[humble] Autostarting lifecycle nodes and example launch file demo (backport #430)

[mergify]

This resolves #418 which implements autostarting lifecycle nodes. This is complete and ready for a review

You'll notice a couple of key changes worth explaining:

1. There is a new is_lifecycle_node attribute of the node and lifecycle nodes which is needed to remove a circular dependency on the LifecycleNode within the LifecycleTransition class which only is type checking. I replace this type check with checking if a non-None object (1) has the attribute at all and (2) has a lifecycle attribute with appropriate logging between the difference of a non-lifecycle node being attempted vs a non-node. This has been tested as well to function using the demos.

2. You will also notice that I refactored lifecycle node to have a separate util LifecycleEventManager, who handles the event emitting, handling, and topic listening for lifecycle nodes. This way, this can be used in lifecycle-components as well! No changes were made here except removing the self.__current_state variable which was completely unused. The LifecycleEventManager is only created if the node requests autostart at Launch time and otherwise has no overhead nor exposes the interfaces/event handler/emitter if its a non-lifecycle node.

3. The component nodes don't add a / before the node names with the namespaces. This messes with the node event matcher. I add in a leading / so that the action.node_name == node_name which has the / forcably applied in the node event matcher

4. I tested LifecycleNode, ComposableNodeContainer, LoadCompoableNodes for all cases: autostart=True autostart=False, and autostart field not supplied. You can also run any experiments you like using the 2 extra launch files I provide in the examples directory which shows all the features at work/

   ---

   This is an automatic backport of pull request Autostarting lifecycle nodes and example launch file demo #430 done by Mergify.

[mergify]

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Changes to be committed:
	new file:   launch_ros/examples/lifecycle_autostart_pub_sub_launch.py
	new file:   launch_ros/examples/lifecycle_component_autostart_pub_sub_launch.py
	modified:   launch_ros/launch_ros/actions/lifecycle_node.py
	modified:   launch_ros/launch_ros/descriptions/__init__.py
	new file:   launch_ros/launch_ros/descriptions/composable_lifecycle_node.py
	modified:   launch_ros/launch_ros/descriptions/composable_node.py
	modified:   launch_ros/launch_ros/utilities/__init__.py
	new file:   launch_ros/launch_ros/utilities/lifecycle_event_manager.py
	modified:   test_launch_ros/test/test_launch_ros/actions/test_lifecycle_node.py

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   launch_ros/launch_ros/actions/load_composable_nodes.py
	both modified:   launch_ros/launch_ros/event_handlers/on_state_transition.py

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[christophebedard]

Note: #449 is a follow-up fix to the PR that this backports, so it should be backported after this too.

[christophebedard]

@emersonknapp since you requested this backport, would you be willing to fix the merge conflicts?

[emersonknapp]

@christophebedard done!

[christophebedard]

@Mergifyio rebase

[mergify]

rebase

✅ Branch has been successfully rebased

[christophebedard]

Pulls: #476
Gist: https://gist.githubusercontent.com/christophebedard/7a7fa64091a1902884e0cc5fd18b7e8d/raw/594011c5cb234e83c9d082ce107e21d7fb767e6a/ros2.repos
BUILD args: --packages-above-and-dependencies launch_ros test_launch_ros
TEST args: --packages-above launch_ros test_launch_ros
ROS Distro: rolling
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/16687

• Linux
• Linux-aarch64
• Linux-rhel
• Windows

[christophebedard]

@ros-pull-request-builder retest this please

[christophebedard]

This isn't imported and it doesn't exist in Humble: https://github.com/ros2/launch/blob/rolling/launch/launch/some_entities_type.py

[ahcorde]

what's the status of this PR @emersonknapp @christophebedard ?

[emersonknapp]

Ah, sorry I've let it linger so long. There's a couple utilities that this diff depends on that aren't in this backport so it doesn't work right now. Requires just a bit of manual tweaking, should be easy but I haven't been able to get to it yet.

Maybe a priority in the next week or two, since I mention it briefly in my roscon talk 😅