Program to test for a race condition in rostopic handlers

ros_race_condition.py

# Program to test for a race condition in rostopic handlers
# Run (note the single & to put the first pub in the background and simultaneously start the second)
# $ rostopic pub -1 /test_topic1 std_msgs/String "data: 'hello1'" & rostopic pub -1 /test_topic2 std_msgs/String "data: 'hello2'"
# Both topic handlers should fire nearly simultaenously. 
# Each topic reads the global variable, then increments it by 1. 
# When one thread increments the GLOBAL from 1 to 3, you have a race condition. 

import rospy
from std_msgs.msg import String
import threading

GLOBAL = 1

def handler1(msg): 
    global GLOBAL 

    rospy.loginfo("In thread %s/%s, GLOBAL is %d", threading.current_thread().ident, threading.current_thread().name, GLOBAL)
    GLOBAL += 1
    rospy.loginfo("Incremented global in thread %s, now GLOBAL is %d", threading.current_thread().name, GLOBAL)

def handler2(msg): 
    global GLOBAL 

    rospy.loginfo("In thread %s/%s, GLOBAL is %d", threading.current_thread().ident, threading.current_thread().name, GLOBAL)
    GLOBAL += 1
    rospy.loginfo("Incremented global in thread %s, now GLOBAL is %d", threading.current_thread().name, GLOBAL)


def main(): 
    rospy.init_node(b'TestNode')
    
    rospy.Subscriber(b'/test_topic1', String, handler1)
    rospy.Subscriber(b'/test_topic2', String, handler2)
    
    print("Waiting for publish on /test_topic1 and /test_topic2")

    rospy.spin()

if __name__ == '__main__':
    main()