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Is it possible to shut down a service from its client?

asked 2018-06-11 08:26:32 -0600

Ravi Joshi gravatar image

I have a ROS service written in Python as shown below-

from beginner_tutorials.srv import *
import rospy

def handle_add_two_ints(req):
    print "Returning [%s + %s = %s]"%(req.a, req.b, (req.a + req.b))
    return AddTwoIntsResponse(req.a + req.b)

def add_two_ints_server():
    rospy.init_node('add_two_ints_server')
    s = rospy.Service('add_two_ints', AddTwoInts, handle_add_two_ints)
    print "Ready to add two ints."
    rospy.spin()

if __name__ == "__main__":
    add_two_ints_server()

The service client is written in C++ as shown below-

#include "ros/ros.h"
#include "beginner_tutorials/AddTwoInts.h"

int main(int argc, char **argv){
  ros::init(argc, argv, "add_two_ints_client");

  ros::NodeHandle n;
  ros::ServiceClient client = n.serviceClient<beginner_tutorials::AddTwoInts>("add_two_ints");
  beginner_tutorials::AddTwoInts srv;
  srv.request.a = 10;
  srv.request.b = 20;
  if (client.call(srv)){
    long int sum = srv.response.sum;
    ROS_INFO("Sum: %ld", sum);
    if (sum > 100){
      // calling 'ros::shutdown()' stops only this node as expected
      ros::shutdown();
    }
  } else {
    ROS_ERROR("Failed to call service add_two_ints");
    return -1;
  }

  return 0;
}

Depending on the response from the service, I want to stop both the client and server (i.e., service written in Python above) node. Any suggestions, please?

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1 Answer

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answered 2018-06-11 09:38:46 -0600

updated 2018-06-11 15:53:16 -0600

Hi,

It's indeed possible, but I wouldn't recommend it to you, as other node can still be using this service, or the service can probably be restarted in other way (for example, wait a parameter to be on, or wait for an other service to be called).

To make the server kill himself : What you can do is to set a flag to shutdown the service : (Warning : not safe, the script can terminate before the response is sent, use at your own risk)

from beginner_tutorials.srv import *
import rospy

manual_shutdown = False

def handle_add_two_ints(req):
    global manual_shutdown
    print "Returning [%s + %s = %s]"%(req.a, req.b, (req.a + req.b))
    response = AddTwoIntsResponse(req.a + req.b)
    manual_shutdown = True
    return response 

def add_two_ints_server():
    rospy.init_node('add_two_ints_server')
    s = rospy.Service('add_two_ints', AddTwoInts, handle_add_two_ints)
    print "Ready to add two ints."
    r = rospy.Rate(10)
    while not rospy.is_shutdown() and not manual_shutdown:
        r.sleep()
    rospy.sleep(1)
    s.shutdown()

if __name__ == "__main__":
    add_two_ints_server()

Also, you can replace the signal_shutdown by what you want or even put the "manual_shutdown" in the while-loop and do thing after the loop.

I used a while loop instead of rospy.spin() , you can check why here : https://answers.ros.org/question/1103...

For completion, you can check these questions : https://answers.ros.org/question/1981... or https://answers.ros.org/question/1099...

Edit 2 : To make the client kill the server (make a node kill another node):

You can apply the method 1 above to create a "kill me" service and call it from the client.

Or even simpler, you just have to use the rosnode command :

node1:

import rospy
def node1():
    rospy.init_node('node1')
    r = rospy.Rate(10)
    while not rospy.is_shutdown():
        r.sleep()

if __name__ == "__main__":
    node1()

node 2:

import rospy
from subprocess import call
def node2():
    rospy.init_node('node2')
    rospy.sleep(10) # Wait 10 second to kill node1
    call(["rosnode", "kill", "node1"], shell=True) # be careful here https://stackoverflow.com/questions/3172470/actual-meaning-of-shell-true-in-subprocess

if __name__ == "__main__":
    node2()

Edit 1 : Some more answers :

(1) My code is not good at all so I edited it, if you don't return immediately after setting manual_shutdown = True, the client will have an error since the connection is broken (in rospy, all callback are in a thread). The error :

ERROR: transport error completing service call: unable to receive data from sender, check sender's logs for details

You can try it by adding a rospy.sleep(1) after the manual_shutdown=True to see the error

You can try to minimize the effect by putting the flag to True just before the return and putting a rospy.sleep() after the loop, but it's quite a ugly method. I'm still searching a correct way to do this

(2) you can add and you SHOULD add a rospy.sleep() or a rospy.rate() in the loop in Python, otherwise you CPU will work for nothing. You can check with the command top the CPU usage :

top without rospy.rate(10 ... (more)

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Comments

Thanks a lot. I have four queries (1) The flag manual_shutdown is set inside def handle_add_two_ints(req). On the other hand while not rospy.is_shutdown() is running and checking the flag. What would happen if rospy.signal_shutdown is called before def handle_add_two_ints(req) return?

Ravi Joshi gravatar imageRavi Joshi ( 2018-06-11 10:50:50 -0600 )edit

(2) I believe it would be nicer to add rate.sleep() inside while not rospy.is_shutdown() where rate = rospy.Rate(10). I am not sure about it. What do you say?

Ravi Joshi gravatar imageRavi Joshi ( 2018-06-11 10:52:34 -0600 )edit

(3) As per this post, rospy.init_node should be called along with disable_signals=True. So it should be rospy.init_node('add_two_ints_server', disable_signals=True)

Ravi Joshi gravatar imageRavi Joshi ( 2018-06-11 10:57:33 -0600 )edit

(4) Instead of rospy.signal_shutdown("Because"), we also have service.shutdown(). In this scenario, which one do you prefer and why?

Ravi Joshi gravatar imageRavi Joshi ( 2018-06-11 10:59:14 -0600 )edit

That a lot of interesting question, I will try to answers them :)

lmathieu gravatar imagelmathieu ( 2018-06-11 11:23:42 -0600 )edit

Pedantic perhaps, but: this is not an actual answer: the question was whether a service server can be shutdown by a client. The code shown here makes the server shutdown itself.

gvdhoorn gravatar imagegvdhoorn ( 2018-06-11 14:45:47 -0600 )edit

You are actually right @gvdhoorn, It's even a duplicate of : https://answers.ros.org/question/1747... , I was so busy trying to see if I could that I didn't think if I should. But hey, I'm gonna edit my answer one last time for the sake of completion :)

lmathieu gravatar imagelmathieu ( 2018-06-11 15:44:16 -0600 )edit

Very informatic answer! Thank you very much.

Ravi Joshi gravatar imageRavi Joshi ( 2018-06-11 20:01:21 -0600 )edit

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Asked: 2018-06-11 08:26:32 -0600

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Last updated: Jun 11 '18