On Fri, Mar 25, 2016 at 8:51 AM, David T. Lewis <lewis@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@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@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