Launch files from inside "master" node

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I am currently trying to create a master launch file which takes inputs from the users joystick. I currently a simple implementation of the roslaunch API but when I run as is I encounter the error: signal only works in main thread The intended operation is that a button press will launch a node (or set of nodes) in the background that can be terminated with the master node.

I have tried using system calls to force the process to launch another, but I encountered the same error. Is there a way to launch - launch files from a node efficiency and reliably?

#!/usr/bin/python
import roslaunch
import rospy
from sensor_msgs.msg import Joy
from geometry_msgs.msg import Twist
from math import*
import sys
import thread
import subprocess
import os

calibration_request = False
request_complete = False

def launch_calibration():
    print("INSIDE launch calibration")
    uuid = roslaunch.rlutil.get_or_generate_uuid(None, False)
    roslaunch.configure_logging(uuid)

    cli_args = ['outdoor_waypoint_nav', 'sim_calibration.launch']
    roslaunch_file = roslaunch.rlutil.resolve_launch_arguments(cli_args)
    roslaunch_args = cli_args[2:]
    parent = roslaunch.parent.ROSLaunchParent(uuid, roslaunch_file)

    try:
        parent.start()
        rospy.Duration(1)
    except rospy.ROSInterruptException:
        parent.shutdown()

# def launch_capture_waypoint():
def joy_CB(joy_msg):
    print("in callback")
    # return
    global calibration_request
    global request_complete

    if joy_msg.buttons[calibration_num] == True:
        print("X button pressed !")
        # return
        # launch_calibration()
        # bashCommand()
        launch_calibration()
        calibration_request = True
    else: 
        calibration_request = False
    if joy_msg.buttons[end_button_num] == True:
        request_complete = True

def main():
    global calibration_num
    global calibration_sym
    global end_button_num
    global end_button_sym
    global request_complete

    rospy.init_node('master', anonymous=False)

    calibration_num = rospy.get_param("/master/calibration_num")
    calibration_sym = rospy.get_param("/master/calibration_sym")

    end_button_num  = rospy.get_param("/master/end_button_num")
    end_button_sym = rospy.get_param("/master/end_button_sym")

    rate = rospy.Rate(1) # hz
    while not rospy.is_shutdown():
        print("looping")
        rospy.Subscriber("/joy_teleop/joy", Joy, callback=joy_CB)
        rate.sleep()

if __name__ == '__main__':
    try:
        main()
    except rospy.ROSInterruptException:
        sys.exit(0)
        # pass