On Mon, 13 Nov 2023 22:31:16 GMT, Brent Christian <bchri...@openjdk.org> wrote:
> 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](https://docs.oracle.com/javase/specs/jls/se18/html/jls-17.html#jls-17.4.5): > _"There is a happens-before edge from the end of a constructor of an object > to the start of a finalizer (ยง12.6) for that object."_ src/java.base/share/classes/java/lang/ref/Reference.java line 552: > 550: * of this method. > 551: * Invocation of this method does not itself initiate reference > processing, > 552: * garbage collection, or finalization. My understanding was that it is not the object instance that is being guarded, only that the reference holding the object is considered a strong root and is only used to delimit a range of bytecodes for which the reference is considered to be strong. In particular, the invocation of the method itself has no semantics, only that a control flow could reach that statement and the reference was considered strong as long as the reference was in a scope that included the reachability fence. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/16644#discussion_r1401310991
