Can an object be finalized while still weakly reachable?

[Martin Buchholz]

Sherman,

Thank you very much for pointing me at that old thread.  I was indeed
going down the same path and stumbling over the same obstacles!  I
still think we can do better, but it's definitely not easy.

On Tue, May 17, 2016 at 8:15 AM, Xueming Shen <xueming.shen at oracle.com> wrote:
> On 5/17/16 12:55 AM, Martin Buchholz wrote:
>>
>> Thanks, Peter.
>>
>> My current theory is indeed that I made a mistake, and have
>> encountered my first real finalization resurrection bug.
>> ZipFile + Inflater have 4 finalize methods and a WeakHashMap in play!
>
> there was a long discussion when we touched that part of the code last time.
> just
> for your reference:-)
>
> http://mail.openjdk.java.net/pipermail/core-libs-dev/2011-April/thread.html#6545
>
> -sherman
>
>> My static reference was finalized because it used to be unreachable,
>> not because it is now weakly reachable!
>>
>> On Mon, May 16, 2016 at 11:49 PM, Peter Levart <peter.levart at gmail.com>
>> wrote:
>>>
>>> Hi Martin,
>>>
>>>
>>>
>>> On 05/17/2016 05:19 AM, Martin Buchholz wrote:
>>>>
>>>> I have some evidence that an object's finalize method can run while a
>>>> weak reference pointing to it is not yet cleared, which surprised me.
>>>>
>>>> E.g.
>>>> class F { protected void finalize() { assert wref.get() != this; } }
>>>> static WeakReference wref = new WeakReference(new F());
>>>>
>>>> If this is a bug, I can try to give y'all a repro recipe.
>>>> If not, we should fix the docs
>>>> """When the weak references to a weakly-reachable object are cleared,
>>>> the object becomes eligible for finalization."""
>>>>
>>>> (It's also quite possible I made a mistake diagnosing this)
>>>
>>>
>>> What can happen with above code is that you get a NPE from dereferencing
>>> wref in finlailze(). In case NPE is not thrown and the program constructs
>>> only a single instance of F then assert should succeed.
>>>
>>> It is possible that you made a mistake. Can you post the real code?
>>>
>>> Regards, Peter
>>>
>