linux-kernel - Re: [RFC patch 7/7] [PATCH] glibc: nptl: Add support for attached pthread

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Date:	Sun, 3 Apr 2016 12:08:16 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Darren Hart <darren@...art.com>,
	Ingo Molnar <mingo@...nel.org>,
	Michael Kerrisk <mtk.manpages@...glemail.com>,
	Davidlohr Bueso <dave@...olabs.net>, Chris Mason <clm@...com>,
	Carlos O'Donell <carlos@...hat.com>,
	Torvald Riegel <triegel@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [RFC patch 7/7] [PATCH] glibc: nptl: Add support for attached
 pthread_mutexes

On Sat, 2 Apr 2016, Peter Zijlstra wrote:
> On Sat, Apr 02, 2016 at 11:09:20AM -0000, Thomas Gleixner wrote:
> > To undo the attachment each involved thread needs to call
> > 
> >     pthread_mutex_detach_np(&mutex);
> >         
> > When the last user detaches the kernel state is destroyed.
> 
> So I was fully expecting pthread_mutex_{at,de}tach_np() to not exist and
> be internal to pthread_mutex_{init,destroy}().
> 
> Is there a reason this is not so?

init/destroy are only called once and not on all threads using the futex. If
you want to hide that, then you need to add it to all pthread_mutex_*
operations and attach on the first call.

That's possible, but for simplicity we made it explicit.

Thanks,

	tglx