Optimize JVM array hashing without reflection#3312
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Motivation: HashCode.hash iterates JVM arrays through java.lang.reflect.Array, adding reflective per-element access and boxing in a shared utility. Modification: Dispatch all nine JVM array kinds to typed while loops. Add a directional test that uses the original reflective algorithm as the parity oracle across primitive, reference, empty, null-element, and nested arrays. Add a JMH benchmark for primitive and reference arrays. Result: Hash values remain compatible while JDK 17 JMH measurements improve by roughly 39x to 135x for the measured 16- and 256-element arrays. Tests: - JDK 17 Scala 2.13 HashCodeSpec: 3 tests passed - JDK 17 Scala 3.3.8 HashCodeSpec: 3 tests passed - JDK 17 JMH: Int[16] 824.277 to 6.106 ns/op; Int[256] 12749.433 to 183.033 ns/op; AnyRef[16] 635.492 to 13.945 ns/op; AnyRef[256] 9491.604 to 240.387 ns/op - sbt +headerCheckAll and checkCodeStyle passed - scalafmt --list --mode diff-ref=origin/main passed - git diff --check passed - qodercli formal stdout review found no must-fix findings References: Refs #3300
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Motivation
HashCode.hashiterates JVM arrays throughjava.lang.reflect.Array, adding reflective per-element access and boxing in a shared utility. A focused JDK 17 JMH comparison showed this path is substantially slower than typed array loops.Modification
whileloops.java.lang.reflect.Arrayalgorithm as the parity oracle for primitive, reference, empty, null-element, and nested arrays.Result
Hash values remain compatible while the measured array paths improve by roughly 39x to 135x. JDK 17, 2 forks, 5 warmup iterations, 8 measurement iterations, 250 ms each:
mainInt[16]Int[256]AnyRef[16]AnyRef[256]Tests
sbt "actor-tests / Test / testOnly org.apache.pekko.util.HashCodeSpec"- passed, 3 testssbt "++3.3.8" "actor-tests / Test / testOnly org.apache.pekko.util.HashCodeSpec"- passed, 3 testssbt "bench-jmh/Jmh/run -wi 5 -i 8 -f 2 -w 250ms -r 250ms -t 1 -p size=16,256 .*HashCodeArrayBenchmark.*"- passed; results abovesbt +headerCheckAll- passedsbt checkCodeStyle- passedscalafmt --list --mode diff-ref=origin/main- passedgit diff --check- passedqodercliformal stdout review - no must-fix findingsReferences
Refs #3300