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Groups > comp.lang.java.programmer > #10733

Re: Volatile keyword

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On 12/13/2011 08:54 AM, Peter Duniho wrote:
> On 12/12/11 11:37 PM, Robert Klemme wrote:
>> [...]Bottom line is that the JVM spec does not make
>> any guarantees here (§17.7 see Lew's reference).
>
> I think it's worth being careful about "does not make any guarantees
> here". The implication of 17.7 is that there _is_ in fact a guarantee,
> for certain 64-bit fields marked as "volatile". Specifically, those
> which are of the type "double" or "long". This is true even on 32-bit
> systems.

And what guarantee is there?  Can you unambiguously formulate that and 
provide reference to the JLS so everybody can check it?

>>> In 32 bit, there is an assembler instruction cmpxchg8b designed to let
>>> you implement a light weight atomic 64-bit read.
>>
>> Since you do not know on what JVM your Java program will run when you
>> write it (or at least someone can choose to use a different JVM model)
>> it is safer to code under the assumption that a long and double write is
>> two operations i.e. not atomic.
>
> There is no need to make that assumption provided the field involved is
> marked "volatile".

I beg to differ - but I am eagerly waiting to be convinced otherwise.

Cheers

	robert

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Thread

Volatile keyword "raphfrk@gmail.com" <raphfrk@gmail.com> - 2011-12-12 04:51 -0800
  Re: Volatile keyword Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-12-12 14:31 +0000
    Re: Volatile keyword "raphfrk@gmail.com" <raphfrk@gmail.com> - 2011-12-12 06:52 -0800
  Re: Volatile keyword Lew <lewbloch@gmail.com> - 2011-12-12 06:34 -0800
  Re: Volatile keyword markspace <-@.> - 2011-12-12 10:00 -0800
    Re: Volatile keyword Tom Anderson <twic@urchin.earth.li> - 2011-12-12 18:41 +0000
      Re: Volatile keyword Patricia Shanahan <pats@acm.org> - 2011-12-12 11:43 -0800
    Re: Volatile keyword Roedy Green <see_website@mindprod.com.invalid> - 2011-12-12 11:15 -0800
      Re: Volatile keyword Robert Klemme <shortcutter@googlemail.com> - 2011-12-13 08:37 +0100
        Re: Volatile keyword Peter Duniho <NpOeStPeAdM@NnOwSlPiAnMk.com> - 2011-12-12 23:54 -0800
          Re: Volatile keyword Robert Klemme <shortcutter@googlemail.com> - 2011-12-14 19:39 +0100
            Re: Volatile keyword Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-12-14 10:59 -0800
            Re: Volatile keyword Patricia Shanahan <pats@acm.org> - 2011-12-14 11:00 -0800
              Re: Volatile keyword Robert Klemme <shortcutter@googlemail.com> - 2011-12-14 22:35 +0100
  Re: Volatile keyword Roedy Green <see_website@mindprod.com.invalid> - 2011-12-12 10:55 -0800

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