RFR: 8332586: Avoid cloning empty arrays in java.lang.reflect.{Method,Constructor} [v6]

[Roger Riggs]

On Fri, 31 May 2024 18:39:33 GMT, jengebr <duke at openjdk.org> wrote:

>> Improve `java/lang/reflect/Method.java`  by eliminating needless cloning of Class[0] instances.  This cloning is intended to prevent callers from changing array contents, but many Methods have zero exceptions or zero parameters, and returning the original `Class[0]` is sufficient.
>> 
>> Results from the included JMH benchmark:
>> Before:
>> 
>> Benchmark                                    Mode  Cnt  Score   Error  Units
>> ConstructorBenchmark.getExceptionTypes       avgt    5  6.526 ± 0.183  ns/op
>> ConstructorBenchmark.getExceptionTypesEmpty  avgt    5  5.803 ± 0.073  ns/op
>> ConstructorBenchmark.getParameterTypes       avgt    5  6.521 ± 0.188  ns/op
>> ConstructorBenchmark.getParameterTypesEmpty  avgt    5  5.747 ± 0.087  ns/op
>> MethodBenchmark.getExceptionTypes            avgt    5  6.525 ± 0.163  ns/op
>> MethodBenchmark.getExceptionTypesEmpty       avgt    5  5.783 ± 0.130  ns/op
>> MethodBenchmark.getParameterTypes            avgt    5  6.518 ± 0.195  ns/op
>> MethodBenchmark.getParameterTypesEmpty       avgt    5  5.742 ± 0.028  ns/op
>> 
>> 
>> After:
>> 
>> Benchmark                                    Mode  Cnt  Score   Error  Units
>> ConstructorBenchmark.getExceptionTypes       avgt    5  6.590 ± 0.124  ns/op
>> ConstructorBenchmark.getExceptionTypesEmpty  avgt    5  1.351 ± 0.061  ns/op
>> ConstructorBenchmark.getParameterTypes       avgt    5  6.651 ± 0.132  ns/op
>> ConstructorBenchmark.getParameterTypesEmpty  avgt    5  1.353 ± 0.150  ns/op
>> MethodBenchmark.getExceptionTypes            avgt    5  6.701 ± 0.151  ns/op
>> MethodBenchmark.getExceptionTypesEmpty       avgt    5  1.422 ± 0.025  ns/op
>> MethodBenchmark.getParameterTypes            avgt    5  6.629 ± 0.142  ns/op
>> MethodBenchmark.getParameterTypesEmpty       avgt    5  1.273 ± 0.169  ns/op
>
> jengebr has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fixing nits in benchmark

Marked as reviewed by rriggs (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/19327#pullrequestreview-2091692284