java reactive flow - can a subscriber return value?

Question

I am trying to implement java reactive flow (observer design patter).

I made use of samples available. i have no problem sending values to the subscribers but i cannot make the subscriber to send the publisher back a value. Is there any way i can make it return a value after lets say process it?

i am happy to hear any other approach also.

i tried this sample https://dzone.com/articles/reactive-streams-in-java-9

i am using it for automated trading. i have a each thread for each stock. each thread sends messages to strategies... once the strategy is success, i want it to send me back the result