8371319: java.lang.reflect.Method#equals doesn't short-circuit with same instances

[liach]

There is currently no shortcut for fast equals for Method or Constructor. While the comparison for declaring class, name (interned strings' identity), and return type are very efficient with identity comparison, the comparison for parameter type is not so much: We always have to iterate through every parameter.

Luckily, even though we are burdened with the different method and constructor instance due to setAccessible, their parameter type arrays are shared most of the time; in particular, in the same root method/constructor hierarchy, all instances share the same method object. Thus, we can perform a == check on the incoming array to provide a fast path.

Benchmark numbers before and after:

Benchmark                                    Mode  Cnt  Score   Error  Units
ExecutableCompareBenchmark.distinctParams    avgt    5  1.189 ± 0.024  ns/op
ExecutableCompareBenchmark.equalMethods      avgt    5  2.449 ± 0.033  ns/op
ExecutableCompareBenchmark.sameMethodObject  avgt    5  0.541 ± 0.027  ns/op

Benchmark                                    Mode  Cnt  Score   Error  Units
ExecutableCompareBenchmark.distinctParams    avgt    5  1.186 ± 0.042  ns/op
ExecutableCompareBenchmark.equalMethods      avgt    5  1.078 ± 0.049  ns/op
ExecutableCompareBenchmark.sameMethodObject  avgt    5  0.395 ± 0.018  ns/op

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Issue

• JDK-8371319: java.lang.reflect.Method#equals doesn't short-circuit with same instances (Enhancement - P4)

Reviewers

• Jorn Vernee (@JornVernee - Reviewer)

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8371319: java.lang.reflect.Method#equals doesn't short-circuit with same instances

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At the time when this comment was updated there had been 7 new commits pushed to the master branch:

• 2910032: 8370966: Create regression test for the hierarchical memory limit fix in JDK-8370572
• 76a1109: 8251928: [macos] the printer DPI always be 72, cause some content lost when print out
• e1c9526: 8361339: Test gc/shenandoah/TestLargeObjectAlignment.java#generational fails on macOS aarch64 with OOM: Java heap space
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[forax]

Hello Chen,
Beware !

You may have also to test with ZGC (during the relocation phase),
because == may not be as fast as a pointer check.

[liach]

Remi, are you talking about my optimization code or the == case in my benchmark?
I think the Method/Constructor equals implementations are already == heavy; it might not hurt that much with one more == before the array content comparisons.