RFR: 8280041: Retry loop issues in java.io.ClassCache

[Roman Kennke]

On Fri, 14 Jan 2022 19:27:18 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> JDK-8277072 introduced java.io.ClassCache, but there seem to be at least two issues with it:
>   - The cache cannot disambiguate between cleared SoftReference and the accidental passing of `null` value; in that case, the retry loop would spin indefinitely;
>   - If retry loop would spin several times, every time discovering a cleared SoftReference, it would create and register new SoftReference on the ReferenceQueue. However, it would not *drain* the RQ in the loop; in that case, we might have the unbounded garbage accumulating in RQ; 
> 
> Attention @rkennke, @plevart.
> 
> Additional testing:
>   - [x] Linux x86_64 fastdebug `java/io/ObjectStreamClass`
>   - [x] Linux x86_64 fastdebug `tier1`
>   - [x] Linux x86_64 fastdebug `tier2`
>   - [ ] Linux x86_64 fastdebug `tier3`

Marked as reviewed by rkennke (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/7092