Re: Ada.Execution_Time

["Randy Brukardt" <randy@rrsoftware.com>]

"Niklas Holsti" <niklas.holsti@tidorum.invalid> wrote in message 
news:8nm30fF7r9U1@mid.individual.net...
> Dmitry A. Kazakov wrote:
>> On Sat, 18 Dec 2010 23:20:20 +0200, Niklas Holsti wrote:
...
>> On a such platform the implementation would be as perverse as RM D.14
>> is. But the perversion is only because of the interpretation.
>
> Bah. I think that when RM D.14 says "time", it really means time. You
> think it means something else, perhaps a CPU cycle count. I think the 
> burden of proof is on you.
>
> It seems evident to me that the text in D.14 must be interpreted using
> the concepts in D.2.1, "The Task Dispatching Model", which clearly
> specifies real-time points when a processor starts to execute a task and
> stops executing a task. To me, and I believe to most readers of the RM,
> the execution time of a task is the sum of these time slices, thus a
> physical, real time.

For the record, I agree more with Dmitry than Niklas here. At least the 
interpretation *I* had when this package was proposed was that it had only a 
slight relationship to real-time. My understanding was that it was intended 
to provide a window into whatever facilities the underlying system had for 
execution "time" counting. That had no defined relationship with what Ada 
calls "time". As usch, I think the name "execution time" is misleading, (and 
I recall some discussions about that in the ARG), but no one had a better 
name that made any sense at all.

In particular, there is no requirement in the RM or anywhere else that these 
"times" sum to any particular answer. I don't quite see how there could be, 
unless you were going to require a tailored Ada target system (which is 
definitely not going to be a requirement).

Perhaps the proposers (from the IRTAW meetings) had something else in mind, 
but if so, they communicated it very poorly.

                             Randy.