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From: Venkatesh Srinivas <me@endeavour.zapto.org>
Date: Sat,  7 May 2011 22:44:34 -0400
Message-ID: <BANLkTimu7W5+y4BwZzrUr-+_jkqsLRi+NA@mail.gmail.com>
To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
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Subject: Re: [9fans] _xinc vs ainc
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On Sat, May 7, 2011 at 9:24 PM, Bakul Shah <bakul@bitblocks.com> wrote:
> On Sat, 07 May 2011 20:25:25 EDT erik quanstrom <quanstro@quanstro.net> =
=C2=A0wrote:
>> > > the difference, and my main point is that the loop in ainc means
>> > > that it is not a wait-free algorithm. =C2=A0this is not only sub opt=
imal,
>> > > but also could lead to incorrect behavior.
>> >
>> > I think a more likely possibility for the change is to have a
>> > *copy* of what was incremented. lock incl 0(ax) won't tell you
>> > what the value was when it was incremented.
>>
>> you can read the code. =C2=A0that value is not used by the thread librar=
y.
>
> If you want to use the value being atomically incremented,
> there is no more efficient way on x86. May not be used now but
> may be it can be used to make some synchronization primitive
> more efficient?

XADD

-- vs