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

Jason Mehrens jason_mehrens at hotmail.com
Fri Oct 2 14:14:49 UTC 2015


For custom thread factories, do we have to explictly set the CCL for the created thread or should that be a documented as a warning to all who use it?  In web apps that can be a form of a memory leak.


From: core-libs-dev <core-libs-dev-bounces at openjdk.java.net> on behalf of Roger Riggs <Roger.Riggs at Oracle.com>
Sent: Thursday, October 1, 2015 9:12 AM
To: Core-Libs-Dev
Subject: RFR 9: 8138696 : java.lang.ref.Cleaner - an easy to use alternative    to finalization

Please review a proposal for public Cleaner API:

A Cleaner is proposed to provide an easy to use alternative to
finalization. The service would provide easy registration and
cancellation of cleanup functions for objects. Applications create a
cleanup service for their own use and the service terminates when it is
no longer in use.

Finalization has a long history of issues both in usage and performance.
PhantomReferences have been proposed as the alternative GC based
mechanism for cleaning functions but it has been left as an exercise to
the developer to construct the necessary mechanisms to handle
ReferenceQueues, handle threading issues and robust termination.

The Cleaner performs cleaning functions when objects are unreachable as
found by garbage collection using the existing mechanisms of
PhantomReference, WeakReference, SoftReferences, and ReferenceQueues. It
manages a thread that dequeues references to unreachable objects and
invokes the corresponding cleaning function. Registered cleaning
functions can be cleared if no longer needed, can be invoked explicitly
to perform the cleanup immediately, or be invoked when the object is not
reachable (as detected by garbage collection) and handled by a cleanup

The java.lang.ref package is proposed for the Cleaner because it is
complementary to the reference classes and reference queues and to make
it easy to find.

It is not a goal to replace all uses of finalization or sun.misc.Cleaner
in the JDK.
Investigation will evaluate if and in what cases the Cleaner can replace
A subsequent task will examine uses of finalization and propose specific
on a case by base basis.

Please review and comment:




Thanks, Roger

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