Fix: make ProjectIndex thread-safe for parallel builds (backport #12832) - #12927
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Backport of #12832 to maven-3.10.x. Switch ProjectIndex backing maps from HashMap to ConcurrentHashMap to fix root cause of index corruption under parallel builds (-T). Add null guards for both index and project lookups with enriched error messages. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
gnodet
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Aug 30, 2026
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Clean backport of #12832 to maven-3.10.x. The adaptation is correct — on master a null guard already existed and was only enhanced, whereas on maven-3.10.x the code had bare auto-unboxing with no null guard, so introducing both the ConcurrentHashMap switch and the full null guards from scratch is the right approach.
Observations (informational):
- File paths correctly use the
maven-3.10.xlayout (maven-core/...) rather than the master layout (impl/maven-core/...) - The
Integer idx+ null check +int index = idxpattern correctly prevents NPE from auto-unboxing - All three maintenance branches are covered: #12926 (maven-4.0.x), #12927 (maven-3.10.x), #12928 (maven-3.9.x)
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Claude Code on behalf of Guillaume Nodet
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Summary
Backport of #12832 to
maven-3.10.x.ProjectIndexbacking maps fromHashMaptoConcurrentHashMapto fix root cause of index corruption under parallel builds (-T)indicesandprojectslookups with enriched error messages mentioning parallel builds and extensions as possible causesTest plan
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