Classes in the java.lang.ref package would benefit from an update to bring the spec in line with how the VM already behaves. The changes would focus on happens-before edges at some key points during reference processing.

A couple key things we want to be able to say are:
* Reference.reachabilityFence(x) happens-before reference processing occurs for 'x'.
* Cleaner.register() happens-before the Cleaner thread runs the registered cleaning action.

This will bring Cleaner in line (or close) with the memory visibility guarantees made for finalizers in JLS 17.4.5[1]:
"There is a happens-before edge from the end of a constructor of an object to the start of a finalizer (§12.6) for that object."

1. https://docs.oracle.com/javase/specs/jls/se18/html/jls-17.html#jls-17.4.5