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Re: Volatile happens before question

From Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com>
Subject Re: Volatile happens before question
Newsgroups comp.lang.java.programmer
References <09848313-2372-4c23-8f52-fa84c612c100@u32g2000yqe.googlegroups.com> <1e7b4r38kmn2f$.1kwqeem7f8lxb.dlg@40tude.net> <4YydnRFXi_2GZojSnZ2dnUVZ_rKdnZ2d@earthlink.com>
Date 2012-01-17 17:14 -0800
Message-ID <g1vrm3pvpsvj.z6mde7z8uo6d.dlg@40tude.net> (permalink)

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On Tue, 17 Jan 2012 14:49:58 -0800, Patricia Shanahan wrote:

> On 1/17/2012 8:17 AM, Peter Duniho wrote:
>> On Tue, 17 Jan 2012 04:04:52 -0800 (PST), raphfrk@gmail.com wrote:
>>
>>> The spec says that all writes to volatiles can be considered to happen
>>> before all subsequent reads.  What does "subsequent" mean, is that
>>> with regards to real time?
>>
>> Essentially, yes.  I believe the exact language talks about synchronization
>> order" or something, but the basic idea is the order in which program
>> statements are effectively executed.
> ...
> 
> Even before analyzing the entire thread so far, I'm going to disagree
> with this comment, because it can lead to an incorrect intuition.

I have to admit, I didn't think my statement was specific enough for you to
disagree on the point with which you chose to disagree.

> Real time order is a total order, or can be made into one by adding a
> tie breaker using the processor number for events that happen on the
> same cycle in different processors.
> 
> The potential incorrect intuition is that there is a total order of all
> events in a Java program. There isn't. [...]

I think I understand what you're saying and I don't disagree, but the fact
remains that it is reasonable to consider the order of execution of
statements within the program relative to each other, as if it _were_
possible to identify a total order.  After all, any time there's a conflict
(e.g. two different threads writing atomically to the same memory location
at once), the CPU does pick a winner, even if non-deterministically.

Some statements may occur concurrently, and of course directly germane to
this discussion is the fact that the apparent order of execution (i.e. the
observable results) for any given thread is dependent on what's observing
that thread (i.e. without synchroniation, the observable data may mutate in
a different way in one thread than it does in another).  Synchronization is
all about removing these ambiguities.

IF you feel my statement was not specific enough to avoid confusing
someone, that's fine with me.  But outright disagreement?  Seems like you
have to infer too much to get that far.  :)

