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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada,comp.lang.c++,comp.realtime,comp.software-eng
Subject: Re: Teaching new tricks to an old dog (C++ -->Ada)
Date: 12 Mar 2005 10:43:14 +0000
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Date: 2005-03-12T10:43:14+00:00
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Pascal Obry <pascal@obry.org> writes:

> CTips <ctips@bestweb.net> writes:
> 
> > > protected type Atomic_Integer is
> > >    procedure Increment;
> > > private
> > >    Value : Integer;
> > > end Atomic_Integer;
> > > -- Implementation
> > > protected body Atomic_Integer is
> > >    procedure Increment is
> > >    begin
> > >       Value := Value + 1;
> > >    end Increment;
> > > end Atomic_Integer;
> > >
> > 
> > Will that generate:
> >    L0:
> >        lwlock temp,&Value
> >        add    temp,temp,1
> >        stwcond temp,&Value
> >        if( failed ) goto L0;
> > or will it generate something much more heavy-weight.

Google shows me lwlock as a C function in the PostGres support groups;
I don't know what machine architecture has these instructions? PowerPC?

It could be used by any compiler as part of a low-level
implementation, of course, but it's hardly likely that a C compiler
could use it off its own bat. Why whould it want to unless you the
programmer tells it to?

If you're talking about assembler inserts in C -- for Pete's sake, we
can insert assembler in Ada as a last resort if it's needed.

What happens with lwlock about priority inversion?

> 
> No protected type implementations will be so light. This is impossible as it
> brings far more than atomic integer. For an atomic integer it is possible to
> declare :
> 
>    Value : Integer;
>    pragma Atomic (Value);

I don't think this will make

  Value := Value + 1;

atomic, though!

-- 
Simon Wright                               100% Ada, no bugs.