RFR: 8277072: ObjectStreamClass caches keep ClassLoaders alive [v2]

[Peter Levart]

On Mon, 15 Nov 2021 21:35:06 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 incrementally with two additional commits since the last revision:
> 
>  - Use ForceGC instead of System.gc()
>  - Convert test to testng

A patch is worth a thousand words. Here's what I meant when I said this could be elegantly solved with ClassValue:

https://github.com/plevart/jdk/commit/6e16e5e526c7f3d868b16543f2f3418c751068e4

Note this is not tested. Just an idea.

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