Stop joint_trajectory_controller execution at rostopic event

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I'm on Ubuntu 14.04 with ROS Indigo.

I am using joint_trajectory_controller to control a single actuated joint robotic hand. After having send a control_msgs::FollowJointTrajectoryGoal to joint_trajectory_controller through an actionlib::SimpleActionClient<control_msgs::FollowJointTrajectoryAction>, I'm listening for an event on a particular topic.

When this event occurs, I would like to interrupt the execution of the previously sent trajectory and stop the hand joint at the current position.

I have tried to get the joint value from the joint state topic and to publish this of the joint_trajectory_controller but this does not stop the execution of the previous trajectory.

I also tried to send an empty goal to the topic /hand_name/joint_trajectory_controller/follow_joint_trajectory/goal but this didn't work either.

An outline of the code is the following:

std::shared_ptr<actionlib::SimpleActionClient<control_msgs::FollowJointTrajectoryAction>> client;
client = std::make_shared<actionlib::SimpleActionClient<control_msgs::FollowJointTrajectoryAction>>("/hand_name/joint_trajectory_controller/follow_joint_trajectory", true);

if (client->waitForServer(ros::Duration(1,0))){
        control_msgs::FollowJointTrajectoryGoal joint_goal = create_trajectory_goal(joint_position);
        client->sendGoalAndWait(joint_goal, ros::Duration(0.5));
}

int id = 0;
while(id == 0){
    ROS_INFO("I'm waiting for event!\n");
    std_msgs::Int8::ConstPtr id_ptr;
    id_ptr = ros::topic::waitForMessage<std_msgs::Int8>("/event_topic", n);
    id = id_ptr->data;

    if (!id) {
        ROS_INFO("No event yet!\n");
    } else {
        ROS_INFO("Event detected with id %d!\n", id);

        // THIS IS WHERE I NEED TO STOP THE JOINT TRAJECTORY CONTROLLER AND SEND ANOTHER TRAJECTORY

    }
}

Thank you in advance for the help.