Ada/UNIX

Ada/UNIX

[Karl Nyberg]

In article <206@imspw6.UUCP> bob@imspw6.UUCP (Bob Burch) writes (among other
stuff):

>The tale concerning Ada/UNIX comes back the same way and sounds the same
>no matter which way you turn your ear.  There was the article in the Aug.
>1 issue of Government Computer News, there are the comments from the Nov.
>RICIS symposium ("Ada on UNIX doesn't work"), and, to me at least, aside
>from and in addition to my own experiences with UNIX/Ada, it sounds
>about the same no matter who I talk to.

(1) I guess you haven't read the article in GCN to which you refer.  Either
that, or you weren't interested enough to check the facts.

(2) Or perhaps you haven't talked to enough people.

The GCN article (a widely respected professional computer journal, you will
note*) mentioned (if I remember correctly) that the requirements for Ada,
UNIX, and REAL TIME software FOR A PARTICULAR APPLICATION were such that all
the requirements could not be fully met in their current environment.  Ada
and UNIX were chosen (and used) for the MIS portions of the application as
best I can recall.

Many of the Ada compiler vendors, some of whose products are even written in
Ada and run on UNIX, are developing and marketing their products quite
successfully.  They wouldn't be doing so if their customers weren't using
their products profitably.  The list of companies developing commercial
applications in Ada, and on UNIX, continues to grow.  These include database
management systems, editors, and the like.  For more information on the
widespread use of Ada, call the Ada Information Clearinghouse (703)685-1477
and ask for their Ada in Use Database.  For more information on particularly
commercial applications, contact Dave Dikel, ddikel@ajpo.sei.cmu.edu,
(703)847-6741, Chairman of the SIGAda Commercial Applications Users Group.

Or (3) perhaps you're afraid that Ada WILL succeed, and that you are already
so far behind the competitive power curve that the only way you can salvage
your situation is to try to drag Ada down and hope that it will go away.
Well, it won't.  As you quote Stroustrup, Ada is here to stay.

But enough proseletyzing.  If you don't want to hear it, you won't.  Ten
years ago, you might have been one of those completely uninterested in UNIX,
and now you claim the ability to look into the future where it is concerned.
Far be it from me to try breaking through the brick wall.  I've got Ada code
to complete for my VAX/ULTRIX and PC/DOS machines to get my products to
market and continue to make money.  It's a better way to spend my time...

-- Karl --

* As an aside, I have had a number of articles published by GCN (and BYTE,
and Ada Letters), so I don't intend this as a slur on the paper.  However,
PLEASE consider their purpose.  It's not like their articles have been
reviewed for technical details and indepth understanding.  Such publications
"sell" by grabbing their readers attention with bold headlines.

Ada/UNIX

[rracine]

A reference was made to a study of Ada running on top of UNIX, which was
written up in GCN.  The reference made it seem that the language was the
problem.  Being one of the participants in the study, I can state that
the Operating System was the problem.  

The context of the study was as follows.  The Space Station Freedom Project
(that is really its correct name) decided many years ago to use Ada for all
new software.  The project is also trying to use commercial software when
possible.  So they had a number of folks (including us) look at the 
feasibility of having a System V Interface Definition (SVID) conforming
operating system be the ON-BOARD operating system for the Space Station
Freedom.

Without going into too much detail, the results we came up with are:

1) For real-time software, current implementations of SVID do not give the
   application program (in any language) enough of the processor.  There
   is too much overhead taken in Signaling, for example.

2) There are Ada implementations which are sufficient for the program,
   either with real-time operating systems under the run-time environment,
   or with their own run-time environments.

3) Since the Ada applications need the speed, and non-real-time software
   (comercial systems) need the SVID interface, why not procure a SVID
   (or POSIX) implementation ON TOP of an Ada run-time environment?

NASA (and the on-board computer contractor) are still stating a long term
SVID requirment, but I think we at least are making them look a little
closer at the implementations.

As far as Ada interfacing to UNIX, the additional overhead of converting
differing types of data is the only problem one should compare with C++,
and that can be negligible.  One could look at tasking, but C++ doesn't
have tasking.  If one really stretches one's imagination, you could call
UNIX a multitasking system, but then the comparison is unfair -- Ada is
much, much faster in all measurements.  Try to do synchronous communication
in C++.  Current Ada implementations have a one-way communication time
on the order of 50 microseconds.  The best we could do in C was a couple
of orders of magnitude longer (some number of milliseconds).

