Paul King created GROOVY-11966:
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Summary: 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
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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