From: Carlos O'Donell <carlos@redhat.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH] Bug #20116: Clarify barrier-like and mutex-like behaviours of PD->lock.
Date: Tue, 14 Mar 2017 01:07:00 -0000 [thread overview]
Message-ID: <7299daa1-f56f-ecca-5e04-76279b9afde1@redhat.com> (raw)
In-Reply-To: <116d8b2d-dad1-c5f6-8cf7-59e0c969381d@redhat.com>
On 02/14/2017 06:32 AM, Florian Weimer wrote:
> On 02/13/2017 07:49 PM, Florian Weimer wrote:
>> On 02/13/2017 02:29 PM, Carlos O'Donell wrote:
>>> + It is important to point out that PD->lock is being used as a POSIX
>>> + barrier and a POSIX mutex. The lock is taken in the parent to force
>>> + the child to wait, and then the child releases the lock, in effect a
>>> + barrier. However, this barrier-like effect is used only for
>>> + synchronizing the parent and child. After startup the lock is used
>>> + like a mutex to create a critical region during which a single owner
>>> + modifies the thread parameters.
>>
>> I had missed that the lock was reused for the scheduler parameter.
>>
>> But the current code still does not make sense to me. Why do we need to
>> keep a copy of the scheduler parameters at all? Is this just a cache to
>> improve performance, similar to what we used to do for the PID?
>
> The cache is used in the implementation of PTHREAD_PRIO_PROTECT mutexes. There are data races:
>
> https://sourceware.org/bugzilla/show_bug.cgi?id=21160
>
> I expect that the use of ->lock to protect these members will go away eventually.
Yes, it's used in tpp.
Given your current understand is the above additional text sufficient
to clarify the situation?
--
Cheers,
Carlos.
next prev parent reply other threads:[~2017-03-14 1:07 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-13 13:29 Carlos O'Donell
2017-02-13 18:49 ` Florian Weimer
2017-02-14 11:32 ` Florian Weimer
2017-03-14 1:07 ` Carlos O'Donell [this message]
2017-03-14 6:58 ` Florian Weimer
2017-03-14 12:26 ` Torvald Riegel
2017-05-03 19:25 ` Carlos O'Donell
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