Use of ractors makes coverage non-deterministic

[fdr]

I didn't see any previous mention of ractors in the issue tracker, so I suspect I may be the first reporter to have tried to use them. In my case, I had a short-lived ractor that would exit at some indeterminate time in the course of my test suite.

What I've found is that it makes the coverage numbers fluctuate chaotically. I suspect something like an inherited at_exit hook may be to blame.

If a mechanical theory for this does not jump out at you, I will try to write a minimizing test demonstrator. But I figured you may expect things to misbehave this way, and nobody has asked about it on the issue tracker yet.

[colszowka]

@fdr I don't think this has been brought up before, and granted that ractors aren't yet very common in use in ruby as far as I know I think it's possible it wasn't yet tried out. It would be nice to know whether this is related to simplecov or the ruby stdlib coverage module itself in the first place, because in the latter case this issue should be reported in the ruby issue tracker first.

If you try to make an isolated example, could you please first try to do it with the coverage module first?

[fdr]

Interesting, I didn't consider that. I'll research the matter. Maybe I'll close this until I have the time, it may still be useful to someone running a search.

[jaynetics]

I just spent quite a bit of time finding this out, so maybe this issue should stay open :)

It seems to be a problem with Ruby's own Coverage module, so I've opened an issue in the Ruby bug tracker.