Hello Carlos, Kumas, On 7/16/20 9:50 PM, Carlos O'Donell wrote: > On 7/15/20 3:50 PM, Michael Kerrisk (man-pages) wrote: >> On Fri, 26 Jun 2020 at 10:54, Michael Kerrisk (man-pages) >> <mtk.manpages@xxxxxxxxx> wrote: >>> >>> Hi Carlos, >>> >>> Could you comment here, as this was your text in pthread_rwlockattr_setkind_np(3)? >>> >>> On 6/25/20 2:32 PM, Kumar Kartikeya Dwivedi wrote: >>>> Hi, >>>> In pthread_rwlockattr_setkind_np(3), the explanation for >>>> PTHREAD_RWLOCK_PREFER_WRITER_NP reads: >>>> >>>>> This is ignored by glibc because the POSIX requirement to support >>>>> recursive writer locks would cause this option to create trivial >>>>> deadlocks; >>>> >>>> I think this should be "reader locks" instead, since it is >>>> undefined[1] for a thread holding a write lock to call >>>> pthread_rwlock_wrlock(3) again (glibc returns EDEADLK, musl simply >>>> deadlocks). There's no such requirement in POSIX either. Please let me >>>> know if I'm missing something. >>>> >>>> [1]: https://pubs.opengroup.org/onlinepubs/007908799/xsh/pthread_rwlock_wrlock.html > > I agree with Kumar, and the comment I provided in commit 0d255e74c0 lines up > with my intent and Kumar's requested correction (which is why it's always important > to comment things to provide intent for the implementation!). > > 8< --- 8< --- 8< > Clarify that it is recursive read locks on the read-write lock that > make it difficult to implement PTHREAD_RWLOCK_PREFER_WRITER_NP. > > Update the libc-alpha URL and provide the URL to the POSIX wording > that is quoted in the comment. > > Signed-off-by: Carlos O'Donell <carlos@xxxxxxxxxx> Thanks for the patch, Carlos. Applied. Thanks for the report, Kumar! Cheers, Michael > > diff --git a/man3/pthread_rwlockattr_setkind_np.3 b/man3/pthread_rwlockattr_setkind_np.3 > index b381972dc..a91c43552 100644 > --- a/man3/pthread_rwlockattr_setkind_np.3 > +++ b/man3/pthread_rwlockattr_setkind_np.3 > @@ -80,7 +80,7 @@ starved. > This is intended as the write lock analog of > .BR PTHREAD_RWLOCK_PREFER_READER_NP . > This is ignored by glibc because the POSIX requirement to support > -recursive writer locks would cause this option to create trivial > +recursive read locks would cause this option to create trivial > deadlocks; instead use > .B PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP > which ensures the application developer will not take recursive > @@ -102,7 +102,8 @@ read locks thus avoiding deadlocks. > .\" the writers to acquire and release the lock, and the writers will be > .\" suspended waiting for every existing read lock to be released. > .\" --- > -.\" http://sources.redhat.com/ml/libc-alpha/2000-01/msg00055.html > +.\" https://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_rwlock_rdlock.html > +.\" https://sourceware.org/legacy-ml/libc-alpha/2000-01/msg00055.html > .\" https://sourceware.org/bugzilla/show_bug.cgi?id=7057 > .TP > .B PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
