RFR: 8269907 memory leak - Dirty Nodes / Parent removed [v2]

[Kevin Rushforth]

On Thu, 22 Jul 2021 11:50:11 GMT, Florian Kirmaier <fkirmaier at openjdk.org> wrote:

>> After thinking about this issue for some time, I've now got a solution.
>> I know put the scene in the state it is, before is was shown, when the dirtyNodes are unset, the whole scene is basically considered dirty. 
>> This has the drawback of rerendering, whenever a window is "reshown", but it restores sanity about memory behaviour, which should be considered more important.
>
> Florian Kirmaier has updated the pull request incrementally with one additional commit since the last revision:
> 
>   JDK-8269907
>   The bug is now fixed in a new way. Toolkit now supports registering CleanupListeners, which can clean up the dirty nodes, avoiding memoryleaks.

I took a closer look, and the current PR has at least one problem. The call to `synchronizeSceneNode` must only be done with the `renderLock` held. If you are using this in production, then it likely means you aren't hitting the cases where this would break. I recommend either my earlier suggestion of hooking into the existing listener, or else you will need to acquire the `renderLock`. If the latter, then one thing you will want to avoid is running both a regular sync pass and a cleanup pass in the same pulse. I see that you try to ensure that by only adding the listener if the scene is not showing, but since you might have to also check in the listener itself (not sure).

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PR: https://git.openjdk.java.net/jfx/pull/584