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Bug ID: 6789085 Applet Deadlock During Initialization
6789085 : Applet Deadlock During Initialization

Details
Type:
Bug
Submit Date:
2008-12-25
Status:
Closed
Updated Date:
2011-01-26
Project Name:
JDK
Resolved Date:
2009-02-06
Component:
deploy
OS:
windows_xp
Sub-Component:
plugin
CPU:
x86
Priority:
P3
Resolution:
Fixed
Affected Versions:
6
Fixed Versions:
6u14

Related Reports

Sub Tasks

Description
FULL PRODUCT VERSION :
all Java 1.6.x versions

ADDITIONAL OS VERSION INFORMATION :
Windows XP and Windows Vista

A DESCRIPTION OF THE PROBLEM :
We observe an occasional deadlock during applet initialization. Using JConsole, we see that the AWT-EventQueue-0 thread is deadlocked with the applet initialization thread. The stack trace shows the deadlock occurs before our applet code. It's during the construction of the JApplet. Here's the stack trace of both threads:

Name: Thread-39
State: BLOCKED on sun.awt.windows.WDesktopProperties@2a3135 owned by:
AWT-EventQueue-0
  Total blocked: 1  Total waited: 0

Stack trace:
sun.awt.windows.WDesktopProperties.removePropertyChangeListener(Unknown Source)
sun.awt.windows.WToolkit.removePropertyChangeListener(Unknown Source)
   - locked sun.awt.windows.WToolkit@19616c7
javax.swing.plaf.metal.MetalLookAndFeel$AATextListener.dispose(Unknown Source)
javax.swing.plaf.metal.MetalLookAndFeel.flushUnreferenced(Unknown Source)
javax.swing.plaf.metal.MetalLookAndFeel.initComponentDefaults(Unknown Source)
javax.swing.plaf.basic.BasicLookAndFeel.getDefaults(Unknown Source)
javax.swing.plaf.metal.MetalLookAndFeel.getDefaults(Unknown Source)
javax.swing.UIManager.setLookAndFeel(Unknown Source)
javax.swing.UIManager.setLookAndFeel(Unknown Source)
javax.swing.UIManager.initializeDefaultLAF(Unknown Source)
javax.swing.UIManager.initialize(Unknown Source)
javax.swing.UIManager.maybeInitialize(Unknown Source)
   - locked java.lang.Object@1c8c58
javax.swing.UIManager.getUI(Unknown Source)
javax.swing.JPanel.updateUI(Unknown Source)
javax.swing.JPanel.<init>(Unknown Source)
javax.swing.JPanel.<init>(Unknown Source)
javax.swing.JPanel.<init>(Unknown Source)
javax.swing.JRootPane.createGlassPane(Unknown Source)
javax.swing.JRootPane.<init>(Unknown Source)
javax.swing.JApplet.createRootPane(Unknown Source)
javax.swing.JApplet.<init>(Unknown Source)
com.adaptiveplanning.ui.desktop.aptreetable.APTreeTableApplet.<init>(APTreeTableApplet.java:40)
sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
java.lang.reflect.Constructor.newInstance(Unknown Source)
java.lang.Class.newInstance0(Unknown Source)
java.lang.Class.newInstance(Unknown Source)
sun.applet.AppletPanel.createApplet(Unknown Source)
sun.plugin.AppletViewer.createApplet(Unknown Source)
sun.applet.AppletPanel.runLoader(Unknown Source)
sun.applet.AppletPanel.run(Unknown Source)
java.lang.Thread.run(Unknown Source)

------------------------------------------------------------------------------

Name: AWT-EventQueue-0
State: BLOCKED on java.lang.Object@1c8c58 owned by: Thread-39
  Total blocked: 1  Total waited: 0

Stack trace:
javax.swing.UIManager.maybeInitialize(Unknown Source)
javax.swing.UIManager.getLookAndFeel(Unknown Source)
com.sun.java.swing.plaf.windows.DesktopProperty$WeakPCL.propertyChange(Unknown
Source)
java.beans.PropertyChangeSupport.firePropertyChange(Unknown Source)
java.beans.PropertyChangeSupport.firePropertyChange(Unknown Source)
java.beans.PropertyChangeSupport.firePropertyChange(Unknown Source)
sun.awt.windows.WDesktopProperties.diffPropertyChanges(Unknown Source)
   - locked sun.awt.windows.WDesktopProperties@2a3135
sun.awt.windows.WDesktopProperties.access$100(Unknown Source)
sun.awt.windows.WDesktopProperties$DiffPropertyChanges.run(Unknown Source)
java.awt.event.InvocationEvent.dispatch(Unknown Source)
java.awt.EventQueue.dispatchEvent(Unknown Source)
java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
java.awt.EventDispatchThread.pumpEvents(Unknown Source)
java.awt.EventDispatchThread.pumpEvents(Unknown Source)
java.awt.EventDispatchThread.run(Unknown Source)


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
This happens intermittently as the apple loads in the IE browser

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
No deadlock
ACTUAL -
Sometimes deadlocks

REPRODUCIBILITY :
This bug can be reproduced occasionally.

Comments
SUGGESTED FIX

http://sa.sfbay.sun.com/projects/deployment_data/6u14/6789085.0
2009-01-09 
EVALUATION

The deadlock during applet construction is caused by creation of the
JApplet on a thread which is not the Event Dispatch Thread.
Unfortunately for compatibility reasons the init(), start(), stop(),
and destroy() methods of applets are not called on the EDT. However,
it seems that construction of the Applet object can probably safely be
moved on to the EDT, since in the new Java Plug-In the code for
resizing the applet and placing it in its containing frame was
rewritten and moved on to the EDT for thread safety.

This fix is only being made for the new Java Plug-In because the old
Java Plug-In is very fragile in this area and we do not want to
introduce risk for customers relying on it for compatibility reasons.

An attempt was made to write a targeted test for this change, but this
attempt was unsuccessful; the original race condition is hard to
provoke. For this reason there is no explicit test case for this bug.

Tested with the Pogo.com applets, NeuroDNA's NeuroKernel, the JavaFX
samples, and other applets.
2009-01-09 
EVALUATION

Swing is a single-threaded toolkit, 
obviously plugin doesn't call JApplet.init() on Event Dispatch Thread

there are two solutions for this problem:

1) User should wrap all Swing related code in JApplet.init() method
with SwingUtilities.invokeAndWait() or invokeLater()

2) Plugin calls JApplet.init() on the correct thread

reassign to the plugin team
2008-12-25 
EVALUATION

Plugin team commented that they aware of the fact that Applet in initialized
in incorrect thread and it can't be changed for compatibility reasons,
so the only option for user is to create all Swing components on the right thread manually like we require for standalone applications
2008-12-25 
EVALUATION

Here is the standard pattern for Swing standalone applications

public class Pattern {

    private static void createGui() {
        final JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.setSize(200, 200);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) throws Exception {
        SwingUtilities.invokeAndWait(new Runnable() {
            public void run() {
                Pattern.createGui();
            }
        });
    }
}
2008-12-25


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