POSIX standards.

POSIX standards.

[Craig MacFarlane]

Does anyone have any information regarding the POSIX standards?
I'd like to know what it encompasses, how much has been implemented,
where it may be obtained, is there a DEC Ada version, and anything else
that may be important.

Thanks,
Craig M.
University of California, Irvine
Department of Information and Computer Science
cmacfarl@paris.ics.uci.edu

Re: POSIX standards.

[David Emery]

The POSIX Ada Binding (IEEE P1003.5) is currently undergoing a ballot
recirculation.  I'd expect that we'll need one more recirculation
before final approval, probably 2Q92.  

POSIX .5 covers the set of services defined in POSIX .1, including
files, directories, processes, signals, etc.  It also includes an
interpretation of some Ada features (e.g. TEXT_IO) in a POSIX context.
It does not cover facilities covered in other POSIX documents (e.g.
real-time, security, system administration, networking, etc.)  

P1003.5 is defined in terms of the Ada 83 standard, and in terms of
the facilities provided by .1.  Some parts of the POSIX Ada Binding do
not provide functionality that Ada programmers would like
(particularly with respect to tasking), because these facilities are
not available from IEEE P1003.1.  In particular, IO that blocks only
one task in a program, instead of the entire program, is not supported
by current .1 semantics and is therefore not supported by the Ada
binding (no matter how much we'd like to require it, this would
represent a significant extension to current POSIX semantics, and
would probably break many otherwise conforming POSIX-compliant
operating systems.) 

The current binding is defined in terms of Ada 83.  An Ada9X binding
would probably look different, to take advantage of some new 9X
features.  Conversly, you should be able to use the Ada 83 (P1003.5)
Ada Binding from within an Ada 9X program.  No Ada9X work on POSIX is
currently under way, although the real-time people are studying Ada9X
as the target language for the P1003.20 Ada real-time binding.

A follow-on project, IEEE P1003.20, includes the facilities defined in
the POSIX real-time documents, P1003.4 and P1003.4a.  It is also
examining the current release of CIFO and ExTRA to understand their
influences on a POSIX real-time system programmed in Ada.  One current
issue is to resolve the impact of Ada9X on this work.

The POSIX Ada binding document defines the set of standard package
specifications and provides English text describing the semantics of
those packages.  You currently do not have to have a copy of POSIX .1
(which is defined in terms of C) to understand POSIX .5.  However,
there is an effort in the IEEE POSIX committee to develop a
language-independent (LI) definition of POSIX, and then require all
language bindings to be "thin" documents that mostly contain
references back to the LI document.  This approach is controversial,
as it would require the Ada programmer to read both the LI definition
and the Ada binding to understand the semantics of the Ada binding.

In part due to the controversy over the LI definition of POSIX,
neither the Ada binding nor the FORTRAN binding have been registered
as ISO committee documents.  Therefore, in the near term, the Ada (and
FORTRAN) binding will be an IEEE standard only.

You can obtain a copy of the current draft (Draft 7) by contacting
	Anna Kaczmarek
	IEEE Standards Office
	P.O. Box 1331
	445 Hoes Ln.
	Piscataway, NJ 08855-1331
	(908) 562-3811
I think the draft costs about $35 (it's about 350 pages all told).  

Several vendors are planning implementations of the Ada binding.  In
general, I'd expect that you'll purchase an implementation from your
compiler vendor, as some features of the binding require cooperation
from the compiler and its runtime.  

You should therefore contact your compiler vendor for information on
implementations.  

The next IEEE POSIX meeting will be held at Irvine CA, the week of
January 13.  We are actively soliciting participants for the Ada
Real-Time bindings work, as well as Ada Bindings to other parts of
POSIX.  

				dave emery
				P1003.5 Technical Editor
				emery@mitre.org