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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: GNAT 4.8 atomic access to 64-bit objects
Date: Fri, 15 Nov 2013 22:19:15 +0100
Organization: cbb software GmbH
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Date: 2013-11-15T22:19:15+01:00
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On Fri, 15 Nov 2013 20:08:54 +0100, Stefan.Lucks@uni-weimar.de wrote:

> On Thu, 14 Nov 2013, Dmitry A. Kazakov wrote:
> 
>> Is there a way to change this without machine code insertions?
> 
> I guess, putting your 64-bit object into a protected object is not an 
> option?

It is supposed to be lock-free. Using protected object would be very last
resort [*].

I was considering:

procedure Load
(  Ptr : in out T;
   Ret : in out T;
   Model : int := ATOMIC_RELAXED
);
pragma Import (Intrinsic, Load, "__atomic_load");

The problem with this is that GNAT's implementation of intrinsic import
seems incapable to deal with overloaded GCC built-ins. Unfortunately, all
__atomic_* built-ins are sort of templates.

--------------------------
* I wonder why RM does not mandate pragma Atomic always legal. After all,
the compiler could always implement it using a hidden protected object.
Except when access occurs on the context of a protected action. Which is
statically known (or else program is erroneous). Within a protected action
it already atomic.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de