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Subject: Re: [boost] [lockfree] review
From: Gottlob Frege (gottlobfrege_at_[hidden])
Date: 2011-08-26 21:52:24


On Thu, Aug 25, 2011 at 7:38 AM, Alexander Terekhov <terekhov_at_[hidden]> wrote:
>
> Gottlob Frege wrote:
>> What's the "independent reads, independent writes" problem?  I've
>> probably heard, seen, or mistakenly had a bug due to it once, but
>> don't know it by name.
>
> IRIW is an example that highlights remote write atomicity:
>
> T1: X = 1;
> T2: Y = 1;
> T3: A = X; B = Y;
> T4: C = Y; D = X;
>
> A == 1 && B == 0 && C == 1 && D == 0 is possible without remote write
> atomicity.
>

I would not be surprised by those resultant values.

> Another example is
>
> T1: X = 1;
> T2: if (X) Y = 1;
> T3: A = Y; B = X;
>
> A == 1 && B == 0 is possible without remote write atomicity.
>

I'm comfortable with that as well.

> SC is basically "no local reordering" plus remote write atomicity.
>
> In 'modes' model, remote write atomicity is a separate mode apart from
> reordering.
>
> regards,
> alexander.
>

Thanks
Tony


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