RFR: 8356255: Add Stable Field Updaters to allow efficient lazy field evaluations [v3]

[Shaojin Wen]

On Wed, 7 May 2025 07:46:45 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> This sketch shows how "Stable Updaters" can be used to create stable computations of `@Stable` fields. Only one updater is needed per class, similar to `AtomicIntegerFieldUpdater`.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add a method handle based field updater

src/java.base/share/classes/jdk/internal/lang/stable/StableFieldUpdater.java line 173:

> 171:         if (!underlying.type().parameterType(0).equals(Object.class)) {
> 172:             underlying = underlying.asType(underlying.type().changeParameterType(0, Object.class));
> 173:         }

Suggestion:

        var type = underlying.type();
        if (type.returnType() != int.class || type.parameterCount() != 1) {
            throw new IllegalArgumentException("Illegal underlying function: " + underlying);
        }
        if (!type.parameterType(0).equals(Object.class)) {
            underlying = underlying.asType(type.changeParameterType(0, Object.class));
        }

underlying.type() is used 4 times, local variables should be used

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PR Review Comment: https://git.openjdk.org/jdk/pull/25040#discussion_r2077031643