Hi
Firstly i am not sure if i titled the question correctly but here is what i want to do.
in exercise 4.3 we have the following code:
# import the empty module from std_servs Service interface
from std_srvs.srv import Empty
# import the ROS2 Python client libraries
import rclpy
from rclpy.node import Node
class ClientAsync(Node):
def __init__(self):
# Here you have the class constructor
# call the class constructor to initialize the node as service_client
super().__init__('service_client')
# create the Service Client object
# defines the name and type of the Service Server you will work with.
self.client = self.create_client(Empty, 'moving')
# checks once per second if a Service matching the type and name of the Client is available.
while not self.client.wait_for_service(timeout_sec=1.0):
# if it is not available, a message is displayed
self.get_logger().info('service not available, waiting again...')
# create an Empty request
self.req = Empty.Request()
def send_request(self):
# send the request
self.future = self.client.call_async(self.req)
def main(args=None):
# initialize the ROS communication
rclpy.init(args=args)
# declare the node constructor
client = ClientAsync()
# run the send_request() method
client.send_request()
while rclpy.ok():
# pause the program execution, waits for a request to kill the node (ctrl+c)
rclpy.spin_once(client)
if client.future.done():
try:
# checks the future for a response from the Service
# while the system is running.
# If the Service has sent a response, the result will be written
# to a log message.
response = client.future.result()
except Exception as e:
# Display the message on the console
client.get_logger().info(
'Service call failed %r' % (e,))
else:
# Display the message on the console
client.get_logger().info(
'the robot is moving' )
break
client.destroy_node()
# shutdown the ROS communication
rclpy.shutdown()
if __name__ == '__main__':
main()
I would like to create a part of the “main” method inside the class ClientAsync but i dont know on how to correctly “inhert” the rclpy.spin_once() method this is something i imagine i will be looking at quite a lot in ros.
so the method program should look something similar to this:
# import the empty module from std_servs Service interface
from std_srvs.srv import Empty
# import the ROS2 Python client libraries
import rclpy
from rclpy.node import Node
import time
class ClientAsync(Node):
def __init__(self):
# Here you have the class constructor
# call the class constructor to initialize the node as service_client
super().__init__('service_client')
# create the Service Client object
# defines the name and type of the Service Server you will work with.
self.client = self.create_client(Empty, 'moving')
self.client2 = self.create_client(Empty, "/stop")
self.reset_gazebo = self.create_client(Empty, "/reset_simulation")
# checks once per second if a Service matching the type and name of the Client is available.
while not self.client.wait_for_service(timeout_sec=1.0):
# if it is not available, a message is displayed
self.get_logger().info('service not available, waiting again...')
# create an Empty request
self.req = Empty.Request()
def send_request(self):
# send the request
self.future = self.client.call_async(self.req)
def start_moving(self):
self.send_request()
while rclpy.ok(): #this should be inherited somehow from the main() function
# pause the program execution, waits for a request to kill the node (ctrl+c)
rclpy.spin_once()
if self.future.done():
try:
# checks the future for a response from the Service
# while the system is running.
# If the Service has sent a response, the result will be written
# to a log message.
response = self.future.result()
except Exception as e:
# Display the message on the console
self.get_logger().info(
'Service call failed %r' % (e,))
else:
# Display the message on the console
self.get_logger().info(
'the robot is moving' )
break
def main(args=None):
# initialize the ROS communication
rclpy.init(args=args)
# declare the node constructor
client = ClientAsync()
# run the send_request() method
client.start_moving()
client.destroy_node()
# shutdown the ROS communication
rclpy.shutdown()
if __name__ == '__main__':
main()
basically in def start_moving is where i block the execution of the program with the spin_once inside a while loop untill the response is recived
thanks ziga