Jean-Francois,
The problem with holding listeners weakly is that people commonly create
listener objects on the fly and then retain no other references to them
once they've added them. So these listeners are thrown away on the next
GC cycle, and they stop working.
One solution to this is to have a tagging interface (we call ours
WeakListener) that tells the event source that it should hold the
listener weakly. All listeners that don't implement this interface are
held strongly. This way, you as the implementer of the listener are
telling the event source whether to hold the listener weakly (meaning
you better have a strong reference to it) or strongly (meaning you don't
have to). As you say, it's pretty easy to write a listeners collection
that honors this WeakListener interface and throws away the expired
listeners when you ask for the current list of listeners. (We don't use
an iterator, but rather a method that returns an array of listeners, for
thread safety reasons.)
Luke
Jean-Francois Poilpret wrote:
>...
>To Howard:
>During the night (French people say that the "night gives good advice";-)),
>I thought of a quite easy workaround, that can be done at the event
>supplying service level: just use a weak reference to the listeners (instead
>of a strong one), I think that should do the trick.
>Maybe it would even be possible to write a general "WeakEventListeners"
>class to manage all that for the event supplier:
>- when addListener, is called generate a weak reference to the added
>listener and store it in the list
>- create a specific Iterator for WeakEventListeners that would skip the refs
>that have become weak-reachable (and remove these from its list at the same
>time).
>
>
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