RFR: 8242888: Convert dynamic proxy to hidden classes

[Chen Liang]

On Thu, 23 May 2024 03:28:30 GMT, Chen Liang <liach at openjdk.org> wrote:

> Please review this change that convert dynamic proxies implementations to hidden classes, intended to target JDK 24.
> 
> Summary:
> 1. Adds new implementation while preserving the old implementation behind `-Djdk.reflect.useLegacyProxyImpl=true` in case there are compatibility issues.
> 2. ClassLoader.defineClass0 takes a ClassLoader instance but discards it in native code; I updated native code to reuse that ClassLoader for Proxy support.
> 3. ProxyGenerator changes mainly involve using Class data to pass Method list (accessed in a single condy) and removal of obsolete setup code generation.
> 
> Testing: tier1 and tier2 have no related failures.
> 
> Comment: Since #8278, Proxy has been converted to ClassFile API, and infrastructure has changed; now, the migration to hidden classes is much cleaner and has less impact, such as preserving ProtectionDomain and dynamic module without "anchor classes", and avoiding java.lang.invoke package.

Hmm, actually, looking at the specs of the method again, does it imply that Proxy classes are never unloaded once defined in a ClassLoader, as seen in `Proxy::getProxyClass`:

> If a proxy class for the same permutation of interfaces has already been defined by the class loader, then the existing proxy class will be returned

If that's the case, Remi's suggestion on passing classdata to a non-hidden class might be better, and it seems to accomplish that in hotspot isn't too hard too.

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PR Comment: https://git.openjdk.org/jdk/pull/19356#issuecomment-2128186405