On Wed, 29 May 2024 15:20:56 GMT, Chen Liang <li...@openjdk.org> wrote:
> Also, have you considered micro-optimize Constructor.hashCode too? Given its
> similar status to Method.
Not at this time. This PR is motivated by observing Method.hashCode as a
hotspot in a Spring heavy application when migrating to an ARM based platform.
We did not observe Constructor.hashCode to be a hotspot in this application.
> src/java.base/share/classes/java/lang/reflect/Method.java line 99:
>
>> 97: private Method root;
>> 98: // Hash code of this object
>> 99: private int hash;
>
> We can declare this field `@Stable`, like the `methodAccessor`.
This was something that I tried and I observed a performance regression on the
ARM platform that I was testing. From my understanding, `@Stable` tells the
compiler to trust the contents of this field which is only given when the field
holder is a known constant. This is generally true for cases like `Enums` but
not usually for `Method`.
Benchmark Mode Cnt Score Error Units
# Intel Skylake
MethodHashCode.benchmarkHashCode avgt 5 1.113 ± 1.146 ns/op
# Arm Neoverse N1
MethodHashCode.benchmarkHashCode avgt 5 3.204 ± 0.001 ns/op
> src/java.base/share/classes/java/lang/reflect/Method.java line 388:
>
>> 386: int hc = hash;
>> 387:
>> 388: if (hc == 0) {
>
> Should we add an extra field `hashIsZero` like in `String` to avoid repeated
> computation if the hash is 0?
Unlike with `String`, I don't often see cases where `Method` results in a
hashCode of zero, which should be weighed with the overhead of adding in an
additional variable. I believe some of the reasoning for handling zero-hashed
Strings was about how easy it is to construct hash collisions and feed the JVM
with bad Strings from an external actor. I don't believe this is an issue for
`Method`.
-------------
PR Comment: https://git.openjdk.org/jdk/pull/19433#issuecomment-2137699178
PR Review Comment: https://git.openjdk.org/jdk/pull/19433#discussion_r1619053915
PR Review Comment: https://git.openjdk.org/jdk/pull/19433#discussion_r1619079001
