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Date: Wed, 18 Jan 2012 16:34:50 -0800
From: Patricia Shanahan <pats@acm.org>
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Subject: Re: Volatile happens before question
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On 1/18/2012 4:12 PM, markspace wrote:
> 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.
>
>

I'm curious about the "values out of thin air" statement about hardware.
Could you give some information about how it happens?

Patricia