RFR: 8208088: Memory Leak in ControlAcceleratorSupport [v3]

[Kevin Rushforth]

On Tue, 23 Mar 2021 14:30:56 GMT, Ambarish Rapte <arapte at openjdk.org> wrote:

>> The method `ControlAcceleratorSupport.doAcceleratorInstall(final List<? extends MenuItem> items, final Scene scene)` adds a `ChangeListener` on `MenuItem.acceleratorProperty()`. This listener is not removed when the MenuItem is removed from scenegraph.
>> Adding and removing a MenuItem results in multiple copies of the listener added to MenuItem.acceleratorProperty().
>> 
>> Fix is to remove the listener when MenuItem is removed.
>> Fix can be verified by checking the number of instances of `ControlAcceleratorSupport.lambda` using _jvisualvm_. 
>> Without this fix, the number of `ControlAcceleratorSupport.lambda` increase in multiple of number of MenuItems being removed and added back.
>> With fix, the count is always same as number of MenuItems in scenegraph.
>> 
>> Also there is another ListChangeListener added to a `ObservableList<MenuItem> items` in the method `ControlAcceleratorSupport.doAcceleratorInstall(final ObservableList<MenuItem> items, final Scene scene)`. There was a TODO note to remove this listener.
>> This listener is added on `MenuBarButton.getItems()` and not on `Menu.getItems()`.  This `MenuBarButton` is created by `MenuBarSkin` to show a `Menu`. This `MenuBarButton` gets disposed when the related `Menu` is removed from scenegraph, and so the added `ListChangeListener` gets GCed. Hence it is not required to explicitly remove the listener. 
>> Added a comment explaining this behavior in place of the TODO.
>
> Ambarish Rapte has updated the pull request incrementally with one additional commit since the last revision:
> 
>   correct test

The fix looks good.

The test looks OK as far as it goes, although I note that it is testing for the leak in an indirect way, since it looks at the `changeListenerMap` rather than checking the listeners of `menuitem.acceleratorProperty()` which is what we really care about. Is there a way to test it more directly? If not then I think this is fine.

modules/javafx.controls/src/test/java/test/javafx/scene/control/ControlAcceleratorSupportTest.java line 46:

> 44:     public static void setup() throws Exception {
> 45:         for (int i = 0; i < 4; i++) {
> 46:             System.gc();

Maybe call `System.runFinalization()`, too?

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Marked as reviewed by kcr (Lead).

PR: https://git.openjdk.java.net/jfx/pull/429