EventListenerList & WeakReference: a match made in heaven

Question

It makes so much sense I wonder why Sun didn't implement EventListenerList with WeakReferences. That would save almost everyone from some memory leaks.
Well, not everyone is so behind. I managed to find this:
http://www-iiuf.unifr.ch/iiufdev/doc/public/iiuf/iiuf/util/EventListenerList.html
http://www-iiuf.unifr.ch/iiufdev/doc/
Any thoughts?

Answer 1

Is this a dead cat?I don't think so.
I group listeners in to two categories:
1) Those that can be held by weak references (because there is some other "strong" reference keeping them from being GCed before their time).
2) Those that are only held by the listener list.
In the first case it makes sense to hold a weak reference from the listener list. In the second case a strong reference must be held.
The problem is in deciding which category a particular listener falls into.
How would more bugs be created: Putting listeners into the wrong category, or holding strong references to all listeners and forgetting to remove them at the proper time?
I don't know the answer.
One thing I have tried is to create a Proxy listener that holds a weak reference to its target. When the target is GCed the Proxy can remove itself from the listener list by putting the WeakReferences on a ReferenceQueue.
You could probably make a generic weak listener proxy using reflection and the java.lang.reflect.Proxy class. I was working on this at one point, but never finished it.