Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!aioe.org!eternal-september.org!feeder.eternal-september.org!mx04.eternal-september.org!.POSTED!not-for-mail
From: markspace <-@.>
Newsgroups: comp.lang.java.programmer
Subject: Re: Volatile happens before question
Date: Fri, 20 Jan 2012 08:56:09 -0800
Organization: A noiseless patient Spider
Lines: 25
Message-ID: <jfc6bc$569$1@dont-email.me>
References: <09848313-2372-4c23-8f52-fa84c612c100@u32g2000yqe.googlegroups.com> <f8b028b6-9f5b-4838-bae3-9a1d1b0716d3@l1g2000vbc.googlegroups.com> <jf7239$k2b$1@dont-email.me> <726da9ce-57f4-4136-b50b-56a032aca196@f1g2000yqi.googlegroups.com> <jf78bd$s4v$1@dont-email.me> <652cb878-fb2f-4361-8f70-61bc493cebf6@r16g2000yqi.googlegroups.com> <jf7crq$p30$1@dont-email.me> <6280ea10-c656-40fa-ba3d-50f24d471978@j15g2000yqb.googlegroups.com> <jf7n1d$ojv$1@dont-email.me> <6b44805b-ff63-41ba-8060-cbd92164f9d6@o9g2000yqa.googlegroups.com> <jf9kid$vac$1@dont-email.me> <240ac224-9713-4931-89f6-aeb7578aee09@m11g2000yqe.googlegroups.com> <jf9o0f$kmr$1@dont-email.me> <5ff9ba43-a357-4c0b-9c26-0a90242884d5@m11g2000yqe.googlegroups.com> <jfa23r$o3p$1@dont-email.me> <ababef97-5d65-4295-9906-90f7f2311e61@k28g2000yqc.googlegroups.com> <jfatbb$tuo$1@dont-email.me> <626c6bb6-103f-4b89-8484-316641c0476c@18g2000yqe.googlegroups.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Fri, 20 Jan 2012 16:56:12 +0000 (UTC)
Injection-Info: mx04.eternal-september.org; posting-host="XjIWM99mD7Ijfdu600oVPA"; logging-data="5321"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/qRCQhQCvsHw+lROnAmMAVr3EDnuvGyR0="
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:8.0) Gecko/20111105 Thunderbird/8.0
In-Reply-To: <626c6bb6-103f-4b89-8484-316641c0476c@18g2000yqe.googlegroups.com>
Cancel-Lock: sha1:xInLacH20zzpp+IAr4SrMlYqJ0Y=
Xref: x330-a1.tempe.blueboxinc.net comp.lang.java.programmer:11524

On 1/20/2012 3:23 AM, raphfrk@gmail.com wrote:

> The issue is that a read of the old value doesn't guarantee that no
> update has happened.
...
> Even though WA happens after RB in the synchronization ordering,
> there is no relationship between R-read and W-write.  The reason is
> that WA and RB have no happens-before relationship.


I don't think this is quite correct.  No update is in progress in your 
trace.  What I think they're talking about is causality, or the idea 
that map.get() might see a write from the future.  That is, a write from 
the map.put().  I don't see anywhere in the JLS where it says that reads 
can't be reordered across this type memory barrier.

I'll have to dig out JCIP since at this point I think trying to read the 
math heavy sections of the JLS have defeated me.  The read from the 
future thing kinda makes sense, since I don't recall anything that 
prevents it.  Maybe there is though...

Note I already mentioned this about 4 posts ago... ;-)