.schedThread);
if (idleWaitTime > 0) {
this.schedThread.setIdleWaitTime(idleWaitTime);
}
这段代码在干嘛呢？
就是创建了调度线程，并且执行
public void execute(Thread thread) {
thread.start();
}
schedThreadExecutor.execute(this.schedThread);的调用其实就是去启动调度线程。那么接下来我们就要进行对QuartzSchedulerThread的run方法进行分析了。
QuartzSchedulerThread的run方法源码分析
先看下整块代码：
@Override
public void run() {
boolean lastAcquireFailed = false;
while (!halted.get()) {
try {
// check if we're supposed to pause...
synchronized (sigLock) {
//这里的paused对应QuartzScheduler的start方法中启动
while (paused && !halted.get()) {
try {
// wait until togglePause(false) is called...
sigLock.wait(1000L);
} catch (InterruptedException ignore) {
}
}
if (halted.get()) {
break;
}
}
//获取可用线程数 qsRsrcs是QuartzSchedulerResources对象
int availThreadCount = qsRsrcs.getThreadPool().blockForAvailableThreads();
if(availThreadCount > 0) { // will always be true, due to semantics of blockForAvailableThreads...
List<OperableTrigger> triggers = null;
long now = System.currentTimeMillis();
//清除调度改变的信号
clearSignaledSchedulingChange();
try {
//到JobStore中获取下次被触发的触发器
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;
}
if (triggers != null && !triggers.isEmpty()) {
now = System.currentTimeMillis();
//这里为什么triggers的第一个对象就是最早需要被执行的？
long triggerTime = triggers.get(0).getNextFireTime().getTime();
long timeUntilTrigger = triggerTime - now;
//如果第一条下次触发时间大于当前时间则进入等待
while(timeUntilTrigger > 2) {
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) {
}
}
}
//等待的过程中看看有没有收到调度信号
if(releaseIfScheduleChangedSignificantly(triggers, triggerTime)) {
break;
}
now = System.currentTimeMillis();
timeUntilTrigger = triggerTime - now;
}
// this happens if releaseIfScheduleChangedSignificantly decided to release triggers
if(triggers.isEmpty())
continue;
// set triggers to 'executing'
List<TriggerFiredResult> bndles = new ArrayList<TriggerFiredResult>();
boolean goAhead = true;
synchronized(sigLock) {
goAhead = !halted.get();
}
if(goAhead) {
try {
List<TriggerFiredResult> res = qsRsrcs.getJobStore().triggersFired(triggers);
if(res != null)
bndles = res;
} 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;
}
}
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)
if (bndle == null) {
qsRsrcs.getJobStore().releaseAcquiredTrigger(triggers.get(i));
continue;
}
// 下面是开始执行任务
JobRunShell shell = null;
try {
//构造执行对象，JobRunShell实现了Runnable
shell = qsRsrcs.getJobRunShellFactory().createJobRunShell(bndle);
//这个里面会用我们自定义的Job来new一个对象，并把相关执行Job是需要的数据传给JobExecutionContextImpl(这是我们自定义job的execute方法参数)
shell.initialize(qs);
} catch (SchedulerException se) {
qsRsrcs.getJobStore().triggeredJobComplete(triggers.get(i), bndle.getJobDetail(), CompletedExecutionInstruction.SET_ALL_JOB_TRIGGERS_ERROR);
continue;
}
// 这里是把任务放入到线程池中
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...
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
continue; // while (!halted)
}
long now = System.currentTimeMillis();
long waitTime = now + getRandomizedIdleWaitTime();
long timeUntilContinue = waitTime - now;
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...
qs = null;
qsRsrcs = null;
}
我们可以整体的话 我们是通过一个while循环来保证定时任务不断去运行的。这里就引发了一个我的一个好奇？是不是定时任务的话，基本都是通过while这种形式来实现的呢？因为在我脑海的各种假设中，只有无线循环能够满足。
下面我们就开始进行逐段分析：
// check if we're supposed to pause...
synchronized (sigLock) {
//这里的paused对应QuartzScheduler的start方法中启动
while (paused && !halted.get()) {
try {
// wait until togglePause(false) is called...
sigLock.wait(1000L);
} catch (InterruptedException ignore) {
}
}
if (halted.get()) {
break;
}
}
这块代码可能乍一看很简单，也很容易懂，就是一个while循环，满足条件就等待。但是放在于整个框架中，就有一些微妙了，这种的paused变量会在QuartzScheduler的start方法中启动设置为false，在上一节中我其实也贴出来代码过：
/**
* 调度器开始运行
*/
public void start() throws SchedulerException {
if (shuttingDown|| closed) {
throw new SchedulerException(
"The Scheduler cannot be restarted after shutdown() has been called.");
}
// 通知调度器监控器启动中
notifySchedulerListenersStarting();
if (initialStart == null) { //初始化标识为null，进行初始化操作
initialStart = new Date();
this.resources.getJobStore().schedulerStarted();
startPlugins();
} else {
resources.getJobStore().schedulerResumed();
}
schedThread.togglePause(false);//设置 不暂停
getLog().info(
"Scheduler " + resources.getUniqueIdentifier() + " started.");
//提醒调度器的监听启动
notifySchedulerListenersStarted();
}
中的 schedThread.togglePause(false);,所以只有人为的去掉用schedule.start的方法之后，定时任务才会正在的开始进行跑动。至于其中的paused和halted变量，则是在QuartzSchedulerThread构造方法中初始化的：
QuartzSchedulerThread(QuartzScheduler qs, QuartzSchedulerResources qsRsrcs, boolean setDaemon, int threadPrio) {
super(qs.getSchedulerThreadGroup(), qsRsrcs.getThreadName());
this.qs = qs;
this.qsRsrcs = qsRsrcs;
this.setDaemon(setDaemon);
if(qsRsrcs.isThreadsInheritInitializersClassLoadContext()) {
log.info("QuartzSchedulerThread Inheriting ContextClassLoader of thread: " + Thread.currentThread().getName());
this.setContextClassLoader(Thread.currentThread().getContextClassLoader());
}
this.setPriority(threadPrio);
// start the underlying thread, but put this object into the 'paused'
// state
// so processing doesn't start yet...
paused = true;
halted = new AtomicBoolean(false);
}
可以看到默认paused为true，halted为false。
结束语
本节内容揭开了Quartz的部门神秘面纱，知道他是如何去定时跑动任务的，之后我们会继续详细的跟进。
