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From: Martin <martin.dowie@btopenworld.com>
Newsgroups: comp.lang.ada
Subject: Re: Private or public task ?
Date: Wed, 10 Feb 2010 00:40:22 -0800 (PST)
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Date: 2010-02-10T00:40:22-08:00
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On Feb 10, 8:29=A0am, Hibou57 (Yannick Duch=EAne)
<yannick_duch...@yahoo.fr> wrote:
> On 10 f=E9v, 09:17, Maciej Sobczak <see.my.homep...@gmail.com> wrote:> > =
There are two kinds of blockings: bounded and unbounded. The idea is
> > > that when computing a time budget, you can account for bounded
> > > blockings, but not unbounded ones.
> > > The "potentially blocking" phrase should be understood as really mean=
ing
> > > unbounded.
>
> > Well, I know what you try to convey, but there are traps:
>
> > =A0 =A0delay Some_Static_Constant;
>
> > Is it bounded or unbounded?
>
> > As far as WCET (or any other time-based analysis) goes, the above can
> > be accounted for statically. Still, it is a no-no within any protected
> > operation.
>
> Interesting enigma
>
> I would say Bounded, as it is predictable.
> ... as long as the delay is short, otherwise it will break the other
> rule stating that a protected operation should be fast to execute.
>
> If I try to have a delay X.Y in a protected operation, GNAT just warns
> me =93 potentially blocking operation in protected operation =94, while
> the program is still compiled.
>
> You've said =93 it is a no-no within any protected =94 : do you get a
> compilation error when you do the same ?
>
> I've not seen anything in the Rationale nor in the ARM which
> explicitly disallow it anyway (but as these are long pages I should
> later read again, I may have miss it).

It's isn't predicatable - it will delay for /at least/
Some_Static_Constant. It's up to the task scheduling algorithm (plus
the rest of the program! ;-) as to what happen next...and when!

Cheers
-- Martin