On 06/08/2015 09:47 PM, Kim Barrett wrote:
On Jun 6, 2015, at 11:02 AM, Peter Levart <peter.lev...@gmail.com> wrote:
I understand that it would be desirable for a finalizable object to be made
"untracked" as soon as it is manually cleaned-up. This would most certainly
give a relief to GC as it could reclaim such untracked objects immediately like normal
objects without pushing them through all the finalization steps.
Such feature would need new API. Here's my take on such API incorporated in my
prototype. This feature is mostly independent of other changes in the prototype
and could be provided stand-alone. I choose to incorporate it into the
prototype to compare it's overhead with classical finalization in unchanged and
changed JDKs:
http://cr.openjdk.java.net/~plevart/misc/JEP132/ReferenceHandling/webrev.03/
While changes are needed to do this sort of thing, it seems to me a better
change would be to not use finalize() at all,
You mean FinalReference, right? This is the only remaining Reference
type that isn't cleared automatically by GC. So if a XxxReference is
cleared when it is discovered with referent being xxx-ly-reachable and
later enqueued by ReferenceHandler thread, then GC has less work with
it? Why is automatically cleared Reference more lightweight than
FinalReference? Because GC can reclaim such referent right away in the
same GC cycle as hooking it on the pending list?
but instead use PhantomReference-based cleanup. It provides exactly that kind
of behavior, and has other benefits besides.
There is some discussion about doing exactly that for File{Input,Output}Stream
(see https://bugs.openjdk.java.net/browse/JDK-8080225).
sun.misc.Cleaner is already such thing (a PhantomReference). Would it be
of interest to have a public API similar to sun.misc.Cleaner, but with
the following difference:
- public "Cleaners" would be executed by same thread(s) as finalize()
methods. This would detach their execution from ReferenceHandler thread
which must dispatch all references and must not be disturbed by user code.
Regards, Peter
