在不阻塞主线程的情况下异步调用方法调用

Question

I have a scenario where the spring-boot application have to download a file from downstream application and pass it to the client. The API also needs to update a read flag in the database without blocking the response(main-thread).

A basic async use-case is what I thought of and implemented in the respective API. But, I am getting a behavioral issue with @Async. The annotation is able to spawn a new thread, but its blocking the main-thread and holding the response. The expectation was to return without holding the main-thread. Actually, the async update is the last operation of main-thread, and I guess due to that @Async is blocking the main-thread.

Can anyone please suggest a better solution of this scenario.

Calling class

ResponseEntity<byte[]> parsedResponse = retrieverService.retrieve(id,"html");

retrieverService.update(id);

return parsedResponse;

Async method

@Override
@Async("updateTaskExecutor")
public void update(String id) {
    LOG.info("Updating data for metaTagId: {}", id);
    db.updateReadFlag(id);
}

Async Config

@Configuration
@EnableAsync
public class AsyncConfiguration {

    @Bean(name = "updateTaskExecutor")
    public Executor updateTaskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(100);
        executor.setMaxPoolSize(100);
        executor.setQueueCapacity(100);
        executor.setThreadNamePrefix("UpdateTaskClient-");
        executor.initialize();
        return executor;
    }
}

Answer 1

The Configurations were correct. I was using debugger to check the parallelism. As suggested by @M. Deinum, its not the correct way to check parallelism. After using Thread.sleep(), I could see that asynchronous calls are working as expected. I am able to send the response back, while performing an update query asynchronously.