[gecode-users] Bugs in Gecode/J

[Guido Tack]

Malcolm Ryan wrote:

> I don't mean to hassle you, but I just need to know whether you think
> you can help me with this problem. I am working towards a close paper
> deadline and I need to know whether to stick with Gecode/J in the hope
> that we will be able to sort out these problems, or whether I need to
> look for another solution.

I've run some more experiments, and I can finally reproduce your bug.   
It seems to be a memory management / concurrency issue.  I could not  
reproduce the bug on any 1- or 2-core machine, but only with at least  
4 cores.  I suspect Java's concurrent garbage collector frees some  
memory that is still in use because we didn't get the locking right.
Did you do all your experiments on multi-core machines (i.e., more  
than 2 cores)?  If that's really the problem, you could run your tests  
with a limit on the number of CPUs used.  On Linux, you can achieve  
this using the taskset command.  On Mac OS 10.5, you can follow this  
hint to get control of your processors:
http://www.macosxhints.com/article.php?story=20071116183942199

I hope this helps.  We'll try to figure out the real cause of the  
problem, but concurrency bugs are typically hard to find - it may take  
some time.

Cheers,
	Guido

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