Re: Arguments for single-mutex-exclusion on protected types (Was: Does Ada tasking profit from multi-core cpus?)

["Randy Brukardt" <randy@rrsoftware.com>]

"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message
news:wcczm6bss2i.fsf@shell01.TheWorld.com...
> "Jeffrey R. Carter" <jrcarter@acm.org> writes:
...
> > I don't know. I mentioned it simply because it clearly prevents parallel
> > function calls on multiprocessor systems, and because it seems to
> > prevent the use of the ceiling locking policy on monoprocessors.
>
> I understand the point about multiprocessor systems, but why do you
> say ceiling locking won't work if function calls lock out
> other function calls?

I don't understand Jeffrey's point either, but isn't it true that ceiling
locking is essentially irrelevant on multiprocessor systems? That is, the
point is to get rid of the lock, but you can't do that on a multi-processor
(one processor can be running a lower priority task without anything being
wrong, and that task had better be blocked from accessing the protected
object). So ceiling locking has no advantage on a multi processor, it just
restricts what you can do. If multiple cores continue to grow in popularity,
it seems that the whole ceiling locking thing will become essentially
irrelevant - just another case of premature optimization.

(Can you tell I don't like ceiling locking much??)

                               Randy.