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From Mark Thomas <ma...@apache.org>
Subject Re: RV-Predict bugs
Date Wed, 16 Sep 2015 08:02:11 GMT
On 16/09/2015 02:49, Caldarale, Charles R wrote:
>> From: Mark Thomas [mailto:markt@apache.org] 
>> Subject: Re: RV-Predict bugs
> 
>> My expectation is that once T2 has seen the updated value (originated
>> from another thread) all subsequent reads in T2 of the same field are
>> going to see the same value rather than some of those reads seeing an
>> older value (assuming there are no further changes in other threads).
> 
> The memory model does permit out-of-order reads of the same location, but I can't find
any CPUs that would do this.  (Out-of-order reads of different locations occur frequently,
of course.)

OK. Thanks.

I think that wraps up this part of the discussion for me.

I think we are all agreed that, purely from a re-ordering of reads point
of view (deliberately ignoring transformations), there is a theoretical
issue here based purely on the rules of the JMM but in practise the
issue is never observed because no CPU takes advantage of what the JMM
allows.

Whether or not issues in the category above are worth fixing or not is a
different debate and not one I really want to get into here. I'll just
note that we did fix this bug in Tomcat.

I'll follow up with the questions I have on the transformation aspects
in that part of the thread.

Mark

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