On Tue, 20 Oct 2020 05:22:57 GMT, Kim Barrett <kbarr...@openjdk.org> wrote:
>> @kimbarrett your reworded text is okay. I think "if it initially had some >> other referent value" can be dropped. >> >> For a `Reference` constructed with a `null` referent, we can clarify in the >> spec that such reference object will never >> get cleared and enqueued. I suggest to file a separate issue to follow up. > >> @kimbarrett your reworded text is okay. I think "if it initially had some >> other referent value" can be dropped. >> >> For a `Reference` constructed with a `null` referent, we can clarify in the >> spec that such reference object will never >> get cleared and enqueued. I suggest to file a separate issue to follow up. > > I don't think that clause can be dropped, because of explicit clearing (by > clear() or enqueue()) rather than by the > GC. If the reference was constructed with a null referent, > ref.refersTo(null) cannot tell whether ref.clear() has been > called. > Mandy's comment implied that references with a null referent never get > enqueued. Otherwise when would they get > enqueued? There would be nothing to trigger it. Sorry I should have been clearer. What I try to say is that `Reference(null)` will never be cleared and enqueued by GC since its referent is `null`. Kim is right that `Reference(null)` can be explicitly cleared and enqueued via `Reference::enqueue`. `Reference::clear` on such an "empty" reference object is essentially a no-op. > > But the more we discuss this the more I think allowing an initial null > > referent was a mistake in the first place. :( > > I agree, but here we are. Very hard to know what the compatibility impact of > changing that would be. There are existing use cases depending on `Reference(null)` for example as a special instance be an empty reference or the head of a doubly-linked list of references. This was discussed two years ago [1]. [1] https://mail.openjdk.java.net/pipermail/core-libs-dev/2018-July/054325.html ------------- PR: https://git.openjdk.java.net/jdk/pull/498
