Quartz是运用最广的任务调度框架，它最核心的组成部分是Scheduler、Trigger、JobDetail，然后给Scheduler配置个线程QuartzSchedulerThread，此线程在Scheduler初始化时启动，等待Scheduler start，然后从JobStore里拿到最近要触发的Trigger，以线程等待的方式等到trigger触发时间点，之后就是执行trigger所关联的JobDetail，最后清扫战场。Scheduler初始化、start和trigger执行的时序图如下所示：
其中，最核心的地方是QuartzSchedulerThread运行机制。下面解析一下它的run方法：
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public void run() {
boolean lastAcquireFailed = false;
while (!halted) {
try {
// check if we're supposed to pause...
synchronized (pauseLock) {
while (paused && !halted) {
try {
// wait until togglePause(false) is called...
pauseLock.wait(100L);
} catch (InterruptedException ignore) {
}
}
if (halted) {
break;
}
}
......
}
}
public void run() {
boolean lastAcquireFailed = false;
while (!halted) {
try {
// check if we're supposed to pause...
synchronized (pauseLock) {
while (paused && !halted) {
try {
// wait until togglePause(false) is called...
pauseLock.wait(100L);
} catch (InterruptedException ignore) {
}
}
if (halted) {
break;
}
}
......
}
}
以上是run的最开头的一段，不难看出这是在等待scheduler的start，实际上Quartz就是通过线程的wait或sleep来实现时间调度。继续看代码：
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Trigger trigger = null;
long now = System.currentTimeMillis();
signaled = false;
try {
trigger = qsRsrcs.getJobStore().acquireNextTrigger(
ctxt, now + idleWaitTime);
lastAcquireFailed = false;
} catch (JobPersistenceException jpe) {
if(!lastAcquireFailed) {
qs.notifySchedulerListenersError(
"An error occured while scanning for the next trigger to fire.",
jpe);
}
lastAcquireFailed = true;
} catch (RuntimeException e) {
if(!lastAcquireFailed) {
getLog().error("quartzSchedulerThreadLoop: RuntimeException "
+e.getMessage(), e);
}
lastAcquireFailed = true;
}
Trigger trigger = null;
long now = System.currentTimeMillis();
signaled = false;
try {
trigger = qsRsrcs.getJobStore().acquireNextTrigger(
ctxt, now + idleWaitTime);
lastAcquireFailed = false;
} catch (JobPersistenceException jpe) {
if(!lastAcquireFailed) {
qs.notifySchedulerListenersError(
"An error occured while scanning for the next trigger to fire.",
jpe);
}
lastAcquireFailed = true;
} catch (RuntimeException e) {
if(!lastAcquireFailed) {
getLog().error("quartzSchedulerThreadLoop: RuntimeException "
+e.getMessage(), e);
}
lastAcquireFailed = true;
}
这段代码是从jobStore里拿到下一个要执行的trigger，一般情况下jobStore使用的是RAMJobStore，即trigger等相关信息存放在内存里，如果需要把任务持久化就得使用可持久化JobStore。继续看代码：
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now = System.currentTimeMillis();
long triggerTime = trigger.getNextFireTime().getTime();
long timeUntilTrigger = triggerTime - now;
long spinInterval = 10;
int numPauses = (int) (timeUntilTrigger / spinInterval);
while (numPauses >= 0 && !signaled) {
try {
Thread.sleep(spinInterval);
} catch (InterruptedException ignore) {
}
now = System.currentTimeMillis();
timeUntilTrigger = triggerTime - now;
numPauses = (int) (timeUntilTrigger / spinInterval);
}
if (signaled) {
try {
qsRsrcs.getJobStore().releaseAcquiredTrigger(
ctxt, trigger);
} catch (JobPersistenceException jpe) {
qs.notifySchedulerListenersError(
"An error occured while releasing trigger '"
+ trigger.getFullName() + "'",
jpe);
// db connection must have failed... keep
// retrying until it's up...
releaseTriggerRetryLoop(trigger);
} catch (RuntimeException e) {
getLog().error(
"releaseTriggerRetryLoop: RuntimeException "
+e.getMessage(), e);
// db connection must have failed... keep
// retrying until it's up...
