On Mon, 17 Aug 2026 17:21:51 GMT, Marius Hanl <[email protected]> wrote:
>> This PR creates a WeakReferenceWrapper object to replace direct uses of >> WeakReference in controls where the referent is a user-supplied object of an >> unknown type. >> >> As noted in JEP 401, which is now integrated into JDK 28, "The garbage >> collection APIs in java.lang.ref ... do not allow developers to manually >> manage value objects in the heap. Attempts to create Reference objects for >> value objects throw IdentityException at run time." >> >> Several core JDK classes such as all of the primitive wrappers (e.g., >> `Integer`, `Character`), `Optional`, `LocalDateTime`, and a few others are >> now value types if JDK 28 is run with the `--enable-preview` option. >> >> The `ListView`, `ComboBox`, `TableView`, and `TreeTableView` controls take a >> parameterized item type and hold items of that type. The following places in >> the implementation create weak references to an item. If that item type is a >> value class -- meaning that it does not have identity -- creating the >> `WeakReference` fails. >> >> As noted in the JBS issue, there are 3 cases to consider. >> >> 1. `SelectedItemsReadOnlyObservableList<E>` -- `E` is the item type (created >> by `MultipleSelectionModelBase<T>`) : `ListView`, `TableView`, `ComboBox` >> (due to its skin creating a `ListView<T>`) -- replace with >> `WeakReferenceWrapper` >> >> 2. `TablePosition<S,T>` -- `S` is the item type : `TableView` -- the >> reference is unused, so I removed it >> >> 3. `TableCell<S,T>` and `TreeTableCell<S,T>` -- `S` is the item type : >> `TableView`, `TreeTableView` -- replace with `WeakReferenceWrapper` >> >> The new `WeakReferenceWrapper` class takes a referent of any type and either >> creates a WeakReference (if it has identity) or directly stores the >> reference (if it is null or does not have identity). I added a test for the >> wrapper. >> >> All of the controls tests pass with this fix. I did three test runs as >> follows: >> >> 1. JDK 25 >> 2. JDK 28 without `--enable-preview` >> 3. JDK 28 with `--enable-preview` >> >> Without the fix, 31 controls tests fails on the 3rd run. >> >> --------- >> - [x] I confirm that I make this contribution in accordance with the >> [OpenJDK Interim AI Policy](https://openjdk.org/legal/ai). > > modules/javafx.controls/src/main/java/com/sun/javafx/scene/control/SelectedItemsReadOnlyObservableList.java > line 40: > >> 38: private final ObservableList<Integer> selectedIndices; >> 39: private final Supplier<Integer> modelSizeSupplier; >> 40: private final List<WeakReferenceWrapper<E>> itemsRefList; > > This is still confusing me as also mentioned in the ticket. For example, the > `SelectionModel` has a `selectedItem` property, where we save the item `<T>`. > So the item `T` is saved, without any `WeakReference` handling. > > And this is used in e.g. `ComboBox`, which does not seems to leak memory. So > I wonder why we use a `WeakReference` here. > > The `WeakReference` usage in the `TableCell` is also questionable. > Maybe worth to research in a follow-up? Yes, this is definitely worth a follow-up. This is a very odd use of weak references. It's a short-lived list of previously removed items used in a subsequent change event. Dan Smith @dlsmith-dev suggested something similar in this thread: https://mail.openjdk.org/archives/list/[email protected]/thread/TD7AQH4SNRS4QAQAXTISKIERNK6LINYB/ The use of weak references suggests that when this was implemented, they were worried about a possible leak, so we would need to show that it can't leak in practice. If we can prove using strong references won't lead to a leak, that would be the best solution anyway. ------------- PR Review Comment: https://git.openjdk.org/jfx/pull/2250#discussion_r3798875661
