Often, when you close Gazebo, RViz doesn't close, or when you close RViz, Gazebo (either client or VERY often, server) keeps running, or when you press CTRL-C... same thing. Let's fix it.
We are going to add event handlers that, when Gazebo dies, kills RViz, and when RViz dies, kills Gazebo.
from launch.actions import DeclareLaunchArgument, EmitEvent, RegisterEventHandler
from launch.event_handlers import OnProcessExit
from launch.events import Shutdown
...
gazebo_exit_event_handler = RegisterEventHandler(
event_handler=OnProcessExit(
target_action=gazebo,
on_exit=EmitEvent(event=Shutdown(reason='gazebo exited'))))
rviz_exit_event_handler = RegisterEventHandler(
event_handler=OnProcessExit(
target_action=rviz_cmd,
on_exit=EmitEvent(event=Shutdown(reason='rviz exited'))))
...
ld = LaunchDescription()
...
ld.add_action(gazebo_exit_event_handler)
ld.add_action(rviz_exit_event_handler)
...
Very simple.