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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Portable memory barrier?
Date: Wed, 10 May 2017 19:38:12 -0500
Organization: JSA Research & Innovation
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Date: 2017-05-10T19:38:12-05:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:oeueil$knn$1@gioia.aioe.org...
> On 10/05/2017 02:51, Jere wrote:
>
>> Is there a method besides Atomic?  If I am implementing a generic FIFO 
>> (lock
>> free) and the FIFO elements are complex data types that may not be able 
>> to be
>> atomic, do I have any other options or are protected objects my only way 
>> out?
>
> But you don't need elements atomic only index has to. If I understood 
> Randy's explanation correctly atomic access to the buffer index will give 
> you the barrier between index and element accesses which is all that is 
> required.

Correct. The compiler can't motion (or let the CPU motion) volatile 
reads/writes across an atomic read/write. Thus you can depend on the order 
of volatile operations so long as an atomic operation is interleaved.

                           Randy.