RFR: 8277848 Binding and Unbinding to List leads to memory leak [v7]

[Florian Kirmaier]

On Wed, 11 Jan 2023 11:11:09 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

> Should I expect x here to be unreferenced? No, that's how properties work, b will keep its reference to x.

No, x is not dereferenced. But you should expect that a is no longer referencing b, but both a and b are referencing x.

But I don't see your point - it's worth mentioning, when you bind a ListProperty A, to another ListProperty B, then A doesn't get the value "B", but the value will be the value of the property B.

If you think the PR creates an unwanted behavior, I would appreciate seeing a **unit-test** for it, because it's way easier to discuss on the basis of a test.

Making tests for memory behavior (both for being collectible and being not-collectible) is easy with JMemoryBuddy, which I wrote exactly for this use case.

I'm also happy with an alternative solution - which makes the tests green, which I've provided. I'm not really opinionated.

> IMHO there is a conflict between the property-like behavior of ListProperty and the list-like behavior of the ObservableList that it wraps. On the one hand, a list property is a reference to a list, and on the other hand, we expect it to behave as only referring to the contents of the list. The property like behavior that it inherits (perhaps it shouldn't have done that) has been subverted in that adding a change listener will pretend that a change to the list is the same as replacing the entire list object, so it is not quite a property any more. 

Yes, I agree. I think - it's a complicated topic. I don't want to discuss any details, because I just want to add a fundamental bug, without discussing the whole Property/Collection design.

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PR: https://git.openjdk.org/jfx/pull/689