[jboss-jira] [JBoss JIRA] (JBRULES-3675) java.lang.LinkageError, but only sometimes (multithreading issue)

[Mario Fusco (JIRA)]

    [ https://issues.jboss.org/browse/JBRULES-3675?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12750493#comment-12750493 ] 

Mario Fusco commented on JBRULES-3675:
--------------------------------------

At the moment I am not able to reproduce this issue, but the solution you're suggesting seems reasonable to me.
Can you confirm that synchronizing that loadClass method is enough to definitively solve the problem for you?
                
> java.lang.LinkageError, but only sometimes (multithreading issue)
> -----------------------------------------------------------------
>
>                 Key: JBRULES-3675
>                 URL: https://issues.jboss.org/browse/JBRULES-3675
>             Project: JBRULES
>          Issue Type: Bug
>      Security Level: Public(Everyone can see) 
>          Components: drools-core
>    Affects Versions: 5.4.0.Final
>         Environment: - JBoss 7.1.1
> - drools 5.4.0.Final
> - jdk 1.6u30
> - Windows 7 64 bit
>            Reporter: kenneth westelinck
>            Assignee: Mario Fusco
>             Fix For: 6.0.0.Alpha1
>
>
> See mail on mailinglist:
> {noformat}
> We have an application (A) deployed on JBoss 7.1.1 accepting commands (CQRS,
> but only C and Q :) ). A console application (B) is sending a large volume
> of commands to create entities in A. Entities in A are validated by Drools
> (plain drl files, configured in spring using drools-spring). Most of the
> time this works just fine. But sometimes, we get the following exception:
> java.lang.LinkageError: loader (instance of
> org/drools/rule/JavaDialectRuntimeData$PackageClassLoader): attempted
> duplicate class definition for name:
> "a/b/c/Rule_person_unique___name_656ee3db19d34e689d95e2d6b2be67b6"
>         at java.lang.ClassLoader.defineClass1(Native Method) [rt.jar:1.6.0_30]
>         at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631) [rt.jar:1.6.0_30]
>         at java.lang.ClassLoader.defineClass(ClassLoader.java:615) [rt.jar:1.6.0_30]
>         at org.drools.rule.JavaDialectRuntimeData$PackageClassLoader.fastFindClass(JavaDialectRuntimeData.java:615) [drools-core-5.4.0.Final.jar:5.4.0.Final]
>         at org.drools.util.CompositeClassLoader$CachingLoader.load(CompositeClassLoader.java:254) [knowledge-api-5.4.0.Final.jar:5.4.0.Final]
>         at org.drools.util.CompositeClassLoader$CachingLoader.load(CompositeClassLoader.java:237) [knowledge-api-5.4.0.Final.jar:5.4.0.Final]
>         at org.drools.util.CompositeClassLoader.loadClass(CompositeClassLoader.java:88) [knowledge-api-5.4.0.Final.jar:5.4.0.Final]
>         at java.lang.ClassLoader.loadClass(ClassLoader.java:295) [rt.jar:1.6.0_30]
>         at java.lang.ClassLoader.loadClass(ClassLoader.java:247) [rt.jar:1.6.0_30]
>         at a.b.c.Rule_person___unique___name_656ee3db19d34e689d95e2d6b2be67b6Eval0InvokerGenerated.evaluate(Unknown Source)
>         at a.b.c.Rule_person___unique___name_656ee3db19d34e689d95e2d6b2be67b6Eval0Invoker.evaluate(Unknown Source)
>         at org.drools.rule.EvalCondition.isAllowed(EvalCondition.java:114) [drools-core-5.4.0.Final.jar:5.4.0.Final]
> Any idea where this is coming from or what's causing this. 
> {noformat}
> And the answer:
> {noformat}
> I have never experienced this myself, but after having a quick look at the code I believe this could be a multi-threading problem.
> In the abstract class java.lang.ClassLoader the method loadClass(String, boolean) is synchronized, but both org.drools.util.CompositeClassLoader
> and org.drools.rule.JavaDialectRuntimeData$PackageClassLoader override this method without the use of "synchronized".
> I would suggest you create a JIRA issue for this.
> {noformat}
> We are now trying 5.5.0.CR1 and so far, we have not encountered this issue. I'll keep you posted should the same issue appear on 5.5.0.CR1

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