Revision history [back]

I also faced a same problem, so I tried that fixed this code.

Use a following code if you like:

from example_interfaces.srv import AddTwoInts

import rclpy
import random


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

    node = rclpy.create_node('minimal_client_async')

    cli = node.create_client(AddTwoInts, 'add_two_ints')

    req = AddTwoInts.Request()
    # req.a = 41
    # req.b = 1
    while not cli.wait_for_service(timeout_sec=1.0):
        node.get_logger().info('service not available, waiting again...')

    # future = cli.call_async(req)
    while rclpy.ok():
        req.a = random.randrange(10)
        req.b = random.randrange(10)
        future = cli.call_async(req)
        # rclpy.spin_once(node)
        rclpy.spin_until_future_complete(node, future)
        if future.done():
            try:
                result = future.result()
            except Exception as e:
                node.get_logger().info('Service call failed %r' % (e,))
            else:
                node.get_logger().info(
                    'Result of add_two_ints: for %d + %d = %d' %
                    (req.a, req.b, result.sum))
            # break

    node.destroy_node()
    rclpy.shutdown()


if __name__ == '__main__':
    main()

[environment]
・Ubuntu 20.04.01 LTS (docker)
・ROS2 Foxy