client.call blocks the thread about rclpy HOT 3 CLOSED

    future = cli.call_async(req)
    rclpy.spin_until_future_complete(node, future)
    response = future.result()

from example_interfaces.srv import AddTwoInts
from rclpy.executors import MultiThreadedExecutor

import rclpy
import threading


def run_executor(executor, node):
    executor.add_node(node)
    try:
        executor.spin()
    finally:
        executor.shutdown()


def main(args=None):
    rclpy.init(args=args)
    node = rclpy.create_node('minimal_client')
    cli = node.create_client(AddTwoInts, 'add_two_ints')

    # Run executor that uses a thread pool in another thread so main thread is free to do what it wants
    exec = MultiThreadedExecutor(num_threads=4)
    thread = threading.Thread(target=run_executor, args=(exec, node), daemon=True)
    thread.start()

    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...')

    response = cli.call(req)

    node.get_logger().info(
        'Result of add_two_ints: for %d + %d = %d' %
        (req.a, req.b, response.sum))

    node.destroy_node()
    rclpy.shutdown()


if __name__ == '__main__':
    main()