thread: don't assume the underlying acceptable priority range

[doudou]

This change is needed by ruby/ruby#2093

Basically, the range of acceptable thread priorities should not be assumed by the spec,
only that invalid priorities are clamped to the acceptable range. The only thing the changed
spec assumes is that 255 and -255 are outside this range.

[eregon]

I think it's important we test the exact range of valid values, as this is the best ways to ensure the various Ruby implementations support the same range, as mentioned in https://bugs.ruby-lang.org/issues/15438#note-10.

If MRI agrees to change the range, then we can specify it per Ruby version with a version guard (ruby_version_is).

[eregon]

Closing since the corresponding PR to ruby/ruby was closed: ruby/ruby#2087
Let's resolve https://bugs.ruby-lang.org/issues/15438 first.

FWIW, I think it would be fine to change priority limits if we expose Thread::MIN_PRIORITY and Thread::MAX_PRIORITY.

[doudou]

ruby/ruby#2087 was closed because of a mixup I've done. The "right" PR is ruby/ruby#2093.

[doudou]

In any case, I'm going to modify #2087 to not change the min priority, and propose the min priority change later. I think the bugfix is too important to be blocked by the min priority change.

[eregon]

👍 Sounds like a good approach to me.

BTW, if you need to modify specs, you can also do it directly in the ruby/ruby PR.

[doudou]

BTW, if you need to modify specs, you can also do it directly in the ruby/ruby PR.

Good to know, thanks.