RFR 9: 8138696 : java.lang.ref.Cleaner - an easy to use alternative to finalization

[Kim Barrett]

On Dec 8, 2015, at 2:26 PM, Peter Levart <peter.levart at gmail.com> wrote:
> 
> On 12/08/2015 07:25 PM, Kim Barrett wrote:
>> On Dec 8, 2015, at 3:09 AM, David Holmes <david.holmes at oracle.com>
>>  wrote:
>> 
>>> Question: what happens if an object is registered simultaneously with multiple Cleaners? Do we need to warn the user against that?
>>> 
>> Aside: I like David's suggested "action" terminology.
>> 
>> 
>>> Question: what happens if an object is registered simultaneously with
>>> multiple Cleaners? Do we need to warn the user against that?
>>> 
>> Registering an object with multiple Cleaners, or even the same Cleaner
>> multiple times, is not a problem, so long as the various cleanup
>> actions can cope with that.  This is even expected to occur in
>> practice.  Consider the conversion of a class hierarchy away from
>> using finalize() to instead using Cleaners.  A base class may register
>> a cleanup action for the state associated with that (base) class.  A
>> derived class may independently register a cleanup action for the
>> additional state associated with that derived class.  The derived
>> class's cleanup action might be registered with the same or a
>> different Cleaner than that used by the base class.
>> 
>> 
> 
> One thing to note is that independent actions registered on the same referent may execute in arbitrary order (each registration is a separate PhantomReference). If order is important then something like the following will be required:

Yes, although I think such interactions will turn out to be quite rare
in practice, once the different cleanups no longer need to take into
consideration the registered object.