On a related subject, if I have a multi-threaded program in which one thread modifies facts in real time according to some external events and another thread call run() on the engine periodically, do I have to synchronize the two threads so that no facts are modified when the engine is inside run()? Thanks.
Regards,
Shan Ming Woo
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: Friday, September 02, 2005 6:17 AM
To: jess-users@sandia.gov
Subject: Re: JESS: Rule firing twice
I went back and looked over your first message and this time paid
attention to the deffunction canBeginProcessing. Holy corrupted data
structures, Batman! You can't modify a fact on the *left* side of a
rule! The Rete network is *not* re-entrant, which is why it's
carefully protected against interference from other threads. But that
protection doesn't help if a predicate function changes the object
it's working on, sending a PropertyChangeEvent which modifies the fact
that's being pattern-matched!
This is something like writing a Java equals() method that changes the
object and its hashCode() when you call it. Try to store such an
object in a HashMap!
Change canBeginProcessing to be a pure predicate function; call
setProcessedEntity (and beginProcessing) on the *right* side of the
rule, after you've made this decision.
(deffunction canBeginProcessing(?station)
(if (and (neq ?station nil)) then
;; Get the entity that can be processed.
(bind ?entity (call ?station beginProcessing))
;; Assign the entity to the current station.
(call ?station setProcessedEntity ?entity)
;; Return true if there is an entity.
(return (neq ?entity nil))
else
(return FALSE)))
I think Nicolas Fortin wrote:
[Charset iso-8859-1 unsupported, filtering to ASCII...]
> Dr. Friedman-Hill,
>
> I've been curious and I've had another idea. Just before to call the
> Rete.run() method in my Java program, I have checked the agenda activations.
> It has strengthened my doubt about something wrong, since for the
> troublesome rule (process-entity), there are two activations with the same
> facts :
>
> PROCESS:
> [Activation: PROCESS::process-entity f-15, f-42 ; time=45 ; salience=0]
> [Activation: PROCESS::process-entity f-15, f-42 ; time=45 ; salience=0]
> STATUS:
> For a total of 7 activations in all modules.
>
> Is it really abnormal ?
>
> Thanks in advance,
>
> Nicolas
>
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Ernest Friedman-Hill
Advanced Software Research Phone: (925) 294-2154
Sandia National Labs FAX: (925) 294-2234
PO Box 969, MS 9012 [EMAIL PROTECTED]
Livermore, CA 94550 http://herzberg.ca.sandia.gov
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