问.flatMap()线程卡住

EN

  public static void main(String[] args) {
    Flux.fromIterable(Arrays.asList("a","b","c"))
        .flatMap(a -> Mono.just(a).subscribeOn(Schedulers.parallel()))
        .doOnNext(
            a ->
                System.out.println(
                    "Receivedededed " + a + " on thread:" + Thread.currentThread().getName()))
        .flatMap(
            a -> {
              System.out.println(
                  "Received: " + a + " on threads: " + Thread.currentThread().getName());
              if ("a" == a) return getCreditScore(a);
              else return Mono.just(a);
            })
        .subscribe(a -> System.out.println("afka" + a));

    System.out.println("Main Thread Free");

    try {
      Thread.sleep(Integer.MAX_VALUE);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }

Receivedededed a on thread:parallel-1
Received: a on threads: parallel-1
Main Thread Free