RFR: 8271820: Implementation of JEP 416: Reimplement Core Reflection with Method Handle [v15]

[Alan Bateman]

On Tue, 26 Oct 2021 16:35:34 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 with a new target base due to a merge or a rebase. The pull request now contains 40 commits:
> 
>  - Fall back to the VM native reflection support if method handle cannot be created
>  - fix bug id in test
>  - Merge
>  - Merge branch 'master' of https://github.com/openjdk/jdk into reimplement-method-invoke
>  - Merge branch 'master' of https://github.com/openjdk/jdk into reimplement-method-invoke
>  - Separate paramFlgas into paramCount and flags fields
>  - Minor cleanup.  Improve javadoc in CallerSensitiveAdapter
>  - Fix left-over assignment
>  - Remove duplicated microbenchmarks
>  - Avoid pitfall with unwanted inlining in some cases.  Also remove boxing/unboxing to focus on the invocation cost
>  - ... and 30 more: https://git.openjdk.java.net/jdk/compare/97d3280e...64738bb2

src/java.base/share/classes/jdk/internal/reflect/AccessorUtils.java line 34:

> 32:  */
> 33: public class AccessorUtils {
> 34:     static boolean isIllegalArgument(Class<?> accessorType, RuntimeException e) {

It might be useful to add a method description. In isolation, it's not immediately clear what it does.

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