Quartz的线程池解析

【org.quartz.core相关类图】

可以看到核心类为QuartzScheduler

【QuartzScheduler构造函数】

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);

    if(shouldRunUpdateCheck())
        updateTimer = scheduleUpdateCheck();
    else
        updateTimer = null;

    getLog().info("Quartz Scheduler v." + getVersion() + " created.");
}

这里创建了一个QuartzSchedulerThread并在ThreadExecutor（默认DefaultThreadExecutor ）中运行。这里的ThreadExecutor并非我们关心的，继续看QuartzSchedulerThread的run方法。

【QuartzSchedulerThread#run()】

run方法比较长，大意就是根据Trigger找出要运行的job然后在线程池中执行。下面是run方法的代码片段：

JobRunShell shell = null;
try {
    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...
    getLog().error("ThreadPool.runInThread() return false!");
    qsRsrcs.getJobStore().triggeredJobComplete(triggers.get(i), bndle.getJobDetail(), CompletedExecutionInstruction.SET_ALL_JOB_TRIGGERS_ERROR);
}

这里的ThreadPool必须实现org.quartz.spi.ThreadPool接口。

【ThreadPool实现类】

ThreadPool的默认实现类是org.quartz.simpl.SimpleThreadPool。

String tpClass = cfg.getStringProperty(PROP_THREAD_POOL_CLASS, SimpleThreadPool.class.getName());

（from org.quartz.impl.StdSchedulerFactory#instantiate()）

这个线程池非常简单，都没有BlockingQueue：

private LinkedList<WorkerThread> availWorkers = new LinkedList<WorkerThread>(); // SimpleThreadPool成员
private LinkedList<WorkerThread> busyWorkers = new LinkedList<WorkerThread>(); // SimpleThreadPool成员

如果与Spring集成，使用org.springframework.scheduling.quartz.SchedulerFactoryBean且配置了taskExecutor（java.util.concurrent.Executor的实现类），则会使用org.springframework.scheduling.quartz.LocalTaskExecutorThreadPool。

if (this.taskExecutor != null) {
    mergedProps.setProperty(StdSchedulerFactory.PROP_THREAD_POOL_CLASS,
            LocalTaskExecutorThreadPool.class.getName());
}

（from org.springframework.scheduling.quartz.SchedulerFactoryBean#initSchedulerFactory）

也可以自定义实现类，并为quartzProperties配置org.quartz.threadPool.class参数。