The problem is that the count field is changing faster than Jess can
keep up. This can happen if the PropertyChangeEvents don't specify the
name of the changed field or the new value. Under these circumstances,
Jess has to fetch the new property value from the bean itself, and if
the property is changing rapidly, this will obviously give rise to the
behaviour you're seeing. Make sure your PropertyChangeEvents specify
"count" for the name, and an Integer object with the new value for the
new-value field, and you shouldn't see this happening.
Another possibility arises when the above conditions are met, but the
engine is running on one thread while the change notifications are
coming on another (as is usually the case) and the events are simply
coming so fast that the change-thread is starving the run-thread --
i.e., changes are occurring faster than activations can fire. Since
you've got this single trap object, whenever the count increases, any
old activations are removed and a new one is created, so old ones are
simply being skipped; this is how you've defined the problem.
To fix this, you need an architectural change. You could definstance
the network event objects themselves as they arrive; then each one
could hang around in the Rete network as long as it took to be
processed. A rule could be responsible for undefinstancing each event
after it was recorded. Alternatively, the trap could create a regular
Jess fact to represent each network event and assert it, if for some
reason definstancing the event objects themselves is not feasible or
desirable.
I think Grant Jokerst wrote:
[Charset iso-8859-1 unsupported, filtering to ASCII...]
> Hello all,
> I am new to Jess and I am trying to use it to apply rules against network
> events (such as SNMP traps). I have been able to apply rules to the events
> by placing the events in a Queue and modifying a count property in a
> TrapListener class. The TrapListener class uses a PropertyChangeSupport
> object to notify Jess of changes to the count (via firePropertyChange)
> similiar to the "jess/examples/simple/Simple.java" code. The rules work
> fine as long as multiple events do not come in at the same time. However,
> if events come in rapidly (which is generally the case with network events),
> the rule "new-event" does not always fire. I have tried various
> synchronization techniques to no avail.
>
> The rules look something like:
> ....
> (deftemplate jobject (slot class) (slot OBJECT))
> (defclass traplstn TrapListener extends jobject)
> (defclass trapd Trapd extends jobject)
>
> ;; This rule will fire any time an event comes in and prints out the count
> (defrule new-event
> (traplstn (count ?count) )
> =>
> (printout t "ALERT: received trap, count is " ?count crlf)
> )
>
> (defrule startup
> =>
> ;; Instantiate the daemon
> (definstance trapd (bind ?thetrapd (new Trapd)))
> ;; Instantiate a listener to the daemon which queues up the traps
> (definstance traplstn (bind ?thetraplstn (new TrapListener)))
> ;; Add the queue from the TrapListener for thetrapd to send
> ;; The count is incremented and set every time an event comes in.
> (call ?thetrapd addListener (?thetraplstn getQueue))
> )
>
> (reset)
> ;; we must "run-until-halt" b/c there will be nothing on the agenda
> ;; until an event comes in
> (run-until-halt)
> ......
>
> Ideas, anyone?
>
> Thanks,
> Grant
>
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---------------------------------------------------------
Ernest Friedman-Hill
Distributed Systems Research Phone: (925) 294-2154
Sandia National Labs FAX: (925) 294-2234
Org. 8920, MS 9012 [EMAIL PROTECTED]
PO Box 969 http://herzberg.ca.sandia.gov
Livermore, CA 94550
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