[Nut-upsdev] patch: Replace many usleep and some sleep calls with nanosleep

[Frédéric Bohé]

On Sun, 2011-11-13 at 20:51 -0500, Charles Lepple wrote:
> On Nov 13, 2011, at 3:32 PM, Regid Ichira wrote:
> 
> > --- On Sat, 11/12/11, Arnaud Quette <aquette.dev at gmail.com> wrote:
> > 
> >>>>> -             usleep(250000);
> >> 
> >>>>> +             struct timespec delay = {0, 250e6}; nanosleep(&delay, NULL);
> >> 
> >>>> Would it be better to define a local version of usleep in terms of
> >>>> nanosleep?  I suspect the library version already does that, but if the
> >>>> library version is going away, a local version is much more concise and
> >>>> readable than calling nanosleep directly.  If there are concerns about
> >>>> linking, the local version could be, e.g, u_sleep, since all the calls
> >>>> are getting touched anyway.
> >> 
> >>> Using AC_REPLACE_FUNCS(... usleep ...) in configure.in and providing a
> >>> common/usleep.c->usleep() replacement implementation, in case the
> >>> system doesn't provide it, is a better way to go. At least for now.
> >>> That way, we avoid regression, while supporting systems that do not
> >>> provide usleep.
> >> 
> >> What would be more worthwhile (IMHO) is to modify the code to make use
> >> of the remaining time returned by nanosleep. Otherwise, I am not sure
> >> I see the benefit of this change.
> >>  
> > 
> >  Does that summarize to:
> > 
> > 1. Have a valid C code for:
> > 
> >    int
> >    substitution_usleep(delay, remaining_time)
> 
> My point was that if we are going to change everything, we should *use* the remaining time. But given that the delays are very short to begin with, and given that the drivers tend not to rely on the precision or accuracy of usleep(), I wonder why we would bother replacing all of these calls to begin with?
> 
> Before we delve into discussions of implementation, I still think it is useful to find out what is going on in the Win32 libraries. If the underlying code sleeps with millisecond precision, using nanosleep() is a step in the wrong direction, IMHO.

What I understand from MSDN docs is that "sleep" functions (Sleep,
WaitFor*) API only allows milliseconds. But by default the actual
granularity is even bigger than a millisecond. You can set this
granularity to a minimum (via timeBeginPeriod function) but this has an
impact on the whole system so it has to be used carefully.



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