Provide for local callbacks on parameter events in parameter node API

[tfoote]

This is a follow up to discussions in #595 and #608 and somewhat related to #296 but for the post change callbacks not validation stage which would be a 3rd callback type proposed.

It would be valuable to not rely on parameter events being published but use the internal node interface API to get the events in a callback for different interfaces. Along with that change if there was a more fully featured API for registering callbacks for parameter changes locally, the parameter event publishing could also be split out into a separate component that could obviate the need for a parameter to turn that functionality on and off in the constructor of the parameter, and avoid the dependencies on the clock and topics interface for the core parameter API.

[ros-discourse]

This issue has been mentioned on ROS Discourse. There might be relevant details there:

https://discourse.ros.org/t/security-ramifications-of-global-parameter-events/15924/8

[clalancette]

This was actually completed for Iron, so closing this out.

[jrutgeer]

@clalancette
It seems this issue is not fully complete, see this TODO item in the code.

I came across this due to someone asking about disabling /parameter_events subscribers on Robotics Stack Exchange.

So I think this should be reopened.

[clalancette]

It seems this issue is not fully complete, see this TODO item in the code.

This issue is indeed complete; we now provide a local callback that can be used. If you'd like to track changing the code in time_source.cpp to use that, please feel free to open a new issue.

[jrutgeer]

If you'd like to track changing the code in time_source.cpp to use that, please feel free to open a new issue.

Ok.

However, @fujitatomoya a few lines above in this thread there's a reference to a commit where you seem to already have implemented this?

fujitatomoya added a commit to fujitatomoya/rclcpp that referenced this issue on Oct 1, 2019
fujitatomoya@5f21f03

[fujitatomoya]

@jrutgeer to be honest, i do not remember... probably i was working on the experimental patch? bad memory, sorry 😓

created tracking issue for this, #2370