RFR: 8251397: Add release fence to ClassValueMap constructor

[Severin Gehwolf]

On Thu, 10 Sep 2020 08:08:10 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> * Release fence guarantees that cacheArray field will published with a non-null value.
>> * Without this fix, CacheValueMap.cacheArray can sometimes be seen as null.
>> 
>> This is a follow up to @PaulSandoz's feedback
>> [here](https://mail.openjdk.java.net/pipermail/core-libs-dev/2020-August/068248.html) for the first attempt to fix
>> [JDK-8251397](https://bugs.openjdk.java.net/browse/JDK-8251397).  In this update, the fence has been moved to
>> `initializeMap()` and added Paul's suggested comment.
>> Annotating `classValueMap` with `@Stable` is outside the scope of this issue.
>
> Marked as reviewed by shade (Reviewer).

Just noting here that @galderz is a Red Hat employee and should be covered by the Red Hat OCA:
https://www.oracle.com/technical-resources/oracle-contributor-agreement.html#r

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

PR: https://git.openjdk.java.net/jdk/pull/94