RFR: 8251397: Add release fence to ClassValueMap constructor

[Severin Gehwolf]

On Mon, 14 Sep 2020 08:25:51 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> @galderz The PR has this synopsis `8251397: Add release fence to ClassValueMap constructor`. The bug has this `8251397:
>> NPE on ClassValue.ClassValueMap.cacheArray`. @dholmes-ora asked to make them matching. Let's fix that first.
>
> You can add what you have as synopsis now via /summary and the bot.

@galderz Now it's the other way round. Commit message the bot mentions
[here](https://github.com/openjdk/jdk/pull/94#issuecomment-691478179) should be something like this:

8251397: NPE on ClassValue.ClassValueMap.cacheArray

Add release fence to ClassValueMap constructor.

* Release fence guarantees that cacheArray field will published
  with a non-null value.
* Without this fix, CacheValueMap.cacheArray can sometimes be
   seen as null.

Reviewed-by: shade, psandoz

The first line can be achieved by force-pushing with the changed commit message. I know David said to not force push,
but the review is done and no other way to achieve this except changing the bug synopsis which isn't great either. The
latter lines can be added with /summary e.g.


Add release fence to ClassValueMap constructor.

* Release fence guarantees that cacheArray field will published
  with a non-null value.
* Without this fix, CacheValueMap.cacheArray can sometimes be
   seen as null.

The `Reviewed-by:` line comes from the reviewers.

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

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