How can I invoke a new @Async method but wait a condition?

Question

I have a Spring Boot app that implements an AMQP MessageListener. This listener invoke to an @Async method managed by ThreadPoolTaskExecutor with pool size. The problem occurs when there are many incoming messages, so these messages are lost because there are no asynchronous workers available.

I am using Spring Core 5.0.7-RELEASE, Java 8

This is my code:

AsyncConfigurator:

@EnableAsync
@Configuration
public class AsyncConfiguration extends AsyncConfigurerSupport {

    @Override
    @Bean("docThreadPoolTaskExecutor")
    public Executor getAsyncExecutor() {
        final ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(4);
        executor.setMaxPoolSize(8);
        executor.setWaitForTasksToCompleteOnShutdown(true);
        executor.setThreadNamePrefix("DocWorkerThread-");
        executor.initialize();
        return executor;
    }

My Back Service ( MyAsyncService ):

    @Async("docThreadPoolTaskExecutor")
    @Override
    public void generaDocumento(String idUser, int year) {
       //... some heavy and slow process
    }

My message listener:

...
    @Autowired
    private MyAsyncService myAsyncService;

    @Override
    @EntryPoint
    public void onMessage(Message message) {
        try {
            final String mensaje = new String(message.getBody(), StandardCharsets.UTF_8); 
            final MyPojo payload = JsonUtils.readFromJson(mensaje , MyPojo.class);

            myAsyncService.generaDocumento(payload.getIdUser(), Integer.valueOf(payload.getYear()));

        } catch ( Throwable t ) { 
            throw new AmqpRejectAndDontRequeueException( t );
        }
    }

I need someone to give me some idea to solve this.

Answer 1

ThreadPoolTaskExecutor has a queue by default. Messages should be added to the queue when you reach the corePoolSize . When the queue is full then more workers will be started until you reach the maxPoolSize . You can check the current queue size by executor.getThreadPoolExecutor().getQueue().size() to verify if the messages are really lost or just stuck in the queue.