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https://issues.apache.org/jira/browse/GROOVY-11966?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18076650#comment-18076650
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Paul King commented on GROOVY-11966:
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[~emilles] It is in the PR description: the Grails Parallel compilation of GSP
pages.
> AnnotationNode.isTargetAllowed introduces concurrent write to shared
> ListHashMap
> --------------------------------------------------------------------------------
>
> Key: GROOVY-11966
> URL: https://issues.apache.org/jira/browse/GROOVY-11966
> Project: Groovy
> Issue Type: Bug
> Reporter: Paul King
> Assignee: Paul King
> Priority: Major
>
> h3. Summary
> {{AnnotationNode.isTargetAllowed}} (and {{getRetentionPolicy}}) lazily caches
> its result via {{classNode.redirect().getNodeMetaData(Target.class,
> factory)}}, which delegates to {{NodeMetaDataHandler.getNodeMetaData(Object,
> Function)}} and ultimately calls {{computeIfAbsent}} on a {{ListHashMap}}.
> {{ListHashMap}} is documented as not thread-safe.
> The {{ClassNode}} for built-in annotations like {{@CompileStatic}},
> {{@Inject}}, {{@Target}}, etc. is shared process-wide via
> {{ClassHelper.makeCached}} (SoftReference cache keyed by {{Class}}). Parallel
> compiles in the same JVM (Gradle {{--parallel}}, multi-source-set builds,
> Grails worker pools) therefore race on the same metadata map.
> h3. Symptom
> {{ArrayIndexOutOfBoundsException}} from {{ListHashMap.toMap}} /
> {{ListHashMap.put}} during the array-to-{{HashMap}} resize. Concretely, one
> thread can finish the {{evolve}} branch and bump {{size}} past
> {{keys.length}} while another thread is mid-{{toMap}} reading {{keys[i]}}.
> h3. Affects
> Master only. Path was introduced by GROOVY-6526 (commit {{e16c9fb618}}) and
> is exercised on every annotation by GROOVY-11838's default-target
> enforcement. Groovy 5 returned a precomputed {{int}} field with no
> shared-state access.
> h3. Fix options
> * Add dedicated {{volatile int allowedTargets}} and {{volatile
> RetentionPolicy retentionPolicy}} fields to {{ClassNode}}; lazy-init from
> {{AnnotationNode}}, bypassing {{NodeMetaDataHandler}} for these two lookups.
> Idempotent computation, safe under races, no lock.
> * Switch {{NodeMetaDataHandler.newMetaDataMap()}} default to
> {{ConcurrentHashMap}} (atomic {{computeIfAbsent}}). Wider scope, fixes any
> similar latent races in other metadata callers.
> * Synchronise the read-modify-write in
> {{NodeMetaDataHandler.getNodeMetaData(Object, Function)}}.
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