SpringBoot【注解 01】@Scheduled实现定时任务的串行和并行执行

在SpringBoot中，如果使用@Scheduled注解来定义多个定时任务，默认情况下这些任务将会被安排在一个单线程的调度器中执行。这意味着，这些任务将会串行执行，而不是并行执行。当一个任务正在执行时，其他被触发的任务将会等待当前任务完成后再开始执行，这可能导致任务执行上的阻塞，特别是当某个任务执行时间较长时，可能会延迟后续任务的启动时间，影响定时任务的准时性。

@Scheduled

• 1.问题代码及测试结果
• 2.定时任务实现并行
• • 2.1 使用自定义线程池（添加类）
  • 2.2 使用异步处理（添加类和注解）
  • 3.总结

    1.问题代码及测试结果

    问题代码：

        @Scheduled(cron = "*/1 * * * * *")    public void a() throws InterruptedException {        log.info("A Start {}!", System.currentTimeMillis());        Thread.sleep(2000);        log.info("A End {}!", System.currentTimeMillis());    }    @Scheduled(cron = "*/1 * * * * *")    public void b() {        log.info("B Start {}!", System.currentTimeMillis());        log.info("B End {}!", System.currentTimeMillis());    }

    部分测试结果：

    15:38:29.001 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716968309001!15:38:29.001 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716968309001!15:38:29.001 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716968309001!15:38:31.003 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716968311003!15:38:31.003 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716968311003!15:38:31.003 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716968311003!15:38:32.002 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716968312002!15:38:34.003 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716968314003!15:38:34.003 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716968314003!15:38:34.003 [scheduling-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716968314003!

    结果分析：

    • A和B是串行的。

      2.定时任务实现并行

      2.1 使用自定义线程池（添加类）

      可以通过配置一个自定义的TaskScheduler或者ThreadPoolTaskScheduler来为@Scheduled任务提供一个线程池，从而允许多个任务并行执行。例如，可以在配置类中定义一个ThreadPoolTaskScheduler Bean：

      @Configurationpublic class AsyncConfig {    @Bean    public ThreadPoolTaskScheduler taskScheduler() {        ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();        // 设置线程池大小        scheduler.setPoolSize(10);         scheduler.setThreadNamePrefix("my-scheduled-task-");        return scheduler;    }}

      并确保你的配置类被扫描到，且在@EnableScheduling注解的上下文中。

      测试代码：

          @Scheduled(cron = "*/1 * * * * *")    public void a() throws InterruptedException {        log.info("A Start {}!", System.currentTimeMillis());        Thread.sleep(2000);        log.info("A End {}!", System.currentTimeMillis());    }    @Scheduled(cron = "*/1 * * * * *")    public void b() {        log.info("B Start {}!", System.currentTimeMillis());        log.info("B End {}!", System.currentTimeMillis());    }

      部分测试结果：

      15:16:18.003 [my-scheduled-task-2] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716966978003!15:16:18.003 [my-scheduled-task-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716966978003!15:16:18.003 [my-scheduled-task-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716966978003!15:16:19.002 [my-scheduled-task-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716966979002!15:16:19.002 [my-scheduled-task-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716966979002!15:16:20.004 [my-scheduled-task-2] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716966980004!15:16:20.004 [my-scheduled-task-3] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716966980004!15:16:20.004 [my-scheduled-task-3] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716966980004!15:16:21.003 [my-scheduled-task-1] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716966981003!15:16:21.003 [my-scheduled-task-4] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716966981003!15:16:21.003 [my-scheduled-task-4] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716966981003!15:16:22.001 [my-scheduled-task-2] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716966982001!15:16:22.001 [my-scheduled-task-2] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716966982001!15:16:23.004 [my-scheduled-task-1] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716966983004!15:16:23.004 [my-scheduled-task-3] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716966983004!15:16:23.004 [my-scheduled-task-3] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716966983004!

      结果分析：

      • A和B是并行的；
      • A和A或者B和B是串行的。

        2.2 使用异步处理（添加类和注解）

        结合@Async注解和@EnableAsync可以使得每个@Scheduled任务在独立的线程中异步执行。

        首先需要在配置类中启用异步支持，并配置一个线程池，然后在每个定时任务方法上添加@Async注解。

        @EnableAsync@Configurationpublic class AsyncConfig {    @Bean    public Executor taskExecutor() {        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();        executor.setCorePoolSize(10);        executor.setMaxPoolSize(20);        executor.setQueueCapacity(200);        executor.setThreadNamePrefix("Async-");        executor.initialize();        return executor;    }}

        测试代码：

            @Async    @Scheduled(cron = "*/1 * * * * *")    public void a() throws InterruptedException {        log.info("A Start {}!", System.currentTimeMillis());        Thread.sleep(2000);        log.info("A End {}!", System.currentTimeMillis());    }    @Async    @Scheduled(cron = "*/1 * * * * *")    public void b() {        log.info("B Start {}!", System.currentTimeMillis());        log.info("B End {}!", System.currentTimeMillis());    }

        部分测试结果：

        15:26:52.008 [Async-2] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716967612008!15:26:52.008 [Async-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716967612008!15:26:52.009 [Async-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716967612009!15:26:53.002 [Async-4] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716967613002!15:26:53.002 [Async-3] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716967613002!15:26:53.002 [Async-3] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716967613002!15:26:54.001 [Async-6] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716967614001!15:26:54.001 [Async-5] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716967614001!15:26:54.001 [Async-5] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716967614001!15:26:54.010 [Async-2] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716967614010!15:26:55.002 [Async-8] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716967615002!15:26:55.002 [Async-7] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716967615002!15:26:55.002 [Async-7] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716967615002!15:26:55.002 [Async-4] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716967615002!15:26:56.001 [Async-10] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716967616001!15:26:56.001 [Async-9] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716967616001!15:26:56.001 [Async-9] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716967616001!15:26:56.002 [Async-6] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716967616002!15:26:57.001 [Async-3] INFO  c.x.e.m.SchedulerTask - [a,44] - A Start 1716967617001!15:26:57.001 [Async-1] INFO  c.x.e.m.SchedulerTask - [b,52] - B Start 1716967617001!15:26:57.001 [Async-1] INFO  c.x.e.m.SchedulerTask - [b,53] - B End 1716967617001!15:26:57.002 [Async-8] INFO  c.x.e.m.SchedulerTask - [a,46] - A End 1716967617002!

        测试结果分析：

        • A和B是并行的；
        • A和A或者B和B也是并行的。

          3.总结

          如有错误，请小伙伴儿们不吝赐教。

          定时任务有不同的需求，使用串行还是并行要结合业务进行选择。