Hi Peter,
On 10/21/2015 4:02 AM, Peter Levart wrote:
Hi Roger,
I think this is a good compromise. Having the low-level extended
functionality in the JDK for internal use until it is proven. Dropping
Cleanable.clear() is also a correct move. I currently don't see a use
for it. If one registers a cleaning function, why would one then try
to change his mind? It's better to decide upfront before registering.
You could make final clear() in XxxCleanable classes throw UOE like
it's done for get() in XxxCleanableRef. This way no Reference methods
will be usefully accessible from Cleanable instance that is given to
users and nobody will be tempted to cast it to Reference.
The Reference.clear() function cannot be disabled completely. During a
normal
close of a resource the Cleanable.clean() is invoked and it needs to
clear() the Reference.
This eliminates the overhead on the Reference processing system when
closes occur properly.
We're currently investigating an application with 12 million finalizable
References; that
puts quite a load on gc. It is better to clear the references when the
GC behavior is no long needed.
About clear(); in the case you raised about coordinating cleanup
between the subclass and superclass.
One design is for the superclass to expose the Cleanable object it
creates to the subclass.
The subclass would register its own cleanup arranging to call the
performCleanup of the super's Cleanable.
It would also want to clear() the super's Cleanable so it never was
invoked by the GC but
still encapsulates the super's cleanup behavior.
Thanks, Roger
Regards, Peter
On 10/20/2015 08:28 PM, Roger Riggs wrote:
Sorry for the silence, JavaOne preparations and the availability of
folks who wanted
to review have stretched things out.
The Cleaner API was very simple and saw feature creep as the ideas
for how it might be used
were explored. There are concerns about committing to supporting
subclassable
CleanableReferences in all future JDK versions before there had been
a chance to
see how if they would be useful and necessary to address the need to
reduce the
use of finalization within the OpenJDK and beyond.
Recent updates:
- The Cleaner implementation classes and the CleanableReference
abstract classes are
now in the jdk.internal.misc package and are available within the
java.base module.
- The Cleanable.clear method has been dropped; there is no current
use case.
Since the CleanableReferences extend Reference, clear() is
available when subclassing.
- The tests have been extended to cover the exported and internal APIs
The Runnable thunk version is very convenient to code but does
transparently create
an additional object to hold the bindings.
As the Cleaner is applied to the various uses of finalize we'll see
how they would be used
and can re-evaluate the exported API needs.
Updated Javadoc:
http://cr.openjdk.java.net/~rriggs/cleaner-doc/
Updated Webrev:
http://cr.openjdk.java.net/~rriggs/webrev-cleaner-8138696/
Thanks, Roger
