RFR: JDK-8310913 Move ReferencedKeyMap to jdk.internal so it may be shared [v8]

[Chen Liang]

On Thu, 13 Jul 2023 15:07:35 GMT, Jim Laskey <jlaskey at openjdk.org> wrote:

>> java.lang.runtime.ReferencedKeyMap was introduced to provide a concurrent caching scheme for Carrier objects. The technique used is generally useful for a variety of caching schemes and is being moved to be shared in other parts of the jdk. The MethodType interning case is one example.
>
> Jim Laskey has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update test to check for gc.

src/java.base/share/classes/jdk/internal/util/ReferencedKeyMap.java line 354:

> 352:      */
> 353:     @SuppressWarnings("unchecked")
> 354:     K intern(K key) {

Should this be made static for type safety?

public static <E> E intern(ReferencedKeyMap<E, ReferenceKey<E>> m, E key)

which will save the 2 unchecked casts at `get` and `putIfAbsent`.


In addition, it would be nice if we can compute a more proper key for interning than the query key, via a binary operator; for example, we want a `String` to go through `String::intern`, or a `BaseLocale` to format its language, script, region, and variant and intern them (see https://github.com/openjdk/jdk/pull/14404/files#diff-c0e20847ffb6e33bcf62ff52b1b5b4c8a85520ca101a6f54128d97289cd8c2f9R169-R172)

src/java.base/share/classes/jdk/internal/util/ReferencedKeySet.java line 71:

> 69:  * @param <T> the type of elements maintained by this set
> 70:  */
> 71: public class ReferencedKeySet<T> extends AbstractSet<T> {

Suggestion:

public final class ReferencedKeySet<T> extends AbstractSet<T> {

Make this class final.

src/java.base/share/classes/jdk/internal/util/ReferencedKeySet.java line 97:

> 95:      * @param <E> the type of elements maintained by this set
> 96:      */
> 97:     public static <E> jdk.internal.util.ReferencedKeySet<E>

Suggestion:

    public static <E> ReferencedKeySet<E>

src/java.base/share/classes/jdk/internal/util/ReferencedKeySet.java line 185:

> 183:      * @return the old element if present, otherwise, the new element
> 184:      */
> 185:     public T intern(T e) {

I would like to see an additional `T intern(T e, UnaryOperator<T> internFunction)`, where the `internFunction` behaves like `LocalObjectCache::normalizeKey`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14684#discussion_r1266902706
PR Review Comment: https://git.openjdk.org/jdk/pull/14684#discussion_r1266911305
PR Review Comment: https://git.openjdk.org/jdk/pull/14684#discussion_r1266897522
PR Review Comment: https://git.openjdk.org/jdk/pull/14684#discussion_r1266914091