RFR: 8280041: Retry loop issues in java.io.ClassCache [v4]

[Peter Levart]

On Fri, 21 Jan 2022 11:04:22 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`
>>   - [x] Linux x86_64 fastdebug `tier3`
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:
> 
>  - Guarantee progress for at least one thread
>  - Merge branch 'master' into JDK-8280041-classcache-problems
>  - Test summary
>  - GC sanity test
>  - NullValueTest
>  - Merge branch 'master' into JDK-8280041-classcache-problems
>  - Fix

This looks good, although I don't know whether the additional check for strongReferent != null is needed in clearStrong(). This is all racy code and you have already got a non-null return from getStrong() in case you are calling clearStrong()...

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Marked as reviewed by plevart (Reviewer).

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