code: protected T getOrCreateRxClient(Server server) {
          T client =  rxClientCache.get(server);
          if (client != null) {
              return client;
          } 
          else {
              client = createRxClient(server);
              client.subscribe(listener);
              client.subscribe(eventSubject);
              T old = rxClientCache.putIfAbsent(server, client);
              if (old != null) {
                  return old;
              } else {
                  return client;
              }
          }
      }
docs: Look up the client associated with this Server.
  @param host
  @param port
  @return