On Sat, 21 Aug 2021 22:37:05 GMT, Mandy Chung <mch...@openjdk.org> wrote:
>> This reimplements core reflection with method handles. >> >> For `Constructor::newInstance` and `Method::invoke`, the new implementation >> uses `MethodHandle`. For `Field` accessor, the new implementation uses >> `VarHandle`. For the first few invocations of one of these reflective >> methods on a specific reflective object we invoke the corresponding method >> handle directly. After that we spin a dynamic bytecode stub defined in a >> hidden class which loads the target `MethodHandle` or `VarHandle` from its >> class data as a dynamically computed constant. Loading the method handle >> from a constant allows JIT to inline the method-handle invocation in order >> to achieve good performance. >> >> The VM's native reflection methods are needed during early startup, before >> the method-handle mechanism is initialized. That happens soon after >> System::initPhase1 and before System::initPhase2, after which we switch to >> using method handles exclusively. >> >> The core reflection and method handle implementation are updated to handle >> chained caller-sensitive method calls [1] properly. A caller-sensitive >> method can define with a caller-sensitive adapter method that will take an >> additional caller class parameter and the adapter method will be annotated >> with `@CallerSensitiveAdapter` for better auditing. See the detailed >> description from [2]. >> >> Ran tier1-tier8 tests. >> >> [1] https://bugs.openjdk.java.net/browse/JDK-8013527 >> [2] >> https://bugs.openjdk.java.net/browse/JDK-8271820?focusedCommentId=14439430&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-14439430 > > Mandy Chung has updated the pull request incrementally with one additional > commit since the last revision: > > Remove separate accessor for static vs instance method > > There is no effective difference when using MethodHandle::dropArgument for > static method. Removing Static*Accessor and Instance*Accessor simplifies > the implementation. Right, early on splitting instance and static accessor implementations looked like a win for at least the instance accessor on micros, but it seems much of this win gets eaten up in more complex benchmarks since the hot call-site in `Method.invoke` sees more implementations and will be penalized by becoming bi- or megamorphic. Merging the split implementations back and accepting the need for a `dropArguments` combinator in the static case appears to be the right choice for maintainability and peak performance. A bit more overhead setting up - especially when reflecting on static methods (which is all the cold start benchmark does) - but I think that's the right trade-off in this case. ------------- PR: https://git.openjdk.java.net/jdk/pull/5027
