SWT - 每次在 StyledText 中添加文本时都会创建新的 TextLayout

My GUI written in SWT gets slower while running. I found - using Sleak tool - that a TextLayout instance is created each time a character is added in my StyledText instance.

Using the snippet provided by eclipse.org, I noticed the same problem.

I work on Linux Ubuntu with the last version of SWT.

You can find a little snippet after this message: run Snippet163 using Sleak to see instances of TextLayout.

package styledtext;

import org.eclipse.swt.SWT;
import org.eclipse.swt.custom.StyleRange;
import org.eclipse.swt.custom.StyledText;
import org.eclipse.swt.custom.StyledTextLineSpacingProvider;
import org.eclipse.swt.events.SelectionAdapter;
import org.eclipse.swt.events.SelectionEvent;
import org.eclipse.swt.graphics.DeviceData;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.layout.GridData;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

public class Snippet163 {
    
    private static Display display;
    private static Shell shell;

    public static void main(String[] args) {
        DeviceData data = new DeviceData();
        data.tracking = true;
        display = new Display(data);
        Sleak sleak = new Sleak();
        sleak.open();

        shell = new Shell(display);
        shell.setText("Snippet 163");
        shell.setLayout(new GridLayout());
        shell.setSize(800, 600);

        run();


        shell.open();
        while (!shell.isDisposed()) {
            if (!display.readAndDispatch())
                display.sleep();
        }
        display.dispose();
    }


    private static void run() {
        StyledText text = new StyledText (shell, SWT.V_SCROLL | SWT.H_SCROLL );
        //text.setAlwaysShowScrollBars(true);   
        text.setLayoutData(new GridData(SWT.FILL, SWT.FILL, true, true));
        
        
        /* useless ?
        text.setLineSpacingProvider(new StyledTextLineSpacingProvider() {
            public Integer getLineSpacing(int lineIndex) {
                return 5;
            }
        });     
        */
        
        text.setText("0123456789 ABCDEFGHIJKLM NOPQRSTUVWXYZ");
        // make 0123456789 appear bold
        StyleRange style1 = new StyleRange();
        style1.start = 0;
        style1.length = 10;
        style1.fontStyle = SWT.BOLD;
        text.setStyleRange(style1);
        // make ABCDEFGHIJKLM have a red font
        StyleRange style2 = new StyleRange();
        style2.start = 11;
        style2.length = 13;
        style2.foreground = display.getSystemColor(SWT.COLOR_RED);
        text.setStyleRange(style2);
        // make NOPQRSTUVWXYZ have a blue background
        StyleRange style3 = new StyleRange();
        style3.start = 25;
        style3.length = 13;
        style3.background = display.getSystemColor(SWT.COLOR_BLUE);
        text.setStyleRange(style3);
        
        
        Button button = new Button(shell, SWT.PUSH);
        button.setText("insert!");
        button.addSelectionListener(new SelectionAdapter() {
            
            @Override
            public void widgetSelected(SelectionEvent e) {
                for (int i = 0; i < 10; i++) {
                    text.insert("Update ! " + i + "\n");
                }
            }
        });
    }

}

package styledtext;


import java.io.ByteArrayOutputStream;
import java.io.PrintStream;

import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.Color;
import org.eclipse.swt.graphics.Cursor;
import org.eclipse.swt.graphics.DeviceData;
import org.eclipse.swt.graphics.Font;
import org.eclipse.swt.graphics.FontData;
import org.eclipse.swt.graphics.GC;
import org.eclipse.swt.graphics.Image;
import org.eclipse.swt.graphics.Point;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.graphics.Region;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Event;
import org.eclipse.swt.widgets.Label;
import org.eclipse.swt.widgets.List;
import org.eclipse.swt.widgets.Listener;
import org.eclipse.swt.widgets.MessageBox;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Text;

/**
 * Instructions on how to use the Sleak tool with a standlaone SWT example:
 * 
 * Modify the main method below to launch your application.
 * Run Sleak.
 * 
 */
public class Sleak {
    Display display;
    Shell shell;
    List list;
    Canvas canvas;
    Button start, stop, check;
    Text text;
    Label label;
    
