On Tue, 11 Jul 2023 13:16:21 GMT, Chen Liang <li...@openjdk.org> wrote:
> 1. I think the type profile pollution only happens with the instance-field > approach, as I recall different instance fields' MHs pollute profiling. The > comment need to be corrected if I'm right. What happens is not really 'profile pollution'. The issue is that C2 can not inline through non-constant method handles. So we always get an indirect call through the MethodHandle's [invokeBasic stub](https://github.com/openjdk/jdk/blob/a1cfc9695405fe517fae1b9f760ae42b85f66be9/src/hotspot/cpu/x86/methodHandles_x86.cpp#L165). > When this line is removed, the next call to asInterfaceInstance will return a > wrapper with a new implementation class, even if the old instance is still in > a local variable. The WeakReference inside the implementation points to the `Lookup` object. I think this Lookup goes out of scope after `asInterfaceInstance` returns, right? (it's not saved inside the returned instance or class). So, it would be immediately eligible for GC. I think a SoftReference would work better for the cache (which the GC clears less eagerly). Or the returned interface instance could save a reference to the Lookup object in order to keep it reachable. > The MHP implementation class weak reference is not cleared by gc, even though > the wrapper is no longer reachable. Note that when running in interpreted mode (which is likely for these tests), a variable is 'alive' from the perspective of the GC until the method ends. i.e. the `{ ... }` used in the test does nothing WRT GC. You would have to explicitly make `c1` `null` for the class to be unreachable. ------------- PR Comment: https://git.openjdk.org/jdk/pull/13197#issuecomment-1630856453
