RFR: 8351565: Implement JEP 502: Stable Values (Preview) [v6]

[Per Minborg]

On Sun, 16 Mar 2025 18:43:26 GMT, Luca Kellermann <duke at openjdk.org> wrote:

>> Per Minborg has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 246 commits:
>> 
>>  - Merge branch 'master' into implement-jep502
>>  - Clean up exception messages and fix comments
>>  - Rename field
>>  - Rename method and fix comment
>>  - Rework reenterant logic
>>  - Use acquire semantics for reading rather than volatile semantics
>>  - Add missing null check
>>  - Simplify handling of sentinel, wrap, and unwrap
>>  - Fix JavaDoc issues
>>  - Fix members in StableEnumFunction
>>  - ... and 236 more: https://git.openjdk.org/jdk/compare/4e51a8c9...d6e1573f
>
> src/java.base/share/classes/jdk/internal/lang/stable/StableValueFactories.java line 77:
> 
>> 75:         int i = 0;
>> 76:         for (K key : keys) {
>> 77:             entries[i++] = Map.entry(key, StableValueImpl.newInstance());
> 
> `Map.entry` causes `null` keys to throw a `NullPointerException`, meaning there can't be stable functions/maps with a `null` input/key. They can however have `null` values. Is that intended?

Yes. The keys need to be non-null. I have added info about this in the docs now.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23972#discussion_r2020715235