RFR: 8372946 - TreeMap sub-map entry spliterator is expensive [v2]

[Oli Gillespie]

On Tue, 27 Jan 2026 20:17:18 GMT, Oli Gillespie <ogillespie at openjdk.org> wrote:

>>> I suppose you mean Spliterators.spliteratorUnknownSize?
>> 
>> Yes. Thanks for corecting me.
>> 
>>> Hmm - I made the change this way to be consistent with the existing SubMapKeyIterator and DescendingSubMapKeyIterator, simply adding the same functionality for the Entry versions.
>> 
>> I made the recommendation given the starting point is to address a performance regression, instead of to enhance the sub-map entry spliterator to be on par with the `DescendingSubMapKeyIterator`.
>> 
>> From this starting point, I believe we can easily identify `EntrySetView` inherits `Set::spliterator` which is slow because the spliterator calls `size()` frequently. This root problem is easily fixed with using `Spliterators.spliteratorUnknownSize`, which also has the minimal behavioral impact.
>> 
>> In contrast, functional enhancement to spliterators is really a can of worms where you can never find an end - sometimes you add more flags, sometimes other splitting strategies. And in your example, you already have a test case failing due to the functional enhancements while you did make new tests to verify them.
>> 
>> So let's keep it simple, fix the bug, and leave the functional enhancements for another time. This also makes backporting the fix much easier.
>
> Okay sounds good to me! Thanks for the suggestion, I'll update later this week.

I created https://github.com/openjdk/jdk/pull/29485 to add test cases before making this change - that required a slight functional tweak so I didn't want to include it in this change.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28608#discussion_r2741453002