RFR: 8277848 Binding and Unbinding to List leads to memory leak [v4]

[John Hendrikx]

On Wed, 22 Jun 2022 04:55:39 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

> Fundamentally, the problem does not arise from bindings, but from the fact that `ListPropertyBase` adds a `ListChangeListener` to its wrapped `ObservableList`.

Yes, I would agree.  The cause is the eager setup of listeners on other properties, resulting in the target being tied to the lifecycle of the observed property.  The listener itself serves no purpose until the `ListProperty` itself is observed in some fashion.  A `ListProperty` could be processing thousands of "changes" to update its internal state, but if it is not observed or called directly, nobody cares.  The end result is that the property cannot be garbage collected and is processing every change event, even though everything has lost interest in it.

This is basically another case where it is better to only listen (or bind) to other targets when absolutely necessary (when the source itself is being observed) and to remove the listener (or binding) when no longer observed, basically lazy versus eager observation. Lazy observation would completely remove the need for using weak references, simplifying the logic and making the whole system much easier to reason about.

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