Add watchdog_interval method

[Mr0grog]

This adds a new watchdog_interval method that returns the current watchdog interval in seconds (or 0 if no interval is set). Fixes #6.

A few notes here:

• I tried to keep this simple by just adding a watchdog_interval method and not changing any other code. That said, it might be convenient if watchdog? returned false if disabled and the interval (instead of true) if enabled. That would work fine for most people (since floats are truthy), but might be subtly breaking if someone is literally comparing the return value to true.

• Revised the docs for watchdog? a bit to hopefully make them clearer for users who aren’t already deeply familiar with sd_notify, instead of focusing on under-the-hood bits like environment variables. Happy to change this back if you don’t like that.

• Added tests for watchdog? since there weren’t any.

• Added an example of using watchdog to the README. It’s a little complex! Let me know if you have ideas for making it simpler or clearer, or if I should remove it.

• When I ran Rubocop, I got a huge number of errors, mostly from cops that are probably new since this gem last received a major update. I went ahead and turned most of them off in the config, although I did add required_ruby_version to the gemspec file since that seemed like a good idea. I set the value (>= 2.3.0 >= 2.2.0) based on the GitHub Actions CI job. Let me know if I should change or remove it.

[Mr0grog]

Given how many cops I had to turn off in this PR, it might be better to disable them all here and explicitly turn on the ones you want. I’m not sure which you want, though, so I just turned off all the new and/or error-triggering ones.

[agis]

I guess the issue is that rubocop was never pinned to a specific version. I'd suggest to just disregard all the offenses, given that it's not a requirement in the CI, and just revert this change here, since it's out of context of this PR.

[Mr0grog]

OK, would it be good to at least remove this Rubocop config file, then? It seems a little confusing to have an unusable .rubocop.yml file here.

[Mr0grog]

Just checking in on this, since it's been sitting for a year. Anything you need from me to land this, @agis?

[agis]

Apologies for the radio silence. Left some comments, thanks for this!

[agis]

I think it would be a clearer API if we returned nil when the value isn't set. Also I'd prefer to limit this rescue to the place it's intended for, i.e

def self.watchdog_interval
  wd_usec = Integer(ENV["WATCHDOG_USEC"]) rescue nil
  wd_usec && wd_usec / 1e6
end

WDYT?

[Mr0grog]

I think it would be a clearer API if we returned nil when the value isn't set.

Sure. (Just for background, I usually try to avoid returning a different types as a general practice so the JIT can keep methods optimized. This probably isn’t a method that’s going to be on a hot path, though, so that’s not a big deal here.)

[agis]

I guess the issue is that rubocop was never pinned to a specific version. I'd suggest to just disregard all the offenses, given that it's not a requirement in the CI, and just revert this change here, since it's out of context of this PR.

[agis]

What's the rationale behind this requirement?

[Mr0grog]

See the PR description:

When I ran Rubocop, I got a huge number of errors, mostly from cops that are probably new since this gem last received a major update. I went ahead and turned most of them off in the config, although I did add required_ruby_version to the gemspec file since that seemed like a good idea. I set the value (>= 2.3.0 >= 2.2.0) based on the GitHub Actions CI job. Let me know if I should change or remove it.

That is, Rubocop required that I add required_ruby_version or disable that cop. It seemed more reasonable in this case to add it to the gemspec and ask you if you wanted a different value.

From your other comments, it sounds like you'd rather just ignore Rubocop for this repo, though, so I can pull this back out if that’s what you’d like. (Is that what you’d like?)

[agis]

I see, thanks for elaborating. In that case, yes, let's remove the rubocop config completely.

[agis]

This could be simplified to `assert SdNotify.watchdog?

[Mr0grog]

@agis OK, I think I’ve made all the changes you asked for and this is ready for re-review.

Since this PR was originally written, GitHub dropped support for Ubuntu 20.04, so I had to update the CI config a bit — the “old” tests run in Ubuntu 22.04, and use Ruby 2.1 since Ruby 2.2 is no longer supported by the ruby/setup-ruby action on any Ubuntu versions supported on GitHub Actions. I’m assuming based on your previous comments about required_ruby_version that you do want to support Ruby 2.1, but I can also just remove the “old” tests entirely if this is not right. (Also: Ruby 2.1 should be installable just fine on Ubuntu 24.04, so we could move all this into the main test job instead having a separate “old” one. The main test job just needs to bundle exec so it gets the right minitest version.)

[agis]

Thanks!