On 2017-01-05 06:26 AM, Hal Murray wrote:
[do something N years in the future]
Except that's not how things are programmed. Programming it that way would
be very inefficient in a part of the kernel that has to be ultra-efficient.
Since you don't know how many seconds it will from now, you can't schedule a
timeout. The current setup of UTC doesn't let me know how many seconds it
will be in the future. People can talk about it, but computers don't always
store things that way. ...
Are there any performance critical chunks of code that want to wait until N
years from now? I doubt it.
If I ask for 6 months rather than a few years, then you also have to consider
daylight savings. Actually, you have to consider it anyway. Congress might
change the start/stop times again and your wait-until might hit one of them.
I think that means that if you want to schedule something a long time in the
future specified as date and time rather than seconds from now, you have to
wakeup a bit early and recompute how long to wait. For leap seconds, the bit
early has to be a few months, depending on how long it takes you to update
your leap file. For daylight savings, I don't think you can predict a value
of a bit early. Congress isn't dependable.
How far in advance were the last daylight savings changes announced?
Roughly a year and a half or so, I think. I haven't researched when the
announcement might have officially been made by the Dept of Commerce,
who, I believe, would have been responsible for that:
Daylight saving time in the United States >> Second extension (2005)
https://en.wikipedia.org/wiki/Daylight_saving_time_in_the_United_States
"By the Energy Policy Act of 2005, daylight saving time (DST) was
extended in the United States beginning in 2007.[9]"
"... Wyoming Senator Michael Enzi and Michigan Representative Fred Upton
advocated the extension from October into November especially to allow
children to go trick-or-treating in more daylight."
Energy Policy Act of 2005
https://en.wikipedia.org/wiki/Energy_Policy_Act_of_2005
"The Energy Policy Act of (Pub.L. 109–58) is a bill passed by the United
States Congress on July 29, 2005, and signed into law by President
George W. Bush on August 8, 2005,..."
I'd put that is a category of "reasonable notice of change", but not all
jurisdictions are so responsible.
[More generally I'd put the whole notion of Daylight Savings Time in the
category of "stupid", but there's no fighting city hall....]
-Brooks
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