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Groups > comp.lang.java.programmer > #10925
| Newsgroups | comp.lang.java.programmer |
|---|---|
| From | Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> |
| Subject | Re: reading the JLS (17.4.5) |
| References | <slrnjerm1c.fvg.avl@gamma.logic.tuwien.ac.at> <wOWdnRqBm-mNvHPTnZ2dnUVZ_omdnZ2d@earthlink.com> <slrnjf1lan.fvg.avl@gamma.logic.tuwien.ac.at> <17674291.80.1324436881159.JavaMail.geo-discussion-forums@prez5> |
| Message-ID | <slrnjf36lv.fvg.avl@gamma.logic.tuwien.ac.at> (permalink) |
| Date | 2011-12-21 08:37 +0000 |
Lew <lewbloch@gmail.com> wrote:
> Andreas Leitgeb wrote:
>> Given some (simplified) sample code:
>> class Test {
>> /*non-vol*/ int n1;
>> volatile int v1;
>>
>> void t1() {
>> n1 = 1;
>> v1 = n1; // v1 uses n1
>> }
>>
>> void t2() {
>> int r1=v1, r2=r1*n1; // r2 uses r1
>> assert ! (r1 == 1 && r2 != 1) : "huh?";
>> }
>> }
>> Two threads T1 and T2 may at some point run t1() and t2()
>> respectively, then I should expect, per transitivity of
> You have to establish a /happens-before/ between the invocations
> of t1() an t2().
> If two threads begin to execute the methods, you cannot guarantee
> that t1() will /happen-before/ t2(), so the read of 'v1' in the
> latter could result in the default value.
Perhaps you found the/a sore spot of my (mis?)understanding.
*iff* a *volatile* read gets to see the result of a *volatile*
write, then doesn't that say anything about that the write must
have "happened-before" the read?
In my example, I didn't mean to imply, that r1 would always
turn out to be 1. But *if* it does, then could anything be
assumed about r2 ?
If the write to v1 (but not to n1) in t1() were in a
synchronized(this)-block, and so were the read of v1
(but not n1) in t2(), then would anything be implied
about r2 *if* observing r1 == 1 in T2?
In practice, I think that establishing a happens-before
based on observation of a read's value is quite essential,
but I may of course be wrong here. I don't even see how one
could determine the order in which synchronized blocks for
a common monitor are actually passed through by different
threads, other than by observing reads.
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reading the JLS (17.4.5) Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-12-18 12:10 +0000
Re: reading the JLS (17.4.5) markspace <-@.> - 2011-12-18 06:57 -0800
Re: reading the JLS (17.4.5) Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-12-20 17:54 +0000
Re: reading the JLS (17.4.5) markspace <-@.> - 2011-12-20 10:50 -0800
Re: reading the JLS (17.4.5) Patricia Shanahan <pats@acm.org> - 2011-12-20 12:12 -0800
Re: reading the JLS (17.4.5) Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-12-21 08:54 +0000
Re: reading the JLS (17.4.5) Patricia Shanahan <pats@acm.org> - 2011-12-21 10:56 -0800
Re: reading the JLS (17.4.5) markspace <-@.> - 2011-12-21 12:02 -0800
Re: reading the JLS (17.4.5) Patricia Shanahan <pats@acm.org> - 2011-12-18 09:21 -0800
Re: reading the JLS (17.4.5) Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-12-20 18:35 +0000
Re: reading the JLS (17.4.5) Lew <lewbloch@gmail.com> - 2011-12-20 19:08 -0800
Re: reading the JLS (17.4.5) Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-12-21 08:37 +0000
Re: reading the JLS (17.4.5) Patricia Shanahan <pats@acm.org> - 2011-12-21 10:46 -0800
Re: reading the JLS (17.4.5) markspace <-@.> - 2011-12-21 12:09 -0800
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