Setting `use_sim_time` on one node enables ros time on all nodes

[mikaelarguedas]

Bug report

Required Info:

• Client library:
  • rclcpp 45d74ba

Steps to reproduce issue

Add a print in the time source onparameter_event callback by applying this patch to rclcpp

diff --git a/rclcpp/src/rclcpp/time_source.cpp b/rclcpp/src/rclcpp/time_source.cpp
index bfd0ea2..0952d85 100644
--- a/rclcpp/src/rclcpp/time_source.cpp
+++ b/rclcpp/src/rclcpp/time_source.cpp
@@ -225,9 +225,11 @@ void TimeSource::on_parameter_event(const rcl_interfaces::msg::ParameterEvent::S
     }
     if (it.second->value.bool_value) {
       parameter_state_ = SET_TRUE;
+      RCUTILS_LOG_ERROR("enabling ros time!")
       enable_ros_time();
     } else {
       parameter_state_ = SET_FALSE;
+      RCUTILS_LOG_ERROR("disabling ros time!")
       disable_ros_time();
     }
   }

Shell 1: run a C++ listener:

ros2 run demo_nodes_cpp listener

Shell 2: run another C++ node:

ros2 run demo_nodes_cpp add_two_ints_server

Shell 3:
Set use_sim_time on the listener:

$ ros2 param set listener use_sim_time true
Set parameter successful

Expected behavior

Shell 1 should print:

[ERROR] []: enabling ros time!

Shell 2 should not print anything

Actual behavior

Both shells print

[ERROR] []: enabling ros time!

Additional information

This is due to the fact that:

• /parameter_events is a global topic and its messages don't contain any node specific information. We could:
  • add information about the node in the message (see Add RclHeader message rcl_interfaces#27 for a proposal)
  • make the parameter_events topic namespaced on the nodes (discussed in Parameters refactor ros2#432)
• rclcpp is listening to parameter_events and parsing its data to know what's hosted on the same node. It should instead leverage its own parameter server (created in all nodes by default) to get notified when a new value of use_sim_time has been set

This seems to be a problem for parameters in general, but for use_sim_time, I've been finding this issue to be convenient. In my use cases, I'm either running in real time or simulation, never both at the same time. Being able to set use_sim_time on one node and have the whole system switch has been more convenient that trying to enumerate all nodes and switch them all with separate commands.

It seems if we get parameters like use_sim_time scoped to nodes, there still needs to be a way to switch the whole system to simulation mode at once, possibly triggered by the presence of gazebo

[wjwwood]

I think this is addressed with ros2/rcl_interfaces#51?

Being able to set use_sim_time on one node and have the whole system switch has been more convenient that trying to enumerate all nodes and switch them all with separate commands.

I think that's better left to the configuration management system, e.g. having launch set all nodes based on one setting from the user.

[Darkproduct]

I think that's better left to the configuration management system, e.g. having launch set all nodes based on one setting from the user.

I strongly disagree with this. I often run multiple launch files as well as using ros2 run directly for nodes in development or for having them in another terminal and I absolutely hate that there is no "global" way for setting a parameter.

A nice thing is, that you can leave rviz running and restart everything and you still have the changes made to rviz, BUT by running rviz2 you wont set the use_sim_time param and when restarting the simulation you'll get some errors, along the lines of "can't use messages from the feature/past" and so on. I think you should be able to set the time source at the time you source your ws or adding a new command like ros2 time set clock x.

The current system leads to obscure parameter files, like navigation2/nav2_bringup/nav2_params, where you find every node listed with use_sim_time parameter, which makes the whole thing a lot less readable. There are even multiple nodes without "any" parameters, but they need to get this one.

[fujitatomoya]

I think that at node initialization would be okay with user configuration. but it makes sense to enable/disable use_sim_time gracefully after launch the all system, this could be useful for development and simulation. which i think can be done the following command.

root@tomoyafujita:~/ros2_ws/colcon_ws# ros2 node list
/add_two_ints_server
/listener
root@tomoyafujita:~/ros2_ws/colcon_ws# for node in `ros2 node list`; do echo $node; ros2 param set $node use_sim_time true; done
/add_two_ints_server
Set parameter successful
/listener
Set parameter successful
root@tomoyafujita:~/ros2_ws/colcon_ws# for node in `ros2 node list`; do echo $node; ros2 param get $node use_sim_time; done
/add_two_ints_server
Boolean value is: True
/listener
Boolean value is: True

[Darkproduct]

I just found this: https://answers.ros.org/question/368802/ros2-set-parameters-from-file-and-directly/?answer=369015#post-id-369015

For example, to set the ROS parameter use_sim_time for all nodes in a launch file, you can something like

import launch
import launch_ros.actions

def generate_launch_description():
    return launch.LaunchDescription([
        launch_ros.actions.SetParameter(name='use_sim_time', value=True),
        # 'use_sim_time' will be set on all nodes following the line above
    ])

Havn't tested this yet.