I actually went so far as to write a "JessManager" class that interfaces
JESS with my application.
It is a class that owns and runs a Rete engine when needed.
It provides functions to add and remove Java objects as facts. It
listens to the objects propertyChanges to be notified of changes.
It has a separate thread that runs the Rete engine as necessary. The
thread usually sleeps but is notified as soon as a fact was changed.
Why not just call runUntilHalt()? Because this way, I can add flags
telling whether a run is in progress and a monitor to wait for the run
to stop. With the same monitor I can start and end something like a
transaction to do changes to my facts while JESS is not running. This
way I can add multiple related facts without JESS interfering by firing
rules at the same time.
It also has a startup and shutdown procedure.
Unfortunately my JessManager has many dependencies with the rest of the
application so that it would require some work to make it standalone and
useable it in a different application. For instance, it can only add
facts that are subclasses of the "generic data object" class of my
application.
But while writing that class, I was wondering if there wasn't or
shouldn't be something like that in JESS. The ability to tell JESS: "I
am going to do some changes but wait before you start firing" or "please
stop firing any new rule until I tell you" or "tell me when you have no
more rule to fire" is in my opinion very valuable.
Regards,
Florian Fischer
Shi Paul wrote:
Hi Henrique and others,
Ernest's reply is only good for single thread execution, while I have
at least 2 threads running. It's kinda like reproducer/consumer
scenario. I have Jess running in its own thread (consumer thread), I
have my other threads running as facts-collecting threads (producer
thread). So once those facts-collecting threads stop running, I need
to stop Jess thread but the problem is when I call Rete.halt() I don't
know if it's still busy.
I tried Rete.listActivations() before stopping it, it seems doesn't
work as well (the test result revealed that). I didn't try Scott's
suggestion since I want the solution in the API level instead of
adding a new rule in the knowledge base as I think the solution
shouldn't be across 2 different domains. Does anybody has othe good
suggestions?
Thanks,
Paul
From: "Henrique Lopes Cardoso" <[EMAIL PROTECTED]>
Reply-To: [email protected]
To: [email protected]
Subject: Re: JESS: How do I determine Jess engine has finished firing
rules
Date: Mon, 12 Feb 2007 09:43:05 +0000
Why don't you use Rete.run() instead of runUntilHalt() and wait for
the method to return?
Read Ernest's reply.
Cheers,
Henrique
Shi Paul wrote:
Hmmm, I wouldn't say it's a nice solution although it might work. I
looked through the Rete api, there is a Rete.listActivations, I'm
wondering if I could count on that, before calling rete.halt in the
main thread, I'd use that API in a while loop and let main thread
sleep for a few seconds if that doesn't return 0.
From: "Krasnigor, Scott L (N-AST)" <[EMAIL PROTECTED]>
Reply-To: [email protected]
To: [email protected]
Subject: RE: JESS: How do I determine Jess engine has finished
firing rules
Date: Fri, 09 Feb 2007 15:59:11 -0500
The easiest thing to do is add a rule with a low salience (I use
-1000)
that will always match and add whatever action on the rhs that you
want
to use to signal all rules are done being processed. This rule will
always be added to the end of the agenda, so when it fires, you know
there are no more rules waiting to be fired.
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
On Behalf Of Shi Paul
Sent: Friday, February 09, 2007 1:46 PM
To: [email protected]
Subject: Re: JESS: How do I determine Jess engine has finished firing
rules
Hi,
Actually I have created its own thread and then in that thread I call
rete.runUntilHalt. Then I run into this issue just mentioned, can you
give
me some more specifics about the solution as how to determin if the
engine
is not busy and can safely be stopped? I'd imagine that the main
thread
could just wait on some semaphore the jess thread operates or call
into
some
API which does the same thing.
Thanks,
Paul
>From: "Ernest Friedman-Hill" <[EMAIL PROTECTED]>
>Reply-To: [email protected]
>To: [email protected]
>Subject: Re: JESS: How do I determine Jess engine has finished firing
rules
>Date: Fri, 9 Feb 2007 13:19:29 -0500
>
>
>On Feb 9, 2007, at 12:15 PM, Shi Paul wrote:
>
>>Hi there,
>>Is there an API to determine the rule engine has completed its
work.
I'd
>>like to call rete.halt() to stop the engine, but I'm wondering what
if
>>the engine is still firing rules when I call that. Can anybody shed
some
>>lights on it?
>>
>
>Jess doesn't create any threads on its own. If you call rete.run(),
then
>run() returns when, and only when, there are no more rules to
fire. If
you
>have multiple threads, then you can set up your own notification
scheme
>based on that.
>
>
>---------------------------------------------------------
>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://www.jessrules.com
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