spring quartz使用多线程并发“陷阱”

定义一个job：ranJob，设置每秒执行一次，设置不允许覆盖并发执行

<bean id="rankJob" class="com.chinacache.www.logstat.job.RankJob" />
<bean id="rankJobDetail"
    class="org.springframework.scheduling.quartz.MethodInvokingJobDetailFactoryBean">
    <property name="targetObject" ref="rankJob" />
    <property name="targetMethod" value="execute" />
    <property name="concurrent" value="<span style="color: #ff0000;"><strong>false</strong></span>" />
</bean>
<bean id="rankJobTrigger" class="org.springframework.scheduling.quartz.SimpleTriggerBean">
    <property name="jobDetail" ref="rankJobDetail" />
    <!-- 单位 ms，半小时 1800000 ms -->
    <property name="repeatInterval" value="<span style="color: #ff0000;"><strong>1000</strong></span>" />
</bean>

job代码：

System.out.println("Start job");
ExecutorService exec = Executors.newFixedThreadPool(1);

Thread thread = new Thread(new Runnable() {
    @Override
    public void run() {
        System.out.println("thread start");
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("thread end");
    }
});
exec.execute(thread);
System.out.println("end job");

程序输出结果：

Start job
end job
<span style="color: #ff0000;"><strong>thread start</strong></span>
Start job
end job
thread start
Start job
end job
thread start
Start job
end job
thread start
<strong><span style="color: #ff0000;">thread end</span></strong>

从结果可以看到，job的并发覆盖配置似乎根本没有生效，原因是：job没有关注多线程执行情况

修改job代码，添加如下代码在job访问最后，线程处理完job才结束，

while (!exec.isTerminated()) {
    // 等待所有子线程结束，才退出主线程
}

修改代码后程序结果：

Start job
thread start
thread end

可以看到job始终没有结束，说明ExecutorService始终没有终止，看看文档，加入shutdonw()方法，job所有代码如下：

public void execute() throws InterruptedException {
    System.out.println("Start job");
    ExecutorService exec = Executors.newFixedThreadPool(1);

    Thread thread = new Thread(new Runnable() {
        @Override
        public void run() {
            System.out.println("thread start");
            try {
                Thread.sleep(3000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("thread end");
        }
    });
    exec.execute(thread);
    exec.shutdown();
       while (!exec.isTerminated()) {
           // 等待所有子线程结束，才退出主线程
       }
    System.out.println("end job");
}

打印结果如下：

Start job
thread start
thread end
end job

Start job
thread start
thread end
end job

Start job
thread start
thread end
end job

OK，至此spring quartz多线程并发问题解决。回顾下，我们要使用isTerminated()方法等多线程结束后在结束job；多线程任务派发结束后，要使用shutdown()方法顺序关闭线程（等待正在执行任务，不接受新任务）