    Object [] oldObjects = new Object [0];
    Error [] oldErrors = new Error [0];
    Object [] objects = new Object [0];
    Error [] errors = new Error [0];
    
    public static void main (String [] args) {
        DeviceData data = new DeviceData();
        data.tracking = true;
        Display display = new Display (data);
        Sleak sleak = new Sleak ();
        sleak.open ();

        while (!sleak.shell.isDisposed ()) {
            if (!display.readAndDispatch ()) display.sleep ();
        }
        display.dispose ();
    }
    
    public void open () {
        display = Display.getCurrent ();
        shell = new Shell (display);
        shell.setText ("S-Leak");
        list = new List (shell, SWT.BORDER | SWT.V_SCROLL);
        list.addListener (SWT.Selection, new Listener () {
            public void handleEvent (Event event) {
                refreshObject ();
            }
        });
        text = new Text (shell, SWT.BORDER | SWT.H_SCROLL | SWT.V_SCROLL);
        canvas = new Canvas (shell, SWT.BORDER);
        canvas.addListener (SWT.Paint, new Listener () {
            public void handleEvent (Event event) {
                paintCanvas (event);
            }
        });
        check = new Button (shell, SWT.CHECK);
        check.setText ("Stack");
        check.addListener (SWT.Selection, new Listener () {
            public void handleEvent (Event e) {
                toggleStackTrace ();
            }
        });
        start = new Button (shell, SWT.PUSH);
        start.setText ("Snap");
        start.addListener (SWT.Selection, new Listener () {
            public void handleEvent (Event event) {
                refreshAll ();
            }
        });
        stop = new Button (shell, SWT.PUSH);
        stop.setText ("Diff");
        stop.addListener (SWT.Selection, new Listener () {
            public void handleEvent (Event event) {
                refreshDifference ();
            }
        });
        label = new Label (shell, SWT.BORDER);
        label.setText ("0 object(s)");
        shell.addListener (SWT.Resize, new Listener () {
            public void handleEvent (Event e) {
                layout ();
            }
        });
        check.setSelection (false);
        text.setVisible (false);
        Point size = shell.getSize ();
        shell.setSize (size.x / 2, size.y / 2);
        shell.open();
    }
    
    void refreshLabel () {
        int colors = 0, cursors = 0, fonts = 0, gcs = 0, images = 0, regions = 0;
        for (int i=0; i<objects.length; i++) {
            Object object = objects [i];
            if (object instanceof Color) colors++;
            if (object instanceof Cursor) cursors++;
            if (object instanceof Font) fonts++;
            if (object instanceof GC) gcs++;
            if (object instanceof Image) images++;
            if (object instanceof Region) regions++;
        }
        String string = "";
        if (colors != 0) string += colors + " Color(s)\n";
        if (cursors != 0) string += cursors + " Cursor(s)\n";
        if (fonts != 0) string += fonts + " Font(s)\n";
        if (gcs != 0) string += gcs + " GC(s)\n";
        if (images != 0) string += images + " Image(s)\n";
        if (regions != 0) string += regions + " Region(s)\n";
        if (string.length () != 0) {
            string = string.substring (0, string.length () - 1);
        }
        label.setText (string);
    }
    
    void refreshDifference () {
        DeviceData info = display.getDeviceData ();
        if (!info.tracking) {
            MessageBox dialog = new MessageBox (shell, SWT.ICON_WARNING | SWT.OK);
            dialog.setText (shell.getText ());
            dialog.setMessage ("Warning: Device is not tracking resource allocation");
            dialog.open ();
        }
        Object [] newObjects = info.objects;
        Error [] newErrors = info.errors;
        Object [] diffObjects = new Object [newObjects.length];
        Error [] diffErrors = new Error [newErrors.length];
        int count = 0;
        for (int i=0; i<newObjects.length; i++) {
            int index = 0;
            while (index < oldObjects.length) {
                if (newObjects [i] == oldObjects [index]) break;
                index++;
            }
            if (index == oldObjects.length) {
                diffObjects [count] = newObjects [i];
                diffErrors [count] = newErrors [i];
                count++;
            }
        }
        objects = new Object [count];
        errors = new Error [count];
        System.arraycopy (diffObjects, 0, objects, 0, count);
        System.arraycopy (diffErrors, 0, errors, 0, count);
        list.removeAll ();
        text.setText ("");
        canvas.redraw ();
        for (int i=0; i<objects.length; i++) {
            list.add (objectName (objects [i]));
        }
        refreshLabel ();
        layout ();
    }
    
