1:44 p.m.
I am trying to unload a KnowledgePackage that is already loaded in my
KnowledgeBase. The call:
this.knowledgeBase.removeKnowledgePackage(knowledgePackage.getName());
hangs (never returns). I had a similar problem with adding a
KnowledgePackage to a KnowledgeBase and someone on here suggested that there
was a synchronization problem in the internal implementation of the add
method in the KnowledgeBase class, and that problem went away when I
downloaded M1 files (from Feburary 10th of this year). However, I just got
to test the removing of the KnowledgePackage and I seem to have a similar
problem (?).
Here is my unload rule:
rule "MyRule 1.0"
when
mpr : MyObject()
eval(mpr.isKnowledgeBaseLoaded("ACTIVE_KP"))
then
mpr.print("Rule MyRule 1.0 Executed");
mpr.removeKnowledgeBase("ACTIVE_KP");
end
The statement "Rule MyRule 1.0 Executed" is printed, and I am able to debug
the code all the way to the line outlined above, and that is when it goes in
a black hole. Any ideas why this is happening? Is this something fixed in
M2? Here is the log:
INFO|11904/0|10-05-13 13:19:54|Exception in thread "Thread-5"
org.drools.runtime.rule.ConsequenceException: rule: MyRule 1.0
INFO|11904/0|10-05-13 13:19:54|
INFO|11904/0|10-05-13 13:19:54| at
org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handleException(DefaultConsequenceExceptionHandler.java:23)
INFO|11904/0|10-05-13 13:19:54| at
org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:981)
INFO|11904/0|10-05-13 13:19:54| at
org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:918)
INFO|11904/0|10-05-13 13:19:54| at
org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1130)
INFO|11904/0|10-05-13 13:19:54| at
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:739)
INFO|11904/0|10-05-13 13:19:54| at
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingMemory.java:705)
INFO|11904/0|10-05-13 13:19:54| at
org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKnowledgeSessionImpl.java:200)
INFO|11904/0|10-05-13 13:19:54| at
com.medcpu.mpu.pp.engine.Drools.fireRules(Drools.java:459)
INFO|11904/0|10-05-13 13:19:54| at
com.medcpu.mpu.MpuExecutor.executeRules(MpuExecutor.java:191)
INFO|11904/0|10-05-13 13:19:54| at
com.medcpu.mpu.MpuExecutor.initiateRuleExecution(MpuExecutor.java:431)
INFO|11904/0|10-05-13 13:19:54| at
com.medcpu.mpu.MpuExecutor.propertyChanged(MpuExecutor.java:147)
INFO|11904/0|10-05-13 13:19:54| at
com.medcpu.mpu.MpuExecutor.run(MpuExecutor.java:498)
INFO|11904/0|10-05-13 13:19:54| at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
INFO|11904/0|10-05-13 13:19:54| at
java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
INFO|11904/0|10-05-13 13:19:54| at java.lang.Thread.run(Unknown Source)
INFO|11904/0|10-05-13 13:19:54|Caused by: java.lang.NullPointerException
INFO|11904/0|10-05-13 13:19:54| at
org.drools.reteoo.RuleTerminalNode.doRemove(RuleTerminalNode.java:369)
INFO|11904/0|10-05-13 13:19:54| at
org.drools.common.BaseNode.remove(BaseNode.java:95)
INFO|11904/0|10-05-13 13:19:54| at
org.drools.reteoo.ReteooBuilder.removeRule(ReteooBuilder.java:237)
--
View this message in context:
http://drools-java-rules-engine.46999.n3.nabble.com/removeKnowledgePackag...
Sent from the Drools - User mailing list archive at Nabble.com.
3:15 p.m.
I found out one more thing, this call above consistently happens with that
rule and the package it is unloading. I checked another rule that unloads
another package and it works consistently fine.
What could be the problem? I am assuming that if there are threads launched
by Drools to execute rules that that would be taken into account by Drools'
removeKnowledgePackage correct? So, there shouldn't be a deadlock. So,
something is causing that call to hang on that package, but not on another
package. Anybody has any idea where I can look for a possible solution or
even where to start looking?
Thanks.
--
View this message in context:
http://drools-java-rules-engine.46999.n3.nabble.com/removeKnowledgePackag...
Sent from the Drools - User mailing list archive at Nabble.com.
3:41 p.m.
If it's package dependent it might be hard for the devs to reproduce.
To facilitate debugging, and to gather information for a JIRA post, try detecting the
deadlock. When the call hangs try connecting to the JVM using JConsole. (It's
included in the JDK for java5 and later.) From JConsole, go to the "Threads" tab
and click the "Detect Deadlock" button.
If you're on a linux (and I think also Solaris) system you can perform a "kill
-3" on the JVM process to get the same information. It will dump the thread state to
stdout.
