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

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Randy Brukardt" <randy@rrsoftware.com> writes:

> "Jeffrey R. Carter" <jrcarter@acm.org> wrote in message
> news:B0ULh.28294$PF.23764@attbi_s21...
>> Randy Brukardt wrote:
>> >
>> > Nothing serious, but it's less than ideal:
>>
>> My concern was that you said it was impossible in Ada 95. It may not be
>> ideal, but it doesn't seem to be impossible.
>
> I was thinking about a solution that doesn't clutter the cliient's view of
> the library with (usually) irrelevant details (such as whether the library
> is implemented with protected objects). After all, information hiding is
> good!

Info hiding is good, but one can't always have it, sadly.

If we have human beings specifying numeric priorities of things, then we
have the property that priorities only have meaning relative to other
priorities.  And that property implies that priorities are a global
issue -- can't be neatly encapsulated.  That's true whether we're
talking about priority of tasks, or PO's (ceilings), or I/O events,
or anything else.  So I wouldn't blame this on ceilings specifically --
I'd blame on the general model (numeric priorities, set by
programmers).

In a non-real-time context, it's easy to make it all automatic.  I
haven't typed "nice" on Unix very often lately, and yet my editor
responds well, even when I have a compute-bound process also running.

In a real-time context, we have various partial solutions (earliest
deadline first, and so forth).

- Bob