RFR: 8277072: ObjectStreamClass caches keep ClassLoaders alive [v3]

[Peter Levart]

On Tue, 30 Nov 2021 11:25:48 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> The caches in ObjectStreamClass basically map WeakReference<Class> to SoftReference<ObjectStreamClass>, where the ObjectStreamClass also references the same Class. That means that the cache entry, and thus the class and its class-loader, will not get reclaimed, unless the GC determines that memory pressure is very high.
>> 
>> However, this seems bogus, because that unnecessarily keeps ClassLoaders and all its classes alive much longer than necessary: as soon as a ClassLoader (and all its classes) become unreachable, there is no point in retaining the stuff in OSC's caches.
>> 
>> The proposed change is to use WeakReference instead of SoftReference for the values in caches.
>> 
>> Testing:
>>  - [x] tier1
>>  - [x] tier2
>>  - [x] tier3
>>  - [ ] tier4
>
> Roman Kennke 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 six additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'jdk-plevart/JDK-8277072-peter' into JDK-8277072
>  - Use ClassValue to solve JDK-8277072
>  - Use ForceGC instead of System.gc()
>  - Convert test to testng
>  - Fix indentation of new testcase
>  - 8277072: ObjectStreamClass caches keep ClassLoaders alive

I think most "hard work" (the tests) is still yours. I just removed a chunk of legacy code and replaced it with one-liners :-). I'm glad that this actually works! Please, continue...

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PR: https://git.openjdk.java.net/jdk/pull/6375