linux-kernel - Re: nanosleep() uses CLOCK_MONOTONIC, should be CLOCK

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Date:	Mon, 23 Jun 2008 14:43:21 +0200 (CEST)
From:	Roman Zippel <zippel@...ux-m68k.org>
To:	Michael Kerrisk <mtk.manpages@...glemail.com>
cc:	Bart Van Assche <bart.vanassche@...il.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	john stultz <johnstul@...ibm.com>, Ingo Molnar <mingo@...e.hu>
Subject: Re: nanosleep() uses CLOCK_MONOTONIC, should be CLOCK_REALTIME?

Hi,

On Mon, 23 Jun 2008, Michael Kerrisk wrote:

> >> Is there a reason to use CLOCK_MONOTONIC, instead of CLOCK_REALTIME?  Is it
> >> intentional?  If yes, then I should document this in the man-pages.  If not,
> >> then it should be fixed.
> >
> > CLOCK_MONOTONIC works fine even if ntpd steps the clock forward or
> > backward, CLOCK_REALTIME not. So the man page should be fixed.
> 
> Thanks for your reply, but I'm not quite convinced yet.  The things
> is: the Solaris man page also says "CLOCK_REALTIME".  (Of course that
> man page may just be parroting the standard.)  Could there not be some
> reasonable semantics for a nanosleep() that was based on
> CLOCK_REALTIME?

CLOCK_MONOTONIC is optional, that's probably the reason it's not mentioned 
there. If you check the man page for clock_settime, it specifically 
mentions that pending relative timer (including nanosleep) aren't affected 
by the changed time, thus if CLOCK_MONOTONIC and CLOCK_REALTIME advance 
equally, it doesn't matter which you use for relative timer.

bye, Roman
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