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From: wojtek@power.com.pl (Wojtek Narczynski)
Newsgroups: comp.lang.ada
Subject: Re: Reprise: 'in out' parameters for functions
Date: 15 Apr 2004 18:52:01 -0700
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Date: 2004-04-15T18:52:01-07:00
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>> Or the simplest possible: two protected counters, try to get the
>> sum atomically.
 
> Since this is trivial, I can only assume that you have two protected 
> counters with no support for external locking in mind.

I had in mind implementing it without the need to resort to
abstraction inversion, which I understand as -for example-
implementing semaphores over protected objects, which are implemented
over semaphores.

> Actually, you can even do that, by having one counter have a Sum operation 
> that calls the other. However, this whole subject is probably silly.

Yes, this is silly because I oversimplifed the problem.

The original problem I run into was how to implement a highly
concurrent, space and time efficient list, tree, and finally lock
manager.

And before that, I wanted to grab a ready implementation of this
(list, tree) from some library, but I could not find such a thing...

> Reminds me of a lot of improvement requests for Ada 9X.  "We want to do 
> such and such."
> 
> "Well, here is a simple example of how to do it in current Ada."
> 
> "Oh, but our software development plan doesn't allow us to use 
> Unchecked_Conversion."

Yes, I should probably have dropped protected type in favor of raw
semaphores.

Regards,
Wojtek