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

[Quan Anh Mai]

On Mon, 31 Mar 2025 14:22:16 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> 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?

@mcimadamore That atomic load under the lock is unnecessary because the load will never be concurrent with any store. I believe `relaxed` has to be used because C++ lacks the ability to perform atomic operations and non-atomic operations on the same object until C++ 20 with `std::atomic_ref`.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/23972#discussion_r2021289826