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To: "David E. Tweten" <tweten@frihet.com>
cc: Bruce Evans <bde@zeta.org.au>, current@freebsd.org
Subject: Re: fixing accesses to volatile variable `time' 
In-reply-to: Your message of "Thu, 05 Sep 1996 19:22:16 PDT."
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Date: Fri, 06 Sep 1996 13:03:47 -0700
From: Wayne Scott <wscott@ichips.intel.com>
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> bde@zeta.org.au said:
> >1. time.tv_sec is long, and accesses to longs are not guaranteed to 
> >   be atomic.  They happen to be atomic on i386's.
> 
> To satisfy my curiosity, just who makes this "guarantee?"  Obviously, 
> access to a bit is inherently atomic, but I don't recall reading any C 
> language specification indicating that chars, shorts, or int accesses are 
> atomic whereas longs aren't.


Intel guarantees that 32-bit accesses on a 32-bit boundary are atomic on
all 32-bit Intel Architecture processors.

	(Pentium Pro manual volume 3 page 7-2)

So as long as you align the time data structure correctly, there is no problem.

-----------
Wayne Scott		        MD6 Architecture
wscott@ichips.intel.com		Work #: (503) 264-4165
Disclaimer:  All views expressed are my own opinions, and not necessarily 
             those of Intel Corporation.