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From: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: mtk.manpages@gmail.com, Carlos O'Donell <carlos@redhat.com>,
	linux-man <linux-man@vger.kernel.org>
Subject: Re: POSIX writer locks can't be recursive
Date: Fri, 26 Jun 2020 10:54:35 +0200
Message-ID: <8d7edc37-6b5f-1dd9-5f7f-b4e15a9ae39a@gmail.com> (raw)
In-Reply-To: <CAP01T764kz5T+m+8sV0o30enBL1TagF7RQSjU0XcVJ0PvL0PTg@mail.gmail.com>

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

Cheers,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

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