--- On Thu, 5/13/10, malkhafaji <moe.alkhafaji(a)medcpu.com> wrote:
From: malkhafaji <moe.alkhafaji(a)medcpu.com>
Subject: Re: [rules-users] removeKnowledgePackage Call Hangs!!
To: rules-users(a)lists.jboss.org
Date: Thursday, May 13, 2010, 3:15 PM
I found out one more thing, this call above consistently
happens with that
rule and the package it is unloading. I checked another
rule that unloads
another package and it works consistently fine.
What could be the problem? I am assuming that if there are
threads launched
by Drools to execute rules that that would be taken into
account by Drools'
removeKnowledgePackage correct? So, there shouldn't be a
deadlock. So,
something is causing that call to hang on that package, but
not on another
package. Anybody has any idea where I can look for a
possible solution or
even where to start looking?
Thanks.
--
View this message in context:
http://drools-java-rules-engine.46999.n3.nabble.com/removeKnowledgePackag...
Sent from the Drools - User mailing list archive at
Nabble.com.
_______________________________________________
rules-users mailing list
rules-users(a)lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users
5:09 p.m.
Thanks Greg. I just did what you suggested, and although I was able to
regenerate the exact same scenario, I clicked on Detect Deadlock from
JConsole and it said: No deadlock detected.
--
View this message in context:
http://drools-java-rules-engine.46999.n3.nabble.com/removeKnowledgePackag...
Sent from the Drools - User mailing list archive at Nabble.com.
5:18 p.m.
Again, there is probably no deadlock because if you look at the bold part of
the stack trace I posted in the first post (and again below), it seems like
it is throwing a NullPointerException and it is somehow killing the thread
without returning back to my application (from Drools). Here are my
findings:
1. It is throwing a NullPointerException (at
org.drools.reteoo.RuleTerminalNode.doRemove(RuleTerminalNode.java:369
).
2. The thread that threw the exception (Thread-15) check the logs below,
disappeared from my list on JConsole (it is not displayed in the list of
threads) which tells me that it was destroyed by an error that was later
sucked in by another code in the stack and the call never returned to my
application.
Exception in thread "Thread-15"
org.drools.runtime.rule.ConsequenceException: ru
le: MyRule 1.0
at org.drools.runtime.rule.impl.DefaultConsequenceExceptionHandler.handl
eException(DefaultConsequenceExceptionHandler.java:23)
at
org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:981
)
at
org.drools.common.DefaultAgenda.fireNextItem(DefaultAgenda.java:918)
at
org.drools.common.DefaultAgenda.fireAllRules(DefaultAgenda.java:1130)
at
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingM
emory.java:739)
at
org.drools.common.AbstractWorkingMemory.fireAllRules(AbstractWorkingM
emory.java:705)
at
org.drools.impl.StatefulKnowledgeSessionImpl.fireAllRules(StatefulKno
wledgeSessionImpl.java:200)
at com.medcpu.mpu.pp.engine.Drools.fireRules(Drools.java:459)
at com.medcpu.mpu.MpuExecutor.executeRules(MpuExecutor.java:191)
at
com.medcpu.mpu.MpuExecutor.initiateRuleExecution(MpuExecutor.java:431
)
at com.medcpu.mpu.MpuExecutor.propertyChanged(MpuExecutor.java:147)
at com.medcpu.mpu.MpuExecutor.run(MpuExecutor.java:498)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown
Source
)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown
Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
at
org.drools.reteoo.RuleTerminalNode.doRemove(RuleTerminalNode.java:369
)
at org.drools.common.BaseNode.remove(BaseNode.java:95)
at
org.drools.reteoo.ReteooBuilder.removeRule(ReteooBuilder.java:237)
at
org.drools.reteoo.ReteooRuleBase.removeRule(ReteooRuleBase.java:413)
at
org.drools.common.AbstractRuleBase.removeRule(AbstractRuleBase.java:7
29)
at
org.drools.common.AbstractRuleBase.removePackage(AbstractRuleBase.jav
a:657)
at
org.drools.impl.KnowledgeBaseImpl.removeKnowledgePackage(KnowledgeBas
eImpl.java:166)
at
com.medcpu.mpu.pp.engine.Drools.removeKnowledgeBase(Drools.java:482)
--
View this message in context:
http://drools-java-rules-engine.46999.n3.nabble.com/removeKnowledgePackag...
Sent from the Drools - User mailing list archive at Nabble.com.
10:50 a.m.
OK. So, I did an isolated test, and only tested two KP including this bad
one. Both packages have their complete set of rules. But now, the other
package is able to remove this faulty one.
