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From: Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Oberon and Wirthian languages
Date: Mon, 21 Apr 2014 11:16:56 -0700
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Date: 2014-04-21T11:16:56-07:00
List-Id: <comp.lang.ada>

On 04/21/2014 06:06 AM, Simon Clubley wrote:
>
> What I have not checked however is if a record assignment in Ada to a bit
> field record variable marked as Atomic would result in all the bit fields
> listed in the assignment being _guaranteed_ to be updated at the same time
> or whether there would just be a atomic update of each component in
> isolation.

If you have a record:

type Register_Info is record
    A : Boolean;
    ...
end record;

for Register_Info use record
    A at 0 range 0 .. 0;
    ...
end record;

and an atomic object of the type:

Register : Register_Info;
pragma Atomic (Register);

If the compiler accepts the pragma, then assignment to Register (as opposed to 
its components) is atomic:

Register := (A => True, ...);

Though the best bet is to do it and check the generated code.

-- 
Jeff Carter
"I like it when the support group complains that they have
insufficient data on mean time to repair bugs in Ada software."
Robert I. Eachus
91