Max Zerzouri created DROOLS-2514: ------------------------------------ Summary: 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: 7.7.0.Final, 7.3.0.Final, 7.2.0.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). -- This message was sent by Atlassian JIRA (v7.5.0#75005)