Learn how to trigger an event in order to execute some action when our ROS program ends. This is an answer to the following question on ROS Answers:  https://answers.ros.org/question/309529/how-can-i-perform-some-actions-after-the-program-ends/.

Related Resources

• ROS Development Studio (ROSDS)
• Robot Ignite Academy
• ROS Basics Course (Python)

Step 1: Get your development environment ready

Either of the following will do:

1. Use the ROS Development Studio (ROSDS), an online platform for developing for ROS within a PC browser. Easy-peasy. I’m using this option for this post. 
   1. Once you log in, click on the New ROSject button to create a project that will host your code. Then Click on Open ROSject to launch the development/simulation environment.
   2. To open a “terminal” on ROSDS, pick the Shell app from the Tools menu.
   3. You can find the IDE app on the Tools menu.
2. You have ROS installed on a local PC. Okay, skip to Step 2.

Next step!

Step 2: Create a package with the code given in the post

1. If you are working on ROSDS, please create a ROSject first, as indicated in Step 1.

2. Open a terminal and create a package that holds the Python code:

user:~$ cd catkin_ws/src
user:~/catkin_ws/src$ catkin_create_pkg test_shutdown rospy
Created file test_shutdown/CMakeLists.txt
Created file test_shutdown/package.xml
Created folder test_shutdown/src
Successfully created files in /home/user/catkin_ws/src/test_shutdown. Please adjust the values in package.xml.
user:~/catkin_ws/src$ cd test_shutdown/src
user:~/catkin_ws/src/test_shutdown/src$ touch test_shutdown.py
user:~/catkin_ws/src/test_shutdown/src$ chmod +x test_shutdown.py

3. Open test_shutdown.py in the IDE and paste in the following code:

#!/usr/bin/env python
import rospy
from std_msgs.msg import String

def talker():

    pub = rospy.Publisher('chatter', String, queue_size=10)
    rospy.init_node('talker', anonymous=True)
    rate = rospy.Rate(10) # 10hz
    while not rospy.is_shutdown():
        hello_str = "hello world %s" % rospy.get_time()
        rospy.loginfo(hello_str)
        pub.publish(hello_str)
        rate.sleep()

try:
    talker()
except rospy.ROSInterruptException:
    rospy.loginfo("TEST")

4. Compile and run the code: go back to the catkin_ws directory and run the following commands

user:~/catkin_ws$ catkin_make
user:~/catkin_ws$ source devel/setup.bash
user:~/catkin_ws$ rospack profile
user:~/catkin_ws$ rosrun test_shutdown test_shutdown.py

(PS: Please run nohup roscore & to start ROS master in the background if you get an error that says “cannot connect to master”)

5. Stop the program with Ctrl + C:

Nothing happened? Yes, nothing happened like the OP explained. The OP expected that the word “TEST” would be printed, but it wasn’t. Let’s fix that next.

Step 3: Modify the code so that it triggers some actions when our ROS program ends

The key tool here is the rospy.on_shutdown() hook, which takes a function that should be called when ROS gets the shutdown signal.

Replace the code in test_shutdown.py with the following code that creates the shutdown hook function and registers it.

#!/usr/bin/env python

import rospy
from std_msgs.msg import String

def talker():

    pub = rospy.Publisher('chatter', String, queue_size=10)
    rospy.init_node('talker', anonymous=True)
    rate = rospy.Rate(10) # 10hz
    while not rospy.is_shutdown():
        hello_str = "hello world %s" % rospy.get_time()
        rospy.loginfo(hello_str)
        pub.publish(hello_str)
        rate.sleep()

def my_shutdown_hook():
    rospy.loginfo("It's shutdown time!")

try:
    rospy.on_shutdown(my_shutdown_hook)
    talker()
except rospy.ROSInterruptException:
    rospy.loginfo("TEST")

Now run the program again and then stop it with Ctrl + C:

user:~/catkin_ws$ rosrun test_shutdown test_shutdown.py
[INFO] [1586198566.464600]: hello world 1586198566.46
[INFO] [1586198566.564763]: hello world 1586198566.56
^C[INFO] [1586198568.326002]: It's shutdown time!

And that was it! Of course, the shutdown hook could perform more useful tasks, like stopping the robot for example.

Extra: Video of the post

Here below you have a “sights and sounds” version of this post, just in case you prefer it that way. Enjoy!

Feedback

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Edited by Bayode Aderinola