Node seems to unwantedly automatically unsubcribe from topic

edit

Hi,

Note: Edits have been made and I found a workaround , see EDIT 5, 6 and 7 below.

General information and context: WIndows 8.1 64-bit running Virtual Box VM: Ubuntu 16.04.6 LTS with ROS Kinetic. I'm running a setup where a Husarion Rosbot 2.0 is driving around in the generic maze world, publishing /odom, /scan and listening to /cmd_vel among other things. The published odometry and laserscan are used by the obstacle_detector package made by tysik (github. This all working fine.

The following is where the issue is: I have written two nodes in python, the first is called obstacle_visualisation and it subscribes to the /obstacles topic that the obstacle_detector is publishing, as well as the /odom topic from Gazebo. It filters on range and reclassifies moving obstacles as agents, then publishes this to the /sfmmpdm_obstacles topic.

rostopic echo /sfmmpdm_obstacles continuously shows filtered obstacle data so this seems to be running correct as well.

The second node is called sfm_mpdm and it subscribers to the /sfmmpdm_obstacles topic as well as the /odom topic. In the callback methods for these subscriptions I have a print statement writing either 'callbackOdom' or 'callbackSFMObs'. The /odom continues to work, but somehow the /sfmmpdm_obstacles topic gets unsubscribed without me telling it to.

The rqt_graph while everything is working looks like:https://imgur.com/V5ooPo3

And when it breaks down it looks like:https://imgur.com/DhPiIgs

Sequentially the printed 'callbackSFMObs' also stop at that moment.

I subscribe to the topics using the following python code:

#!/usr/bin/env python

import rospy;
import numpy as np
import pygame

from obstacle_detector.msg import SFMObstacles
from nav_msgs.msg import Odometry
from geometry_msgs.msg import Twist
from tf.transformations import euler_from_quaternion

def main_loop():
    # Initialize node, publisher and subscribers.
    rospy.init_node('sfm_mpdm')
    rospy.Subscriber("sfmmpdm_obstacles", SFMObstacles, callbackSFMObs)
    rospy.Subscriber("odom", Odometry, callbackOdom)
    pub = rospy.Publisher('cmd_vel', Twist, queue_size = 1)

    # Loop at 'rate' times per second.
    elapsed = 0                 # Initialize in game delta time
    step_count = 0                  # Initialize forward simulation counter
    previous_time = rospy.get_rostime() # Get current time 

    rate = rospy.Rate(100)  # 100 Hz
    while not rospy.is_shutdown():
        # --- Time keeping, run at 100 Hz ---
        now = rospy.get_rostime()
        # Calculate elapsed time between loops in nanoseconds (a.k.a. delta time).
        time_difference =(now - previous_time).to_nsec()    
        previous_time = now
        # Calculate delta time from ms to s.
        seconds = elapsed / 1000.0      
        # Calculate from nanoseconds to milliseconds    
        elapsed = time_difference / 1000000.0   
        # Count the amount of steps in the elapsed time. Default is 10 per second.
        step_count += elapsed / 100.0   


        # Other code that runs in this loop, snipped for readability.

        # --- Set up and publish the /cmd_vel topic to the Rosbot. --- 
        twist = Twist()
        twist.linear.x = twist_linear_x
        twist.linear.y = 0
        twist.linear.z = 0
        twist.angular.x = 0
        twist.angular.y = 0
        twist.angular.z = twist_angular_z
        # pub.publish(twist) 
        rate.sleep()

# --- Starting point ---
if __name__ == '__main__':
    try:
        main_loop()
    except rospy.ROSInterruptException:
        pass

pygame.quit()
quit()

Why does is suddenly stop being subscribed to the /sfmmpdm_obstacles topic (the subscription to the /odom topic continues just fine, which ... (more)