我正在rxjava代码中为调度程序线程池使用java.util.concurrent.executorservice：

public class Test {
        ExecutorService poolA = newFixedThreadPool(10, threadFactory("Scheduler-A-%d"));
        Scheduler schedulerA = Schedulers.from(poolA);
        private ThreadFactory threadFactory(String pattern) {
        return new ThreadFactoryBuilder()
                .setNameFormat(pattern).build();
        }

        @Test
        public void testSubscribeOn() {
            log("Starting");
            final Observable<String> obs = simple();
            log("Created");
            obs
                    .doOnNext(Utils::log)
                    .map(x -> x+1) 
                    .doOnNext(Utils::log)
                    .subscribeOn(schedulerA)
                    .map(x -> x+2) 
                    .doOnNext(Utils::log)
                    .subscribe( 
                         x -> log("Got " + x),
                         Throwable::printStackTrace,
                         () -> log("Completed"));

            log("exiting");
        }
    }

    public class Utils {
        private static long start = System.currentTimeMillis();

        public static void log(Object label) {
            System.out.println(
                    System.currentTimeMillis() - start + "\t| " +
                            Thread.currentThread().getName() + "\t| " +
                            label);
        }
    }

我观察到的是，主线程在调度程序线程开始工作之前退出，因此不显示来自调度程序线程的输出。据我所知，executorservice线程不是守护进程线程，那么为什么会出现这种行为呢？