Increase thread safety of EventListenerList

Name: jl125535 Date: 04/14/2004


FULL PRODUCT VERSION :
java version "1.4.2"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2-b28)
Java HotSpot(TM) Client VM (build 1.4.2-b28, mixed mode)

A DESCRIPTION OF THE REQUEST :
EventListenerList should synchronize getListeners() and getListenerList() methods to complement the synchronized add() and remove() methods.

I suggest EventListenerList be reimplemented using AWTEventMulticaster which is thread safe.

JUSTIFICATION :
Not synchronizing getListeners() and getListenerList() undoes the benefit of synchronizing the add and remove methods, because removing a listener while processing getListeners() can result in ArrayOutOfBoundsExceptions.
Also the re-assignment of the listener list at the bottom of the add and remove is not atomic so using the return of getListenerList() is problematic in a multi-threaded application.

This means for example you cannot reliably remove a Document listener using a program thread, while the document is being updated by the user on the Swing thread.

(Incident Review ID: 246793)
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