So, it is when I had my complete set of KPs (about 10 of them) all active,
and then attempted to remove this faulty one that is when I got the
exception. By the way, I caught the exception in my application and moved
on, so it is definitely not hanging.
I hope this serves as a good hint to what is happening. It will take me some
time to go through my KP to find the faulty rule or package. Any ideas what
could cause this error? Apparently this KP that refuses to unload, did
unload in my isolated example (in the same application/code). So, what could
be the problem?
--
View this message in context:
http://drools-java-rules-engine.46999.n3.nabble.com/removeKnowledgePackag...
Sent from the Drools - User mailing list archive at Nabble.com.
2:34 p.m.
Any help is appreciated. I am stuck on this. I stripped everything down to
two simple drls, and one of them loads the other as a new KP, and then tries
to unload it.
Any ideas why the removeKnowledgePackage could possibly throw a
NullPointerException in M1?? This is really hurting us as we are going live
with this in a couple of weeks or so.
Any help would be greatly appreciated!
--
View this message in context:
http://drools-java-rules-engine.46999.n3.nabble.com/removeKnowledgePackag...
Sent from the Drools - User mailing list archive at Nabble.com.
3:20 a.m.
Why are you trying to remove a knowledge package while you are in the middle of running
rules? I'm not a drools developer and don't know whether it has been designed to
allow this area of code to be re-entrant but to me it seems like you are trying to pull
the rug (or at least part of it) out from underneath it. I'd assume that you are
getting null pointers because rules that are on the activation queue are suddenly no
longer present in the knowledge base, or some other similar reason.
There's probably two other approaches that you could take which may be safer:
1. Each rule have an activation object (shared across a rules package). They will only
fire if the appropriate package is in the knowledge base, when you no longer want a set of
rules to fire then you remove the appropriate activation object.
2. Don't remove the knowledge packages while the rules are still running, instead
populate a list of packages which need removing, either stored within the knowledgebase or
using a global to pass it back to the application. When you want to change the knowledge
package have your rule export the package you want to remove and then use the context to
abort the firing of the knowledge session. Your application code can then remove the
knowledge packages you have selected and then restart the firing of the session.
Thomas
-----Original Message-----
From: rules-users-bounces(a)lists.jboss.org [mailto:rules-users-
bounces(a)lists.jboss.org] On Behalf Of malkhafaji
Sent: 17 May 2010 20:35
To: rules-users(a)lists.jboss.org
Subject: Re: [rules-users] removeKnowledgePackage Call Hangs!!
Any help is appreciated. I am stuck on this. I stripped everything down to
two simple drls, and one of them loads the other as a new KP, and then tries
to unload it.
Any ideas why the removeKnowledgePackage could possibly throw a
NullPointerException in M1?? This is really hurting us as we are going live
with this in a couple of weeks or so.
Any help would be greatly appreciated!
--
View this message in context: http://drools-java-rules-
engine.46999.n3.nabble.com/removeKnowledgePackage-Call-Hangs-
tp815616p824494.html
Sent from the Drools - User mailing list archive at Nabble.com.
_______________________________________________
rules-users mailing list
rules-users(a)lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users
**************************************************************************************
This message is confidential and intended only for the addressee. If you have received
this message in error, please immediately notify the postmaster(a)nds.com and delete it from
your system as well as any copies. The content of e-mails as well as traffic data may be
monitored by NDS for employment and security purposes. To protect the environment please
do not print this e-mail unless necessary.
NDS Limited. Registered Office: One London Road, Staines, Middlesex, TW18 4EX, United
Kingdom. A company registered in England and Wales. Registered no. 3080780. VAT no. GB 603
8808 40-00
**************************************************************************************
5:16 p.m.
Thanks for the post Thomas. Actually, I wanted to load and unload KBs WHILE I
am running the rules. That was not a problem at all, and it is not a problem
with many other KBs.
I was inspired by your post (so thank you very much) and started looking to
maybe externalizing the removal from the rules themselves, however, I
"accidentally" came across the fix!! I found out that as long as you keep
the stateless session active across engine runs, it is a problem with the
unloading (and again unloading ONLY sometimes with some packages). So, I
disposed of the session at the end of every execution (which is something I
probably should do anyways with a stateless session) and recreated one from
the KnowledgeBase when I execute the rules again. This works like a charm!!!
Now, I am able to load and unload package from within the rules themselves
during execution. That fixed it!
Thanks Thomas again for the "inspiration" that led me to the answer.
--
View this message in context:
http://drools-java-rules-engine.46999.n3.nabble.com/removeKnowledgePackag...
Sent from the Drools - User mailing list archive at Nabble.com.
5390
days inactive
5395
days old
8 comments
3 participants
participants (3)
-
Greg Barton -
malkhafaji -
Swindells, Thomas