ros2 param set, on_parameter_event called twice

[MarcTestier]

Bug report

Required Info:

• Operating System:
  • Ubuntu 18.04
• Installation type:
  • source
• Version or commit hash:
  • 2049b2f
• DDS implementation:
  • Fast-RTPS
• Client library (if applicable):
  • rclcpp

Steps to reproduce issue

ros2 param set /parameter_events plop 42

Expected behavior

Call on_parameter_event once with the new/changed/deleted parameters

Actual behavior

Call on_parameter_event twice, the first time with no parameters then with the new/changed/deleted parameters

Additional information

When I set a parameter using the parameter client in a node, on_parameter_event is called once, as it should be, but when I set a parameter using command line, the on_parameter_event is called twice. And the first time it's triggered, there is no parameters inside. The output using a node :

[INFO] [parameter_events]: 
Parameter event:
 new parameters:
  foo
 changed parameters:
 deleted parameters:

The output using command line ros2 param set /parameter_events plop 42 :

[INFO] [parameter_events]: 
Parameter event:
 new parameters:
 changed parameters:
 deleted parameters:

[INFO] [parameter_events]: 
Parameter event:
 new parameters:
  plop
 changed parameters:
 deleted parameters:

I created a simple/minimal file to test this : here, based on the demos pkg.

I'm not 100% sure whether the issue should be here or in rclcpp, but since it only happens when I use the command line, I'm posting it here.

[MarcTestier]

I just tried using ROS 2 bouncy installed with the deb pkgs and this problem doesn't appear, but it still appears using the one from source.

[wjwwood]

That is strange, but I didn't have a chance to reproduce it yet. I don't have an ideas off the top of my head as to why it would be called twice. I don't think it's expected behavior.

Have you tried creating a C++ program that just sets the parameter on the node from another process (rather than from within the same node/process)? If it also doesn't get called twice in that case I'd say it's definitely an issue with this tool, otherwise it might be related to where the node is being set from.

[MarcTestier]

Have you tried creating a C++ program that just sets the parameter on the node from another process (rather than from within the same node/process)? If it also doesn't get called twice in that case I'd say it's definitely an issue with this tool, otherwise it might be related to where the node is being set from.

If you mean having a NODE 1 set param on NODE 2, then yes I did and on_parameter_event is called once.