I'm working on a Java application with Swing-based GUI. The application uses JTextPane
to output log messages as follows: 1) truncate existing text to keep total text size under the limit; 2) append new text; 3) scroll to the end (actual logic is slightly different, but it's irrelevant here).
I was using Eclipse with JVM Monitor to determine reasonable text size limit and found significant memory leak. I tried to remove UndoableEditListener
s from the underlying document and disable automatic caret position updates (by changing the position explicitly with DefaultCaret.NEVER_UPDATE
and JTextPane.setCaretPosition(int)
), but without success. Finally, I decided to disable changing caret position completely, and this fixed the leak.
I have two questions:
Is there an issue with my code? If yes, how can I change it to accomplish the task?
Is it a Swing/JVM bug? If yes, how can I report it?
Details:
Here is SSCCE: GUI with textPane and two buttons, for small and stress tests. FIX
and FIXXX
flags correspond to my attempts to fix memory leak.
package memleak;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.UndoableEditListener;
import javax.swing.text.*;
class TestMain
{
private JTextPane textPane;
// try to fix memory leak
private static final boolean FIX = false;
// disable caret updates completely
private static final boolean FIXXX = false;
// number of strings to append
private static final int ITER_SMALL = 20;
private static final int ITER_HUGE = 1000000;
// limit textPane content
private static final int TEXT_SIZE_MAX = 100;
TestMain()
{
JFrame frame = new JFrame();
JPanel panel = new JPanel();
textPane = new JTextPane();
textPane.setEditable(false);
if (FIX)
{
tryToFixMemory();
} // end if FIX
JScrollPane scrollPane = new JScrollPane(textPane);
scrollPane.setPreferredSize(new Dimension(100, 100) );
panel.add(scrollPane);
JButton buttonSmall = new JButton("small test");
buttonSmall.addActionListener(new ButtonHandler(ITER_SMALL) );
panel.add(buttonSmall);
JButton buttonStress = new JButton("stress test");
buttonStress.addActionListener(new ButtonHandler(ITER_HUGE) );
panel.add(buttonStress);
frame.add(panel);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setVisible(true);
} // end constructor
public static void main(String[] args)
{
@SuppressWarnings("unused")
TestMain testMain = new TestMain();
} // end main
private void append(String s)
{
Document doc = textPane.getDocument();
try
{
int extraLength = doc.getLength() + s.length() - TEXT_SIZE_MAX;
if (extraLength > 0)
{
doc.remove(0, extraLength);
} // end if extraLength
doc.insertString(doc.getLength(), s, null);
if (FIX && !FIXXX)
{ // MEMORY LEAK HERE
textPane.setCaretPosition(doc.getLength() );
} // end if FIX
}
catch (Exception e)
{
e.printStackTrace();
System.exit(1);
} // end try
} // end method append
private void tryToFixMemory()
{
// disable caret updates
Caret caret = textPane.getCaret();
if (caret instanceof DefaultCaret)
{
( (DefaultCaret) caret).setUpdatePolicy(
DefaultCaret.NEVER_UPDATE);
} // end if DefaultCaret
// remove registered UndoableEditListeners if any
Document doc = textPane.getDocument();
if (doc instanceof AbstractDocument)
{
UndoableEditListener[] undoListeners =
( (AbstractDocument) doc).getUndoableEditListeners();
if (undoListeners.length > 0)
{
for (UndoableEditListener undoListener : undoListeners)
{
doc.removeUndoableEditListener(undoListener);
} // end for undoListener
} // end if undoListeners
} // end if AbstractDocument
} // end method tryToFixMemory
private class ButtonHandler implements ActionListener
{
private final int iter;
ButtonHandler(int iter)
{
this.iter = iter;
} // end constructor
@Override
public void actionPerformed(ActionEvent e)
{
for (int i = 0; i < iter; i++)
{
append(String.format("%10d\n", i) );
} // end for i
} // end method actionPerformed
} // end class ButtonHandler
} // end class TestMain
JVM was from official Oracle Java SE Development Kit 8u45 for Linux x64. All tests were done with -Xmx100m
limit.
Both flags are false
:
Small test
Works as expected:
Stress test
GUI freezes at an intermediate point:
Memory is leaking:
At some point there is no memory left and I got the following error:
Exception in thread "AWT-EventQueue-0" java.lang.OutOfMemoryError: GC overhead limit exceeded
at java.util.Formatter.parse(Formatter.java:2560)
at java.util.Formatter.format(Formatter.java:2501)
at java.util.Formatter.format(Formatter.java:2455)
at java.lang.String.format(String.java:2928)
at memleak.TestMain$ButtonHandler.actionPerformed(TestMain.java:117)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6525)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6290)
at java.awt.Container.processEvent(Container.java:2234)
at java.awt.Component.dispatchEventImpl(Component.java:4881)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
at java.awt.Container.dispatchEventImpl(Container.java:2278)
at java.awt.Window.dispatchEventImpl(Window.java:2750)
at java.awt.Component.dispatchEvent(Component.java:4703)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
Exception in thread "AWT-EventQueue-0" java.lang.OutOfMemoryError: GC overhead limit exceeded
at javax.swing.text.GlyphPainter1.modelToView(GlyphPainter1.java:147)
at javax.swing.text.GlyphView.modelToView(GlyphView.java:653)
at javax.swing.text.CompositeView.modelToView(CompositeView.java:265)
at javax.swing.text.BoxView.modelToView(BoxView.java:484)
at javax.swing.text.ParagraphView$Row.modelToView(ParagraphView.java:900)
at javax.swing.text.CompositeView.modelToView(CompositeView.java:265)
at javax.swing.text.BoxView.modelToView(BoxView.java:484)
at javax.swing.text.CompositeView.modelToView(CompositeView.java:265)
at javax.swing.text.BoxView.modelToView(BoxView.java:484)
at javax.swing.plaf.basic.BasicTextUI$RootView.modelToView(BasicTextUI.java:1509)
at javax.swing.plaf.basic.BasicTextUI.modelToView(BasicTextUI.java:1047)
at javax.swing.text.DefaultCaret.repaintNewCaret(DefaultCaret.java:1308)
at javax.swing.text.DefaultCaret$1.run(DefaultCaret.java:1287)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)
Exception in thread "RMI TCP Connection(idle)" java.lang.OutOfMemoryError: GC overhead limit exceeded
at java.lang.Thread.getName(Thread.java:1135)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:677)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Detailed memory statistics show very high counts for java.awt.event.InvocationEvent
, sun.awt.EventQueueItem
, and javax.swing.text.DefaultCaret$1
(absent in the fixed version):
Setting FIX = true
did not improve the situation.
Both flags are true
:
Small test
Now shows that the caret position is not updated:
Stress test
Works and has no indication of memory leak:
The reason for this is that you are running the for loop in the event dispatch thread (see Event Dispatch Thread). This is the thread in which all user interface interactions happens.
If you are running a long task, then you should run it in a different thread, so that the user interface keeps responsive. If you need to make a change on the user interface, like changing text in your JTextPane and setting the caret position out of a different thread than the event dispatch thread, you need to invoke either
EventQueue.invokeLater()
orEventQueue.invokeAndWait()
(see EventQueue).I think the triggered events from setting the caret position are queued in your case and can only be processed, when the loop is finished (cause both are processed in event dispatch thread). So you should try something like this:
Might be even better if you call
EventQueue.invokeAndWait
only after x iterations and cache the previous results, which needs to be displayed.