RFR: 8309622: Re-examine the cache mechanism in BaseLocale

[Daniel Fuchs]

On Fri, 9 Jun 2023 22:17:39 GMT, Naoto Sato <naoto at openjdk.org> wrote:

> This is stemming from the PR: https://github.com/openjdk/jdk/pull/14211 where aggressive GC can cause NPE in `BaseLocale$Key` class. I refactored the in-house cache with WeakHashMap, and removed the Key class as it is no longer needed (thus the original NPE will no longer be possible). Also with the new JMH test case, it gains some performance improvement:
> 
> (w/o fix)
> 
> Benchmark                       Mode  Cnt      Score     Error  Units
> LocaleCache.testForLanguageTag  avgt   20   5781.275 ± 569.580  ns/op
> LocaleCache.testLocaleOf        avgt   20  62564.079 ± 406.697  ns/op
> 
> (w/ fix)
> Benchmark                       Mode  Cnt      Score     Error  Units
> LocaleCache.testForLanguageTag  avgt   20   4801.175 ± 371.830  ns/op
> LocaleCache.testLocaleOf        avgt   20  60394.652 ± 352.471  ns/op

One thing though - WeakHashMap is not thread safe - and I don't see any locks or synchronized to protect access to CACHE. Is that going to cause trouble if two threads compete to add a locale to the map? In other words - how confident are we that the race would be benign?

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PR Review: https://git.openjdk.org/jdk/pull/14404#pullrequestreview-1475096535