Logging meta-ticket

[dhood]

Steps towards the use of logging API and minimal logger severity configuration [limitations in square brackets].

Minimal functionality

• Logger objects in rclpy Expose logging macros in rclpy rclpy#103
• rclpy nodes have loggers associated with them [naming conventions hard-coded] Give nodes a logger rclpy#148
• C++ macros wrapping rcutils [specifying logger name instead of logger object] Implement rclcpp-specific logging macros [taking name not object] rclcpp#389
• Update demos to use logging [callbacks need access to node logger, C++ passing names not logger object] Replace print() in python demos with logger calls demos#190, Use logging macros [logger name instead of object] demos#191
• ROS 2 core using debug logging [no subloggers of nodes' loggers] Add debug logging rcl#187

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Demo/documentation

• Demo of service that sets logger level at runtime for logger name Add demo for logging + logger config demos#194 https://github.com/ros2/ros2/wiki/Logging-and-logger-configuration
• Wiki page on logger configuration https://github.com/ros2/ros2/wiki/Logging

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C++ logger object

• C++ macros taking logger object, factory functions Add Logger class and give one to nodes rclcpp#411 Swap to using logger object for logging macros demos#200
• Node logger name added to nodes in rcl, wrapped in python Store logger name associated with node rcl#212, Get node's logger name from rcl rclcpp#433, Get node's logger name from rcl rclpy#174
• ROS 2 core using subloggers from node's logger

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Enhancements

• Configuration of non-node loggers' context
• Improve ease-of-use of accessing node logger from callbacks
• Wrapping of "throttled" filter in C++ macros (done in Enable throttling logs rclcpp#879)
• Unique context of e.g. "once" for each logger object

[DLu]

The migration guide really should be updated to include some basic usage. It still says to use printf, and it took me an hour to sort through this to figure out the new syntax, and that was once I found this wiki page.

[wjwwood]

The migration guide really should be updated to include some basic usage.

Sorry the migration guide is out-of-date, but the good news is that it's a wiki so you can edit it:

https://github.com/ros2/ros2/wiki/Migration-Guide/_edit

and it took me an hour to sort through this to figure out the new syntax, and that was once I found this wiki page.

I understand that the migration guide was misleading, but if you just do a search (I did incognito) for "ros2 logging", you get something like this:

The first hit is this wiki page that @dhood made that explains how to configure logging and links to examples in both C++ and Python:

https://github.com/ros2/ros2/wiki/Logging

The second hit is a wiki page describing the logging demo she made:

https://github.com/ros2/ros2/wiki/Logging-and-logger-configuration

[wjwwood]

Also, all of our examples and demos use the new logging syntax if you want to look at them for additional examples of using logging, e.g.:

https://github.com/ros2/examples/blob/f6027edfb3a28f012438d1f2d587d0a980e9341c/rclcpp/minimal_subscriber/not_composable.cpp#L27

[DLu]

Thanks for those links, sincerely. Unfortunately, they did not show up in my Google searches for ros2 ros_info or ros2 rclcpp_info.

david.google_fu--

[wjwwood]

No worries, but we're busy in the middle of a release, so we would also (sincerely) appreciate help updating any documentation.

[clalancette]

Given that we've generally completed logging here, I'm going to close this one out.

There are still things to be done in logging (i.e. ros2/rcl_logging#92), but we should use more targeted issues for those.