RFR: 8294589: MenuBarSkin: memory leak when changing skin [v2]

[Andy Goryachev]

On Tue, 4 Oct 2022 15:14:43 GMT, Jeanette Winzenburg <fastegal at openjdk.org> wrote:

>> Andy Goryachev has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8294589: unnecessary null checks
>
> modules/javafx.controls/src/main/java/javafx/scene/control/skin/MenuBarSkin.java line 328:
> 
>> 326:         mouseEventHandler = t -> {
>> 327:             if (getSkinnable() != null) {
>> 328:                 Bounds containerScreenBounds = container.localToScreen(container.getLayoutBounds());
> 
> this null check is wrong: skinnable is guaranteed to never be null - except after dispose, at which time it's illegal to access any of the skin's methods/fields/state. So checking here is smearing over a precondition violation of the caller (most probably a dangling handler/listener) which has to be fixed.
> 
> Note we deliberately removed all null checks in all (cleaned) skins :) If we see any exceptions, the procedure is to 
> 
> - write a test exposing the exception (it's failing), this test belongs into SkinCleanTest
> - find and fix the violator
> - see the test passing
> 
> There might be other exceptions as well (like IOOB or similar) which require a similar procedure, see the available tests. Actually, I think it's a good idea to actively look out for possible macroscopic misbehavior if handlers/listeners are not removed properly. SkinCleanupTest has examples.

agreed.

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PR: https://git.openjdk.org/jfx/pull/906