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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: An Example for Ada.Execution_Time
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Date: Mon, 3 Jan 2011 09:50:08 +0100
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Date: 2011-01-03T09:50:04+01:00
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On Sat, 01 Jan 2011 22:25:30 +0200, Niklas Holsti wrote:

> Perhaps you mean that CPU_Time is unrelated to Ada.Real_Time.Time over 
> longer periods during which the task is sometimes executing, sometimes 
> not.

I mean that

1. The corresponding clocks can be different. Ada cannot influence this.

2. The clocks are not synchronized, i.e. T1 on the Ada.Real_Time.Clock
cannot be translated into T2 on the Ada.Execution_Time.Clock.

> One of the differences between Ada.Real_Time.Time and 
> Ada.Execution_Time.CPU_Time is that the epoch for the former is not 
> specified in the RM. It follows that even if Ada.Real_Time.Time had a 
> visibly numeric value, its meaning would be unknown to the program.
> 
> In contrast, the epoch for CPU_Time is specified in the RM: the creation 
> of the task, a point in real time known to the program.

That does not define it either. An epoch cannot be defined otherwise than
in terms of other clock. The task start time according to
Ada.Real_Time.Time or Ada.Calendar.Time is unknown.

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