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Date: Thu, 1 Oct 1998 13:07:14 -0700 (PDT)
From: Matthew Dillon <dillon@backplane.com>
Message-Id: <199810012007.NAA05774@apollo.backplane.com>
To: Guido van Rooij <guido@gvr.org>,
        Poul-Henning Kamp <phk@critter.freebsd.dk>,
        John Birrell <jb@FreeBSD.ORG>, cvs-committers@FreeBSD.ORG,
        cvs-all@FreeBSD.ORG
Subject: Re: cvs commit: src/lib/libc_r/uthread uthread_gc.c Makefile.inc uthread_init.c uthread_find_thread.c uthread_kern.c uthread_create.c uthread_exit.c
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:    The only thing you can assume as being atomic is a read or write, never
:    a read-modify-write, because you never know what kind of optimizations
:    (or lack thereof) the compiler will perform and also because some cpu's
:    simply do not have a locked RMW capability.

    oops, I meant a 'volatile read or write'.  aka, to guarentee read or write
    atomicy is to guarentee read or write ordering, as in the following 
    example.  Any compiler which reorders the stores in this case 
    (or the loads in the read case) is broken.

    volatile int a;
    volatile int b;

    code() {
	a = 1;
	b = 2;
    }

					-Matt

    Matthew Dillon  Engineering, HiWay Technologies, Inc. & BEST Internet 
                    Communications & God knows what else.
    <dillon@backplane.com> (Please include original email in any response)