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Run a launch script in subscriber callback

asked 2022-03-25 23:22:14 -0600

hwan30 gravatar image

I want to spawn a robot B when robot A pass certain location. Currently, my implementation is having a subscriber subscribe to odom of robot A. When robot A odom msg.pose.pose.position>1, run the launch script ( to launch robot B) in callback. I unsubscribe to the node afterwards since I only need to spawn the robot B once. but I was getting the bad call back error.

(a lot of red lines: [ERROR] [1648267836.094904, 23.063000]: bad callback: <function callback="" at="" 0x7f8b743a9310=""> Traceback (most recent call last): File "/opt/ros/noetic/lib/python3/dist-packages/rospy/topics.py", line 750, in _invoke_callback cb(msg) File "/home/xxx/catkin_ws/src/beginner_tutorials/scripts/py_launch.py", line 28, in callback py_launch() )

is it possible to run a launch script in the subscriber callback? or is there a better way to achieve the above?

#! /usr/bin/env python3

import roslaunch
import rospy
from nav_msgs.msg import Odometry


count=0

    def callback(msg):
        global count
        print(msg.pose.pose.position.z)
    if msg.pose.pose.position.z>1:
        count=count+1
    else:
        pass
    print(count)


if count==1:

    count=count+1

    odom_sub.unregister()

    py_launch()


def py_launch():
    uuid = roslaunch.rlutil.get_or_generate_uuid(None, False)
    roslaunch.configure_logging(uuid)
    launch = roslaunch.parent.ROSLaunchParent(uuid, ["/home/xxx/catkin_ws/src/beginner_tutorials/launch/test_replace.launch"])
launch.start()
rospy.loginfo("started")

rospy.sleep(3)


launch.shutdown()

def odom_listen():
    global odom_sub
    odom_sub = rospy.Subscriber('/odom', Odometry, callback)


if __name__ == '__main__':
    rospy.init_node('en_Mapping', anonymous=True)

    odom_listen()


rospy.spin()
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Comments

Why wait to launch robot B until robot A satisfies msg.pose.pose.position > 1? Why not launch robot B the same time as robot A, and then make robot B do its thing after that condition for robot A evaluates to true?

abhishek47 gravatar image abhishek47  ( 2022-03-26 04:07:06 -0600 )edit

for my specific simulation, I need to only have robot A appears at the beginning, then, when it reaches certain location. second robot B appears from the sky.

hwan30 gravatar image hwan30  ( 2022-03-26 13:18:41 -0600 )edit

2 Answers

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answered 2022-03-27 13:31:07 -0600

ljaniec gravatar image

updated 2022-03-29 02:56:14 -0600

Maybe you could try to use a Gazebo service in ROS? They are in gazebo_msgs.srv, use rospy.wait_for_service("gazebo/spawn_sdf_model"), then s = rospy.ServiceProxy("gazebo/spawn_sdf_model", SpawnModel) etc. like there:

#!/usr/bin/env python
import sys, rospy, tf
from gazebo_msgs.srv import *
from geometry_msgs.msg import *
from copy import deepcopy

if __name__ == '__main__':
  rospy.init_node("spawn_chessboard")
  rospy.wait_for_service("gazebo/delete_model")
  rospy.wait_for_service("gazebo/spawn_sdf_model")
  delete_model = rospy.ServiceProxy("gazebo/delete_model", DeleteModel)
  delete_model("chessboard")
  s = rospy.ServiceProxy("gazebo/spawn_sdf_model", SpawnModel)
  orient = Quaternion(*tf.transformations.quaternion_from_euler(0, 0, 0))
  board_pose = Pose(Point(0.25,1.39,0.90), orient)
  unit = 0.05
  with open("chessboard.sdf", "r") as f:
    board_xml = f.read()
  with open("chess_piece.sdf", "r") as f:
    piece_xml = f.read()

  print s("chessboard", board_xml, "", board_pose, "world")

  for row in [0,1,6,7]:
    for col in xrange(0,8):
      piece_name = "piece_%d_%d" % (row, col)
      delete_model(piece_name)
      pose = deepcopy(board_pose)
      pose.position.x = board_pose.position.x - 3.5 * unit + col * unit
      pose.position.y = board_pose.position.y - 3.5 * unit + row * unit
      pose.position.z += 0.02
      s(piece_name, piece_xml, "", pose, "world")

This example is based on the the book "Programming Robots with ROS. A Practical Introduction to the Robot Operating System", Morgan Quigley, Brian Gerkey, William D. Smart from there.

Like @Mike Scheutzow wrote, I wouldn't call this service in the callback. I think you could try to use Contain Plugin in Gazebo, like this one: http://gazebosim.org/tutorials?tut=co... (but it would be a bit of work, I think).

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Comments

great example, I was able to use rospy.ServiceProxy("gazebo/spawn_sdf_model", SpawnModel) instead of trying to start a launch file the python code. It does what I want to do now. Unfortunately, I still have to do it in the callback. I am not good at writing plugin(c++).When the odom is unsubscribed, and spawning the robot would be the last task. After robot B appears, I don't really need the node anymore.I hope the below implementation is ok. The thing i try to achieve is similar to the chess piece example , I have defined a chessboard +chess piece model. Chess piece are links of the chessboard(vertically connected via prismatic joints) ,when chess piece A is lifted to certain height, the connected link piece is deleted and spawn a new free piece,so that new piece would have all degree of freedom to be moved off ...(more)

hwan30 gravatar image hwan30  ( 2022-03-27 18:58:48 -0600 )edit

count=0

def callback(msg):
    global count
    print(msg.pose.pose.position.z)
    if msg.pose.pose.position.z>1:
        count=count+1
    else:
    pass
print(count)



if count==1:

    count=count+1

    odom_sub.unregister()

    rospy.wait_for_service("gazebo/delete_model")
    rospy.wait_for_service("gazebo/spawn_sdf_model")



    initial_pose = Pose()
    initial_pose.position.x = 0.629
    initial_pose.position.y = -0.369
    initial_pose.position.z = 1
    initial_pose.orientation.x=0
    initial_pose.orientation.y=0
    initial_pose.orientation.z=1.57


    f = open(
        '/home/xxx/robotA_replacement/model.sdf', 'r')
    sdff = f.read()

    spawn_model = rospy.ServiceProxy("gazebo/spawn_sdf_model", SpawnModel)
    spawn_model('robot_name', sdff, "", initial_pose, "world")

    delete_model = rospy.ServiceProxy("gazebo/delete_model", DeleteModel)
    delete_model(model_name="robotA")


def odom_listen():
    global odom_sub
    odom_sub = rospy.Subscriber('/odom', Odometry, callback)
hwan30 gravatar image hwan30  ( 2022-03-27 19:01:14 -0600 )edit
0

answered 2022-03-27 09:48:14 -0600

Mike Scheutzow gravatar image

updated 2022-03-27 09:51:02 -0600

In general it is a bad idea to do any activity that takes a long time in a ros subscriber callback. To avoid race conditions, the implementation is single-threaded, so ALL other subscribers and publishers in the ros node are not allowed to run. This is not an issue for your specific example above because you only 1 subscriber and 0 publishers, but it could become one if you try to add more features.

The error messages are because a lot of odom messages queued up during the 3+ seconds the callback was blocked, and ros did not like that you unregistered the callback while all that data was pending.

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Asked: 2022-03-25 23:22:14 -0600

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Last updated: Mar 29 '22