RFR: 8351565: Implement JEP 502: Stable Values (Preview) [v21]

[Maurizio Cimadamore]

On Mon, 31 Mar 2025 13:32:56 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> Implement JEP 502.
>> 
>> The PR passes tier1-tier3 tests.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Finish and clean up benchmarks

src/java.base/share/classes/jdk/internal/lang/stable/StableValueImpl.java line 161:

> 159: 
> 160:     static String renderWrapped(Object t) {
> 161:         return (t == null) ? UNSET_LABEL : Objects.toString(unwrap(t));

If I read correctly, this implementation is similar to what described here:

https://preshing.com/20130930/double-checked-locking-is-fixed-in-cpp11/

(see section `Using C++11 Acquire and Release Fences`).

We don't need the "relaxed" loads in Java because a reference load in Java can never tear. Correct?

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PR Review Comment: https://git.openjdk.org/jdk/pull/23972#discussion_r2021151169