If this seems too dangerous to merge, we can use the variant used by OmniOS instead, which makes the change Solaris specific.

https://github.com/omniosorg/omnios-build/blob/master/build/python313/patches/mod-posix-sched_priority.patch

Is it guaranteed that a successul syscall clears errno? Because if yes, then the if (max == -1) will still report legitimate -1 priority as an error. The illumos man page says "If unsuccessful, they return -1 and set errno to indicate the error." and I may be reading too much into this, but if errno is not set to indicate an error is a sufficient condition to conclude there's no error I think?

It is not guaranteed, and this simple case confirms that it is not being cleared:

errno = EINVAL;res = sched_get_priority_min(SCHED_OTHER);printf("%d %d\n", res, errno);  // EINVAL is still set

but we can still do it ourselves.

You are right that -1 is still a legitimate priority, and although I don't think it even happens in any Solaris (historically, some schedulers used -60 and 60, the newer ones are using positive values only), it is not impossible (and also, I might be wrong :)).

I updated the code, now it should always work on systems wheresched_get_priority_* is POSIX.1-2001 compliant (which is True for Linux as well as all Unix systems) no matter the priority.

What needs to be done to see this PR merged? The change is obviously improving compatibility with POSIX and there is not known any regression.

Thank you.