Fwd: [webkit-dev] Re: KJS Date Object : thread safetyness / portability concerns

Mon Jan 9 11:30:31 PST 2006

Gmail doesn't reply back to webkit-dev by default, so here's my reply:
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It can be done as a last resort.. the main concern is being able to handle
times <= 0 in the unix epoch. Windows is silly, and while it uses a signed
time_t value (implying it takes negative time values into consideration),
its implementation only works with times > 0 in the unix epoch. anything
less results in the return of a null pointer or errno, depending on which
version of the system library you choose.

On 1/9/06, Mitz Pettel <opendarwin.org at mitzpettel.com> wrote:
>
> In many territories the rules changed several times over the years
> (daylight saving time wasn't introduced until the 20th century). In New
> Zealand, for example, there was no DST between 1946 and 1974.
> On Jan 9, 2006, at 9:11 PM, Justin Haygood wrote:
>
> It would work if the years are equivalent, no?
>
> (the first sunday in april and last sunday in october would be the same
> guaranteed every 28 years between the years 1601 and 2399)
>
> On 1/9/06, Mitz Pettel <opendarwin.org at mitzpettel.com > wrote:
> >
> > I didn't follow the discussion very closely, hence I apologize if this
> > irrelevant here, but the "offset years" technique doesn't play well with
> > daylight saving time, so I think you should only apply it as a last resort
> > (see e.g. <http://bugzilla.opendarwin.org/show_bug.cgi?id=5514>).
> >
> > -- Mitz Pettel
> >
> > On Jan 9, 2006, at 8:54 PM, Justin Haygood wrote:
> >
> > By my calculation, this would mean adding or subtracting 32140800
> > seconds until its within the portable range.
> >
> > Someone should check my math, but the number is from:
> >
> > 60 secs in 1 minute *
> > 60 mins in 1 hour *
> > 24 hours in 1 day *
> > 365 days in 1 year
> >
> > Then to adjust for leap years:
> >
> > 7 leap years in 28 years (7*4 = 28...)
> >
> > 60 secs in 1 minute *
> > 60 mins in 1 hour *
> > 24 hours in 1 day *
> > 7 leap days in 7 leap years
> >
> > Summing gives the answer I gave above. Someone who isn't sick and
> > actually feels like checking a calendar to make sure there are 7 leap years
> > in 28 years should check my math though...
> >
> > On 1/9/06, Justin Haygood <jhaygood at spsu.edu > wrote:
> > >
> > > (Sorry for the subject change -- updating to make it more accurate --
> > > threaded mail readers should still keep it in the thread)
> > >
> > > My proposal:
> > >
> > > Based on http://www.tondering.dk/claus/cal/node3.html#SECTION00370000000000000000
> > > , and some programming knowledge, how about:
> > >
> > >
> > >    - For Windows, check the value of clock. If its 0 or less (it
> > >    sometimes messes up with 0, sometimes it doesn't...), keep adding 28 years
> > >    in seconds until its positive (no need to check for above 2038.. Windows
> > >    uses 64-bit values for time_t if using CRT 8 (aka Visual Studio 2005's CRT)
> > >    to increase portability between Win32 & Win64.
> > >    - Remember the offset in years
> > >    - Then, submit that time to the system local/gmtime function
> > >    (whichever one we choose, aren't we going with the _s versions?)
> > >    - Change the returned year using our remembered offset
> > >    - Voila, immediate portability.
> > >
> > > We might want to do this globally instead of just for one platform. We
> > > might also do this for years above 2038 as well if time_t is 32-bit instead
> > > of 64-bit on a given platform.
> > >
> > > sizeof(time_t) using MSVC 8 compiler and MSVCRT 8 C library: 8
> > > sizeof(time_t) using MinGW GCC 3.4.2 and MSVCRT 6 C library: 4
> > >
> > > On 1/8/06, Justin Haygood <jhaygood at spsu.edu> wrote:
> > > >
> > > > I was thinking, isn't there equivalent years like every 7 (or
> > > > whatever it is) years or so? For negative year values, we simply could
> > > > adjust it to an equivalent year, remember the year offset, and readjust to
> > > > the correct year after letting localtime/gmtime do its magic?
> > > >
> > > > On 1/8/06, Maciej Stachowiak < mjs at apple.com > wrote:
> > > > >
> > > > >
> > > > > On Jan 7, 2006, at 9:23 PM, Justin Haygood wrote:
> > > > >
> > > > > Try telling that to date_object.cpp. It does the Windows
> > > > > equivalent of dumping core anytime a negative date value is used or a new
> > > > > Date object is created.
> > > > >
> > > > >
> > > > > Sounds bad. Do you have any ideas how that could be fixed? I'll
> > > > > have a Windows laptop soon so I may be able to test things myself.
> > > > >
> > > > > Regards,
> > > > > Maciej
> > > > >
> > > > >
> > > > > On 1/8/06, Maciej Stachowiak < mjs at apple.com > wrote:
> > > > > >
> > > > > >
> > > > > > On Jan 7, 2006, at 9:13 PM, Justin Haygood wrote:
> > > > > >
> > > > > > Either one is an issue.
> > > > > >
> > > > > > Windows does do one thing better: it supports dates beyond the
> > > > > > 2038 even in vanilla localtime/gmtime.. it uses 64-bit values since the
> > > > > > epoch by default in CRT 8.
> > > > > >
> > > > > >
> > > > > > Actually I'm not sure we'd use negative time values with the
> > > > > > latest code. Is there a case where this comes up? I think dates are
> > > > > > converted into a consistent narrow range currently.
> > > > > >
> > > > > > Regards,
> > > > > > Maciej
> > > > > >
> > > > > >
> > > > > >
> > > > > > On 1/8/06, Maciej Stachowiak < mjs at apple.com> wrote:
> > > > > > >
> > > > > > >
> > > > > > > On Jan 7, 2006, at 8:57 PM, Justin Haygood wrote:
> > > > > > >
> > > > > > > > The only problem with localtime_r and gmtime_r, when
> > > > > > > implemented in
> > > > > > > > any matter that uses the CRT (We target CRT 8.. its the most
> > > > > > > > current and really the only viable CRT) is that they don't
> > > > > > > work
> > > > > > > > with negative time values, returning a NULL pointer.
> > > > > > > >
> > > > > > > > Since KJS doesn't realize that a NULL pointer can be given
> > > > > > > to it,
> > > > > > > > it crashes miserably once it attempts to use this pointer.
> > > > > > >
> > > > > > > Are the _s variants safe for use with negative time values?
> > > > > > > How about
> > > > > > > vanilla localtime()? It seems like this is an issue
> > > > > > > regardless.
> > > > > > >
> > > > > > > Cheers,
> > > > > > > Maciej
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > >
> > > > >
> > > >
> > >
> > _______________________________________________
> > webkit-dev mailing list
> > webkit-dev at opendarwin.org
> > http://www.opendarwin.org/mailman/listinfo/webkit-dev
> >
> >
> >
>
>
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