ROS Action with no Subscriber

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Iam creating an action server and the process is just rotating turtlesim depending on how many times the goal is set to. As far as I researched, the sample codes for ROS Action have their main function inside the subscriber callback. From my problem, I dont need to have a subscriber so I dont need subscriber callback. What I have tried is to put the main function inside the goal callback, the problem is the preempt. with this method, I cant preempt the server because the goal callback should finish first before other callbacks are called. Another is to have isPreemptRequested() function but when I cancel the goal, It finishes the last rotation first before canceling the goal (it does not cancel/ stop immediately). And for my last try, for the goal callback, I only put the acceptNewGoal() function and put the main function to new function. My problem with this is the main function is not working (probably because I dont have another function with callback to call this function [expected for subscriber callback]). Anyone have done action server with no subscriber? any tips or suggestion?

Here's my last try code:

 #include <ros/ros.h>
 #include <actionlib/server/simple_action_server.h>
 #include <geometry_msgs/Twist.h>
 #include "actn_turtlesim/testAction.h"

 class testAction
{
   protected:
   ros::NodeHandle nh;
   actionlib::SimpleActionServer<actn_turtlesim::testAction> action_srv;
   std::string action_name;

  int rotation;
  int counter;
  double time_diff;
  float PI = 3.14159265359;

  actn_turtlesim::testResult result;
  actn_turtlesim::testFeedback feedback;
  ros::Publisher pub;
  geometry_msgs::Twist vel_msg;

public:

   testAction(std::string name) : 
   action_srv(nh, name, false),
   action_name(name)
  {
      action_srv.registerGoalCallback(boost::bind(&testAction::goalCB, this));
      action_srv.registerPreemptCallback(boost::bind(&testAction::preemptCB, this));
      pub = nh.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel", 1);
      action_srv.start();
      ROS_INFO("Action Server started");
  }

  ~testAction(void)
 {
 }

 void goalCB()
 {
      rotation = action_srv.acceptNewGoal()->rotation;
 }

 void rotate()
{
      if (action_rotate.action_srv.isNewGoalAvailable())
     {
        ros::Rate rate(1);
        ros::Time time_begin = ros::Time::now();
        ros::Time time_end;

       for (counter = 0; rotation != counter; counter++)
       {
          vel_msg.linear.x = 10.0;
          vel_msg.angular.z = PI * 2;
          pub.publish(vel_msg);
          feedback.rotation = counter;
          action_srv.publishFeedback(feedback);
          ROS_INFO("%d Rotation/s done", counter); 
          time_end = ros::Time::now();
          time_diff = time_end.toSec() - time_begin.toSec();
          rate.sleep();
        }
       if (rotation == counter && success == true)
       {
          result.time = time_diff; 
          ROS_INFO("Result: %f secs", time_diff);
          action_srv.setSucceeded(result);
        }
    }
   }

  void preemptCB()
  {
      vel_msg.linear.x = 0.0;
      vel_msg.angular.z = 0.0;
      pub.publish(vel_msg);
      ROS_INFO("%s: Preempted", action_name.c_str());
      ROS_INFO("Result: %f secs", time_diff);
      action_srv.setPreempted();
      success = false;
  }
};

int main(int argc, char** argv)
{
   ros::init(argc, argv, "action_server_turtle");
   testAction action_rotate("turtle_rotate");
   ros::spin();
   return 0;
}