Re: ISO/IEC 14519 - Ada POSIX binding

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

Kilgallen@SpamCop.net (Larry Kilgallen) writes:
> VMS direct IP access uses the QIO system service which returns
> status on every call and after every IO completion.  Layering a
> C-language socket structure on top of that introduces the awful
> "errno" business.  Now should an IP package for Ada go through that
> C-language layer and try to undo the "errno" business, or should it
> call the QIO system service directly and never get tied up in
> "errno" at all ?

The POSIX.5 Ada interface does not have to be implemented on top of
the C interface, so on VMS, a well-written Ada binding would call the
QIO service directly.

As noted elsewhere in this thread, POSIX.5 uses an exception
(Posix.Posix_Error) to report that an error occurred, and an
"errno"-like variable to specify what kind of error occurred.  Thanks
to the exception, a lot of the ugliness goes away, and thanks to the
variable, it is easier to add new error codes to POSIX.5 without
breaking existing apps.
 
> > 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.
> 
> When VMS added Posix-compliant calls it was to allow C programmers
> to use it in a fashion to which they were accustomed.  They did
> _not_ force all programmers to use those C conventions.  Is the MVS
> situation somehow more restrictive ?

No, the other interfaces to the same operating system services are
still available (note the plural: there are several for different
languages like assembler, PL/I and Rexx).  The addition of a POSIX
interface just makes it easier to port applications to mainframes,
which in today's world appears to be a condition for survival.

-- 
Ludovic Brenta.