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action server와 client 작성하기(Python)

  1. 소개
  2. 실습
    1. action server 작성하기
    2. action client 작성하기

1. 소개

  • action은 ROS내의 비동기 통신
    • action client가 action server에게 goal request를 전송
    • action server는 action client에게 goal feedback과 result를 전송
  • 준비
    • action_tutorials_interfaces package
    • Fibonacci.action interface

2. 실습

2-1 action server 작성하기

  • fibonacci_action_server.py 파일 추가하기 (위치 : ~/action_test)
import time


import rclpy
from rclpy.action import ActionServer
from rclpy.node import Node

from action_tutorials_interfaces.action import Fibonacci


class FibonacciActionServer(Node):

    def __init__(self):
        super().__init__('fibonacci_action_server')
        self._action_server = ActionServer(
            self,
            Fibonacci,
            'fibonacci',
            self.execute_callback)

    def execute_callback(self, goal_handle):
        self.get_logger().info('Executing goal...')


        feedback_msg = Fibonacci.Feedback()

        feedback_msg.partial_sequence = [0, 1]


        for i in range(1, goal_handle.request.order):

            feedback_msg.partial_sequence.append(

                feedback_msg.partial_sequence[i] + feedback_msg.partial_sequence[i-1])

            self.get_logger().info('Feedback: {0}'.format(feedback_msg.partial_sequence))

            goal_handle.publish_feedback(feedback_msg)

            time.sleep(1)


        goal_handle.succeed()

        result = Fibonacci.Result()

        result.sequence = feedback_msg.partial_sequence

        return result


def main(args=None):
    rclpy.init(args=args)

    fibonacci_action_server = FibonacciActionServer()

    rclpy.spin(fibonacci_action_server)


if __name__ == '__main__':
    main()
  • action server 실행하기
python3 fibonacci_action_server.py
  • 새 터미널에서 goal 전송하는 명령 실행
ros2 action send_goal fibonacci action_tutorials_interfaces/action/Fibonacci "{order: 5}"
  • action server 재시작(--feedback 옵션으로 feedback이 publish되고 있는지 확인)
ros2 action send_goal --feedback fibonacci action_tutorials_interfaces/action/Fibonacci "{order: 5}"

2-2 action client 작성하기

  • fibonacci_action_client.py 파일 생성 및 복사하기
import rclpy
from rclpy.action import ActionClient
from rclpy.node import Node

from action_tutorials_interfaces.action import Fibonacci


class FibonacciActionClient(Node):

    def __init__(self):
        super().__init__('fibonacci_action_client')
        self._action_client = ActionClient(self, Fibonacci, 'fibonacci')

    def send_goal(self, order):
        goal_msg = Fibonacci.Goal()
        goal_msg.order = order

        self._action_client.wait_for_server()

        self._send_goal_future = self._action_client.send_goal_async(goal_msg, feedback_callback=self.feedback_callback)

        self._send_goal_future.add_done_callback(self.goal_response_callback)

    def goal_response_callback(self, future):
        goal_handle = future.result()
        if not goal_handle.accepted:
            self.get_logger().info('Goal rejected :(')
            return

        self.get_logger().info('Goal accepted :)')

        self._get_result_future = goal_handle.get_result_async()
        self._get_result_future.add_done_callback(self.get_result_callback)

    def get_result_callback(self, future):
        result = future.result().result
        self.get_logger().info('Result: {0}'.format(result.sequence))
        rclpy.shutdown()

    def feedback_callback(self, feedback_msg):
        feedback = feedback_msg.feedback
        self.get_logger().info('Received feedback: {0}'.format(feedback.partial_sequence))


def main(args=None):
    rclpy.init(args=args)

    action_client = FibonacciActionClient()

    action_client.send_goal(10)

    rclpy.spin(action_client)


if __name__ == '__main__':
    main()
  • 먼저 action server를 실행하기
python3 fibonacci_action_server.py
  • 새 터미널에서 action client 실행하기
python3 fibonacci_action_client.py
  • 결과 (action server 출력)
[INFO] [fibonacci_action_server]: Executing goal...
[INFO] [fibonacci_action_server]: Feedback: array('i', [0, 1, 1])
[INFO] [fibonacci_action_server]: Feedback: array('i', [0, 1, 1, 2])
[INFO] [fibonacci_action_server]: Feedback: array('i', [0, 1, 1, 2, 3])
[INFO] [fibonacci_action_server]: Feedback: array('i', [0, 1, 1, 2, 3, 5])
# etc.