问取消订阅后Web3j客户端不退出

EN

public static void main(String[] args) throws InterruptedException {
    Web3j web = Web3j.build(new HttpService("http://10.9.59.138:18001"));
    Observable<EthBlock> observable = web.blockObservable(true);
    Subscription subscription = observable.subscribe(System.out::println);
    Thread.sleep(3000);
    subscription.unsubscribe();
    System.out.println("main say good bye.");
    // jvm not exit!
}