WaitForToppics spends a long time waiting for the thread to join

[sloretz]

While debugging #304 I noticed WaitForTopics spends a lot of time joining the thread it creates (up to 1 second).

launch_ros/launch_testing_ros/launch_testing_ros/wait_for_topics.py

Line 82 in a114e1f

self.__ros_spin_thread.join()

It looks like the thread spins for a whole second before checking if it should shutdown:

launch_ros/launch_testing_ros/launch_testing_ros/wait_for_topics.py

Lines 73 to 74 in a114e1f

	while self.__running:
	self.__ros_executor.spin_once(1.0)

I suspect this could be fixed by deleting _spin_function and using self.__ros_executor.spin as the thread target.
Then the thread could be joined must faster by shutting down the rclpy.Context before trying to join it.

[Keng12]

Couldn't the same be achieved by changing the timeout parameter from 1.0 to 0? I. e.:

self.__ros_executor.spin_once(0.0)

[sloretz]

Couldn't the same be achieved by changing the timeout parameter from 1.0 to 0?

0 means the executor won't wait for work. Without any other blocking it would use up to a full CPU core.

[Keng12]

I see. Then I will implement your suggestions and create a PR.

[jacobperron]

Fixed in #314