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

[Maurizio Cimadamore]

On Thu, 13 Mar 2025 15:22:43 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> Implement JEP 502.
>> 
>> The PR passes tier1-tier3 tests.
>
> 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/StableValueImpl.java line 74:

> 72:     @Override
> 73:     public boolean trySet(T value) {
> 74:         if (wrappedContentAcquire() != null) {

IMHO, if our goal is to do:

Object content = this.content;
if (context != null) return content:
synchronized (...) {
    if (context != null) return content:
    this.context = ...
}


Then we might just use a volatile field and synchronized blocks. I don't see an immediate need for using acquire/release semantics -- especially when using a monitor. E.g. this should look more like a classic double checked locking idiom. (but with a stable field to make the first volatile read more efficient in case the field is already set)

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

PR Review Comment: https://git.openjdk.org/jdk/pull/23972#discussion_r1993850760