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

[Shaojin Wen]

On Mon, 5 May 2025 13:41:22 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`.

src/java.base/share/classes/java/lang/reflect/Method.java line 105:

> 103:                 public int applyAsInt(Method method) {
> 104:                     return method.getDeclaringClass().getName().hashCode() ^ method.getName()
> 105:                             .hashCode();

Suggestion:

                    return method.getDeclaringClass().getName().hashCode() 
                                             ^ method.getName().hashCode();

code indentation alignment

src/java.base/share/classes/jdk/internal/lang/stable/StableFieldUpdater.java line 330:

> 328:                 throw illegalField("non final fields", field);
> 329:             }
> 330:             sun.reflect.misc.ReflectUtil.ensureMemberAccess(

Why not use import here but use the full path?

src/java.base/share/classes/jdk/internal/lang/stable/StableFieldUpdater.java line 350:

> 348:         }
> 349:         final Field[] fields = holderType.getDeclaredFields();
> 350:         for (Field f : fields) {

Suggestion:

        for (Field f : holderType.getDeclaredFields()) {

The local variable fields is only used once and can be simplified

test/jdk/java/lang/StableValue/StableFieldUpdaterExampleTest.java line 132:

> 130:                     Objects.equals(this.bar, that.bar) &&
> 131:                     Objects.equals(this.baz, that.baz);
> 132:         }

Suggestion:

        public boolean equals(Object o) {
            return o instanceof Foo that
                    && Objects.equals(this.bar, that.bar)
                    && Objects.equals(this.baz, that.baz);
        }

In most cases in JDK code, the operator `&&` is placed in front.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/25040#discussion_r2075244737
PR Review Comment: https://git.openjdk.org/jdk/pull/25040#discussion_r2075229805
PR Review Comment: https://git.openjdk.org/jdk/pull/25040#discussion_r2075234183
PR Review Comment: https://git.openjdk.org/jdk/pull/25040#discussion_r2075239678