RFR: 8088420: JavaFX WebView memory leak via EventListener [v9]

[Kevin Rushforth]

On Fri, 27 May 2022 16:47:04 GMT, Jay Bhaskar <jbhaskar at openjdk.org> wrote:

>> This PR is new implementation of JavaEvent listener memory management.
>> Issue  [JDK-8088420](https://bugs.openjdk.java.net/browse/JDK-8088420?filter=-1)
>> 
>> 1. Calling remove event listener does not free jni global references.
>> 2. When WebView goes out of scope (disposed from app) , its Event Listeners are not being garbage collected.
>> 
>> Solution:
>> 1.  Detached the jni global reference from JavaEventListener.
>> 2. Create scoped ref counted wrapper class JavaObjectWrapperHandler for jni global reference.
>> 3. Create unique  JavaObjectWrapperHandler object for each JavaEventListener.
>> 4. EventListenerManager is a singleton class , which stores the JavaObjectWrapperHandler mapped with JavaEventListener.
>> 5. EventListenerManager also stores the JavaEventListener mapped with DOMWindow.
>> 6. When Event listener explicitly removed , JavaEventListener is being forwarded to EventListenerManager to clear the listener.
>> 7. When WebView goes out of scope, EventListenerManager will de-registered all the event listeners based on the ref counts attached with WebView DOMWindow.
>
> Jay Bhaskar has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Adingef else block to unregisterListener

Looks good.

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Marked as reviewed by kcr (Lead).

PR: https://git.openjdk.java.net/jfx/pull/799