Groups > comp.programming.threads > #2238

Re: About lockfree and waitfree... (2nd try)

From	nmm@needham.csi.cam.ac.uk (Nick Maclaren)
Newsgroups	comp.programming.threads, comp.programming, comp.arch
Subject	Re: About lockfree and waitfree... (2nd try)
Date	2014-04-23 21:51 +0100
Organization	Department of Deniable Assertions
Message-ID	<lj994h$n3c$1@needham.csi.cam.ac.uk> (permalink)
References	<lif821$inj$1@news.albasani.net> <lj933b$i85$1@dont-email.me> <lj94gr$c41$1@needham.csi.cam.ac.uk> <lj97cc$hfk$1@dont-email.me>

Cross-posted to 3 groups.

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In article <lj97cc$hfk$1@dont-email.me>,
Stephen Fuld  <SFuld@Alumni.cmu.edu.invalid> wrote:
>>
>Well, I am not a circuits guy, but I am basing this on Ivan's post, 
>quoted below.
>
>>  So the clocks on the cores on a single chip need to be
>> synchronized sub-nanosecond (easy),

Nor am I, but I didn't think that was a known easy task.  However,
it might be - what I am pretty sure is that it is not obviously
so for 100,000 cores, to anyone who hasn't looked at the problem
fairly hard.

>>> Does this solve the TAN problem, at least for a supposed 10,000 core chip?
>>
>> No, for two reasons:
>>
>>      That won't deliver temporarily consistent timestamps, which are
>> the critical requirement for that facilities.  That is essentially
>> sequential consistency on the timestamps.
>
>I thought the TAN problem was stated as no two people get the same 
>number but the numbers need not be strictly sequential (i.e. there nay 
>be holes), and no requester has enough priority to starve another 
>requester.  BTW, did you mean "temporally"?

Yes :-)  Simply getting distinct sequences of keys with each thread's
sequence sequential is easy, but not very useful.  Your description
is correct, but incomplete, because there is also the requirement
for sequential consistency.  And some (many?) algorithms that want
numbers of that form want them consistent with memory accesses.

>>      What many such algorithms need is a timer that can be used to
>> determine in which order memory accesses were made.  I think those
>> are a hopeless idea, but that doesn't stop people wanting them.
>
>I don't think that is what Ivan asked for, but I agree that my proposal 
>doesn't solve that problem.

Nor does anything else, at least not scalably :-)

Regards,
Nick Maclaren.

