rospy logging makes unneccessary requests to roscore when /rosout_disable_topics_generation is unset

[jobafr]

Hi,

this is a follow-up to #1855, because I think the fix there was incomplete.

When the parameter /rosout_disable_topics_generation is unset, the call to get_param_cached in
https://github.com/ros/ros_comm/blob/noetic-devel/clients/rospy/src/rospy/impl/rosout.py#L91
returns the default value (False), but does not persist that default into the local param cache. Every subsequent call to rospy.loginfo/warn/error will then again query roscore the same way.

I tested this on the current ros noetic ubuntu packages as well as on the current ros_comm noetic-devel branch. When using rospy logging a lot, this can lead to roscore consuming high amounts of CPU time and becoming unresponsive to more useful requests (which is how we noticed the problem).

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Steps to reproduce:

Launch three terminal windows:

• In the first one, start roscore
• In the second one, open the roscore logs: tail -f ~/.ros/log/latest/master.log
• In the third one, run a python shell and execute this:

import rospy
rospy.init_node("foo")
for _ in range(100):
    rospy.loginfo("foo")

The second shell now prints this for each log call:

[rosmaster.master][INFO] 2023-07-12 18:54:16,598: +CACHEDPARAM [/rosout_disable_topics_generation] by /foo
[rosmaster.master][INFO] 2023-07-12 18:54:16,599: +CACHEDPARAM [/rosout_disable_topics_generation] by /foo
[rosmaster.master][INFO] 2023-07-12 18:54:16,600: +CACHEDPARAM [/rosout_disable_topics_generation] by /foo
[rosmaster.master][INFO] 2023-07-12 18:54:16,601: +CACHEDPARAM [/rosout_disable_topics_generation] by /foo
[rosmaster.master][INFO] 2023-07-12 18:54:16,603: +CACHEDPARAM [/rosout_disable_topics_generation] by /foo

If you open a fourth shell, and run rosparam set /rosout_disable_topics_generation False, and then execure the same python code again, no '+CACHEDPARAM' calls hit the roscore anymore.

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I'm not sure what the correct behaviour would be here.

• Maybe get_param_cached should set the default on roscore if the value is empty and a default has been provided
• or, alternatively, it could cache "value does not exist on server" in some way, and subscribe to changes normally.
• or, roscore could initialize /rosout_disable_topics_generation to False on startup (I'm unsure as to what that parameter actually does), which would fix the logging issue, but keep the unexpected non-caching behaviour for any other usage of get_param_cached.

[EricGallimore]

We're also running into this issue, especially on machines without many CPU cycles to spare.

One simple approach might be to add <param name="rosout_disable_topics_generation" value="False" /> to rosdistro/etc/ros/roscore.xml

(This was inspired by this post: https://answers.ros.org/question/301590/how-to-always-load-a-parameter-without-adding-it-to-every-launch-file/ )

I think that this will preserve the ability to set the parameter in a different launch file, but would set a default so that the caching works.

For now, we're adding that parameter to our top-level launch files.

[EricGallimore]

I should add that has a huge impact on the CPU utilization of rosmaster. On our system, setting this parameter (to either true or false, it doesn't matter which) halves the rosmaster CPU utilization.

[jobafr]

I should add that has a huge impact on the CPU utilization of rosmaster.

Yes, this is how we found this issue in the first place.