logging: log4cxx support?

[rr-tom-noble]

I'm currently using ROS noetic which I believe uses rosconsole / log4cxx for logging. This appears to be a widely used and customisable logging framework. As far as I can tell, it seems that ROS2 is using its own logging system?

Is there a plan to support log4cxx in the future? If not, what was the reason for moving away from it?

[rr-tom-noble]

Ah, I think I've found my answer here:
ros2/rcl_logging#78

My use-case is that I'm wanting to output the logs in a JSON format. I've read the logging and config documentation here:
https://docs.ros.org/en/humble/Tutorials/Demos/Logging-and-logger-configuration.html

My use-case includes adding custom fields to the output, so I don't think I'd simply be able to make use of the RCUTILS_CONSOLE_OUTPUT_FORMAT environment variable.

From what I can tell, I may need to implement a custom logger, but it's unclear to me:

• Which class this should be inheriting from: rclcpp::Logger ? spdlog::formatter ?
• How I can configure ROS2 to use this custom logger by default (i.e. something akin to the rosconsole config file from ROS1)

[rr-tom-noble]

gabime/spdlog#2861

Something like this may work for my use-case. Is there a way to specify custom spdlog formatters in config?

[fujitatomoya]

@rr-tom-noble i think that you already found the original query with this issue. do you want to keep this open? IMO having formatter with spdlog, ros2/rcl_logging#92 would be the best place to discuss and closing this issue?

[rr-tom-noble]

Hi @fujitatomoya. Yeah, that makes sense. Thanks for confirming

[clalancette]

I think we have a resolution here (to move to a different issue), but I wanted to provide a couple of bits of additional context.

First, most of the details on why we moved from log4cxx to spdlog can be found in ros2/build_farmer#189, ros2/rcl_logging#78, and ros2/rcl_logging#17. In short, log4cxx had a lot of issues surrounding the lifetime of objects at the time I looked at this, and moving to spdlog solved all of them.

One other thing I'll mention is that, until ros2/rcl_logging#92 is solved, you should be able to take a different (though less efficient path). In particular, by default all logs go to the console, to disk, and to the network on the /rosout topic. So if you really want to format your logs in a particular way, you can write a node that subscribes to /rosout, and writes them out however you want. This does involve more network processing, but the good news is that this aggregates the logs from all nodes across the whole network.