Thread

About lockfree and waitfree... aminer <aminer@toto.net> - 2014-04-13 19:54 -0700
  Re: About lockfree and waitfree... "Chris M. Thomasson" <no@spam.invalid> - 2014-04-13 19:38 -0700
    Re: About lockfree and waitfree... "Chris M. Thomasson" <no@spam.invalid> - 2014-04-13 19:47 -0700
      Re: About lockfree and waitfree... aminer <aminer@toto.net> - 2014-04-13 22:56 -0700
      Re: About lockfree and waitfree... "Chris M. Thomasson" <no@spam.invalid> - 2014-04-14 14:08 -0700
        Re: About lockfree and waitfree... "Chris M. Thomasson" <no@spam.invalid> - 2014-04-14 14:23 -0700
          Re: About lockfree and waitfree... Ivan Godard <ivan@ootbcomp.com> - 2014-04-14 16:27 -0700
          Re: About lockfree and waitfree... (2nd try) Ivan Godard <ivan@ootbcomp.com> - 2014-04-14 16:29 -0700
            Re: About lockfree and waitfree... (2nd try) "Chris M. Thomasson" <no@spam.invalid> - 2014-04-15 10:04 -0700
              Re: About lockfree and waitfree... (2nd try) Ivan Godard <ivan@ootbcomp.com> - 2014-04-15 10:34 -0700
                Re: About lockfree and waitfree... (2nd try) "Chris M. Thomasson" <no@spam.invalid> - 2014-04-17 16:35 -0700
                Re: About lockfree and waitfree... (2nd try) Ivan Godard <ivan@ootbcomp.com> - 2014-04-17 17:04 -0700
                Re: About lockfree and waitfree... (2nd try) nmm@needham.csi.cam.ac.uk (Nick Maclaren) - 2014-04-18 09:54 +0100
                Re: About lockfree and waitfree... (2nd try) Ivan Godard <ivan@ootbcomp.com> - 2014-04-18 02:31 -0700
                Re: About lockfree and waitfree... (2nd try) nmm@needham.csi.cam.ac.uk (Nick Maclaren) - 2014-04-18 11:56 +0100
                Re: About lockfree and waitfree... (2nd try) rpw3@rpw3.org (Rob Warnock) - 2014-04-18 11:26 +0000
                Re: About lockfree and waitfree... (2nd try) Ivan Godard <ivan@ootbcomp.com> - 2014-04-18 13:30 -0700
                Re: About lockfree and waitfree... (2nd try) "Chris M. Thomasson" <no@spam.invalid> - 2014-04-21 14:25 -0700
                Re: About lockfree and waitfree... (2nd try) "Chris M. Thomasson" <no@spam.invalid> - 2014-04-21 14:31 -0700
                Re: About lockfree and waitfree... (2nd try) Ivan Godard <ivan@ootbcomp.com> - 2014-04-21 14:53 -0700
                Re: About lockfree and waitfree... (2nd try) "Chris M. Thomasson" <no@spam.invalid> - 2014-04-22 14:21 -0700
                Re: About lockfree and waitfree... (2nd try) "Chris M. Thomasson" <no@spam.invalid> - 2014-04-22 14:36 -0700
                Re: About lockfree and waitfree... (2nd try) Ivan Godard <ivan@ootbcomp.com> - 2014-04-22 15:30 -0700
                Re: About lockfree and waitfree... (2nd try) "Chris M. Thomasson" <no@spam.invalid> - 2014-05-01 00:48 -0700
                Re: About lockfree and waitfree... (2nd try) "Chris M. Thomasson" <no@spam.invalid> - 2014-05-25 13:16 -0700
                Re: About lockfree and waitfree... (2nd try) "Chris M. Thomasson" <no@spam.invalid> - 2014-04-21 14:34 -0700
                Re: About lockfree and waitfree... (2nd try) Robert Wessel <robertwessel2@yahoo.com> - 2014-04-21 16:42 -0500
                Re: About lockfree and waitfree... (2nd try) Ivan Godard <ivan@ootbcomp.com> - 2014-04-21 15:02 -0700
                Re: About lockfree and waitfree... (2nd try) nmm@needham.csi.cam.ac.uk (Nick Maclaren) - 2014-04-22 09:05 +0100
                Re: About lockfree and waitfree... (2nd try) Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2014-04-22 09:27 -0700
                Re: About lockfree and waitfree... (2nd try) Ivan Godard <ivan@ootbcomp.com> - 2014-04-22 09:45 -0700
                Re: About lockfree and waitfree... (2nd try) nmm@needham.csi.cam.ac.uk (Nick Maclaren) - 2014-04-22 18:08 +0100
                Re: About lockfree and waitfree... (2nd try) Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2014-04-23 12:08 -0700
                Re: About lockfree and waitfree... (2nd try) nmm@needham.csi.cam.ac.uk (Nick Maclaren) - 2014-04-23 20:32 +0100
                Re: About lockfree and waitfree... (2nd try) Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2014-04-23 13:21 -0700
                Re: About lockfree and waitfree... (2nd try) nmm@needham.csi.cam.ac.uk (Nick Maclaren) - 2014-04-23 21:51 +0100
                Re: About lockfree and waitfree... (2nd try) Chris Gray <cg@GraySage.COM> - 2014-04-24 10:53 -0600
                Re: About lockfree and waitfree... (2nd try) nmm@needham.csi.cam.ac.uk (Nick Maclaren) - 2014-04-24 18:02 +0100
                Re: About lockfree and waitfree... (2nd try) Stephen Fuld <SFuld@alumni.cmu.edu.invalid> - 2014-04-25 13:39 -0700
                Re: About lockfree and waitfree... (2nd try) "Chris M. Thomasson" <no@spam.invalid> - 2014-04-22 22:08 -0700
            Re: About lockfree and waitfree... (2nd try) George Neuner <gneuner2@comcast.net> - 2014-04-17 21:15 -0400
              Re: About lockfree and waitfree... (2nd try) George Neuner <gneuner2@comcast.net> - 2014-04-17 21:25 -0400
                Re: About lockfree and waitfree... (2nd try) Ivan Godard <ivan@ootbcomp.com> - 2014-04-17 19:17 -0700
                Re: About lockfree and waitfree... (2nd try) George Neuner <gneuner2@comcast.net> - 2014-04-18 00:46 -0400
              Re: About lockfree and waitfree... (2nd try) Ivan Godard <ivan@ootbcomp.com> - 2014-04-17 18:52 -0700
    Re: About lockfree and waitfree... aminer <aminer@toto.net> - 2014-04-13 22:54 -0700

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