Groups > comp.lang.java.programmer > #10849

reading the JLS (17.4.5)

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From	Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at>
Subject	reading the JLS (17.4.5)
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http://java.sun.com/docs/books/jls/third_edition/html/memory.html#17.4

Finally I got time to read and (attempt to) understand the JLS
about concurrency.  There's a couple of wordings that appear
strange to me - maybe because of some insufficiency of my
English-language skills.

But in section 17.4.5 right after "Trace 17.5" there's this
paragraph:

" A set of actions A is happens-before consistent if for all
" reads r in A, it is not the case that either hb(r, W(r)),
" where W(r) is the write action seen by r or that there
" exists a write win A such that w.v = r.v and hb(W(r), w)
" and hb(w, r).

If ever "hb(r, W(r)), where W(r) is the write action seen by r"
then I couldn't help but consider the particular JVM-imple-
mentation utterly broken. How can this "either"-branch not
be empty?

How could a "read" that happens-before a particular "write" *ever*
see the "write"'s value?

Maybe, someone could explain, what that *really* means?

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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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