JavaFX memory leak in TableView with dynamic TableColumns

Question

I am using jdk1.8.0_40

I want to make a TableView which can have dynamically changing columns, but it leaks memory in Old/Tenured gen and eventually hangs the JVM.

Here is a simple program that demonstrates the leak (imports not included):

public class Main extends Application {
    @Override
    public void start(Stage primaryStage) {    
        TableView<ObservableList<String>> tableView = new TableView<>();
        Button button = new Button("button");

        button.setOnAction((actionEvent) -> {
            // Clearing items and/or columns here doesn't remove the leak
            tableView.getItems().clear();
            tableView.getColumns().clear();

            for (int g = 0; g < 50; g++) { // iterate 50 times to see the leak quickly
                TableColumn<ObservableList<String>, String> tableColumn = new TableColumn<>("column");
                tableView.getColumns().add(tableColumn);
            }
                tableView.getItems().add(FXCollections.observableArrayList("1"));

            // clearing the items here removes the leak somehow, but also makes the table useless
            /* tableView.getItems().clear(); */
        });

        primaryStage.setScene(new Scene(new VBox(tableView, button), 800, 600));
        primaryStage.show();
    }    
    public static void main(String[] args) { launch(args); }
}

In the code above pressing the button 2nd time should clear all items and columns, and it does, but some reference somehow persists somewhere.

Some things I've already tried:

• Tried searching for similar issues, but didn't find anything relevant.
• Tried storing all the references in an ArrayList and explicitly remove()-ing them instead of clear() - didn't work.
• Tried using ListView, which works fine, but it isn't a table and can't have columns.
• Tried using different combinations of classes (e.g. StringProperty instead of String), which to no surprise also didn't work.

I have only recently started learning JavaFX so I may just be missing something obvious, if so - sorry for a dumb question.

How do I fix this leak?

If it can't be fixed, is it a bug, or is this intended behavior and I should not create TableColumn dynamically?

Answer 1

To answer my own question in case somebody is also having this issue - this is a bug.

I submitted a JIRA bug report, for more info and maybe updates see https://javafx-jira.kenai.com/browse/RT-40325

Answer 2

If you suspect that there's a leak, you fix it by first identifying it using a profiler.

I rewrote your sample (which wasn't showing any data btw), there doesn't seem to be a leak. Try this and check the console output.

import javafx.application.Application;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class MainLeak extends Application {

    private static final int iterations = 100;
    private static final int columns = 50;
    private static final int rows = 100;

    @Override
    public void start(Stage primaryStage) {

        TableView<ObservableList<StringProperty>> table = new TableView<>();

        Button button = new Button("button");

        button.setOnAction((actionEvent) -> {

            addData( table, iterations);


        });

        addData( table, iterations);

        primaryStage.setScene(new Scene(new VBox(table, button), 800, 600));
        primaryStage.show();
    }

    private void addData( TableView table, int iterations) {

        for (int i = 0; i < iterations; i++) {

            final int index = i;

            addData(table);

            System.gc();

            System.out.println(index + ": free: " + Runtime.getRuntime().freeMemory() / 1024 + " kb, max: " + Runtime.getRuntime().maxMemory() / 1024 + " kb");

        }

    }

    private void addData(TableView table) {

        table.getItems().clear();
        table.getColumns().clear();

        for( int col=0; col < columns; col++) {
            table.getColumns().add(createColumn(col));
        }

        for( int row=0; row < rows; row++) {
            ObservableList<StringProperty> data = FXCollections.observableArrayList();
            for( int col=0; col < columns; col++) {
                data.add(new SimpleStringProperty(String.valueOf( row + " / " + col)));
            }
            table.getItems().add(data);
        }
    }

    private TableColumn<ObservableList<StringProperty>, String> createColumn(final int columnIndex) {

        TableColumn<ObservableList<StringProperty>, String> column = new TableColumn<>();
        String title = "Column " + columnIndex;
        column.setText(title);
        column.setCellValueFactory(cellDataFeatures -> cellDataFeatures.getValue().get(columnIndex));

        return column;
    }

    public static void main(String[] args) {
        launch(args);
    }
}