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

[Rémi Forax]

On Mon, 10 Nov 2025 17:59:02 GMT, Chen Liang <liach at openjdk.org> wrote:

> 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

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.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/28221#issuecomment-3513311587