Make sleep in ros2_control node optional (backport #3213)

[mergify]

Description

The PR makes the sleep that paces the controller manager loop optional. This can be useful in situations where

• Hardware sends data from an internal control loop at a fixed rate
• The hardware interface has a blocking read on that data
• The blocking hardware interface is the only one running in the controller_manager loop or the other ones aren't significantly affected by that.

I am aware, that this would only cover a subset of all applications facing this issue. I was holding this back because of the efforts made in ros-controls/realtime_tools#478 but since this will require more designing, I wanted to propose this simple fix for simple systems at least.

Did you use Generative AI?

I had help from Cursor to generate the tests, specifically commit 296ae28

Additional Information

I've implemented a PoC using this with the ur_robot_driver in UniversalRobots/Universal_Robots_ROS2_Driver#1760. There, I also describe the impact on joint control that this would have.

TODOs

This is a draft PR for now, as a couple of things aren't finalized, yet. However, I would like some input on the first two points on the list below.

• Verify concept -- I would like to verify that this concept would be accepted before implementing further
• Finalize parameter naming -- I just picked a parameter name as I thought it made sense from our use case, but it might not be the best one to describe the behavior.
• Add tests

---

This is an automatic backport of pull request #3213 done by [Mergify](https://mergify.com).

[mergify]

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Changes to be committed:
	modified:   controller_manager/doc/userdoc.rst
	new file:   controller_manager/include/controller_manager/sleeping_policies.hpp
	modified:   controller_manager/package.xml
	modified:   controller_manager/src/ros2_control_node.cpp
	new file:   controller_manager/src/sleeping_policies.cpp
	new file:   controller_manager/test/test_sleeping_policies.cpp

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   controller_manager/CMakeLists.txt

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[codecov]

Codecov Report

❌ Patch coverage is 93.33333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.49%. Comparing base (1a27987) to head (818c345).

Files with missing lines	Patch %	Lines
controller_manager/src/ros2_control_node.cpp	82.35%	2 Missing and 1 partial ⚠️
controller_manager/src/sleeping_policies.cpp	88.46%	2 Missing and 1 partial ⚠️
controller_manager/test/test_sleeping_policies.cpp	98.38%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            jazzy    #3452      +/-   ##
==========================================
+ Coverage   89.43%   89.49%   +0.06%     
==========================================
  Files         161      163       +2     
  Lines       20568    20651      +83     
  Branches     1630     1633       +3     
==========================================
+ Hits        18395    18482      +87     
+ Misses       1502     1498       -4     
  Partials      671      671              

Flag	Coverage Δ
unittests	89.49% <93.33%> (+0.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
controller_manager/test/test_sleeping_policies.cpp	98.38% <98.38%> (ø)
controller_manager/src/ros2_control_node.cpp	65.62% <82.35%> (+9.74%)	⬆️
controller_manager/src/sleeping_policies.cpp	88.46% <88.46%> (ø)

... and 2 files with indirect coverage changes

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[fmauch]

Just tested this with UniversalRobots/Universal_Robots_ROS2_Driver#1760 and works as expected :-)