Re: tasking with GNAT 3.14p on windows

["Chad R. Meiners" <crmeiners@hotmail.com>]

"Jano" <nono@celes.unizar.es> wrote in message
news:MPG.18f2dca67f9d5139896cd@News.CIS.DFN.DE...
> Chad R. Meiners dice...
> >
> > "Jano" <nono@celes.unizar.es> wrote in message
> > news:MPG.18f2a01651aa20aa9896cb@News.CIS.DFN.DE...
> > > trying to know the behavior with blocking I/O. In XP with -gnatP, you
> > > get indefinite wait for user input, but if more than 10 seconds has
> > > passed when you hit enter, you get also the "aborted" print.
> > >
> > > Is that expected behavior? Gnat docs say that polling implements calls
> > > in each loop iteration / function call. Should I assume that if you
> > > haven't loops / calls, abort will never work properly?
> >
> > It seems like reasonable behavior.  System calls are not guaranteed to
be
> > abortable.
>
> That's what I wanted to know. I'm not a RM lawyer, so I don't knew that.
> I'll be glad if someone can point the relevant sections in the RM about
> code not abortable.
>
> > > I feel nevertheless very unsafe using anything else than trivial tasks
> > > in NT. The priority system of NT messes things greatly out of
> > > real_time_class, and that, for example, is never pointed in Gnat docs
> > > (in my knowledge).
> >
> > NT is not a real time operating system.
>
> I know that.
>
> > The task support on NT is not
> > broken; your understanding of Ada tasking is broken. ;)
>
> ;) As I've said, I'm not an Ada RM expert, but I think I'm not totally
> clueless about how a multitasking program should work, if the compiler
> adheres to annex D, as Gnat says. OTOH, as far as I know, Gnat isn't
> validated under win32.
>
> > It is very easy to
> > write system dependent tasking code.  I have written several robust
> > multi-tasking windows applications.  You just have to understand how to
> > implement your os calls so that they play well with tasking.
>
> I've also written multitasking window apps, and I don't like the tricks
> you must do to workaround some NT limitations, and that's about I was
> asking. One of the points of using Ada is to remain as much as possible
> in the system independent side of the world ;-)
>
> > > Also, the faulty ceiling_priority model for protected objects is
> > > mentioned or not? I can't remember...
> >
> > If you don't know then why are spreading FUD about tasking on NT?
>
> Well, I was thinking out loud to see if someone shares my concerns. I
> like to be enlightened by others greater experience. I have nothing
> against Gnat nor intend to spread FUD.
>
> The following points I believe are true, and not mentioned in Gnat NT
> documentation. I will not point the RM sections which I think aren't
> satisfied, but every time I try to read the D annex in detail, I feel a
> bit disturbed about Gnat saying it complies with it, hence my asking:
>
> * You must set your app in realtime priority class because NT priorities
> below that class aren't static.
>
> * You may have two tasks with different priorities specified via pragma
> priority. The two will map to the same NT priority (because there are
> less than in system.priority'range), and your tasks will preempt each
> other even having specified a higher priority for one of them.
>
> * The ceiling priority of protected objects is simply ignored. The
> caller will not inherit the ceiling priority. I was taught that in
> university, and my tests seem to confirm that. To be fair, I have a
> vague remembrance of reading about it, but can remember if it was in
> some papers from my professor or in Gnat docs.
>
> These are valid concerns, I think, and not FUD. The former two I'm
> nearly sure are not in NT docs, and I think are very important for a
> newcomer which wants to experiment with tasking and has windows. You can
> blame me for trying to do realtime tasking in NT, but that's not my
> point. These things I've discovered not in gnat docs, and that was my
> original comment.
>
> Please feel free to correct me.
>
> Kind regards,
>
> --
> -------------------------
> Jano
> 402450.at.cepsz.unizar.es
> -------------------------