On Wed, 1 Sep 2021 01:05:32 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: > > minor cleanup and more test case. > On balance I think removing class-spinning might mean a better overall story > w.r.t. footprint and maintainability. > : > So I think I'm in favor of simplifying and filing a follow-up to try and win > back some of the performance we might be losing on corner-case micros without > the custom class spinning. Great! I'll update the PR with Peter's patch + vh2mh with removal of StaticFieldAccessor/InstanceFieldAccessor inner classes [2] (no significant performance difference between [1] and [2]). > I wish MethodHandles obtained by unreflectGetter/unreflectSetter could be > less sensitive to where they are read from (constant vs. not-constant) and > optimize better in non-constant case. I think we should search in this > direction... to make MethodHandles obtained by > unreflectGetter/unreflectSetter more optimal in non-constant case. Yup, that's what the performance opportunity we should explore to improve MH/VH that will benefit all clients of MH/VH as well as core reflection. [1] http://cr.openjdk.java.net/~mchung/jep416/vh-mh.patch [2] http://cr.openjdk.java.net/~mchung/jep416/vh-mh-2.patch ------------- PR: https://git.openjdk.java.net/jdk/pull/5027
