Unix error handling

[Deryk Barker]

In V10#37 Doug Moen <doug at nixtdc.uucp> writes:

> Here's the obligatory new idea:
> I don't like the fact that Unix kills a process if it blows the stack
> due to an infinite recursive loop.  The problem could be fixed with
> the introduction of an exception handling mechanism that the kernel
> knows about.  If the stack overflows, then the kernel raises an exception
> within the offending process.  The exception unwinds the stack (thereby
> recovering stack space) until a stack frame containing an exception
> handler is found.  If no exception handler is active, then (and only then)
> is the process killed.

Ah,  what  you  want  is the Multics operating system.  The system which
inspired  Unix  in  the  first  place  and  which most Unix people never
mention.   The  facility  you  desire  exists in Multics, with a further
feature:  the  process  is  not  killed  if  no handler is found, but is
suspended  and another level of the command processor is pushed onto the
stack.   If  you  can  somehow  fix  the  problem which caused the stack
overflow  (or  any  other  exception) then you can restart the suspended
procedure  at  the  faulting  instruction.   This even works for missing
routines when you are using the dyamic linking facility (and you thought
OS/2  invented  dynamic links!).  You can create the missing routine and
restart   the  calling  program;  makes  for  a  most  impressive  demo.
Unfortunately,  Honeywell, who inherited Multics from GE in 1971, capped
the  product  in  1984  and  it is no longer sold.  There are still some
systems  in  existence (I'm writing this on one now) and I shall miss it
very  much when it finally goes away.  The finest OS every written - bar
none.

And "David M. Alexander" <david at neon.stanford.edu> replies:

> You must have been reading about AIXv3 setjmp() and longjmp() recently.
> You can use these calls to do exactly that.
> AIXv3 is turning out to be a really nice OS.

Nice  that IBM is finally catching up - some 25 years after the original
Multics design work....

Deryk Barker,
Jupiter Software,
Victoria BC.

"Send Lawyers, Guns and Money,
 Dad, get me out of this!"