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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Robert Dewar's great article about the Strengths of Ada over
 other langauges in multiprocessing!
Date: Thu, 13 Mar 2008 20:12:40 -0500
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Date: 2008-03-13T20:12:40-05:00
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"Alex R. Mosteo" <devnull@mailinator.com> wrote in message
news:63sn1tF29a5oiU1@mid.individual.net...
...
> Although in Ada I don't see much (or any?) use for volatile, non-atomic
shared
> variables outside of protected objects.
>
> Some flaw in my understanding?

Yes, sort of. You're not considering non-tasking uses. The canonical example
for Volatile is reading/writing a memory-mapped hardware device. In that
case, optimizing out the reads/writes can be fatal. It doesn't directly have
anything to do with tasking. (I suppose one could consider the hardware
device as a sort of task, but it would be done with unusual properties.)

Another purpose is for debugging. You can monitor the memory location of a
Volatile object to see what is going on, without the pragma the compiler can
optimize the entire object away leaving nothing to monitor. (Of course, the
pragma also changes the code, which might change the bug you are trying to
find.)

Also, you can use Volatile on any object, whereas Atomic only works on ones
the compiler can do indivisibly (usually no larger than the word size of the
machine).

OTOH, for communication between tasks, you have to use Atomic. (Thus large
objects need a protected object or other scheme for synchronizing access.)

                             Randy.