public class Qqq {
private PublishSubject<Completable> daemon = PublishSubject.create();
    private CompositeDisposable disposables = new CompositeDisposable();
    public Qqq() {

        disposables.add(
                daemon.flatMapCompletable(c -> c)
                        .subscribeOn(Schedulers.computation())
                        .subscribe());

        Single.just(11)
                .subscribe((integer, throwable) -> daemon.onNext(saveDB(integer)));
    }
}