spring-boot @scheduled not running in different threads?

Question

I am configuring a scheduled task to run in different threads. Here is the configuration code

@Configuration
@EnableScheduling
public class SchedulerConfig implements SchedulingConfigurer {
    private final int POOL_SIZE = 10;

    @Override
    public void configureTasks(ScheduledTaskRegistrar scheduledTaskRegistrar) {
        ThreadPoolTaskScheduler threadPoolTaskScheduler = new ThreadPoolTaskScheduler();
        threadPoolTaskScheduler.setPoolSize(POOL_SIZE);
        threadPoolTaskScheduler.setThreadNamePrefix("my-sched-pool-");
        threadPoolTaskScheduler.initialize();
        scheduledTaskRegistrar.setTaskScheduler(threadPoolTaskScheduler);
    }
}

Here is the code that uses it

@Scheduled(fixedRateString = "2000" )
    public void testaMethod() {

         log.debug("here is the message");
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }

I am sleeping the thread for 10s with fixedRate of 2s. so I expect to see different threads in the log but I see only one

logs are here

{"thread":"my-sched-pool-1","level":"DEBUG","description":"here is the message"}
{"thread":"my-sched-pool-1","level":"DEBUG","description":"here is the message"}
{"thread":"my-sched-pool-1","level":"DEBUG","description":"here is the message"}
{"thread":"my-sched-pool-1","level":"DEBUG","description":"here is the message"}

Answer 1

@Scheduled(fixedRateString = "2000" ) does not gurantee testaMethod be executed every 2 seconds, if the time cost is more than 2s, such as Thread.sleep(10000), the new task will be put in a queue. Only when the old one has been executed, the scheduler will fetch the new task from queue and execute it. Since the new task is now the only task in the scheduler, it could be run without creating a new Thread.

To solve this problem, you can combile @Async and @Scheduled

SchedulerConfig

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.TaskScheduler;
import org.springframework.scheduling.annotation.EnableScheduling;
import org.springframework.scheduling.annotation.SchedulingConfigurer;
import org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler;
import org.springframework.scheduling.config.ScheduledTaskRegistrar;

@Configuration
@EnableScheduling
public class SchedulerConfig implements SchedulingConfigurer {
    private final int POOL_SIZE = 10;

    @Override
    public void configureTasks(ScheduledTaskRegistrar scheduledTaskRegistrar) {
        scheduledTaskRegistrar.setTaskScheduler(poolScheduler());
    }

    @Bean
    public TaskScheduler poolScheduler() {
        ThreadPoolTaskScheduler scheduler = new ThreadPoolTaskScheduler();
        scheduler.setThreadNamePrefix("poolScheduler");
        scheduler.setPoolSize(POOL_SIZE);
        return scheduler;
    }

}

SchedulerTask

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;

@Component
public class SchedulerTask {

    @Autowired
    private AsyncTask asyncTask;

    @Scheduled(fixedRateString = "2000" )
    public void testaMethod() {
        asyncTask.asyncMethod();
    }
}

AsyncTask

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.scheduling.annotation.Async;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.stereotype.Component;

@Component
@EnableAsync
public class AsyncTask {

    private Log log = LogFactory.getLog(AsyncTask.class);

    @Async
    public void asyncMethod() {
        log.debug("here is the message");
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

Test results

11:20:54.682 [poolScheduler1] DEBUG com.test.AsyncTask - here is the message
11:20:56.668 [poolScheduler3] DEBUG com.test.AsyncTask - here is the message
11:20:58.668 [poolScheduler2] DEBUG com.test.AsyncTask - here is the message
11:21:00.669 [poolScheduler6] DEBUG com.test.AsyncTask - here is the message
11:21:02.669 [poolScheduler7] DEBUG com.test.AsyncTask - here is the message
11:21:04.669 [poolScheduler4] DEBUG com.test.AsyncTask - here is the message