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NNTP-Posting-Date: Tue, 30 Aug 2016 01:14:30 -0500
From: Gareth Owen <gwowen@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Default values in #define
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Date: Tue, 30 Aug 2016 07:14:30 +0100
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Malcolm McLean <malcolm.mclean5@btinternet.com> writes:

> I see.  So if we implement a semaphore / token /flag system, the
> buffer must also be volatile, even though in fact it can't change when
> the accessor has the token, to prevent the optimiser moving the buffer
> accesses from outside the token guards.

Use a memory barrier in the token acquisition/release code.  
Buffer accesses will not be re-ordered through the memory barrier.