How to achieve wait/notify in flux.subscribe in java

I have just started with functional programming in java and facing some difficulty. I'm writing a method to establish a reactive session with database and return flux object to the caller. Caller will then subscribe to this flux and fetch results accordingly. Trying to mimic this example here

What I have is

return  Flux.usingWhen(
         Mono.just(getDataStore().getRxSession()),
         session -> Flux.from(session.run(query).records()),
         RxSession::close);

and then a different function subscribing to this flux

Flux<Record> rflux =  query.sub();
rflux.takeUntil(//Implement wait and notifier here).subscribe(//notify here);

Found my answer here : https://www.baeldung.com/reactor-core

I can use Subscription interface methods to request next set of records.

Flux<Record> rflux =  query.sub();
rflux.subscribe(new Subscriber<Record>() {
private Subscription s;
@Override
public void onSubscribe(Subscription sub) {
    this.s = sub;
    s.request(reqParam);
}

@Override
public void onNext(Record record) {
    System.out.println("The record that is pulled is " + record.toString());
    s.request(reqParam);
}

@Override
public void onError(Throwable throwable) {

}

@Override
public void onComplete() {

}

});