[concurrency-interest] on happens-before formalism

Joe Bowbeer joe.bowbeer at gmail.com
Fri Feb 3 11:04:27 EST 2012


When this question arose on The Art of Multiprocessor Programming
discussion list a couple years ago, the resolution was that happens-before
(<=) is a strict partial order, therefore reflexive.

In other words, happens-before can be interpreted as
"happens-before-or-is-equal" -- but no one wants to say or write that.

--Joe

On Thu, Feb 2, 2012 at 11:28 PM, David Holmes <davidcholmes at aapt.net.au>wrote:

> It seems to me to be somewhat arbitrary to define this as either reflexive
> or irreflexive as it makes no practical difference to the semantics. I
> think
> irreflexive would be more appropriate in this case as intuitively it
> doesn't
> make sense to say that "A happens-before A". I suspect that by selecting
> reflexive and using a normal/simple notion of poset that the overall
> formalism is simplified.
>
> If you really want to know ask on the Java Memory Model list cc'ed.
>
> Cheers,
> David Holmes
>
> > -----Original Message-----
> > From: concurrency-interest-bounces at cs.oswego.edu
> > [mailto:concurrency-interest-bounces at cs.oswego.edu]On Behalf Of Pavel
> > Rappo
> > Sent: Friday, 3 February 2012 5:18 PM
> > To: Concurrency-interest at cs.oswego.edu
> > Subject: Re: [concurrency-interest] on happens-before formalism
> >
> >
> > Then I think it's very different from Lamport's definition of
> > happened-before which they reference to.
> > Maybe that's why Lamport calls it "happenED-before" (not
> > "happenS-before").
> >
> > Btw, there's such thing as strict partial order, which I guess in
> > this case is more suitable. It's irreflexive, asymmetric and transitive.
> >
> > On 3 Feb 2012, at 09:16, Qingzhou Luo wrote:
> >
> > > I think they did mean reflexive.
> > >
> > > See partial order definition:
> > > http://en.wikipedia.org/wiki/Partially_ordered_set
> > >
> > > On Thu, Feb 2, 2012 at 5:51 PM, Pavel Rappo
> > <pavel.rappo at gmail.com> wrote:
> > > I've been reading "SPECIAL POPL ISSUE The Java Memory Model" by Jeremy
> > > Manson, William Pugh and Sarita Adve.
> > > There's one (yet) thing seems strange to me. Though I think
> > it's actually a
> > > typo it's still worth mentioning.
> > >
> > > page. 8, 2.1: "...Note that all of this means that happens-before is a
> > > partial order: it is reflexive, transitive and anti-symmetric..."
> > >
> > > Am I right saying authors actually meant "irreflexive"?
> > >
> > > --
> > > Sincerely yours, Pavel Rappo.
> > > _______________________________________________
> > > Concurrency-interest mailing list
> > > Concurrency-interest at cs.oswego.edu
> > > http://cs.oswego.edu/mailman/listinfo/concurrency-interest
> > >
> > >
> > >
> > > --
> > > Qingzhou Luo
> > > http://mir.cs.illinois.edu/~qluo2/
> > >
> > > Department of Computer Science
> > > University of Illinois, Urbana Champaign
> > >
> >
> >
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> > Concurrency-interest at cs.oswego.edu
> > http://cs.oswego.edu/mailman/listinfo/concurrency-interest
> >
>
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