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From: markspace <-@.>
Newsgroups: comp.lang.java.programmer
Subject: Re: Volatile happens before question
Date: Wed, 18 Jan 2012 16:12:21 -0800
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On 1/18/2012 3:00 PM, Knute Johnson wrote:
> On 1/18/2012 1:16 PM, markspace wrote:
>> That's what I was thinking. With folks like Brian Goetz and Bartosz
>> saying the system can simply invent values, it's hard to analyze the
>> resulting code for any kind of deterministic behavior. Esp. because Java
>> is a step away from the machine, and I don't know exactly what sort of
>> operations are going to be executed.
>
> I know that the JLS says that variables can have values out of thin air
> but Goetz says on page 36 "When a thread reads a variable without
> synchronization, it may see a stale value, but at least it sees a value
> that was actually placed there by some thread rather then some random
> value. This safety guarantee is called out-of-thin-air safety."


That's a good find.  I can't reconcile that statement with other things 
I'm seeing.  Since real world hardware seems to be able to produce 
values out of thin air, I don't see how Java could prevent this.  It 
seems that one or the other statement is incorrect.