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<p>This looks like a classic problem where unused elements in an
array are not nulled. Looking at the code that updates the `size`
field, there are a few code paths that are not setting unused
elements to null. I also saw no code that ever shrinks the
arrays. So it looks this implementation is only half finished.<br>
</p>
<p>So, yes, I'd say this is a bug.<br>
</p>
<p>
<blockquote type="cite">I'm going to guess there's a very good
reason for this behaviour.</blockquote>
Time pressure and insufficient testing.<br>
</p>
<p>--John<br>
</p>
<div class="moz-cite-prefix">On 04/12/2025 19:40, Cormac Redmond
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAG_-AaDynME6krZL_Lq7eYuKc5dtWPF+Fo4ttVMYXi3gPBwUHg@mail.gmail.com">
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<div class="gmail_default"
style="font-family:verdana,sans-serif">Hi,<br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif">I've traced a memory
issue back to a SortedList (surprisingly), where it's hanging
on to objects that could/should have been GC'd.</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif">SortedList's internal
arrays will only grow (but not shrink) in line with the source
ObservableList (I'm sure there are reasons for this). So even
when your source ObservableList shrinks, SortedList is hanging
on to references to objects the source list once contained,
even though they're completely removed from the source list.</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif">This leads to a
substantial waste of memory, especially when just one
momentarily large dataset leads to a permanent spike in
unnecessary memory usage for the remainder for the
application's lifetime. I'm sure I'm not the first to raise
this or ask about it & I'm going to guess there's a very
good reason for this behaviour. But could someone explain
this? I would have thought SortedList should/could remain as
lean as the source list. FilteredList is somewhat similar,
except it stores an array of ints (indexes), so less of a
memory hit, but still pointless nonetheless.</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif">Example GIF + code
below: setup a typical sortable table (so, ObservableList +
FilteredList + SortableList), where the print button shows
that when you add a lot of data, and remove it, SortedList
retains references to all of the old objects. Some reflection
is used to print that information.</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif"><img
src="cid:part1.Wj8uTVDa.rJ3j4SWw@gmail.com"
alt="sorted_list_mem.gif" class="" width="406" height="562"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif"><br>
</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif">Code to reproduce:</div>
<div class="gmail_default"
style="font-family:verdana,sans-serif"><br>
</div>
<div class="gmail_default" style=""><font face="monospace">public
class SortedListMemWasteDemo extends Application {<br>
<br>
record PotentialLargeData(String info) {}<br>
<br>
public static void main(String[] args) {<br>
launch(args);<br>
}<br>
<br>
@Override<br>
public void start(Stage primaryStage) {<br>
ObservableList<PotentialLargeData> masterData
= FXCollections.observableArrayList(<br>
new PotentialLargeData("Initial info 1"), <br>
new PotentialLargeData("Initial info 2"));<br>
<br>
TableColumn<PotentialLargeData, String> col =
new TableColumn<>("Info");<br>
col.setCellValueFactory(cellData -> new
SimpleStringProperty(cellData.getValue().info()));<br>
<br>
TableView<PotentialLargeData> table = new
TableView<>();<br>
table.getColumns().add(col);<br>
<br>
FilteredList<PotentialLargeData> filteredData
= new FilteredList<>(masterData, item -> true);<br>
SortedList<PotentialLargeData> sortedData =
new SortedList<>(filteredData);<br>
sortedData.comparatorProperty().bind(table.comparatorProperty());<br>
table.setItems(sortedData);<br>
<br>
Button loadManyBtn = new Button("Add 10,000 items");<br>
loadManyBtn.setOnAction(e -> {<br>
System.out.println("Adding 10000 items to master
data");<br>
masterData.clear();<br>
for (int i = 0; i < 10000; i++)
masterData.add(new PotentialLargeData("Info item " + i));<br>
});<br>
<br>
Button reduceBtn = new Button("Reduce to 2");<br>
reduceBtn.setOnAction(e -> {<br>
System.out.println("Reducing master data size to
2");<br>
masterData.setAll(new PotentialLargeData("New
info 1"), new PotentialLargeData("New info 2"));<br>
});<br>
<br>
Button printBtn = new Button("Print interal sizes");<br>
printBtn.setOnAction(e -> {<br>
try {<br>
System.out.println("Items the user sees: " +
sortedData.size());<br>
int[] filtered = (int[])
getFieldValue(filteredData, "filtered");<br>
System.out.println("FilteredList.filtered
length: " + filtered.length);<br>
// This is a hidden and significant waste of
memory<br>
Object[] sorted = (Object[])
getFieldValue(sortedData, "sorted");<br>
System.out.println("SortedList.sorted
length: " + sorted.length);<br>
} catch (Exception ex) {<br>
throw new RuntimeException(ex);<br>
}<br>
});<br>
<br>
primaryStage.setScene(new Scene(new VBox(table,
loadManyBtn, reduceBtn, printBtn), 600, 400));<br>
primaryStage.show();<br>
}<br>
<br>
private static Object getFieldValue(Object object,
String fieldName) throws Exception {<br>
Field field =
object.getClass().getDeclaredField(fieldName);<br>
field.setAccessible(true);<br>
return field.get(object);<br>
}<br>
}</font></div>
<div class="gmail_default" style=""><font face="monospace"><br>
</font></div>
<div class="gmail_default" style=""><font face="monospace"><br>
</font></div>
<div class="gmail_default" style=""><font
face="verdana, sans-serif">Kind Regards,</font></div>
<div class="gmail_default" style=""><font
face="verdana, sans-serif">Cormac</font></div>
</div>
</blockquote>
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