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Groups > comp.programming.threads > #2185
| From | Ivan Godard <ivan@ootbcomp.com> |
|---|---|
| Newsgroups | comp.programming.threads, comp.programming, comp.arch |
| Subject | Re: About lockfree and waitfree... (2nd try) |
| Date | 2014-04-18 02:31 -0700 |
| Organization | A noiseless patient Spider |
| Message-ID | <liqrdp$13i$1@dont-email.me> (permalink) |
| References | <lif821$inj$1@news.albasani.net> <lijqjp$ri0$1@dont-email.me> <lipog6$raa$1@speranza.aioe.org> <lipq6r$l97$1@dont-email.me> <liqp7o$1g2$1@needham.csi.cam.ac.uk> |
Cross-posted to 3 groups.
On 4/18/2014 1:54 AM, Nick Maclaren wrote: > In article <lipq6r$l97$1@dont-email.me>, > Ivan Godard <ivan@ootbcomp.com> wrote: >> >> There is no global timestamp, although the participating programs can >> create one using suitable locking protocols. There are also no atomic >> (pessimistic concurrency) operations. > > See below. > >> We elected to use sequential concurrency because it is the intuitive >> model; many programs are written under the assumption od sequential >> consistency; and it is very difficult to get programs correct under >> weaker models. We elected to use optimistic concurrency because it >> removes the hardware single-point-of-contention that are present in >> pessimistic primitives such as bus locking. We expect that >> low-contention multicore will scale better on a Mill as a result of this >> choice, although high-contention scaling is still bounded by the >> contention, as on any other CPU. > > Do you mean the same thing by sequential consistency and sequential > concurrency? "Sequential concurrency" is not a familiar term to me, nor, it appears, to Google, which has only one cite and that for some slides that appear to have invented the term. So no, I don't :-) > Anyway, all of my investigations and analyses agree with what you > say. I believe that some weak models ARE usable, but only in > combination with enforced programming constraints that prevent the > 'impossibilities' from being obtrusive. And that would mean a > completely new set of programming languages. > > However, I find it odd that there is no global clock, because it > is easy to provide if you already have sequential consistency. > The 'implementation' is just that one thread updates the clock > and others read it. While that does not provide 'physical' > consistency of the time, it's all any sane algorithm needs. I'm describing hardware; there is none in hardware, although a software clock is straightforward if you can accept the drawbacks. Global time is very difficult in hardware. There may be a single global clock, but non-uniform delays in reading the clock mean that two clients of the same clock will not agree on the time. It is certainly possible to have a single global take-a-number that gives a unique number to each client on request, and that can be used to provide a global ordering, but such systems do not scale - tghe take-a-number is a single-point bottleneck, and the round-trip latency to the TAN and back is often non-trivial.
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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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