Multi-threaded process using only one thread per execution [duplicate]

Question

I'm using the ExecutorService on a @EnableScheduling class to submit multiple executions of the same method.

Basically, my configuration is:

@Component
@EnableScheduling
public class JobQueue {
  
  @Autowired
  private JobQueueService jobQueueService;

  private Integer threadPoolSize = 5;

  private ExecutorService executorService = Executors.newFixedThreadPool(threadPoolSize);

  @Scheduled(fixedDelay = 20_000)
  private void run() {
    for (int i = 0; i <= threadPoolSize; i++) {
      Runnable runnableTask = () -> {
        jobQueueService.processPendingJobs();
      };

      executorService.submit(runnableTask);

      // Also, tried with executorService.execute(runnableTask);
    }
  }
}

But, the JobQueueService.processPendingJobs() is running only in single-thread executions, even when it is called multiple times with the for on my scheduled class.

Has Spring a different Autowired implementation for multi-threaded purposes?

I also tried instantiating a new service on for-of loop for each execution:

JobQueueService jobQueueService = new JobQueueService();

...[Runnable code chunk]

And at this time, it calls multiple thread executions, but loses Spring Application Context (Beans and other properties).

Do I have to provide a specific Bean implementation for my JobService to run it in multi-threaded contexts and still use it as an Autowired component?

The processPendingJobs() is annotated with synchronized keyword, is that wrong? If yes, why?

@Service
public class JobQueueService {

  public synchronized void processPendingJobs() {
    // Run logic
  }
}

Answer 1

You can make the call to processPendingJobs() run in a new thread by annotating the method with Spring's @Async annotation. This annotation only works on public methods and they should always be called from another class. To enable asynchronous calling you also need to annotate a @Configuration annotated class with the @EnableAsync annotation.