Save / Dump / Load parameters to / from file using rclcpp

[Mat198]

Description

Create a function to save parameters to a file inside a C++ node. Something like `node->save_parameters(path);'. This can be useful when the parameters are changed inside a callback and the user wants to restart the node with those changes applied.

I understand that the launch files provide sufficient features to load the parameters at start. However, it can be useful to load a configuration set, making it easier to change the file loaded than each parameter individually.

It differs from ros2_persist_parameter_server in that it's not centralized. The parameters are still owned by the node, and it's responsible for managing them. A non-centrilized aproach is better for modularity as it's not necessary to add or remove packages from the central entity when changes are made. The ros2 param dump is also not the best option, given the modularity argument. Maintenance in a central entity is something we would like to avoid.

Motivation

I'm working on an autonomous sprayer called Arbus 4000 JAV. We have several parameters, such as spraying configuration and behaviour ones, in the system. We would like to save these parameters in a persistent way so the user can change them at run time and have them already configured on reboot. Also, it's useful to change between preconfigured spraying behaviours for different crops wich consist in load some parameters.

Design / Implementation Considerations

No response

Additional Information

Does it make sense to be part of the rclcpp, or is it better to have a dedicated class for that?

Is there a better way to do that? Are there any other use cases?

[Barry-Xu-2018]

A new argument needs to be added to ROS-specific arguments to provide the path and file name for saving the parameters.

Besides, node->save_parameters(path); only saves a single node's parameters. Should we consider saving all nodes' parameters? I’m not sure if there’s actually a real need for this. --ros-args --params-file can support to load parameters for multiple nodes.

[Mat198]

I don't think a new ROS-specific argument is absolutely necessary. As I suggested, the file path could be passed in the function call.

Each node should be responsible for its own parameters, so this call should save every parameter of the node that called the function.

The --ros-args --params-file only supports loading during startup. I think it can be useful to load a parameters file during runtime to change between "system configurations".

[Barry-Xu-2018]

I don't think a new ROS-specific argument is absolutely necessary. As I suggested, the file path could be passed in the function call.

Each node should be responsible for its own parameters, so this call should save every parameter of the node that called the function.

Got it.
You mean only a new API is needed. If users want to modify the save path dynamically (without recompiling the program), they should solve it themselves (for example, by using environment variables).
Let's hear the opinions of other community members.