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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Ada.Execution_Time
Newsgroups: comp.lang.ada
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Date: Thu, 16 Dec 2010 09:45:54 +0100
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Date: 2010-12-16T09:45:54+01:00
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On Wed, 15 Dec 2010 16:05:16 -0600, Randy Brukardt wrote:

> I think you are missing the point of CPU_Time. It is an abstract 
> representation of some underlying counter. There is no requirement that this 
> counter have any particular value -- in particular it is not necessarily 
> zero when a task is created. So the only operations that are meaningful on a 
> value of type CPU_Time are comparisons and differences. Arguably, CPU_Time 
> is misnamed, because it is *not* some sort of time type.

Any computer time is a representation of some counter. I think the point is
CPU_Time is not a real time, i.e. a time (actually the process driving the
corresponding counter) related to what people used to call "time" in the
external world. CPU_Time is what is usually called "simulation time." One
could use Duration or Time_Span in place of CPU_Time, but the concern is
that on some architectures, with multiple time sources, this would
introduce an additional inaccuracy. Another argument against it is that
there could be no fair translation from the CPU usage counter to
Duration/Time_Span (which is the case for Windows).

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de