RFR: 8271820: Implementation of JEP 416: Reimplement Core Reflection with Method Handle [v12]

[Peter Levart]

On Fri, 8 Oct 2021 23:31:32 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:
> 
>   Fix left-over assignment

Marked as reviewed by plevart (Reviewer).

Hi Mandy,

I think this is good as first slab. I don't have anything to add at this point. Some optimization ideas to try as followups. I ran benchmarks myself and the results are similar to yours. Some seem like a regression, but don't have big impact on real-world use case such as Jackson (de)serialization. "Const" class is pretty much the same as with recently improved variant with @Stable fields.
I say Go!

src/java.base/share/classes/jdk/internal/reflect/MethodHandleCharacterFieldAccessorImpl.java line 137:

> 135:     {
> 136:         if (isReadOnly()) {
> 137:             ensureObj(obj);     // throw NPE if obj is null on instance field

I think ensureObj(obj) must go before if statement in setChar

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