Re: ISO/IEC 14519 - Ada POSIX binding

[Ludovic Brenta <ludovic.brenta@insalien.org>]

Marin David Condic writes:

> Ludovic Brenta wrote:
> > POSIX has been around for a long time now, and yes, people do rely
> > on it.  The revision process is long and thorough, much like the
> > Ada standard's.
>
> I think you missed my point. If "Standard X" cites "Standard Y" and
> there is any change to "Standard Y", then "Standard X" has a problem
> of being potentially out of date. It doesn't matter how long
> "Standard Y" has been around - it is a separate standard subject to
> its own updates, enhancements, etc. It would be better for "Standard
> X" to specify its needs in such a way that "Standard Y" might be one
> method of solving them, but not necessarily the only method.
 
No, I didn't miss your point.  What I was trying to say is, why should
we need Standard X (Ada sockets) in the first place, if Standard Y
(POSIX.5) already exists?  Especially if Standard Y is an official,
vendor-neutral, portable ISO standard?  But you've answered that
question below.
 
> > POSIX stands for Portable Operating System Interface for uniX.  It
> > defines only the API and its semantics, not how the API is
> > implemented.  If there is an underlying POSIX-compliant operating
> > system, then the implementation is trivial.  If there is an OS
> > that is not POSIX-compliant, then the implementation is a thick
> > binding to the OS.  For bare boards, there is of course a higher
> > implementation cost.  But I submit that:
> >
> Yes, I know what POSIX is. I also know that not every operating
> system on the planet is POSIX-compliant. I also know that there are
> machines with no OS - presumably a sockets package would be an
> optional thing for implementations that didn't require it. I am not
> against POSIX - I just think that if Ada is going to have some kind
> of sockets package, it ought to abstract itself one layer away at
> least so that POSIX is not the only possible answer.
>
> > On the contrary, as I said, POSIX _is_ an abstract interface, and
> > implementations have some freedom in how they implement it.
> >
> It is an "abstract interface" for a UNIX-like implementation. There
> are OS's besides UNIX and possibly in the next ten years or so that
> an Ada standard would have to live, there may be a bunch more
> non-UNIX operating systems out there. I have no objection to POSIX
> or UNIX - just suggesting that an Ada standard would do well to not
> dictate either POSIX or UNIX as the only possible answer.

Maybe you have a point here ("all problems can be solved with an
additional level of indirection", I think was the quote).  It probably
depends on how difficult it would be to implement POSIX.5 sockets on
non-POSIX platforms.  Furthermore, I would think that anyone designing
a new OS in the next ten years would want to make it POSIX-compliant,
because it would be too difficult to try an impose an alternative API.
In fact, you've probably noticed that even the MVS and z/OS mainframe
operating systems became POSIX-compliant for just that reason.

So, if anyone on this newsgroup wants to implement a sockets package
in Ada, I'd suggest they make sure the external API is POSIX.5,
whatever their underlying platform is.

> > P.S. There is already an implementation of the POSIX standard
> > available at no cost under the GPL.  It is called FLORIST and is
> > maintained by ACT.  From what I understand, it is currently a thin
> > binding to a POSIX-compliant underlying OS (including sockets),
> > but providing alternative package bodies is probably feasible for
> > all kinds of platforms.
> 
> I am aware of FLORIST. You'd have a problem getting FLORIST adopted
> as the Ada standard - primarily because it is vendor specific and
> GPL licensed. Other vendors will want an answer that does not put
> GNAT/ACT in the driver's seat. (Although this might be a moot
> issue. One has to wonder how many of the other Ada vendors have a
> vigorous interest in future Ada standards. Or are many of them
> looking at it as a cash-cow to be milked for whatever they can get
> and then move on to more profitable markets?)

I agree with you entirely.  I wasn't trying to suggest that FLORIST
should becomme the Ada standard.  In fact, FLORIST is an
implementation; the Ada standard would only be an interface (API) and
I still think that this API should be POSIX.5, unless it is
*impossible* (not just difficult) to implement POSIX on some platform.
Ease of implementation was the design goal of C, not Ada.

Currently, I am aware of only one platform that remains non-POSIX, and
that is Windows.  Yet I don't think it would be impossible to write a
POSIX.5 thick binding on top of it (I mean for sockets, not the entire
OS).

-- 
Ludovic Brenta.