Interrupting a topic callback to call a service

edit

I am currently facing an issue with my code, which both subcribes to a topic, and runs the server side of a service. The problem i am currently facind is that the topic which i am subscribing to is constantly being published to making, making it impossible for me to call my service. The service response is empty, which i assume i due to the topic callback constantly being running.

Here is the code:

#include "subscriber_and_server.h"

subscriber_and_server::subscriber_and_server() :
    n_("~"),
    state_listener_sub_(n_.subscribe("/states", 1, &subscriber_and_server::callback, this)),
    getCurrent_Event_Service(n_.advertiseService("/state_listener/Get_Current_Event", &subscriber_and_server::get_current_event_callback, this))
{
    std::cout << "subscriber_and_server -  constructed" << std::endl;
}

void subscriber_and_server::callback(const std_msgs::String& input)
{
    if(old_event == current_event){}
    else
    {
        this->current_event = input.data;
        this->old_event = this->current_event;
    }
}

bool subscriber_and_server::get_current_event_callback(state_listener::get_current_event::Request &req, state_listener::get_current_event::Response &res)
{
    res.current_event = this->current_event;
    return true;
}

My main is creating a object of the class subscriber_and_server and ros::spin();.

Anyway to handle this issue? I am currently thinking of making a seperating both callback into seperates nodes, publish the new state if one occur, such that service can handle the issue? Is it somehow possible to avoid this??