releaseTriggerRetryLoop(trigger);
}
signaled = false;
continue;
}
now = System.currentTimeMillis();
long triggerTime = trigger.getNextFireTime().getTime();
long timeUntilTrigger = triggerTime - now;
long spinInterval = 10;
int numPauses = (int) (timeUntilTrigger / spinInterval);
while (numPauses >= 0 && !signaled) {
try {
Thread.sleep(spinInterval);
} catch (InterruptedException ignore) {
}
now = System.currentTimeMillis();
timeUntilTrigger = triggerTime - now;
numPauses = (int) (timeUntilTrigger / spinInterval);
}
if (signaled) {
try {
qsRsrcs.getJobStore().releaseAcquiredTrigger(
ctxt, trigger);
} catch (JobPersistenceException jpe) {
qs.notifySchedulerListenersError(
"An error occured while releasing trigger '"
+ trigger.getFullName() + "'",
jpe);
// db connection must have failed... keep
// retrying until it's up...
releaseTriggerRetryLoop(trigger);
} catch (RuntimeException e) {
getLog().error(
"releaseTriggerRetryLoop: RuntimeException "
+e.getMessage(), e);
// db connection must have failed... keep
// retrying until it's up...
releaseTriggerRetryLoop(trigger);
}
signaled = false;
continue;
}
此段代码是计算下一个trigger的执行时间和现在系统时间的差，然后通过循环线程sleep的方式暂停住此线程，一直等到trigger的执行时间点。继续看代码：
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import org.quartz.core.JobRunShell;
JobRunShell shell = null;
try {
shell = qsRsrcs.getJobRunShellFactory().borrowJobRunShell();
shell.initialize(qs, bndle);
} catch (SchedulerException se) {
try {
qsRsrcs.getJobStore().triggeredJobComplete(ctxt,
trigger, bndle.getJobDetail(), Trigger.INSTRUCTION_SET_ALL_JOB_TRIGGERS_ERROR);
} catch (SchedulerException se2) {
qs.notifySchedulerListenersError(
"An error occured while placing job's triggers in error state '"
+ trigger.getFullName() + "'", se2);
// db connection must have failed... keep retrying
// until it's up...
errorTriggerRetryLoop(bndle);
}
continue;
}
if (qsRsrcs.getThreadPool().runInThread(shell) == false) {
try {
getLog().error("ThreadPool.runInThread() return false!");
qsRsrcs.getJobStore().triggeredJobComplete(ctxt,
trigger, bndle.getJobDetail(), Trigger.INSTRUCTION_SET_ALL_JOB_TRIGGERS_ERROR);
} catch (SchedulerException se2) {
qs.notifySchedulerListenersError(
"An error occured while placing job's triggers in error state '"
+ trigger.getFullName() + "'", se2);
// db connection must have failed... keep retrying
// until it's up...
releaseTriggerRetryLoop(trigger);
}
}
import org.quartz.core.JobRunShell;
JobRunShell shell = null;
try {
shell = qsRsrcs.getJobRunShellFactory().borrowJobRunShell();
shell.initialize(qs, bndle);
} catch (SchedulerException se) {
try {
qsRsrcs.getJobStore().triggeredJobComplete(ctxt,
trigger, bndle.getJobDetail(), Trigger.INSTRUCTION_SET_ALL_JOB_TRIGGERS_ERROR);
} catch (SchedulerException se2) {
qs.notifySchedulerListenersError(
"An error occured while placing job's triggers in error state '"
+ trigger.getFullName() + "'", se2);
// db connection must have failed... keep retrying
// until it's up...
errorTriggerRetryLoop(bndle);
}
continue;
}
if (qsRsrcs.getThreadPool().runInThread(shell) == false) {
try {
getLog().error("ThreadPool.runInThread() return false!");
qsRsrcs.getJobStore().triggeredJobComplete(ctxt,
trigger, bndle.getJobDetail(), Trigger.INSTRUCTION_SET_ALL_JOB_TRIGGERS_ERROR);
} catch (SchedulerException se2) {
qs.notifySchedulerListenersError(
"An error occured while placing job's triggers in error state '"
+ trigger.getFullName() + "'", se2);
// db connection must have failed... keep retrying
// until it's up...
releaseTriggerRetryLoop(trigger);
}
}
此段代码就是包装trigger，然后通过以JobRunShell为载体，在threadpool里执行trigger所关联的jobDetail。
之后的代码就是清扫战场，就不在累述。
本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/cutesource/archive/2009/12/08/4965520.aspx
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