RFR: 8289220: [Shenandoah] TestAllocObjectArrays fails intermittently [v3]

[SUN Guoyun]

> command: make test CONF=fastdebug JTREG="VM_OPTIONS=-Xcomp" TEST=gc/TestAllocHumongousFragment.java
> error info: 
> 
> Caused by: java.lang.NullPointerException: Cannot invoke "sun.util.locale.BaseLocale.getVariant()" because "base" is null
> at java.base/java.util.Locale.forLanguageTag(Locale.java:1802)
> at java.base/sun.util.cldr.CLDRBaseLocaleDataMetaInfo.<clinit>(CLDRBaseLocaleDataMetaInfo.java:41)
> ... 24 more
> 
> Note that the test runs with -XX:ShenandoahGCHeuristics=aggressive -XX:+ShenandoahOOMDuringEvacALot and SoftReferences are involved (LocaleObjectCache uses SoftReferences, used by printf method called in getRandomInstance(Utils.java:511)).
> 
> Maybe we have to deal with the case where the getBaseLocale() return value is null. the call stack is:
> 
> 	at java.base/sun.util.locale.LocaleObjectCache.get(LocaleObjectCache.java:64)
> 	at java.base/sun.util.locale.BaseLocale.getInstance(BaseLocale.java:169)
> 	at java.base/sun.util.locale.InternalLocaleBuilder.getBaseLocale(InternalLocaleBuilder.java:524)
> 	at java.base/java.util.Locale.forLanguageTag(Locale.java:1874)
> 
> in LocaleObjectCache.java:64
> 
> 	 62             if (key == null || newVal == null) {                                
> 	 63                 // subclass must return non-null key/value object               
> 	 64                 return null; // run here
> 	 65             }

SUN Guoyun has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

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

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/14211/files
  - new: https://git.openjdk.org/jdk/pull/14211/files/51883706..a09f1b6f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14211&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14211&range=01-02

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14211.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14211/head:pull/14211

PR: https://git.openjdk.org/jdk/pull/14211