ros2_eventdispatch

ROS(ROS2) are solutions to the inter-process communication problem, among other metaphors

python-eventdispatch (github) uses ROS2 as a message bus for robotics use-cases.

It does so with 3 packages in this upstream super-repo.

1. eventdispatch_python (provides the eventdispatch library)
2. eventdispatch_ros2_interfaces (ROSEvent.msg/srv)
3. eventdispatch_ros2 (ed_node, stage.launch)

---

ed_node

Instantiates a class child of CSBQCVED, Node

class ROS2QueueCVED(CSBQCVED, Node):

CSBQCVED :
Composite
Semaphore
Blackboard
Queue
Condition
Variable
Event
Dispatch

1. ~/dispatch service, subscription
2. ~/dispatch_list service, subscription (batch version)
3. events_module_path ros2 parameter

The events_module_path is a folder that is expected to have an events.py file that defines the following variables:

from events import event_dict, initial_events, events_module_update_blackboard, on_shutdown, make_validator

(note that events.py can be symlinked, and import each other or refactored for reuse)

• event_dict

This is a mapping str -> Class for the blackboard

• initial_events

list[[event primitives]], initial boundary conditions to dispatch

• events_module_update_blackboard

populate the blackboard with assets, ROS adapters, etc.

• on_shutdown

intended to be a graceful handler, but ROS shutdown is blunt

• make_validator

return a class that checks requests, stub to add extra logic

---

stage.launch

Convienence launch file, exposing the 2 most important launch args to ed_node

1. node_name
2. events_module_path

The idea is to stand up various ed_node instances via stage.launch as needed.

Since ed is such a compact framework, it may be more likely to expand capability by growing the Event subclasses in a blackboard than spawning more instances, but is an option anyways.