Quartz源码解析 ---- 触发器按时启动原理

从线程开始, 我们来看下QuartzSchedulerThread类(负责执行触发的Trigger的工作) : 

@Override
    public void run() {
        boolean lastAcquireFailed = false;

        while (!halted.get()) {
            try {
                // check if we're supposed to pause...
                synchronized (sigLock) {
                    while (paused && !halted.get()) {
                        try {
                            // wait until togglePause(false) is called...
                            sigLock.wait(1000L);
                        } catch (InterruptedException ignore) {
                        }
                    }

                    if (halted.get()) {
                        break;
                    }
                }

                int availThreadCount = qsRsrcs.getThreadPool().blockForAvailableThreads();

使用了AtomicBoolean类halted.get()检查触发器是否是暂停状态, 早期版本的Quartz用的还是Boolean, AtomicBoolean类只有在值稳定后才会更新, 保持操作原子性。 从上面代码可以看出, 只要是触发器停止状态或者等待状态, Thread就会一直wait。sigLock同步对象用来随时唤醒将被触发的Trigger(使用notifyAll来进行对wait中线程的唤醒, 如下源码)

 synchronized(sigLock) {
            signaled = true;
            signaledNextFireTime = candidateNewNextFireTime;
            sigLock.notifyAll();
        }

qsRsrcs.getThreadPool().blockForAvailableThreads() // 获取线程池现在可以用线程数

跟Spring集成的配置(建议一般使用10~50个线程): 下面一行代码配置了最大线程数

<prop key="org.quartz.threadPool.threadCount">40</prop>

  


接上面run方法代码:

if(availThreadCount > 0) { // will always be true, due to semantics of blockForAvailableThreads...

                    List<OperableTrigger> triggers = null;

                    long now = System.currentTimeMillis();

                    clearSignaledSchedulingChange();
                    try {
					    // 查找30秒内一定数量的Trigger
                        triggers = qsRsrcs.getJobStore().acquireNextTriggers(
                                now + idleWaitTime, Math.min(availThreadCount, qsRsrcs.getMaxBatchSize()), qsRsrcs.getBatchTimeWindow());
                        lastAcquireFailed = false;
                        ...
                    } 
                        ...
						
                    if (triggers != null && !triggers.isEmpty()) {

                        now = System.currentTimeMillis();
                        long triggerTime = triggers.get(0).getNextFireTime().getTime();
                        long timeUntilTrigger = triggerTime - now;
                        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) {
                                    }
                                }
                            ...
                        }

                        ...

                        boolean goAhead = true;
                        synchronized(sigLock) {
                            goAhead = !halted.get();
                        }
                        if(goAhead) {
                            try {
                                List<TriggerFiredResult> res = qsRsrcs.getJobStore().triggersFired(triggers);
                                if(res != null)
                                    bndles = res;
                            } 
                            ...

                        }

                        for (int i = 0; i < bndles.size(); i++) {                           
                            ...
                          
                            if (bndle == null) {
                                qsRsrcs.getJobStore().releaseAcquiredTrigger(triggers.get(i));
                                continue;
                            }

availThreadCount必然大于0, 因为肯定至少得有一个线程来处理Trigger。

以上代码基本上做的就是以下轮询(服务器启动后不断地执行run方法): 

qsRsrcs.getJobStore().acquireNextTriggers【查找即将触发的Trigger】 ----> 

sigLock.wait(timeUntilTrigger)【等待执行】 ----> 

qsRsrcs.getJobStore().triggersFired(triggers)【执行】----> 

qsRsrcs.getJobStore().releaseAcquiredTrigger(triggers.get(i)) 【释放Trigger】






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转载自blog.csdn.net/wenniuwuren/article/details/42082981