Re: nanosleep() uses CLOCK_MONOTONIC, should be CLOCK_REALTIME?

["Michael Kerrisk" <mtk.manpages@googlemail.com>]

Bart,

On Mon, Jun 23, 2008 at 10:34 AM, Bart Van Assche
<bart.vanassche@gmail.com> wrote:
> On Sun, Jun 22, 2008 at 9:35 AM, Michael Kerrisk <mtk.manpages@gmail.com> wrote:
>> Thomas,
>>
>> (I gues you are the right target for this?)
>>
>> The POSIX.1 specification of nanosleep() says:
>>
>>       But, except for the case of being interrupted by a signal, the
>>       suspension time shall not be less than the time  specified  by
>>       rqtp, as measured by the system clock CLOCK_REALTIME.
>>
>>
>> However, reading kernel/hrtimer.c:sys_nanosleep(), it appears that
>> CLOCK_MONOTONIC is used.
>>
>>    return hrtimer_nanosleep(&tu, rmtp, HRTIMER_MODE_REL, CLOCK_MONOTONIC);
>>
>> 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?

Thanks,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
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