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From "Vasily Zakharov (JIRA)" <j...@apache.org>
Subject [jira] Created: (HARMONY-4762) [classlib][swing][html] Flaw in thread synchronization in BasicTextUI
Date Fri, 07 Sep 2007 15:24:30 GMT
[classlib][swing][html] Flaw in thread synchronization in BasicTextUI
---------------------------------------------------------------------

                 Key: HARMONY-4762
                 URL: https://issues.apache.org/jira/browse/HARMONY-4762
             Project: Harmony
          Issue Type: Bug
          Components: Classlib
            Reporter: Vasily Zakharov


javax.swing.plaf.basic.BasicTextUI has a synchronization mechanism implemented in readLock()/readUnlock()
methods. These methods forward the calls to the corresponding methods of AbstractDocument
class instance in document field.

This mechanism has a flaw - sometimes the document field gets replaced by another thread between
calls to readLock() and readUnlock(). This makes the readUnlock() call to fail.

Here's the simple reproducer:

import javax.swing.JEditorPane;
import javax.swing.JFrame;
public class Test {
    public static void main(String argv[]) {
        try {
            JFrame frame = new JFrame("Test");
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setSize(100, 100);
            JEditorPane pane = new JEditorPane();
            frame.add(pane);
            frame.setVisible(true);
            pane.setPage("file:test.html");
        } catch (Throwable e) {
            e.printStackTrace(System.out);
        }
    }
}

test.html should exist in current directory and may be empty.

This test produces the following exception on Harmony: 

java.lang.Error: This thread doesn't hold read lock.
        at javax.swing.text.AbstractDocument$ReadWriteLock.readUnlock(AbstractDocument.java:868)
        at javax.swing.text.AbstractDocument.readUnlock(AbstractDocument.java:1142)
        at javax.swing.plaf.basic.BasicTextUI.readUnlock(BasicTextUI.java:114)
        at javax.swing.plaf.basic.BasicTextUI.paintSafely(BasicTextUI.java:844)
        at javax.swing.plaf.basic.BasicTextUI.paint(BasicTextUI.java:88)
        at javax.swing.plaf.ComponentUI.update(ComponentUI.java:38)
        at javax.swing.plaf.basic.BasicTextUI.update(BasicTextUI.java:956)
        at javax.swing.JComponent.paintComponent(JComponent.java:897)
        at javax.swing.JComponent.paint(JComponent.java:994)
        at javax.swing.JComponent.paintDoubleBuffered(JComponent.java:1425)
        at javax.swing.JComponent.paintImmediately(JComponent.java:156)
        at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:186)
        at javax.swing.RepaintManager$1.run(RepaintManager.java:80)
        at java.awt.event.InvocationEvent.runAndNotify(InvocationEvent.java:98)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:78)
        at java.awt.EventQueueCore.dispatchEventImpl(EventQueueCore.java:138)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:144)
        at java.awt.EventDispatchThread.runModalLoop(EventDispatchThread.java:74)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:48)

The AbstractDocument instance mentioned on top of this stack is not the instance readLock()
was called for.

The error is intermittent and occurs not so often. To make it stable, one can add Thread.sleep(100)
call to javax.swing.text.html.BlockView.paint() method as follows:

    public void paint(final Graphics g, final Shape allocation) {
        Rectangle rc = allocation.getBounds();
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {}
        boxPainter.paint(g, rc.x, rc.y, rc.width, rc.height, this);
        super.paint(g, allocation);
    }

This change doesn't alter the code logic, but slows it down and makes the error to show off
much more often.

This issue was discovered while investigating HARMONY-4755.


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