RFR: 8278065: Refactor subclassAudits to use ClassValue [v3]

[Roman Kennke]

On Wed, 12 Jan 2022 06:45:02 GMT, Peter Levart <plevart at openjdk.org> wrote:

> I think this looks good. Reviewed. Only a minor nit if you think it would be better, but not necessary if you don't. The following combo:
> 
> ```
>         Boolean result = Caches.subclassAudits.get(cl);
>         assert result != null;
> ```
> 
> could be written as:
> 
> ```
>         boolean result = Caches.subclassAudits.get(cl);
> ```
> 
> ...and it would give the same "message" to the reader. WDYT? No need for another round of reviews if you change this.

Right! I changed it.

BTW, I noticed that Thread.java has a similar subclassAudits machinery with WeakClassKey, which would also benefit from using ClassValue instead. I filed JDK-8279917 to track it.

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PR: https://git.openjdk.java.net/jdk/pull/6637