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From: Anh Vo <anhvofrcaus@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Periodic tasks - organization
Date: Mon, 14 Jul 2008 08:31:07 -0700 (PDT)
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On Jul 14, 2:08=A0am, "Alex R. Mosteo" <devn...@mailinator.com> wrote:
> Maciej Sobczak wrote:
> > Consider a program that has a couple of periodic tasks. Let's say
> > there are two tasks, one with a period of 3s and another with a period
> > of 4s. Let's say that exact triggering is not required.
>
> > The simplest way to do it is to just have appropriate delay statements
> > in main loops of these tasks. The advantage of such a setup is that
> > the tasks are completely self-contained and independent on any other
> > program entity. The disadvantage is that they are bound to the way
> > their periodicity is implemented.
>
> > Another way is to have additional task that will serve as a clock,
> > "ticking" two protected objects that are countdown counters with
> > single entry that waits for the counter to reach zero. In this case
> > the tick would be 1s, as the greatest common divisor of two periods.
> > The working tasks can then wait on respective entries in these
> > protected objects, which are released when the counters reach zero.
> > The advantage of this approach is that the notion of time is extracted
> > from the working tasks themselves and can be easily changed to
> > something else, like waiting on a different kind of clock or an
> > interrupts or whatever without disturbing main working tasks. The
> > disadvantage is that there are more program entities (+ two protected
> > countdowns + 1 ticking task) to handle.
>
> > What can you say about these two approaches? Which would you recommend
> > and when?
>
> I would use "delay until", which prevents any drift and still avoids usin=
g
> extra machinery.- Hide quoted text -
>
> - Show quoted text -

It is even better to use periodic timers built on top
Ada.Real_Time.Timing_Events. Then, explicit tasks are not needed.

Anh Vo