On Tue, 19 Nov 2024 16:08:20 GMT, Hannes Greule <hgre...@openjdk.org> wrote:
>> When core reflection was migrated to be implemented by Method Handles, >> somehow, the method handles are not used for native methods, which are >> generally linkable by method handles. This causes significant performance >> regressions when reflecting native methods, even if their overrides may be >> non-native methods. This is evident in `Object.clone` and `Object.hashCode` >> as shown in the original report. >> >> I believe the blanket restriction previously placed on the native methods >> was because of signature polymorphic methods ([JLS >> 15.12.3](https://docs.oracle.com/javase/specs/jls/se23/html/jls-15.html#jls-15.12.3), >> [JVMS >> 2.9.3](https://docs.oracle.com/javase/specs/jvms/se23/html/jvms-2.html#jvms-2.9.3)) >> for MethodHandle and VarHandle; method handles do not link to the backing >> implementation that throws UOE while core reflection is required to do so. >> I have narrowed the restrictions to be specifically against these methods. >> >> Additionally, I cleaned up another check for invalid varargs flag. >> Together, I clarified the scenarios where native method accessors are used - >> all to bypass restrictions of java.lang.invoke. >> >> Testing: tier 1-5 green > > src/java.base/share/classes/jdk/internal/reflect/MethodHandleAccessorFactory.java > line 430: > >> 428: // Single parameter of declared type Object[] >> 429: Class<?>[] parameters = >> reflectionFactory.getExecutableSharedParameterTypes(method); >> 430: return parameters.length == 1 && parameters[0] == >> Object[].class; > > Would it be possible to check for the `PolymorphicSignature` annotation > instead? I think the main problem with annotation is that annotation creation needs to use `java.lang.reflect.Proxy`, which is unavailable until module system is initialized. Extra allocations are costs too, while checks here only reuse existing objects. In fact, I don't think Java's core libraries ever check for annotations, and the annotation's support class, `jdk.internal.reflect.ConstantPool`, has always been only loaded but never initialized in a simple hello world program since Java 5. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/22169#discussion_r1848692679
