RFR: 8071507: (ref) Clear phantom reference as soft and weak references do

[Mandy Chung]

> On Dec 4, 2015, at 10:07 AM, Kim Barrett <kim.barrett at oracle.com> wrote:
> 
> On Dec 3, 2015, at 6:04 PM, Mandy Chung <mandy.chung at oracle.com> wrote:
>> 
>>> [Indeed, this whole section isn't strictly necessary; all of it can be
>>> inferred from information in other places.]
>> 
>> Agree.  This section is no longer necessary and maybe just remove it:
> 
> I wasn't actually intending to suggest removal.  It seems like there
> is useful overview information to be had here, rather than requiring
> readers to make not necessarily obvious inferences.  My impression is
> that readability is valued more highly than terseness in Java
> documentation.

Actually I considered to remove it in the past but just tried to minimize the spec change.  I believe one purpose of that section was intended to call out the difference that PhantomReference is not automatically-cleared that is no longer true.

In addition it’s clearly mentioned in PhantomReference constructor.  I don’t see the need for it in the package summary.  The reader will look at the PhantomRefererence to use it..

"It is possible to create a phantom reference with a null queue, but such a reference is completely useless: Its get method will always return null and, since it does not have a queue, it will never be enqueued.”

The puzzling part to me is why PhantomReference accepts null ReferenceQueue.   I can’t evaluate how high of the source incompatibility risk if we fixed it but I may propose that in a future release until I have cycle.

Mandy