On Fri, Mar 25, 2016 at 8:51 AM, David T. Lewis <lewis at mail.msen.com> wrote:

> On Thu, Mar 24, 2016 at 10:05:17PM -0700, Eliot Miranda wrote:
> >
> >
> > > On Mar 23, 2016, at 6:55 PM, David T. Lewis <lewis at mail.msen.com>
> wrote:
> > >
> > >> On Wed, Mar 23, 2016 at 05:50:19PM -0700, Eliot Miranda wrote:
> > >>> On Wed, Mar 23, 2016 at 4:51 PM, David T. Lewis <lewis at mail.msen.com>
> wrote:
> > >>>
> > >>>> On Wed, Mar 23, 2016 at 04:22:21PM -0700, Eliot Miranda wrote:
> > >>>>
> > >>>> Turns out this isn't needed for Cog.  I have ioLocalSecondsOffset
> which
> > >>>> answers a value determined at start-up and only changed
> > >>>> via ioUpdateVMTimezone, which itself is controlled by
> > >>>> primitiveUpdateTimezone, #243.  So ioUTCMicroseconds is all that's
> needed
> > >>>> to get at the clock and timezone atomically.
> > >>>
> > >>> If it is updated at start-up, then it's wrong. Think of daylight
> savings
> > >>> time transitions.
> > >>
> > >> So update it automatically once a second or some such?
> > >
> > > Are you joking, or is that a serious question?
> >
> > Yes.  I see two or three system calls in the code below.  gettimeofday,
> one inside localtime and one inside gmtime.  That's expensive.
> >
>
> It's gettimeofday() and localtime(). The #else is fallback for older unix
> platforms.
>

As I said, two or three.

In any case, caching the value and updating it periodically does not sound
> like a good idea to me.
>

Why not?  Why does the time zone need to be determined on every time call
even though it only has a resolution of seconds?  If including the timezone
in every time call slows down accessing the time by, say, 33%, is it a good
idea, when the VM can easily eliminate this overhead?

| c |
c := LargePositiveInteger.
[1 to: 10000000 do: [:i| c basicNew: 8. c basicNew: 8. c basicNew: 8. c
basicNew: 8. c basicNew: 8. c basicNew: 8. c basicNew: 8. c basicNew: 8. c
basicNew: 8. c basicNew: 8]] timeToRun 884



[1 to: 10000000 do: [:i| Time utcMicrosecondClock. Time
utcMicrosecondClock. Time utcMicrosecondClock. Time utcMicrosecondClock.
Time utcMicrosecondClock. Time utcMicrosecondClock. Time
utcMicrosecondClock. Time utcMicrosecondClock. Time utcMicrosecondClock.
Time utcMicrosecondClock]] timeToRun 6412


6412 / 884.0 7.253393665158371

So the overhead of the system calls involved in accessing time are much
greater than the costs of allocating and garbage collecting 64-bit large
integer results; much larger.

Dave
>
>
> > >
> > > Confused,
> > > Dave
> > >
> > >
> > > /* implementation of ioUtcWithOffset(), defined in config.h to
> > > /* override default definition in src/vm/interp.h
> > > */
> > > sqInt sqUnixUtcWithOffset(sqLong *microSeconds, int *offset)
> > > {
> > >  struct timeval timeval;
>


> > >  if (gettimeofday(&timeval, NULL) == -1) return -1;
> > >  time_t seconds= timeval.tv_sec;
> > >  suseconds_t usec= timeval.tv_usec;
> > >  *microSeconds= seconds * 1000000 + usec;
> > > #if defined(HAVE_TM_GMTOFF)
> > >  *offset= localtime(&seconds)->tm_gmtoff;
> > > #else
> > >  {
> > >    struct tm *local= localtime(&seconds);
> > >    struct tm *gmt= gmtime(&seconds);
> > >    int d= local->tm_yday - gmt->tm_yday;
> > >    int h= ((d < -1 ? 24 : 1 < d ? -24 : d * 24) + local->tm_hour -
> gmt->tm_hour);
> > >    int m= h * 60 + local->tm_min - gmt->tm_min;
> > >    *offset= m * 60;
> > >  }
> > > #endif
> > >  return 0;
> > > }
> > >
> > >
> > >
>
>


-- 
_,,,^..^,,,_
best, Eliot
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