What is the default scheduler pool size in spring-boot?

Question

I'm using spring-boot and @Scheduled annotation to execute some tasks.

How can I find out what the default pool size of scheduled tasks is by default in spring-boot?

Reason: the following class does not execute the jobs in parallel, but one after the other. Maybe only a single thread executor is configured by default?

@Service
public class ZipFileTesterAsync {

    @Scheduled(fixedDelay = 60000, initialDelay = 500)
    public void run() throws Exception {
        System.out.println("import 1");
        TimeUnit.MINUTES.sleep(1);
        System.out.println("import 1 finished");
    }

    @Scheduled(fixedDelay = 60000, initialDelay = 1000)
    public void run2() throws Exception {
        System.out.println("import 2");
        TimeUnit.MINUTES.sleep(1);
    }
}

Result: the 2nd job is executed after the first finished.

Answer 1

Yes, all @Scheduled methods share a single thread by default. It is possible to override this behavior by defining a @Configuration such as this:

@Configuration
public class SchedulingConfigurerConfiguration implements SchedulingConfigurer {

    @Override
    public void configureTasks(ScheduledTaskRegistrar taskRegistrar) {
        ThreadPoolTaskScheduler taskScheduler = new ThreadPoolTaskScheduler();
        taskScheduler.setPoolSize(100);
        taskScheduler.initialize();
        taskRegistrar.setTaskScheduler(taskScheduler);
    }
}

This example ensures that all @Scheduled methods share a thread pool of size 100.

Answer 2

The default pool size is 1, and you can set the pool size in application.properties science springboot2.1.0 via changing the value of spring.task.scheduling.pool.size.

spring.task.scheduling.pool.size=20

The same task will be executed in serialized when the trigger period is shorter than the execution duration. And Spring Boot will execute different tasks in parallel with a maximum of 20 threads.

Answer 3

The default scheduler pool size in spring-boot is only one.

In org.springframework.scheduling.config.ScheduledTaskRegistrar:

    /**
     * Schedule all registered tasks against the underlying
     * {@linkplain #setTaskScheduler(TaskScheduler) task scheduler}.
     */
    @SuppressWarnings("deprecation")
    protected void scheduleTasks() {
        if (this.taskScheduler == null) {
            this.localExecutor = Executors.newSingleThreadScheduledExecutor();
            this.taskScheduler = new ConcurrentTaskScheduler(this.localExecutor);
        }
        ...
    }