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

[Brian Goetz]

> Finally, how important is it to be able to unregister a cleaner?  In
> all the years we've had sun.misc.Cleaner that capability has never
> been needed, and leaving it out would simplify the API.

I see this as having two big potential benefits (I'll let Roger confirm 
whether the implementation provides both):

  - Resource release for finalizable objects is generally coded in two 
places; in the explicit close() / release() method, which we hope people 
will use, and in the finalizer, in case the object is collected without 
being closed.  Having two ways to express the same action is 
error-prone; if there's one definition of "release the 
houn^H^H^H^Hresources" then they can't get out of sync.

This requires an atomic means to say "unregister the cleaner, and, if 
its not yet been run, run it now".

  - If you can unregister the cleaner on the happy path (where the user 
explicitly closes the object ), then all the enqueue / reference 
processing / finalization work can be optimized away.