Add end_time_mono to telemetry :stop events

[cheerfulstoic]

The Spandex library needs a 'completion_time' and it's not possible to get the start time at the beginning of the span to calculate it based on the duration

[benwilson512]

Thanks!

[andrewhr]

Hey @cheerfulstoic, giving that's not released yet, are you ok with renaming that to monotonic_time like in :telemetry.span/3?

Reason is, at #1170 I propose some changes and end up using the telemetry.span/3 as implementation detail. Assuming changes at that PR are not an option, I still argue for using the same names just for consistency - sort of unofficial convention.

What do you think?

[cheerfulstoic]

So do you mean that start_time_mono and end_time_mono would both become monotonic_time?

I'm fine with it, though if start_time_mono is changing I think that would be a breaking change, and I'd love for my change to go out sooner than that 😄 But that's probably still possible

[benwilson512]

@cheerfulstoic start_time_mono is not changing. end_time_mono is monotonic. start_time_mono is already monotonic.

[cheerfulstoic]

Yeah, that's fine, but @andrewhr was suggesting changing the key to monotonic_time. Up to you, for sure 😄

[benwilson512]

Apologies, didn't read the full thread. @andrewhr we can add keys but we can't remove any without making it backwards incompatible.

[andrewhr]

My apologies here, some unnecessary noise due some misunderstanding of mine.

The original intend was to leverage the :telemetry conventions. Both start and end events produce a monotonic_time measurement, which is equivalent to ours start_time_mono and end_time_mono. You can see details here.

The proposal was to use those attributes names. My wrong assumption was both start_time_mono and end_time_mono weren't released yet, so reverting them would not break any production code.

Sorry again for the noise, and thanks for pointing out the breaking change!