[coyotos-dev] Sleep, wakeup, and persistence

[Jonathan S. Shapiro]

On Fri, 2007-09-14 at 11:46 -0700, Charles Landau wrote:
> At 2:37 PM -0400 9/14/07, Jonathan S. Shapiro wrote:
> >On Fri, 2007-09-14 at 11:19 -0700, Charles Landau wrote:
> >>  At 2:03 PM -0400 9/14/07, Jonathan S. Shapiro wrote:
> >>  >A process wants to sleep until time X. That is easy if the system keeps
> >>  >running until then, but if the system re-starts what happens?
> >>  >
> >>  >   1. The underlying system may not have a monotonically increasing
> >>  >      clock. Many embedded systems do not.
> >>
> >>  You can store the time base in the checkpoint, and restore it on
> >>  restart. Problem solved.
> >
> >That gets you a monotonically increasing clock. It does not get you an
> >accurate interval, which is also required.
> 
> If you mean an accurate real-time interval, a real-time clock will 
> give you that, nothing else will.

Charlie: we are going in circles. The question at hand is: what does a
real-time clock *mean* in the presence of a restart?

> >  > Perhaps it makes more sense to support different types of sleep:
> >>  sleep until a given real time (and time zone)
> >>  sleep for x seconds from now
> >>  sleep for a given amount of system-up time
> >
> >All of these can be expressed at user level.
> 
> Only if you expose restarts, which would be unfortunate.

You can either have a notion of time or you can avoid exposing
checkpoints. If there is an internally consistent third option, I would
welcome a description. I don't see one.
-- 
Jonathan S. Shapiro
Managing Director
The EROS Group, LLC
www.coyotos.org, www.eros-os.org