@Bean
public TaskExecutor taskExecutor() {
    return new ThreadPoolTaskExecutor();
}

class Test {
    @Autowired
    private TaskExecutor executor;
    private volatile enabled = true;

    public void spawn() {
        executor.execute(new Runnable() {
            @Override
            public void run() {
                while(enabled) {
                    ...
                }
            }
        });
    }
}

Test t = ...;
t.spawn();
t.spawn();

@Bean
public TaskExecutor taskExecutor() {
    final ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
    executor.setCorePoolSize(2);
    return executor;
}