Time measurements

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J de Boyne Pollard

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Oct 11, 2007, 11:17:50 AM10/11/07
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AV> The man page for these functions have the following statement
AV>
AV> All implementations support the system-wide realtime
clock,
AV> which is identified by CLOCK_REALTIME. Its time represents
AV> seconds and nanoseconds since the Epoch. When its time is
AV> changed, timers for a relative interval are unaffected, but
AV> timers for an absolute point in time are affected.
AV>
AV> But it's not clear for me what do they mean under "timers for a
relative
AV> interval". Looks like the code marks one absolute point, then
another
AV> one, and then takes the difference. This will bring problems when
the
AV> time changes (Daylight saving for example). [...]

Changes to and from daylight savings time do not change the number of
seconds and nanoseconds since the Epoch. If your Unix system is doing
this, then it is broken. Changes to and from daylight savings time do
not touch the system clock. These are library mechanisms. On a Unix
system, potentially every individual process can operate in an
individual timezone, with individual DST rules, should one so desire.

J de Boyne Pollard

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Oct 15, 2007, 8:28:58 AM10/15/07
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GCG> [...] a leap second or even a Pope decreeing some number
GCG> of days aren't in this year's calendar) and you are hosed.

RW> This was a one-time adjustment necessitated by the fact
RW> the the leap days of the Julian calendar didn't yield an
RW> accurate enough approxmiation of the solar year and it
RW> took place in 1582.

It look place in (amongst others) 1582, 1700, 1752, 1867, 1873, 1896,
1912, 1918, 1923, and 1929. That's stretching "one-time" quite a lot.

A tip: Don't argue this subject from a parochial viewpoint that
assumes that events in one country, and rules for one religion, apply
universally. Such an argument always falls apart.

RW> Most of them were presumably born after 1990,
RW> because 'older people' already knew better before
RW> this time, but one of the nice things about computers
RW> is that yesterdays mistakes reappear as tomorrows
RW> innovations once the quote of people old enough to
RW> still remember them has dropped to a sufficiently
RW> low value to render them a minority.

Henry Spencer said it more succinctly.

J de Boyne Pollard

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Oct 18, 2007, 1:53:51 PM10/18/07
to
GCG> [...] a leap second or even a Pope decreeing some number
GCG> of days aren't in this year's calendar) and you are hosed.

RW> This was a one-time adjustment necessitated by the fact
RW> the the leap days of the Julian calendar didn't yield an
RW> accurate enough approxmiation of the solar year and it
RW> took place in 1582.

JdeBP> It look place in (amongst others) 1582, 1700, 1752,
JdeBP> 1867, 1873, 1896, 1912, 1918, 1923, and 1929. That's
JdeBP> stretching "one-time" quite a lot.

RW> The 'decree of the pope' took place in 1582. Different
RW> countries switched to the Gregorian calender at different
RW> times in the past.

... which multiple changes are exactly the moving of the measuring
sticks that Golden California Girls was talking about in the message
that you replied to. When the decree was issued is irrelevant. It
was when the changes happened that is relevant. Go back and read
Golden California Girls' message again, carefully this time.

RW> I am hard pressed to believe that you really didn't
RW> understand that

The lack of understanding is yours, not anyone else's.

RW> the relevance to either the discussion in
RW> general or my text in specific is zero.

If that were actually true, you wouldn't have been discussing it in
the first place. But as can be seen from above quote, you were. As I
said, it is you that doesn't understand, not the other people around
you. You didn't understand the message that you replied to, and you
didn't understand the point that I made, either.

RW> Try to address the content of a text instead of trying
RW> to start a completely pointless sidelines flamewar instead.

We are addressing your message content. The content that you wrote is
quoted above.

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