Roger Racine
C.S. Draper Laboratory, Inc.

re: Ada/UNIX

[David E. Emery]

A bit more on this...  I read the Air Force report, and later spoke to
one of the authors.  The specific problem that they encountered
concerned the following: For a multitasking program running as a
single Unix process, Unix does NOT guarantee that I/O invoked by one
task does not block the entire process (i.e. all tasks).  In fact, in
the specific implementation, when one task did I/O, the process (all
tasks) did block.  It is well known in the Unix community that the
basic Unix I/O model calls for blocking.  There are some facilities
for non-blocking I/O in Unix, but they are mostly dependent on the
whims of the device driver writer.

Now many people have said, based on reading this report, that Ada and
Unix don't mix.  They are entitled to their opinions.  However,
blocking I/O is strictly a Unix limitation, Ada's tasking only makes
this limitation obvious to the user.  

In the specific application cited in the article, I understand that
the Unix compiler vendor developed a non-blocking I/O package that
would work on the specific hardware used by the Air Force.  This
solution was not general enough (because of Unix limitations, not Ada
limitations) to be turned into a product.

Incidently, I've been doing systems programming on Unix using Ada for
4 years now.  There are some issues/problems/shortcomings that you
have to address, but this is true of any language on any operating
system.  There are some things that aren't easy to do (try doing
multi-taskin in C on Unix, or in C on VMS...)

So, now you know "The rest of the story".

				dave emery
				emery@mitre.org (new style)
				emery@mitre-bedford.arpa (old style)
				linus!dee

ada/unix

[Bernard Golden]

We have gotten a question from one of our customers regarding ada.  They
are fairly experienced with ada on the alsys compiler, but this will be
their first experience with the telesoft compiler on UNIX.  (And I should
point out that I'm completely unacquainted with ada).

Anyway, their question has to do with using the multiple capabilities (threads,
or somesuch) of ada on UNIX.  They're afraid they'll have to sacrifice
some of the capabilities of ada to run on UNIX.

Is there a good reference book to describe how this facility might work on
UNIX, or even better, is there someone from telesoft who follows this
newsgroup that might be willing to spend a few minutes talking to me on 
this topic?

Please email me, since I probably won't be able to scan this group thoroughly.

Thanks very much.

Bernard Golden
{pyramid,uunet}!infmx!bgolden
415-926-6416

RE: ada/unix

[Keith Shillington @lizard]

> ... their question has to do with using the multiple capabilities (threads,
> or somesuch) of ada on UNIX.  They're afraid they'll have to sacrifice
> some of the capabilities of ada to run on UNIX.

> Is there a good reference book to describe how this facility might work on
> UNIX, or even better, is there someone from telesoft who follows this
> newsgroup that might be willing to spend a few minutes talking to me on 
> this topic?

> Bernard Golden {pyramid,uunet}!infmx!bgolden 415-926-6416

Bernard: I left a message on your voice mail.

Ada (regardless of OS) has full multitasking capabilities.  I would love
to talk to you about them.

I can also recommend several texts: (in order of my preference)

"System Design with Ada", R.J.A. Buhr, Prentice-Hall
"Understanding Concurrency with Ada", Ken Shumate, McGraw-Hill
"Concurrent programming in Ada", Alan Burns, Cambridge University Press

Keith Allan Shillington   telesoft!keith@UCSD.ARPA   619/457-2700x388.ATT
TeleSoft Customer Support ucsd!keith@telesoft.com

Re: ada/unix

[Bernard Golden]

In article <2437@infmx.UUCP> bgolden@infmx.UUCP (Bernard Golden) writes:
>We have gotten a question from one of our customers regarding ada.

Keith Shillington (I think that's the right last name) from Telesoft called
me and we had a very good discussion regarding ADA and its capabilities
on UNIX.  It appears that no capabilities of ADA are sacrificed by running
on UNIX, although UNIX itself provides some facilities (e.g., message queues)
that might make some language features not so important.

It also appears that the 'task' facility could work with our product, IF
the programmer was careful.

So, I got my question answered.  I really appreciate Keith's efforts.  In
addition, I got calls from a couple of other people, but didn't have a 
chance to talk to them.  Thanks to everyone.

-b