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From Peter Firmstone <j...@zeus.net.au>
Subject Re: Progress, and a problem
Date Mon, 13 Dec 2010 01:48:35 GMT
Patricia Shanahan wrote:
> On 12/3/2010 7:15 AM, Gregg Wonderly wrote:
> ...
> > The important issue in FastList is that it was written with the JDK1.4
> > memory model. After moving River to Java 1.5, we'd have the JSR166 work
> > and the new, consistent memory model where volatile has a true meaning.
> > However, this code in particular is quite complex as you have noted, so
> > even adjusting to the new memory model could be problematic.
>
> I've just run a modified, simplified version of my test with java 
> version "1.4.2_19" and an unmodified copy of FastList, and I still get 
> the NullPointerException. This changes my thinking a bit. I had been 
> working from the assumption that the issue was to do with the changes 
> in memory model between 1.4 and 1.5. I now have to consider the 
> possibility of a more basic bug that is independent of the memory model.
>
> If there is anyone with a FastList or Java memory model background who 
> would like to help, please reply. I would welcome another set of eyes 
> on the code, and a cross check on my conclusions so far about how 
> FastList is supposed to work. There seems to be a critical invariant 
> that gets broken, and once that happens we are on track to either a 
> NullPointerException or dropped items.
>
> I can supply my test as a unit test (JDK 1.6, Junit 4) and as a main 
> program (JDK 1.4 or later0. In both forms, all it does is fire up a 
> mixture of threads that repeatedly add items to a FastList and threads 
> that repeatedly remove the first item they can from the FastList. 
> Failures seem to require simultaneous adds and removes.
>
> If I don't nail this problem fairly soon, I may abandon the current, 
> rather complicated, code and switch to writing a concurrent high 
> performance FastList substitute for 1.5 or later.
>
> Patricia
>
I'll have a look tonight, no promises though ;)

Cheers,

Peter.


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