Quartz源码解析 ---- 触发器按时启动原理

1.不停的轮询(while)，直到收到停止任务的要求
2.算出下次触发的时间，比如是 09:10:00 ，减去当前时间 09:00:00 ，也就是还有10分钟才会触发下次任务。那就wait  10分钟
p.s. 最近刚好在看quartz的源码，还是比较容易看懂，建议你也好好看看

QuartzSchedulerThread.class

 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;//下次触发时间-当前时间
                                        if(timeUntilTrigger >= 1)
                                            sigLock.wait(timeUntilTrigger);//这里是关键，等待时间为  下次触发时间-当前时间
                                    } catch (InterruptedException ignore) {
                                    }
                                }
                            }
                            if(releaseIfScheduleChangedSignificantly(triggers, triggerTime)) {
                                break;
                            }
                            now = System.currentTimeMillis();
                            timeUntilTrigger = triggerTime - now;
                        }

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

[java]  view plain  copy

 print ?

1. @Override  
2.     public void run() {  
3.         boolean lastAcquireFailed = false;  
4.   
5.         while (!halted.get()) {  
6.             try {  
7.                 // check if we're supposed to pause...  
8.                 synchronized (sigLock) {  
9.                     while (paused && !halted.get()) {  
10.                         try {  
11.                             // wait until togglePause(false) is called...  
12.                             sigLock.wait(1000L);  
13.                         } catch (InterruptedException ignore) {  
14.                         }  
15.                     }  
16.   
17.                     if (halted.get()) {  
18.                         break;  
19.                     }  
20.                 }  
21.   
22.                 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)

[java]  view plain  copy

 print ?

1. synchronized(sigLock) {  
2.            signaled = true;  
3.            signaledNextFireTime = candidateNewNextFireTime;  
4.            sigLock.notifyAll();  
5.        }  

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

[html]  view plain  copy

 print ?

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

  

接上面run方法代码:

[java]  view plain  copy

 print ?

1. if(availThreadCount > 0) { // will always be true, due to semantics of blockForAvailableThreads...  
2.   
3.                     List<OperableTrigger> triggers = null;  
4.   
5.                     long now = System.currentTimeMillis();  
6.   
7.                     clearSignaledSchedulingChange();  
8.                     try {  
9.                         // 查找30秒内一定数量的Trigger  
10.                         triggers = qsRsrcs.getJobStore().acquireNextTriggers(  
11.                                 now + idleWaitTime, Math.min(availThreadCount, qsRsrcs.getMaxBatchSize()), qsRsrcs.getBatchTimeWindow());  
12.                         lastAcquireFailed = false;  
13.                         ...  
14.                     }   
15.                         ...  
16.                           
17.                     if (triggers != null && !triggers.isEmpty()) {  
18.   
19.                         now = System.currentTimeMillis();  
20.                         long triggerTime = triggers.get(0).getNextFireTime().getTime();  
21.                         long timeUntilTrigger = triggerTime - now;  
22.                         while(timeUntilTrigger > 2) {  
23.                             synchronized (sigLock) {  
24.                                 if (halted.get()) {  
25.                                     break;  
26.                                 }  
27.                                 if (!isCandidateNewTimeEarlierWithinReason(triggerTime, false)) {  
28.                                     try {  
29.                                         // we could have blocked a long while  
30.                                         // on 'synchronize', so we must recompute  
31.                                         now = System.currentTimeMillis();  
32.                                         timeUntilTrigger = triggerTime - now;  
33.                                         if(timeUntilTrigger >= 1)  
34.                                             sigLock.wait(timeUntilTrigger);  
35.                                     } catch (InterruptedException ignore) {  
36.                                     }  
37.                                 }  
38.                             ...  
39.                         }  
40.   
41.                         ...  
42.   
43.                         boolean goAhead = true;  
44.                         synchronized(sigLock) {  
45.                             goAhead = !halted.get();  
46.                         }  
47.                         if(goAhead) {  
48.                             try {  
49.                                 List<TriggerFiredResult> res = qsRsrcs.getJobStore().triggersFired(triggers);  
50.                                 if(res != null)  
51.                                     bndles = res;  
52.                             }   
53.                             ...  
54.   
55.                         }  
56.   
57.                         for (int i = 0; i < bndles.size(); i++) {                             
58.                             ...  
59.                             
60.                             if (bndle == null) {  
61.                                 qsRsrcs.getJobStore().releaseAcquiredTrigger(triggers.get(i));  
62.                                 continue;  
63.                             }  

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】