[jboss-jira] [JBoss JIRA] (DROOLS-2514) Concurrent modification when initialising packages in KnowledgeBuilderImpl

[Max Zerzouri (JIRA)]

    [ https://issues.jboss.org/browse/DROOLS-2514?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13570035#comment-13570035 ] 

Max Zerzouri edited comment on DROOLS-2514 at 5/2/18 5:02 PM:
--------------------------------------------------------------

It's related in that Java 9 adds an extra sanity check, though the check in Drools' case is triggered due to concurrent modification of the {{HashMap}} across multiple threads, rather than simply within the function passed to {{HashMap.computeIfAbsentIfAbsent}}. The article is a bit misleading in saying that the behaviour changed, since it was always incorrect to rely on any usage that might trigger the {{ConcurrentModificationException}}.


was (Author: max.zerzouri):
It's related in that Java 9 adds an extra sanity check, though the check in Drools' case is triggered due to concurrent modification of the {{HashMap}} across multiple threads, rather than simply within the function passed to {{HashMap.computeIfAbsentIfAbsent}}.

> Concurrent modification when initialising packages in KnowledgeBuilderImpl
> --------------------------------------------------------------------------
>
>                 Key: DROOLS-2514
>                 URL: https://issues.jboss.org/browse/DROOLS-2514
>             Project: Drools
>          Issue Type: Bug
>          Components: core engine
>    Affects Versions: 7.2.0.Final, 7.3.0.Final, 7.7.0.Final
>            Reporter: Max Zerzouri
>            Assignee: Mario Fusco
>         Attachments: Main.java, main.drl
>
>
> When parallel compilation is enabled, common structures are modified concurrently by {{KnowledgeBuilderImpl.initPackage}}, resulting in the following stack trace in Java 9/10.
> {code:java}
> Exception in thread "main" java.util.ConcurrentModificationException: java.util.ConcurrentModificationException
>         at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
>         at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
>         at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
>         at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:488)
>         at java.base/java.util.concurrent.ForkJoinTask.getThrowableException(ForkJoinTask.java:600)
>         at java.base/java.util.concurrent.ForkJoinTask.reportException(ForkJoinTask.java:678)
>         at java.base/java.util.concurrent.ForkJoinTask.invoke(ForkJoinTask.java:737)
>         at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateParallel(ForEachOps.java:159)
>         at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateParallel(ForEachOps.java:173)
>         at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:233)
>         at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:497)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.compileRulesLevel(KnowledgeBuilderImpl.java:1238)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.compileRules(KnowledgeBuilderImpl.java:1218)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.compileKnowledgePackages(KnowledgeBuilderImpl.java:1056)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.addPackage(KnowledgeBuilderImpl.java:1047)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.addPackageFromDrl(KnowledgeBuilderImpl.java:553)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.addKnowledgeResource(KnowledgeBuilderImpl.java:773)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.add(KnowledgeBuilderImpl.java:2360)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.add(KnowledgeBuilderImpl.java:2349)
>         at Main.attempt(Main.java:48)
>         at Main.main(Main.java:29)
> Caused by: java.util.ConcurrentModificationException
>         at java.base/java.util.HashMap.computeIfAbsent(HashMap.java:1139)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.initPackage(KnowledgeBuilderImpl.java:1146)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.createPackageRegistry(KnowledgeBuilderImpl.java:1109)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.lambda$getOrCreatePackageRegistry$0(KnowledgeBuilderImpl.java:1105)
>         at java.base/java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1751)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.getOrCreatePackageRegistry(KnowledgeBuilderImpl.java:1105)
>         at org.drools.compiler.builder.impl.TypeDeclarationCache.createTypeDeclarationForBean(TypeDeclarationCache.java:262)
>         at org.drools.compiler.builder.impl.TypeDeclarationCache.getAndRegisterTypeDeclaration(TypeDeclarationCache.java:90)
>         at org.drools.compiler.builder.impl.TypeDeclarationBuilder.getAndRegisterTypeDeclaration(TypeDeclarationBuilder.java:69)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.getAndRegisterTypeDeclaration(KnowledgeBuilderImpl.java:1860)
>         at org.drools.compiler.rule.builder.PatternBuilder.processClassObjectType(PatternBuilder.java:305)
>         at org.drools.compiler.rule.builder.PatternBuilder.build(PatternBuilder.java:181)
>         at org.drools.compiler.rule.builder.PatternBuilder.build(PatternBuilder.java:151)
>         at org.drools.compiler.rule.builder.PatternBuilder.build(PatternBuilder.java:133)
>         at org.drools.compiler.rule.builder.GroupElementBuilder.build(GroupElementBuilder.java:66)
>         at org.drools.compiler.rule.builder.RuleBuilder.build(RuleBuilder.java:105)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.addRule(KnowledgeBuilderImpl.java:1281)
>         at org.drools.compiler.builder.impl.KnowledgeBuilderImpl.lambda$compileRulesLevel$3(KnowledgeBuilderImpl.java:1242)
>         at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183)
>         at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:177)
>         at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1492)
>         at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
>         at java.base/java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:290)
>         at java.base/java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:746)
>         at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
>         at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1603)
>         at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:177)
> {code}
> Looking at the code, it looks like additional concurrency-unsafe modifications are performed, since it accesses the mentioned {{HashMap}} to get a shared {{LinkedList}} which it then modifies.
> Note that the stack trace above is obtained on Java 9/10, as JDK9 added the extra check to {{HashMap.computeIfAbsent}}, but the code relies on race conditions in any JDK version.
> Attached a sample Java class source that can trigger the stack trace reliably on my machine (using OpenJDK 10)—should hopefully be reproducible using JDK9/JDK10 as long as the common ForkJoinPool has more than 1 thread.
> Also attached a "drl" file with the rules generated by the sample class (not needed when testing, as the contents are generated by the sample class).



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