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

Peter Levart peter.levart at gmail.com
Wed Oct 21 08:02:29 UTC 2015

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.

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

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