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From: Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP>
Newsgroups: comp.lang.ada
Subject: Re: Forcing GNAT to use 32-bit load/store instructions on ARM?
Date: Tue, 1 Jul 2014 21:20:00 +0000 (UTC)
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Date: 2014-07-01T21:20:00+00:00
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On 2014-07-01, Niklas Holsti <niklas.holsti@tidorum.invalid> wrote:
> On 14-07-01 23:40 , Simon Clubley wrote:
>> On 2014-07-01, daniel.dmk@googlemail.com <daniel.dmk@googlemail.com> wrote:
>>> So could there be a problem with GNAT's Atomic on ARM?
>>>
>> 
>> Yes, big time.
>
> No. The Atomic guarantee only applies to read/write of the whole record.
> My earlier post in this thread was in error.
>

That's interesting, and depressing, as it reduces the usefulness of
Atomic hugely.

When c.l.a talked a few weeks ago about syntax for the atomic update
of multiple bitfields at the same time, I had thought the general
view was that Atomic on a record resulted in register updates in units
of the record size when updating a single bitfield, but that's clearly
not the case as you have just pointed out.

I think this whole area of the atomic updating of multiple bitfields is
something which needs work in Ada especially now the above revelation
means Ada is even weaker in this specific area than I thought it was.

Thanks for the interesting (if depressing :-)) insight.

Simon.

-- 
Simon Clubley, clubley@remove_me.eisner.decus.org-Earth.UFP
Microsoft: Bringing you 1980s technology to a 21st century world