[rules-users] threw error java.lang.ClassCastException: org.drools.reteoo.FromNode$FromMemory cannot be cast to org.drools.reteoo.BetaMemory

[Davide Sottara]

Drools should lock a KB **internally** when rules are added or removed..
So either there's a bug in the rebuilding process - which should be possible
to isolate even in a single threaded environment, by finding the "right"
sequence of modifications - or there's a lock issue in Drools, which allows
two threads to modify the same KB at the same time.

In other words.. an application level lock could cause the KB to be modified
as a batch of rules is being executed. This could disrupt the correctness
of your results - as part of the data is processed using the old rules and
part using the new ones - but should not affect the knowledge base
integrity.

I was initially inclined to think that two add/delete operations were
attempted
in parallel.. but since they're mutually exclusive, it's less likely..

I'd need to check the KB modification code and see if there's anything that
can go wrong in case it's invoked when the KB is in an "unstable" state.

An important side question - How many sessions do you have? Add and
remove affect the KB, while exec would apply to any individual session
generated from the same KB... so this may complicate the scenario..

Davide

On 04/30/2013 06:03 PM, mohdejaz74 wrote:
> There was indeed a leak in locking.
>
> I have three operations - add, del, exec rules. add and delete were atomic
> but exec was not. Before getting reference to KB in exec rules, I made sure
> add/del were not accessing KB ... but I need lock KB even when rules are
> executing and release the lock when rules have executed (although I get a
> stateful session from KB before executing rules)
>  
> I suspect this error occurs when rules are executing and at the same time
> add/delete rule is invoked.
>
> I've not seen any further errors ... but we are still testing it.
>
> Ejaz
>
>
>
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