Re: rw_lock_held

[Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost>]

> Date: Tue, 6 Feb 2018 19:06:33 +0900
> From: Ryota Ozaki <ozaki-r%netbsd.org@localhost>
> 
> Is there any reason that rw_lock_held checks if it's held
> by *someone*, not by curlwp? It's confusable and most (or all?)
> users of the API seem to expect the latter (held by curlwp).

Wild guesses:

(a) because it seemed fast to just test (owner & RW_THREAD) != 0, or
(b) because Solaris did it.

> So I think we should do either:
> (1) fix rw_lock_held, or
>     - probably it would be rw_read_held() || rw_write_held()
> (2) fix users of rw_lock_held.
>     - it also would replace rw_lock_held with
>       rw_read_held() || rw_write_held()
> 
> I prefer (1) because I think there is no user of the current
> behavior that is difficult to use for users (it may be useful
> as an internal utility function though).

I like (1) too, but check for Solaris compatibility?  It is hard to
imagine that there are correct uses of the current semantics that are
not also correct uses of (1).