    String objectName (Object object) {
        String string = object.toString ();
        int index = string.lastIndexOf ('.');
        if (index == -1) return string;
        return string.substring (index + 1, string.length ());
    }
    
    void toggleStackTrace () {
        refreshObject ();
        layout ();
    }
    
    void paintCanvas (Event event) {
        canvas.setCursor (null);
        int index = list.getSelectionIndex ();
        if (index == -1) return;
        GC gc = event.gc;
        Object object = objects [index];
        if (object instanceof Color) {
            if (((Color)object).isDisposed ()) return;
            gc.setBackground ((Color) object);
            gc.fillRectangle (canvas.getClientArea());
            return;
        }
        if (object instanceof Cursor) {
            if (((Cursor)object).isDisposed ()) return;
            canvas.setCursor ((Cursor) object);
            return;
        }
        if (object instanceof Font) {
            if (((Font)object).isDisposed ()) return;
            gc.setFont ((Font) object);
            FontData [] array = gc.getFont ().getFontData ();
            String string = "";
            String lf = text.getLineDelimiter ();
            for (int i=0; i<array.length; i++) {
                FontData data = array [i];
                String style = "NORMAL";
                int bits = data.getStyle ();
                if (bits != 0) {
                    if ((bits & SWT.BOLD) != 0) style = "BOLD ";
                    if ((bits & SWT.ITALIC) != 0) style += "ITALIC";
                }
                string += data.getName () + " " + data.getHeight () + " " + style + lf;
            }
            gc.drawString (string, 0, 0);
            return;
        }
        if (object instanceof Image) {
            if (((Image)object).isDisposed ()) return;
            gc.drawImage ((Image) object, 0, 0);
            return;
        }
        if (object instanceof Region) {
            if (((Region)object).isDisposed ()) return;
            String string = ((Region)object).getBounds().toString();
            gc.drawString (string, 0, 0);
            return;
        }
    }
    
    void refreshObject () {
        int index = list.getSelectionIndex ();
        if (index == -1) return;
        if (check.getSelection ()) {
            ByteArrayOutputStream stream = new ByteArrayOutputStream ();
            PrintStream s = new PrintStream (stream);
            errors [index].printStackTrace (s);
            text.setText (stream.toString ());
            text.setVisible (true);
            canvas.setVisible (false);
        } else {
            canvas.setVisible (true);
            text.setVisible (false);
            canvas.redraw ();
        }
    }
    
    void refreshAll () {
        oldObjects = new Object [0];
        oldErrors = new Error [0];
        refreshDifference ();
        oldObjects = objects;
        oldErrors = errors;
    }
    
    void layout () {
        Rectangle rect = shell.getClientArea ();
        int width = 0;
        String [] items = list.getItems ();
        GC gc = new GC (list);
        for (int i=0; i<objects.length; i++) {
            width = Math.max (width, gc.stringExtent (items [i]).x);
        }
        gc.dispose ();
        Point size1 = start.computeSize (SWT.DEFAULT, SWT.DEFAULT);
        Point size2 = stop.computeSize (SWT.DEFAULT, SWT.DEFAULT);
        Point size3 = check.computeSize (SWT.DEFAULT, SWT.DEFAULT);
        Point size4 = label.computeSize (SWT.DEFAULT, SWT.DEFAULT);
        width = Math.max (size1.x, Math.max (size2.x, Math.max (size3.x, width)));
        width = Math.max (64, Math.max (size4.x, list.computeSize (width, SWT.DEFAULT).x));
        start.setBounds (0, 0, width, size1.y);
        stop.setBounds (0, size1.y, width, size2.y);
        check.setBounds (0, size1.y + size2.y, width, size3.y);
        label.setBounds (0, rect.height - size4.y, width, size4.y);
        int height = size1.y + size2.y + size3.y;
        list.setBounds (0, height, width, rect.height - height - size4.y);
        text.setBounds (width, 0, rect.width - width, rect.height);
        canvas.setBounds (width, 0, rect.width - width, rect.height);
    }
    
}