Avoiding a circular dependency in a ROS node

edit

how can I publish and subscribe simultaneously on 2 different topics. I have two nodes A and B. A is located in ROS and i am using roslibpy to communicate with B. A publishes first on custom_topic1, B subscribes this, processes it and publishes on custom_topic2 which is then subscribed by A. A processess this again and publishes back on custom_topic1. and then it works in the loop.

I am somehow getting stuck in an infinite loop.

I would want to do something like this :

ros = roslibpy.Ros(host='...', port=9090)
publisher = Topic(ros, '/custom_topic1', 'ros_tutorials/Msg2')
subscriber = Topic(ros, '/custom_topic2', 'ros_tutorials/Msg1')

def publish:
    publisher.publish(Message({'x': 123, 'y': [{'a': 1, 'b': 2, 'c': 3.14, 'e': 7.23, 'f': 2.353}]}))
    subscriber.subscribe(receive_message)
def receive_message(message):
    a = message['j']
    print('a')

Tosimplify it , A -> custom_topic1 -> B -> custom_topic2 -> A -> custom_topic1 (so, A will enter in a loop because it's subscribed to custom_topic2 but publishes that again to custom_topic1).

So this is entering a circular dependency. Any ideas how to avoid it ?

EDIT :

Here is the code for Node1:

import rospy
import sys
import time


from std_msgs.msg import String
from ros_tutorials.msg import VehicleControl
from ros_tutorials.msg import DetectedObjectList

Lane_Width = 2
Brake_Distance = 30

class DemoFunction():
    def __init__(self):
        print("entering constructor")
        #super().__init__('custom_talker')
        self.sub = rospy.Subscriber('objects',DetectedObjectList, self.object_callback)
    self.pub = rospy.Publisher('control',VehicleControl, queue_size = 10)


    def object_callback(self, msg):
        print ("entering callback")
    for obj in msg.objects:
            if self.obj_in_path(obj):
            print("Found object in path: \n{}".format(obj))
            self.send_brake_message()
        else:
            self.normal_driving()
            break

    def send_brake_message(self):
        print("entering brake function")
        self.pub.publish(VehicleControl(accelerator_pedal = 0.0, brake_pedal = 1.0, steering_wheel = 0.0, gear = 1.0))

    def normal_driving(self):
        print("entering normaldriving function")
        self.pub.publish(VehicleControl(accelerator_pedal = 0.0, brake_pedal = 0.0, steering_wheel = 0.0, gear = 1.0))

    def obj_in_path(self,obj):
        print("entering ovbect in path function")
    if (abs(obj.y) < Lane_Width and (obj.x < Brake_Distance)):
        return True
    return False


if __name__ == '__main__':

    print("entering main")
    rospy.init_node('aeb_node')
    try:
        DemoFunction()
        print("entering Try")
        rospy.spin()
    except rospy.ROSInterruptException:
        print("exception thrown")
        pass

This is the code for node 1 which is using ROS_bridge.

def start_sending():
        print('entering start_sending function')
        while True:
            #print('entering while true')
            if not ros.is_connected:
                break
            #print('not entering break and should advertise the publisher')
            publisher.advertise()
            publisher.publish(Message({'id': int(10), 'objects' : [{'id':int(1),'x':2,'y':1,'v_rad':3,'a_rad':4}]}))
            #print('Object found : x distance is : ')
            #time.sleep(0.1)


            def receive_message(message):
                print('entering receive_message')
                #assert message['data'] == 'hello world' , 'Unexpected message content'
                #LOGGER.info('Received message  : %d', message['brake_pedal'])
                a = message['brake_pedal']
                print('brake_pedal : ', a)

            def start_receiving():
                print('entering start receiving')
                listener.subscribe(receive_message)

            listener.subscribe(print)
        publisher.unadvertise()



    ros.on_ready(lambda: print('Is ROS connected ?', ros.is_connected))
    ros.on_ready(start_sending, run_in_thread=True)
    #ros.on_ready(start_receiving, run_in_thread=True)
    ros.get_topics(print)
    ros.get_nodes(print)


    ros.run_forever()

if __name__ == '__main__':

    print('main')

    import logging
    #logging.basicConfig ...