[ros-users] [Discourse.ros.org] [Next Generation ROS] Composition and Parameters: Best Practice Suggestions

[Secretary Birds]

I'm playing around with the manual_composition example code and I want to insert a parameter service for the nodes.

I wasn't sure what the intended implementation path is for that.
I implemented it this way:
    
    // Add some nodes to the executor which provide work for the executor during its "spin" function.
    // An example of available work is executing a subscription callback, or a timer callback.
    auto talker = std::make_shared<composition::Talker>();
    auto tparameter_service = std::make_shared<rclcpp::parameter_service::ParameterService>(talker);
    auto tparameter_client = std::make_shared<rclcpp::parameter_client::SyncParametersClient>(talker);
    exec.add_node(talker);
    auto listener = std::make_shared<composition::Listener>();
    auto lparameter_service = std::make_shared<rclcpp::parameter_service::ParameterService>(listener);
    auto lparameter_client = std::make_shared<rclcpp::parameter_client::AsyncParametersClient>(listener);
    exec.add_node(listener);
    
    // spin will block until work comes in, execute work as it becomes available, and keep blocking.
    // It will only be interrupted by Ctrl-C.
    exec.spin();

By adding the two service/client objects for each node, I am successfully able to send and get params for each individual node using the ros2param tool.

However, I run into issues if I try to connect an **on_parameter_event()** callback.

    auto parameter_event_sub = tparameter_client->on_parameter_event(std::bind(&composition::Talker::event_callback, talker, std::placeholders::_1));

-

    void Talker::event_callback(const rcl_interfaces::msg::ParameterEvent::SharedPtr event)
    {
        std::cout << "Parameter event:" << std::endl << " new parameters:" << std::endl;
        for (auto & new_parameter : event->new_parameters) {
            std::cout << "  " << new_parameter.name << std::endl;
        }
        std::cout << " changed parameters:" << std::endl;
        for (auto & changed_parameter : event->changed_parameters) {
            std::cout << "  " << changed_parameter.name << std::endl;
        }
        std::cout << " deleted parameters:" << std::endl;
        for (auto & deleted_parameter : event->deleted_parameters) {
            std::cout << "  " << deleted_parameter.name << std::endl;
        }
    }
I added one to the talker client **tparameter_client**, but when I set variables to the listener, it still triggers the on_parameter_event. Interestingly, it doesn't add the parameter to the talker, but it does fire its on_parameter_event callback.
So, I'm not sure if that's a bug, or if I'm using the API incorrectly.

I've seen some comments where the parameter service/client stuff may be launched automatically inside the node in the future. So should I be putting it in the Talker class constructer instead? Will that be the intended usage of the parameter service, especially when working with components and composition?
Or have I discovered a bug and should add it to the GitHub Issues?

Thanks.






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