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From: Knute Johnson <nospam@knutejohnson.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: Volatile happens before question
Date: Tue, 17 Jan 2012 15:46:12 -0800
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On 1/17/2012 10:10 AM, markspace wrote:
> On 1/17/2012 9:21 AM, Knute Johnson wrote:
>
>> And if b = 1 could be reordered before a = true then b would be flopping
>> all over the place because as soon as a = true b would again have to
>> be 0.
>
>
> But those reads and writes could be reordered, couldn't they? The read
> of "a" could happen after the read of "b", because there's no
> happens-before relationship there (a is not volatile, nor synchronized
> in any way).
>
> Or is that what you are saying? The actual problem is worse. (And I did
> in fact fubar my explanation and the my reading of the code. It *is*
> broken though.) I'm still looking for references, and I might be close.
> Uno momento....


In his case b cannot be anything but 0 in thread 2 when a is read in the 
if statement.  That doesn't mean it is going to stay that way very long.

And to quote Goetz "When a field is declared volatile, the compiler and 
runtime are put on notice that this variable is shared and that 
operations on it should not be reordered with other memory operations."

-- 

Knute Johnson