RFR: 8338897: Small startup regression remains after JDK-8309622 and JDK-8331932

[Chen Liang]

On Mon, 26 Aug 2024 13:30:18 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> #14404 caused some startup regressions, where the main cause of startup increase in that change was due the use of - and the not very optimized state of - runtime bootstrapped switches. This was remedied by a series of optimizations to the switch bootstrap methods and finally a desugaring of the switch added by #14404. Now @shipilev reports that there appears to be some lingering startup issue from #14404. 
> 
> One thing that stands out is a couple of caches which are being eagerly initialized regardless of user locale. This PR makes those caches lazily initialized and slightly more efficient (no need to implement `UnaryOperator` after inlining some code). Avoids loading 4 classes if running the HelloStream startup test in a locale that's in the set of constant base locales, 2 otherwise. This doesn't really do much to move the needle for startup on my setup, but tentatively it's the only remaining inefficiency I've found that came from #14404.

I personally prefer declaring `LocaleCache` class final as it's not abstract. Waiting for a i18n/locale reviewer too.

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Marked as reviewed by liach (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20713#pullrequestreview-2260737772