[POC] Fix failing ros2param tests

[hidmic]

CI up to ros2param and ros2cli:

• Linux
• Linux repeated
• Linux-aarch64
• macOS
• Windows

[hidmic]

Well, it's finally passing. I have yet to explain why this FIN_WAIT_2 state timeout made all the difference though. FYI @ivanpauno.

[hidmic]

Alright, Ivan's still able to reproduce the failure. It appears it just made it less likely, so this won't do either.

@clalancette @cottsay what shall we do for Galactic? We have:

• the original approach with SO_REUSEADDR, which caused flakes in ros2cli; or
• Ensure only one daemon can run at a time #622 approach with SO_LINGER, which causes flakes in ros2param; or
• an hypothetical third approach using file locks, which we haven't tried yet.

Do we keep trying? Do we stick to a known issue and defer resolution?

[cottsay]

So the behavior that ros2cli will exhibit in Galactic is a flaky test, correct? How likely is it that an end-user would experience the bug "in the wild"?

[hidmic]

So the behavior that ros2cli will exhibit in Galactic is a flaky test, correct? How likely is it that an end-user would experience the bug "in the wild"?

That depends on the implementation. With SO_REUSEADDR, you'd need two ros2 daemon start racing with each other. With SO_LINGER, I suspect you need to run into a simultaneous connection close situation (though that's mostly a guess, we don't really know why ros2param flakes happen).

[clalancette]

Do we keep trying? Do we stick to a known issue and defer resolution?

I would say that we should still try to debug this for Galactic, but as a relatively low priority. So far it seems unlikely that a user will hit this in real-life, so I think it is worthwhile to debug the problem and figure out what is really going on before we make further changes.

[hidmic]

Closing in favor of #652.