rxjava如何让Obserable在新线程执行?报错

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问题描述 相关代码

我希望我创建的observable在非创建线程执行. 并每subscribe一次, 排队执行一次. 代码如下

    public void test(){
        Log.d(TAG, "test() called");
        Observable<SerialSignal> dd = Observable.fromCallable(new Callable<SerialSignal>() {
            @Override
            public SerialSignal call() throws Exception {
                Thread.sleep(2000);
                Log.d(TAG, "call() called" + System.currentTimeMillis()/1000L);
                return null;
            }
        });
        Observable<SerialSignal> d = Observable.create(new ObservableOnSubscribe<SerialSignal>() {
            @Override
            public void subscribe(ObservableEmitter<SerialSignal> emitter) throws Exception {
                Thread.sleep(2000);
                Log.d(TAG, "subscribe() called" + System.currentTimeMillis()/1000L);
                emitter.onNext(null);
            }
        });
        d.subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread());
        d.subscribe(new Observer<SerialSignal>() {
            @Override
            public void onNext(SerialSignal serialSignal) {
                Log.i(TAG, "onNext: subscriber 1" +System.currentTimeMillis() /1000L );
            }
            //省了 onError onComplete 等
        });
        d.subscribe(new Observer<SerialSignal>() {
            @Override
            public void onNext(SerialSignal serialSignal) {
                Log.i(TAG, "onNext: 112 " + System.currentTimeMillis() /1000L);
            }
        });

问题出现的环境背景及自己尝试过哪些方法

你期待的结果是什么？实际看到的错误信息又是什么？

结果test() called 和 call() 都在主线程执行;而且observer的onnext 不执行.
请问哪里写错了吗. 我希望 called 在新线程执行, onNext在Android 主线程执行