On Tue, 21 Nov 2023 22:58:09 GMT, Roger Riggs <rri...@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. The existing docs refer to "invocation" of this method. I've continued with that, and in general have kept this at a bit higher level, in order to simplify understanding. I'm open to more detailed wording, if it would improve understandability, (or if what I have is not functionally accurate). ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/16644#discussion_r1411372474
