RFR: 8184166: SortedList does not free up memory [v3]

[Andy Goryachev]

On Wed, 17 Dec 2025 23:55:23 GMT, Cormac Redmond <duke at openjdk.org> wrote:

>> modules/javafx.base/src/main/java/javafx/collections/transformation/SortedList.java line 280:
>> 
>>> 278: 
>>> 279:         // Null out out-of-range array elements to avoid maintaining object references
>>> 280:         for (int i = size; i < sorted.length; i++) {
>> 
>> Don't we need to null the unused entries only when the `sorted` array shrinks (i.e. when the `size` is reduced)?
>> 
>> so all we do is to handle L259 case `if (c.wasRemoved())` since everywhere else the references are null'ed (L379, L388)?
>
> Yes...and it works fine too if put inside the if(c.wasRemoved()) { } block too but if there are many other additions/permutations _also_ in the change set, then we might be wasting time/CPU nulling indexes that are going to be replaced anyway (i.e., thinking large lists). I felt it was cleaner/safer to just trim at the end of all changes applied in the while loop.
> 
> Let me know what you think. It can be moved if you prefer. I have added comment anyway in the meantime, to mention why it's needed (i.e., only when shrinking). That's done now.
> 
> The other methods you mentioned are only called when a comparator is set, by the way, there's no nulling in this method (updateUnsorted())

The problem with the current change is we are wasting time/CPU always, instead of doing only what's strictly needed.  Just imagine if the `sorted` array is fairly large and contains only a few items - then you are overwriting many `null` entries with `nulls` needlessly.

Besides, we have the exact number of entries to null out (`c.getRemovedSize()`), which makes the life easier.

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PR Review Comment: https://git.openjdk.org/jfx/pull/2000#discussion_r2629016001