<i18n dev> RFR: 8366178: Implement JEP 526: Lazy Constants (Second Preview) [v12]

[Maurizio Cimadamore]

On Fri, 17 Oct 2025 09:25:01 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> Implement JEP 526: Lazy Constants (Second Preview)
>> 
>> The lazy list/map implementations are broken out from `ImmutableCollections` to a separate class.
>> 
>> The old benchmarks are not moved/renamed to allow comparison with previous releases.
>> 
>> `java.util.Optional` is updated so that its field is annotated with `@Stable`.  This is to allow `Optional` instances to be held in lazy constants and still provide constant folding.
>
> Per Minborg has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update javadocs

src/java.base/share/classes/java/lang/LazyConstant.java line 168:

> 166:  * of that lazy constant and instead directly use any constant that it has previously
> 167:  * observed. We call this optimization <em>constant folding</em>. This is only possible if
> 168:  * the reference to the lazy constant is a VM constant (e.g. in cases where

Not sure talking about VM constant is good. We could alternatively say:

"if the lazy constant is stored in a static final field, either directly, or indirectly, via one or more trusted fields (i.e. any combination...)"

src/java.base/share/classes/java/lang/LazyConstant.java line 179:

> 177:  * must be <em>non-null</em>, or a {@link NullPointerException} will be thrown.
> 178:  *
> 179:  * @apiNote Once a lazy constant is initialized with an object, the object cannot ever be

Once a lazy constant is initialized, its contents can never be removed...

src/java.base/share/classes/java/lang/LazyConstant.java line 182:

> 180:  *          removed. This can be a source of an unintended memory leak. More specifically,
> 181:  *          a lazy constant {@linkplain java.lang.ref##reachability strongly references}
> 182:  *          the object it was initialized with. Hence, a lazy constant will hold

s/the object it was initialized with/its contents (here and below)

src/java.base/share/classes/java/lang/LazyConstant.java line 186:

> 184:  *          is collected (if ever).
> 185:  *          <p>
> 186:  *          A {@code LazyConstant} that has a type parameter {@code T} that is an

"A lazy constant whose contents is an array will not optimize access to the the elements of such array. Instead, ..."

src/java.base/share/classes/java/lang/LazyConstant.java line 191:

> 189:  *          Instead, a {@linkplain List#ofLazy(int, IntFunction) lazy list} of
> 190:  *          arbitrary depth can be used, which provides constant components.
> 191:  *          More generally, a lazy constant can hold other lazy constants of

More generally... you said that in the composition section?

src/java.base/share/classes/java/lang/LazyConstant.java line 233:

> 231: 
> 232:     /**
> 233:      * {@return the initialized contents. If not initialized, first computes and

"initialized contents" is not a term you have defined in this javadoc. `get` returns the contents of this lazy constant. If the lazy constant is not initialized...

src/java.base/share/classes/java/lang/LazyConstant.java line 267:

> 265:      */
> 266:     @Override
> 267:     String toString();

I think it might be worth also defining a javadoc for equals/hashCode, to say explicitly that they will also not trigger initialization

src/java.base/share/classes/java/lang/LazyConstant.java line 284:

> 282:      * directly.
> 283:      *
> 284:      * @param computingFunction in the form of a Supplier to be used to compute

Suggestion:

     * @param computingFunction a {@code Supplier} used to initialize

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PR Review Comment: https://git.openjdk.org/jdk/pull/27605#discussion_r2439138229
PR Review Comment: https://git.openjdk.org/jdk/pull/27605#discussion_r2439141653
PR Review Comment: https://git.openjdk.org/jdk/pull/27605#discussion_r2439144255
PR Review Comment: https://git.openjdk.org/jdk/pull/27605#discussion_r2439156012
PR Review Comment: https://git.openjdk.org/jdk/pull/27605#discussion_r2439150170
PR Review Comment: https://git.openjdk.org/jdk/pull/27605#discussion_r2439161143
PR Review Comment: https://git.openjdk.org/jdk/pull/27605#discussion_r2439169909
PR Review Comment: https://git.openjdk.org/jdk/pull/27605#discussion_r2439174349