ROS2 how a node can be notified if one of its own parameters is updated?
In ROS2 each node has its own Parameter Server.
Assume that I have a node that hosts several parameters: PARAM_A, PARAM_B...
Other nodes can modify these parameters.
The node can register a callback using set_on_parameters_set_callback in order to validate parameter changes.
Moreover it can also subscribe to the parameter_events topic.
The node has some functions that have to be called every time a parameter is changed. These functions may be different depending on which parameter has been changed.
Where should these function be called?
To me it looks like set_on_parameters_set_callback should only take care of validate changes.
A callback to parameter_events topic may look the correct place, however, this would be triggered also for events not related with this node, potentially being a waste of resources.
I am also curious about the recommended approach to this.
The callback
set_on_parameters_set_callbackcannot be used, because changes might be rejected after this has been called; e.g. if the new value is outside a required range.To me the main issue is to update local copies of the parameters. It would be possible to always use the parameters through
Node::get_parameterinstead of storing a local copy. However, this is not very efficient, as it both requires locking a mutex and looking up in a std::map.