RFR: 8271820: Implementation of JEP 416: Reimplement Core Reflection with Method Handle [v8]

Peter Levart plevart at openjdk.java.net
Thu Sep 16 07:12:53 UTC 2021

On Wed, 1 Sep 2021 01:05:32 GMT, Mandy Chung <mchung at 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.

Hi Mandy,

Yes, you had exactly the same thoughts as me! So this improves the "Var" case for fields. I also ran tests on my PC with your vh-mh patch on top and here are visualized results (combined with previous results):

jdk18+9 vs. mandy: https://jmh.morethan.io/?gists=7b2399cea71d12dfd3434701ddeed026,80203847700b9ab8baeb346a02efc804
jdk18+9 vs. peter: https://jmh.morethan.io/?gists=7b2399cea71d12dfd3434701ddeed026,b11842fbd48ebbd9234251fded50d52e
jdk18+9 vs. peter+vh2mh: https://jmh.morethan.io/?gists=7b2399cea71d12dfd3434701ddeed026,2a61a99909415f9e0ab53b125628b11d
mandy vs. peter: https://jmh.morethan.io/?gists=80203847700b9ab8baeb346a02efc804,b11842fbd48ebbd9234251fded50d52e
mandy vs. peter+vh2mh: https://jmh.morethan.io/?gists=80203847700b9ab8baeb346a02efc804,2a61a99909415f9e0ab53b125628b11d
peter vs. peter+vh2mh: https://jmh.morethan.io/?gists=b11842fbd48ebbd9234251fded50d52e,2a61a99909415f9e0ab53b125628b11d


PR: https://git.openjdk.java.net/jdk/pull/5027

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