LaunchConfiguration is not read from ComposableNode when included inside a group action about launch_ros

[wjwwood]

Maybe you need to use the scoped argument for the GroupAction? I need to look in more detail at why you are using the group, but I guess the scope option needs to be flipped or the scope mechanism has a bug in it or something.

[wjwwood]

Maybe it has to do with the delayed evaluation of the substitution? I'm not sure...

[wjwwood]

I think since the load of the composable nodes is done asynchronously (with an event handler) the group has already ended and undone the scope:

launch_ros/launch_ros/launch_ros/actions/composable_node_container.py

Line 73 in c5e2aa2

composable_node_descriptions=self.__composable_node_descriptions,

I'm not sure how to fix this, a few options:

• perform the substitutions in ComposableNodeContainer::execute() before registering the event
• change how the containers are loaded to avoid the delay in evaluating the substitutions (i.e. do not use an event)
• store the launch config state and make sure it is used for the evaluation in the event handler (sort of like lambda capture or something)

[jrgnicho]

Also experiencing the same issue with ComposableNodeContainer where my python launch file looks like this

def generate_launch_description():
   
    container =  ComposableNodeContainer(
            node_name= 'perception',
            node_namespace= launch.substitutions.LaunchConfiguration('global_ns'),
            package= 'rclcpp_components',
            node_executable = 'component_container',
            composable_node_descriptions = [
                ComposableNode(
                package='crs_perception',
                node_plugin='crs_perception::LocalizeToPart',
                node_name='part_localization',
                node_namespace = launch.substitutions.LaunchConfiguration('global_ns')),
                ],
            output = 'screen'
        )    
    
    return launch.LaunchDescription([
        launch.actions.DeclareLaunchArgument('global_ns', default_value = ['/my_ns']),
        container])

It runs fine when I call it from the command line
but when I call it from an xml launch file

	    <include file="$(find-pkg-share crs_application)/launch/perception.launch.py">
	    	<arg name="global_ns" value="$(var group_ns)"/>
	    </include>

It errors out saying that the launch configuration 'global_ns' does not exist. Removing the argument has no effect either

[jacobperron]

I did some investigation and I can confirm the launch configuration dropped by the event handler:

launch_ros/launch_ros/launch_ros/actions/composable_node_container.py

Lines 95 to 105 in 8c05ebb

	RegisterEventHandler(
	event_handler=OnProcessStart(
	target_action=self,
	on_start=[
	LoadComposableNodes(
	composable_node_descriptions=self.__composable_node_descriptions,
	target_container=self
	)
	]
	)
	)

Looking through the commit history, the whole event handler strategy for loading seems vestigial; it was originally used in the LoadComposableNodes action, but since moved to the container action (see #16). I don't think it is necessary to use an event and we can simply return the load node action. See #170 for proposed fix.