RFR: 8160821: VarHandle accesses are penalized when argument conversion is required [v6]

[Vladimir Ivanov]

On Wed, 3 Dec 2025 23:41:01 GMT, Chen Liang <liach at openjdk.org> wrote:

>> src/java.base/share/classes/java/lang/invoke/VarHandle.java line 2036:
>> 
>>> 2034:         // from two writes (they must not be tearable)
>>> 2035:         private record Adaption(VarHandle vh, MethodHandle mh) {}
>>> 2036:         private @Stable Adaption adaption;
>> 
>> Is a soft reference needed here? The situation looks similar to `MH.asTypeSoftCache`. It can keep some classes referred by `vh` alive for unnecessarily long.
>
> I don't think we can use a SoftReference here if we need to achieve constant folding.
> 
> Looking at inline_reference_get0, I think we might introduce another field property to trust a reference (potentially in an array) if both that reference and the referent within the reference is non-null.  I think that belongs to a separate RFE. What do you think?

Then it makes sense to limit the caching to safe cases only for now. Otherwise, it would functionally regress due to a possible memory leak.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28585#discussion_r2587156042