RFR: 8277072: ObjectStreamClass caches keep ClassLoaders alive

[Joe Darcy]

On Fri, 12 Nov 2021 21:43:42 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
>  - [ ] tier3
>  - [ ] tier4

If the intent of this change is to alter the lifetimes of the objects in question in a meaningful way, I recommend a CSR for the behavioral compatibility impact.

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