On 03/01/2017 19:54, Cyrus Daboo wrote:
Hi Ted,
--On January 3, 2017 at 1:51:54 PM -0500 Ted Lemon <mellon(_at_)fugue(_dot_)com>
wrote:
No that simply does not work. Repeating events or alarms may not
involve
any UI at all, but the device may need to trigger those at a specific
local time - that means time zone information has to be taken into
account somewhere. This is a crucial fact of any calendaring and
scheduling system that those of us who have been using iCalendar
(RFC5545) fully appreciate.
This is true, but any specific local time will always occur at a
specific
universal time, so this isn't actually a problem.
No! That is not true because a future local time is not guaranteed to
be at a specific universal time because local government can change
their time zone (or more likely) their daylight savings time
transition at any time between now and said future time. i.e., you
cannot "pre-cache" all the local time -> UTC mappings for a future
recurring event and then just use the UTC values, because the time
zone definition may change.
So an application sensitive to that needs to specify its timing in terms
of local time, but that should not force the fundamental time
distribution system to operate in that mode.
Maybe we need two time distribution systems, one that accurately does
the ranging and flywheel management and distributes precision time for
technical purposes, and a separate one that manages the offsets and
jumps relative to the underlying precision continuous time distribution
system.
Stewart