RFR: 8289220: Locale.forLanguageTag throws NPE due to soft ref used in locale cache being cleared [v3]

[SUN Guoyun]

On Tue, 6 Jun 2023 18:45:50 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

>> For hotspot, when GC occurs, it causes all threads to run to the nearest safepoint and then freeze. Generally, safepoints are generated at branch jumps, method ends(ret instructions), loops instructions, and so on. Therefore, the purpose of this patch is to make the creation and use of a softReferences in the same method without branch, jumps and loops in between, that is ensure that GC will not occur in the process of the sofeReferences be created and used.
>> 
>> That's why I didn't use `Reference.reachabilityFence(locale)`.
>
> This reasoning seems invalid. There are method calls in there, and you rely on inlining heuristics for this not to break. Please use reachabilityFence instead.

Thanks @fisk @rose00 for the explanation. This patch is indeed based on the idea that small functions are inlined, cause `-Xcomp` be used, and I have seen with parameter `-XX:+PrintCompilation -XX:+PrintInlining` that functions `Key::<init>` and `getBaseLocale` are inlined. 
But as @rose00  say, it's not safe, so reachabilityFence should be used. please review again.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14211#discussion_r1220780841