[GTK] problematic runtime behavior in table when deleting many rows #3607

import org.eclipse.swt.*;
import org.eclipse.swt.layout.*;
import org.eclipse.swt.widgets.*;

public class GtkTablePerformanceIssue {
	private static final int HUGE_COUNT = 500_000;
	private static final int LARGE_COUNT = 50_000;
	private static final int SMALL_COUNT = 5;

	public static void main(String[] args) {
		final Display display = new Display();
		final Shell shell = new Shell(display);
		shell.setText("GTK Table remove performance");
		shell.setLayout(new GridLayout(1, false));

		final Table table = new Table(shell, SWT.VIRTUAL | SWT.MULTI | SWT.H_SCROLL | SWT.V_SCROLL | SWT.FULL_SELECTION);
		table.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true));
		table.addListener(SWT.SetData, event -> {
			final TableItem item = (TableItem)event.item;
			item.setText("Item " + table.indexOf(item));
		});

		final Label explanation = new Label(shell, SWT.NONE);
		explanation.setText("When shrinking, select a row which won't exist after the shrink.");

		final Button huge = new Button(shell, SWT.PUSH);
		huge.setText("Reset to " + HUGE_COUNT + " rows");
		huge.addListener(SWT.Selection, event -> table.setItemCount(HUGE_COUNT));

		final Button large = new Button(shell, SWT.PUSH);
		large.setText("Reset to " + LARGE_COUNT + " rows");
		large.addListener(SWT.Selection, event -> table.setItemCount(LARGE_COUNT));

		final Button shrink = new Button(shell, SWT.PUSH);
		shrink.setText("Shrink to " + SMALL_COUNT + " rows");
		final Label result = new Label(shell, SWT.NONE);
		result.setLayoutData(new GridData(SWT.FILL, SWT.CENTER, true, false));
		shrink.addListener(SWT.Selection, event -> {
			final long start = System.nanoTime();
			table.setItemCount(SMALL_COUNT);
			final long elapsedMillis = (System.nanoTime() - start) / 1_000_000;
			result.setText("setItemCount(" + SMALL_COUNT + "): " + elapsedMillis + " ms");
			result.getParent().layout();
		});

		table.setItemCount(LARGE_COUNT);
		table.select(8);
		shell.setSize(500, 400);
		shell.open();
		while (!shell.isDisposed()) {
			if (!display.readAndDispatch()) {
				display.sleep();
			}
		}
		display.dispose();
	}
}