Pete

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Thread

Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-17 04:04 -0800
  Re: Volatile happens before question Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2012-01-17 08:17 -0800
    Re: Volatile happens before question markspace <-@.> - 2012-01-17 08:50 -0800
      Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-17 09:00 -0800
    Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-17 08:54 -0800
      Re: Volatile happens before question markspace <-@.> - 2012-01-17 11:24 -0800
    Re: Volatile happens before question Patricia Shanahan <pats@acm.org> - 2012-01-17 14:49 -0800
      Re: Volatile happens before question Knute Johnson <nospam@knutejohnson.com> - 2012-01-17 15:49 -0800
      Re: Volatile happens before question Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2012-01-17 17:14 -0800
        Re: Volatile happens before question Patricia Shanahan <pats@acm.org> - 2012-01-17 18:17 -0800
          Re: Volatile happens before question Joshua Maurice <joshuamaurice@gmail.com> - 2012-01-19 16:45 -0800
  Re: Volatile happens before question Knute Johnson <nospam@knutejohnson.com> - 2012-01-17 08:18 -0800
    Re: Volatile happens before question markspace <-@.> - 2012-01-17 08:33 -0800
      Re: Volatile happens before question Knute Johnson <nospam@knutejohnson.com> - 2012-01-17 08:49 -0800
        Re: Volatile happens before question Knute Johnson <nospam@knutejohnson.com> - 2012-01-17 09:21 -0800
          Re: Volatile happens before question markspace <-@.> - 2012-01-17 10:10 -0800
            Re: Volatile happens before question Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-01-17 10:28 -0800
              Re: Volatile happens before question markspace <-@.> - 2012-01-17 10:41 -0800
                Re: Volatile happens before question Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-01-17 11:06 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-17 12:09 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-17 12:12 -0800
                Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-17 12:38 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-17 13:35 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-17 14:41 -0800
                Re: Volatile happens before question Patricia Shanahan <pats@acm.org> - 2012-01-17 14:55 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-17 15:27 -0800
                Re: Volatile happens before question Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2012-01-17 17:37 -0800
                Re: Volatile happens before question Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2012-01-17 17:42 -0800
            Re: Volatile happens before question Knute Johnson <nospam@knutejohnson.com> - 2012-01-17 15:46 -0800
              Re: Volatile happens before question markspace <-@.> - 2012-01-17 16:14 -0800
                Re: Volatile happens before question Knute Johnson <nospam@knutejohnson.com> - 2012-01-17 20:01 -0800
                Re: Volatile happens before question Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2012-01-17 20:37 -0800
                Re: Volatile happens before question Knute Johnson <nospam@knutejohnson.com> - 2012-01-17 21:52 -0800
                Re: Volatile happens before question Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2012-01-17 23:47 -0800
                Re: Volatile happens before question Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2012-01-18 00:08 -0800
                Re: Volatile happens before question Knute Johnson <nospam@knutejohnson.com> - 2012-01-18 09:04 -0800
                Re: Volatile happens before question Steven Simpson <ss@domain.invalid> - 2012-01-18 11:22 +0000
                Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-18 06:24 -0800
                Re: Volatile happens before question Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2012-01-18 07:32 -0800
                Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-18 08:34 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-18 10:12 -0800
                Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-18 11:15 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-18 11:59 -0800
                Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-18 12:24 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-18 13:16 -0800
                Re: Volatile happens before question Knute Johnson <nospam@knutejohnson.com> - 2012-01-18 15:00 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-18 16:12 -0800
                Re: Volatile happens before question Patricia Shanahan <pats@acm.org> - 2012-01-18 16:34 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-18 17:17 -0800
                Re: Volatile happens before question Patricia Shanahan <pats@acm.org> - 2012-01-18 19:03 -0800
                Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-18 15:30 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-18 16:10 -0800
                Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-19 08:18 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-19 09:40 -0800
                Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-19 10:10 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-19 10:39 -0800
                Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-19 12:13 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-19 13:31 -0800
                Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-19 16:14 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-19 21:16 -0800
                Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-20 03:23 -0800
                Re: Volatile happens before question "raphfrk@gmail.com" <raphfrk@gmail.com> - 2012-01-20 06:46 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-20 08:56 -0800
                Re: Volatile happens before question Lew <noone@lewscanon.com> - 2012-01-20 11:12 -0800
                Re: Volatile happens before question Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2012-01-18 17:06 -0800
                Re: Volatile happens before question Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-01-19 12:46 -0800
                Re: Volatile happens before question markspace <-@.> - 2012-01-19 13:38 -0800
                Re: Volatile happens before question Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2012-01-18 07:32 -0800
                Re: Volatile happens before question Lew <noone@lewscanon.com> - 2012-01-18 00:06 -0800
                Re: Volatile happens before question Knute Johnson <nospam@knutejohnson.com> - 2012-01-18 09:23 -0800
                Re: Volatile happens before question Joshua Maurice <joshuamaurice@gmail.com> - 2012-01-19 17:07 -0800
                Re: Volatile happens before question Joshua Maurice <joshuamaurice@gmail.com> - 2012-01-19 17:12 -0800
                Re: Volatile happens before question Joshua Maurice <joshuamaurice@gmail.com> - 2012-01-19 19:22 -0800
  Re: Volatile happens before question Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-01-17 10:24 -0800

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