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https://issues.apache.org/jira/browse/GROOVY-12281?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Paul King reassigned GROOVY-12281:
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Assignee: Paul King
> Investigate mitigating class-loader pinning by ClassInfo.globalClassValue
> under the default ClassValue implementation
> ---------------------------------------------------------------------------------------------------------------------
>
> Key: GROOVY-12281
> URL: https://issues.apache.org/jira/browse/GROOVY-12281
> Project: Groovy
> Issue Type: Improvement
> Reporter: Paul King
> Assignee: Paul King
> Priority: Major
> Attachments: GROOVY-12281-Assessmentv2.pdf
>
>
> Follow-up from review discussion on [PR
> #2798|https://github.com/apache/groovy/pull/2798] (GROOVY-12142), preserving
> the analysis from that review. A {{ClassValue}} realizes the chain _key class
> → association → value → everything reachable from it_, and the association
> lives as long as the key class
> ([JDK-8136353|https://bugs.openjdk.org/browse/JDK-8136353], working as
> intended). The {{ClassValue}} implementation class itself prevents no
> unloading; what matters is the key's origin: a Groovy-loaded key class dies
> with Groovy's loader (fine), but a JDK/platform key class is effectively
> immortal, so any value reachable from it that was loaded by Groovy's loader
> pins that loader forever. Indirection counts — a JDK-typed value (e.g. an
> {{ArrayList}}) whose _elements_ are Groovy-loaded re-creates the pin one
> level down.
> {{ClassInfo.globalClassValue}} is static with unknown keys, including
> platform classes ({{String}} receives a {{ClassInfo}} in essentially every
> Groovy program), so the default {{ClassValue}} path pins the loader; today's
> only remedy is the global {{groovy.use.classvalue=false}} escape hatch, which
> trades away the per-class fast path for all keys.
> The general mitigation — {{SoftReference}}-wrapped values with a
> check-remove-recompute protocol — requires that recomputation be legal, and
> for {{ClassInfo}} it is not in general: a {{ClassInfo}} can carry
> non-recomputable state (modified metaclasses, category state), so a
> softly-collected value could silently discard user metaclass customizations.
> Approaches to investigate:
> * soft values while a {{ClassInfo}} is pristine, hardening the reference on
> first mutation — only classes with customized metaclasses would then pin, a
> far smaller set;
> * per-key policy: platform-loader keys get soft/map treatment, Groovy-loader
> keys stay strong (the key-origin rule applied mechanically);
> * splitting {{ClassInfo}} into recomputable and stateful parts;
> * revisiting whether the map-based implementation should become the default,
> with {{ClassValue}} as the opt-in fast path.
> Recompute cost and dispatch-path performance need measurement for any
> candidate.
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