RFR: 8341243: Use ArraySupport.SOFT_MAX_ARRAY_LENGTH for max array size in java.base

[Stuart Marks]

On Mon, 30 Sep 2024 15:14:31 GMT, Eirik Bjørsnøs <eirbjo at openjdk.org> wrote:

> Please review this cleanup PR which updates code and tests in `java.base` to consistently use  `jdk.internal.util.ArraySupport.SOFT_MAX_ARRAY_LENGTH` when referring to the JVM's maximum array size implementation limit. Currently, instances of `Integer.MAX_VALUE - 8` are found across the code base, with varying degrees of documentation. It would be good to consolidate on a single source of truth, with proper documentation.
> 
> This PR is a follow-up to #20905 where the same change was requested in `java.util.zip`.
> 
> My understanding is that javac will fold this constant value into the byte code of the compiled use sites, as such this change should not affect class loading or cause startup issues. 
> 
> Instances selected for this PR were found searching for "Integer.MAX_VALUE - 8". The PR replaces these with `ArraySupport.SOFT_MAX_ARRAY_LENGTH`, while trimming or amending some code comments where appropriate. (`SOFT_MAX_ARRAY_LENGTH` already has a good explainer which does not need repetition at each use site).
> 
> I also searched for instances of `Integer.MAX_VALUE - 1` and `Integer.MAX_VALUE - 2`, no convincing candidates were found.
> 
> Instances outside `java.base` were deliberately left out to limit the scope and review cost of this PR.
> 
> Tests updated to use `SOFT_MAX_ARRAY_LENGTH` are updated with the jtreg tag `@modules java.base/jdk.internal.util`.
> 
> Testing: No new tests are added in this PR, the `noreg-cleanup` label is added to the JBS. The five affected tests have been run manually. GHA tests run green.

test/jdk/java/lang/StringBuffer/HugeCapacity.java line 51:

> 49:             // Maximum array length supported by the JVM implementation
> 50:             int maxArrayLength = ArraysSupport.SOFT_MAX_ARRAY_LENGTH;
> 51:             String str = "Z".repeat(maxArrayLength);

Same comment as in the corresponding code in the StringBuilder test.

test/jdk/java/lang/StringBuilder/HugeCapacity.java line 83:

> 81:             // Maximum array length supported by the JVM implementation
> 82:             int maxArrayLength = ArraysSupport.SOFT_MAX_ARRAY_LENGTH;
> 83:             String str = "Z".repeat(maxArrayLength);

The comment is a bit misleading. I'm not sure any comment is warranted, as you had observed, there's a big description next to SOFT_MAX_ARRAY_LENGTH. I'm also not sure a new local variable maxArrayLength adds anything.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21268#discussion_r1782068899
PR Review Comment: https://git.openjdk.org/jdk/pull/21268#discussion_r1782068601