RFR: 6983726: Reimplement MethodHandleProxies.asInterfaceInstance [v22]

Tue Jul 11 18:21:34 UTC 2023

On Tue, 11 Jul 2023 17:07:00 GMT, Mandy Chung <mchung at openjdk.org> wrote:

>  Just to be clear, the test should pass even if it keeps Lookup as the referent, right?

No. The test will not because there's no reference to the `Lookup` except in `asInterfaceInstance` itself; the `Lookup`s thus are always eligible for GC, even if there's living wrapper instance, as shown in the first broken `assertTrue(cl.referTo(c2.getClass()))` test. The `Class` object for implementation, however, is always reachable as long as any wrapper instance is reachable.

The alternative to keeping Classes in weak reference is to keep a lookup in the hidden class and cache that particular lookup, which IMO only complicates both the support code (have to distinguish from `Lookup` returned by `defineHiddenClass` and edit spinned bytecode).

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PR Comment: https://git.openjdk.org/jdk/pull/13197#issuecomment-1631281648