multi_executor.py

import rclpy
from rclpy.node import Node

import threading
from std_msgs.msg import String


class MinimalPublisher(Node):

    def __init__(self, name):
        super().__init__(f'minimal_publisher_{name}')
        self.publisher_ = self.create_publisher(String, 'topic', 10)
        timer_period = 0.5  # seconds
        self.timer = self.create_timer(timer_period, self.timer_callback)
        self.i = 0
        self.name = name

    def timer_callback(self):
        msg = String()
        msg.data = f'Hello World {self.name}: {self.i}'
        self.publisher_.publish(msg)
        self.get_logger().info('Publishing: "%s"' % msg.data)
        self.i += 1


class MinimalSubscriber(Node):

    def __init__(self, name):
        super().__init__(f'minimal_subscriber_{name}')
        self.subscription = self.create_subscription(
            String,
            'topic',
            self.listener_callback,
            10)
        self.subscription  # prevent unused variable warning

    def listener_callback(self, msg):
        self.get_logger().info('I heard: "%s"' % msg.data)


def main(args=None):
    rclpy.init(args=args)
    rclpy.init(args=args)
    print('hi1')

    minimal_publisher = MinimalPublisher('pub1')
    minimal_subscriber = MinimalSubscriber('sub1')
    print('hi2')

    minimal_publisher2 = MinimalPublisher('pub2')
    minimal_subscriber2 = MinimalSubscriber('sub2')

    # WORKS.
    # executor = rclpy.executors.MultiThreadedExecutor()
    # executor.add_node(minimal_publisher)
    # executor.add_node(minimal_subscriber)
    # executor.add_node(minimal_publisher2)
    # executor.add_node(minimal_subscriber2)
    # executor_thread = threading.Thread(target=executor.spin, daemon=True)
    # executor_thread.start()
    # executor_thread.join()

    # This doesn't work.
    executor1 = rclpy.executors.MultiThreadedExecutor()
    executor2 = rclpy.executors.MultiThreadedExecutor()
    executor1.add_node(minimal_publisher)
    executor1.add_node(minimal_subscriber)
    executor2.add_node(minimal_publisher2)
    executor2.add_node(minimal_subscriber2)
    executor_thread1 = threading.Thread(target=executor1.spin, daemon=True)
    executor_thread1.start()
    executor_thread1.join()
    executor_thread2 = threading.Thread(target=executor2.spin, daemon=True)
    executor_thread2.start()
    executor_thread2.join()


if __name__ == '__main__':
    main()