🚀 go-pugleaf

In article <id.SQ3W.IB6@ferranti.com>, peter@ferranti.com (peter da silva) writes:
>> OK, try this. VMS has something called an AST (Asynchronous System Trap) which
>> is similar to a user-mode interrupt.
>
>Yes, I'm familiar with it from RMX.  There, at least, unless you're working
>in assembler it's something to be used with extreme care lest you trash the
>language runtime.

RMX? No extra care required in VMS, from assembler or HLL. (Apart from the
usual synchronisation techniques, of course.)

>> This may occur at any time: for instance,
>> an asynchronous I/O can call an AST routine when the I/O completes. When the
>> AST routine completes, control returns to the code that was executing at the
>> time the AST occurred. (The analogy in NT is the APC, or Asynchronous
>> Procedure Call.)
>
>And in UNIX the analog is a "signal". Now, a signal is a little "safer" than
>an AST (at least as under RMX), in that it's guaranteed to run in your task
>context.

So is an AST in VMS, and an APC in NT. Nothing "unsafe" about it.

They aren't exactly analagous. An AST also carries a (program-provided)
value, a signal is one of a particular set of values. A signal can come
from another process, an AST can only occur from (or on behalf of) the current
process.

>> how can I use these non-reentrant routines safely in an AST
>> routine without screwing things up?
>
>You can't. Can you really do
>
>	WRITE (*,10) AA
> 10	FORMAT (1X,80A1)
>
>in an AST under VMS?

Don't know about FORTRAN, but I've done I/O in BASIC, BLISS, and Pascal from
ASTs with no hassles.

>> >But the UNIX operating system interface is centered on the file system.
>
>> But that doesn't mean that I can put an ACL on a UNIX operating system object.
>
>A UNIX "operating system object" *is* a file. If the file system supports ACLs
>you certainly can. What "operating system objects" are you trying to put an
>ACL on?

NT (for example) supports at least two file systems, DOS and NTFS. NTFS has
ACLs, DOS doesn't. If an operating system object is a file, which filing
system does it use?  If I only use DOS, does that mean that NT suddenly loses
the ability to use ACLs?

>Go read the Plan 9 papers, or get an Amiga. It's not new technology by
>any means: AmigaDOS was shipped in 1985, and based on an older operating
>system from Cambridge called Tripos (note, not all interesting O/S
>design is from the US).

I know, I've been to the restaurant that the operating system was named after.
:-)

>-- 
>Peter da Silva                                            `-_-'
>Ferranti International Controls Corporation                'U` 
>Sugar Land, TX  77487-5012 USA
>+1 713 274 5180                            "Zure otsoa besarkatu al duzu gaur?"

PJDM
--
Peter Mayne                     | My statements, not Digital's.
Digital Equipment Corporation   |
Canberra, ACT, Australia        | "AXP!": Bill the Cat