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Re: Volatile happens before question

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Subject Re: Volatile happens before question
Date Thu, 19 Jan 2012 13:31:36 -0800
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On 1/19/2012 12:13 PM, raphfrk@gmail.com wrote:
> On Jan 19, 6:39 pm, markspace<-@.>  wrote:
>> On 1/19/2012 10:10 AM, raph...@gmail.com wrote:
>>
>>> However, you can't say that RB happens-before WA.  Therefore, there is
>>> no happens before path between W-write and R-read.  They are
>>> effectively concurrent.
>>
>> There doesn't need to be a happens-before here, however.  It's a *read*,
>> and doesn't create a data race.  The only thing you care about is that
>> writes happen-before reads.
>
> The point is that the read has to happen before the write, since the
> read is checking if a write lock happened.
>
> In reality, something like this is allowed
>
> writeCounter.increment()
> ->  update stored in memory
> map.put()
> ->  written immediately


I'm pretty sure that's the exact opposite of what is allowed.  Remember 
that AtomicInteger::increment() is documented to have the same semantics 
as both reading and writing a volatile.  I.e., from the perspective of a 
given execution order, the write from increment() is guaranteed to 
happen first.  Writes and reads may not be reordered around it.  I don't 
think write are allowed to be interleaved with other writes this way.

>
> Seeing that writeCounter is still the old value doesn't mean that
> map.put hasn't been committed to memory yet.


It's seeing writes from the future I'm most worried about right now. 
The read in the reader thread could see (perhaps) a write from the 
future, the map.put().  I'm looking around for something like "a read 
that happens before a a volatile read may not be reordered beyond a a 
write to that same volatile."

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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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