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Date: Wed, 17 Oct 2001 16:12:41 +0200
From: Jean-Marc Bourguet <jbourguet@free.fr>
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Subject: Re: Container reqs
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Date: 2001-10-17T16:13:30+02:00
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Ted Dennison wrote:
> 
> In article <3BCD2EC3.3B3C4498@free.fr>, Jean-Marc Bourguet says...
> >
> >4) whatever you do -- trying to modify the datastructure simultaneously
> >via iterators from different tasks -- is save.
> >
> >From my experience,
> >  * level 4 is useless because you still need synchronisation
> >    for other reasons when its whole generality is needed.  Achieving it
> >    has a major performance impact (every operation has to be
> >protected).
> 
> But your "level 4" is exactly what is needed for the "gender-bender"
> server-to-server queue we were referring to. This is a *quite* common need. Its
> come up in every multitasking Ada app I've ever written of at least moderate
> complexity. Your assertion is quite wrong too. When used as I described, it is
> the *only* communication the two server tasks need. In fact, it is the only safe
> communication method they can have.

There is a possibility I don't understand what you are refering to -- so
if you
think it is the case, please explain it more thorougly.

For a queue defined by three operations (is_empty, enqueue, dequeue) out
of
which two are modifying, the difference between level 3 and level 4 is
so
small that it has only a signification if you are also looking at the
other
containers.

I'm arguing that level 4 (where it is substantially different than level
3)
is not usefull and that level 3 is usefull but quite application
specific
so one is better providing it on a tailored way in each application
(I don't remember having ever needed concurrent modifications via
iterators
for exemple which is the requirement I reacted to initially.).

Yours,

-- Jean-Marc