java - 如何防止 JTextPane.setCaretPosition(int) 中的内存泄漏？

Question

我正在使用基于 Swing 的 GUI 开发 Java 应用程序。该应用程序使用 JTextPane 输出日志消息，如下所示:1) 截断现有文本以使总文本大小保持在限制范围内； 2)追加新文本； 3) 滚动到最后(实际逻辑略有不同，但此处无关紧要)。

我在使用 Eclipse 和 JVM Monitor 来确定合理的文本大小限制时发现了严重的内存泄漏。我试图从底层文档中删除 UndoableEditListener 并禁用自动插入符号位置更新(通过使用 DefaultCaret.NEVER_UPDATE 和 JTextPane.setCaretPosition(int) 显式更改位置) )，但没有成功。最后，我决定完全禁用更改插入符位置，这修复了漏洞。

我有两个问题:

1. 我的代码有问题吗？如果是，我该如何改变它来完成任务？

2. 它是 Swing/JVM 错误吗？如果是，我该如何举报？

详情:

这是 SSCCE:带有 textPane 和两个按钮的 GUI，用于小型测试和压力测试。 FIX 和 FIXXX 标志对应于我修复内存泄漏的尝试。

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 来自用于 Linux x64 的官方 Oracle Java SE 开发工具包 8u45。所有测试均在 -Xmx100m 限制条件下完成。

两个标志都是false:

小测试

按预期工作:

压力测试

GUI 在中间点卡住:

内存泄漏:

有时内存不足，我收到以下错误:

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)

详细的内存统计显示 java.awt.event.InvocationEvent、sun.awt.EventQueueItem 和 javax.swing.text.DefaultCaret 的计数非常高$1(固定版本中不存在):

设置 FIX = true 并没有改善这种情况。

两个标志都是true:

小测试

现在显示插入符位置未更新:

压力测试

工作并且没有内存泄漏的迹象:

Answer 1

这样做的原因是您在事件分派(dispatch)线程中运行 for 循环(参见 Event Dispatch Thread)。这是发生所有用户界面交互的线程。

如果您正在运行一个长任务，那么您应该在不同的线程中运行它，以便用户界面保持响应。如果您需要在用户界面上进行更改，例如更改 JTextPane 中的文本以及将插入符号位置设置在与事件分发线程不同的线程之外，您需要调用 EventQueue.invokeLater() 或 EventQueue.invokeAndWait()(参见 EventQueue)。

我认为设置插入符号位置的触发事件在您的情况下排队并且只能在循环完成时处理(因为两者都在事件调度线程中处理)。所以你应该尝试这样的事情:

@Override
public void actionPerformed(ActionEvent e)
{
  new Thread(new Runnable() {
    @Override
    public void run() {
      for (int i = 0; i < iter; i++)
      {
        final String display = String.format("%10d\n", i);
        try {
          EventQueue.invokeAndWait(new Runnable() {
            @Override
            public void run() {
              append(display);
            }
          });
        } catch (Exception e) {
          e.printStackTrace();
        }
      } // end for i
    }
  }).start();
} 

如果仅在 x 次迭代后调用 EventQueue.invokeAndWait 并缓存需要显示的先前结果，可能会更好。