feat(util): add ConcurrentHashtable with lock-free D1/D2 composite-key tables#11675
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feat(util): add ConcurrentHashtable with lock-free D1/D2 composite-key tables#11675dougqh wants to merge 3 commits into
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…y tables Mirrors Hashtable's D1/D2 API with concurrent access guarantees: lock-free get via AtomicReferenceArray volatile reads, synchronized getOrCreate with double-checked re-read on miss. Eliminates composite key object allocation on hot read paths — the same structural advantage Hashtable.D2 has over HashMap<Pair<K1,K2>,V>, but thread-safe. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
…t class; add D2 benchmark Extract bucketIndex and forEach into ConcurrentHashtable.Support, mirroring the Hashtable.Support pattern. Add ConcurrentHashtableD2Benchmark comparing get and getOrCreate throughput against ConcurrentHashMap and ConcurrentSkipListMap. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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🟢 Java Benchmark SLOs — All performance SLOs passed
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… ConcurrentHashtable Two gaps filled per-dimension (D1 and D2): - Chain collision: force multiple entries into the same bucket (CollidingKey with fixed hashCode for D1; pigeonhole via 2-bucket table for D2) and verify all entries are reachable after concurrent inserts. - Concurrent distinct keys: 16 threads each insert a unique key simultaneously, verifying final size and that every key is retrievable — exercises concurrent inserts to different buckets, which the single-shared-key test does not cover. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Summary
ConcurrentHashtablewithD1(single-key) andD2(composite-key) inner classes, mirroring theHashtableAPI with concurrent access guaranteesget/getOrCreatefast path viaAtomicReferenceArrayvolatile bucket reads; synchronized only on miss with double-checked re-read under lockbucketIndex,forEach) extracted intoConcurrentHashtable.Support, following theHashtable.SupportpatternD2.get(K1, K2)andD2.getOrCreate(K1, K2, creator)accept key parts directly — no composite key object allocated for the lookup, unlikeConcurrentHashMap<Pair<K1,K2>, V>where EA must conservatively treat the key as escaping even on hits (ownership-transfer contract)ConcurrentHashtableD1TestandConcurrentHashtableD2Test(JUnit 5), including a concurrency correctness test verifying exactly one entry is created under 16 racing threadsConcurrentHashtableD2BenchmarkcomparinggetandgetOrCreatethroughput againstConcurrentHashMapandConcurrentSkipListMapwith sharedScope.Benchmarkstate (all threads hitting the same table)Test plan
./gradlew :internal-api:test --tests "datadog.trace.util.ConcurrentHashtable*"— all tests pass./gradlew :internal-api:jmhCompileGeneratedClasses— benchmark compiles cleanConcurrentHashtableD2Benchmarklocally to validate get/getOrCreate throughput advantage over CHM and CSLM🤖 Generated with Claude Code