Spring3.2.11与Quartz2.2.1整合时内存泄漏的问题的解决

　　Quartz是一款定时任务调度的开源框架，使用起来比较方便。并且Spring的support包对Quartz有集成。但是笔者在web应用使用的过程中却遇到了内存泄漏的问题。

问题的产生

 笔者在使用Spring+Quartz的用法如下（熟悉Spring+Quartz的可以跳过直接看问题）：

1.配置Scheduler工厂

<bean id="schedulerFactory" class="org.springframework.scheduling.quartz.SchedulerFactoryBean">
</bean>

2.编写Job的实现类QuartzJob，用来执行任务

//这里须继承spring的QuartzJobBean
public class QuartzJob extends QuartzJobBean {/**
     * 任务执行内容。
     */
    @Override
    protected void executeInternal(JobExecutionContext context) throws JobExecutionException {
        // 执行任务的代码
    }
}

3.将Scheduler工厂生产的scheduler注入到业务逻辑类中。这里注意，注入的其实是由schedulerFactory生产出来的scheduler实例（对Spring不熟悉的人会自然而然的认为注入的是schedulerFactory的实例，这是因为Spring的SchedulerFactoryBean实现了FactoryBean接口，所以注入的结果会是FactoryBean.getObject()获得的实例，题外话）。

  <bean id="taskService" class="com.xxxx.xx.service.impl.TaskServiceImpl" init-method="init" scope="singleton">
    <property name="scheduler">
      <ref bean="schedulerFactory"/>
    </property>
  </bean>

public class TaskServiceImpl {
    private Scheduler scheduler;/**
     * 由spring通过工厂注入，此实例为单例。
     * @param scheduler
     */
    public void setScheduler(Scheduler scheduler) {
        this.scheduler = scheduler;
    }

4.在业务逻辑类TaskServiceImpl中，使用scheduler执行任务。这里可以动态对任务执行增加、删除、重启等等操作。还有一个重要的特性是可以动态的改变Cron表达式，对任务的定时规则进行更改。

    /**
     * 新增任务。
     * @param jobName
     * @param jobGroup
     * @param cron
     */
    public void addJob(String jobName, String jobGroup, String cron, String kindId) {
        try {
            if (StringUtil.isEmpty(jobName) || StringUtil.isEmpty(jobGroup) || StringUtil.isEmpty(cron)) {
                throw new BusinessException("定时任务创建失败，参数为空");
            }
            JobDetail jobDetail = JobBuilder.newJob(QuartzJob.class).withIdentity(jobName, jobGroup).build();
            jobDetail.getJobDataMap().put("JobKind", kindId);
            //表达式调度构建器
            CronScheduleBuilder scheduleBuilder = CronScheduleBuilder.cronSchedule(cron);
            //按新的cronExpression表达式构建一个新的trigger
            CronTrigger trigger = TriggerBuilder.newTrigger().withIdentity(jobName, jobGroup).withSchedule(scheduleBuilder).build();
            scheduler.scheduleJob(jobDetail, trigger);
            log.info("新增定时任务，name:" + jobName + ",group:" + jobGroup + ",cron:" + cron);
        } catch (SchedulerException e) {
            // 对异常的处理
        }
    }

注意18行的scheduler是由Spring注入的。

这种用法在使用过程中没有问题，但在web应用在Tomcat6中热部署时出险了以下严重警告，如果忽略这种警告，在频繁的reload后会造成Tomcat 的 Permgen space OOM。

Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [/feeder##1.5.0] appears to have started a thread named [scheduler_Worker-1] but has failed to stop it. This is very likely to create a memory leak.
Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [/feeder##1.5.0] appears to have started a thread named [scheduler_Worker-2] but has failed to stop it. This is very likely to create a memory leak.
Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [/feeder##1.5.0] appears to have started a thread named [scheduler_Worker-3] but has failed to stop it. This is very likely to create a memory leak.
Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [/feeder##1.5.0] appears to have started a thread named [scheduler_Worker-4] but has failed to stop it. This is very likely to create a memory leak.
Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [/feeder##1.5.0] appears to have started a thread named [scheduler_Worker-5] but has failed to stop it. This is very likely to create a memory leak.
Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads
SEVERE: The web application [/feeder##1.5.0] appears to have started a thread named [scheduler_Worker-6] but has failed to stop it. This is very likely to create a memory leak.
Jun 24, 2014 5:14:38 AM org.apache.catalina.loader.WebappClassLoader clearReferencesThreads

问题的原因

究其原因是开启的scheduler_Worker线程没有关闭。但Spring的SchedulerFactoryBean实现了DisposableBean接口，表示web容器关闭时会执行destroy()，执行内容如下：

    /**
     * Shut down the Quartz scheduler on bean factory shutdown,
     * stopping all scheduled jobs.
     */
    public void destroy() throws SchedulerException {
        logger.info("Shutting down Quartz Scheduler");
        this.scheduler.shutdown(this.waitForJobsToCompleteOnShutdown);
    }

表示工厂已经做了shutdown。所以，问题出现在真正执行的scheduler.shutdown(true)。

原来这是Quartz的bug(见https://jira.terracotta.org/jira/browse/QTZ-192)，在调用scheduler.shutdown(true)后，Quartz检查线程并没有等待那些worker线程被停止就结束了。

网上说在Quartz2.1版本已经修补了这个bug，但笔者使用的2.2.1版本仍旧有问题。

问题的解决

那么问题如何解决，这里有一个不太美观的方案：在调用scheduler.shutdown(true)后，增加一点睡眠时间，等待worker线程全部停止。如下：

1。自定义schedulerFactory继承Spring的SchedulerFactoryBean，覆盖destroy()增加延时。

public class SchedulerFactoryBeanWithShutdownDelay extends SchedulerFactoryBean {

    /**
     * 关于Quartz内存泄漏的不太美观的解决方案：
     * 在调用scheduler.shutdown(true)后增加延时，等待worker线程结束。
     */
    @Override
    public void destroy() throws SchedulerException {
        super.destroy();
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }
}

2。把spring配置文件中的SchedulerFactoryBean替换为自定义的工厂即可。

<bean id="schedulerFactory" class="com.sinosoft.ms.task.SchedulerFactoryBeanWithShutdownDelay">
</bean>

 OK，问题解决。