Requirement:Only start all nodes and then this ros2 launch process exit

[lianggangMei]

When we launch al lot of nodes with run/run_async in ros2 launch, because ros2 launch process has high cpu uasge so we don't need an event loop and visit all entities of all included LaunchDescription instances. Only start all nodes and then this ros2 launch process exit, which is similar to: ros2 run node1 ros2 run node2 ros2 run node3 ros2 run node4 ... exit

 def run(self, *, shutdown_when_idle=True) -> int: 
     """ 
     Run an event loop and visit all entities of all included LaunchDescription instances. 

     This should only ever be run from the main thread and not concurrently with 
     asynchronous runs (see `run_async()` documentation). 

[clalancette]

I guess I'm not sure why you would use launch at all in this situation. Couldn't you just write a bash script that did this instead? What would be the advantage of having this in launch?

[lianggangMei]

Thanks clalancette because we need LaunchDescription py as below to config, it is easier/better to maintain and extend for our projects.

from launch import LaunchDescription from launch_ros.actions import Node

here we can do a lot of things.

...

def generate_launch_description(): return LaunchDescription( [ Node(