Re: [musl] Simple question regarding read-write locks precedence

[Markus Wichmann <nullplan@gmx.net>]

On Tue, Mar 31, 2020 at 11:26:46AM -0400, Rich Felker wrote:
> Thanks. While I specifically did not implement (or define a macro for)
> PTHREAD_RWLOCK_PREFER_WRITER_NP because it's misleading to advertise
> support for it when it fundamentally can't work,
> PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP seems like a viable
> extension to support. Anyone else see potential problems supporting it
> that I might be missing?
>
> Rich

I do see one problem: The manpage (the only spec available) contradicts
itself. In the Description section, it says (of the new option):

|Setting the lock kind to this avoids writer starvation as long as any
|read locking is not done in a recursive fashion.

OK, but in the Bugs section:

|Setting the lock kind to PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP
|allows writers to run, but, as the name implies a writer may not lock
|recursively.

Well, which is it? Are writers or readers not supposed to recurse? I
thought writers aren't supposed to recurse, anyway. Or is it possible we
need to file a bug report to Michael Kerrisk? Maybe it was supposed to
say "reader" here, then it would make sense. As it stands, though, the
spec is unclear.

Ciao,
Markus