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From: Bob Duff <bobduff@theworld.com>
Newsgroups: comp.lang.ada
Subject: Re: Q: tasks and recursion, binary tree
Date: Wed, 06 May 2015 08:27:29 -0400
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Date: 2015-05-06T08:27:29-04:00
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gautier_niouzes@hotmail.com writes:

>     count: Natural:= 0;
>     pragma Volatile(count);
...
>         count:= count + 1;

You need an atomic increment.  Volatile doesn't do that (see the RM for
what it actually does).  Pragma Atomic doesn't do that either.
So the code has a data race, which makes it erroneous, which means
anything could happen (the program might crash, or might get wrong
answers, or might get correct answers).

You could create a protected object that encapsulates Count.
Or with GNAT you could look at System.Atomic_Counters.

- Bob