The following program produces a crash when the detach
and reattach button are pressed repeatedly.

Running on a Pentium 166MHz PC with 32 Mb or RAM.



import java.awt.*;
import java.awt.event.*;

/**
* @author Michael Averbukh
*/
public
class CBWindow
extends Frame
{
public
CBWindow()
{ super.setTitle("main window");
setLayout( new BorderLayout() );
addWindowListener( new WindowAdapt() );
setBounds( 100 , 100, 400, 300 );
createPanel();
}

class WindowAdapt
extends WindowAdapter
{
public void
windowClosing( WindowEvent event )
{ System.exit(0);
}
}

public void
createPanel()
{ cbpanel = new CBPanel( this );
add( "Center", cbpanel );
setVisible( true );
}

public synchronized void
createFrame()
{ remove( cbpanel );
cbframe = new CBFrame( this );
cbframe.setVisible( true );
}

private CBPanel cbpanel;
private CBFrame cbframe;

public static void
main( String[] args )
{ new CBWindow();
}
}

class CBPanel
extends Panel
implements ActionListener
{
CBPanel( CBWindow parent )
{ this.parent = parent;
setLayout( new BorderLayout(10,10) );

detachButton = new Button( "Detach Window" );
detachButton.addActionListener( this );
Label label = new Label("Panel");
label.setAlignment( Label.CENTER );

Panel headerPanel = new Panel();
headerPanel.setLayout( new BorderLayout() );
headerPanel.add( "West", detachButton );
headerPanel.add( "Center", label );
add( "North", headerPanel );
}

public void
actionPerformed( ActionEvent event )
{ Object source = event.getSource();
if ( source == detachButton )
{ parent.createFrame();
}
}

private Button detachButton;
private CBWindow parent;
}

class CBFrame
extends Frame
implements ActionListener
{
CBFrame( CBWindow parent )
{ super.setTitle("Frame");
this.parent = parent;
setLayout( new BorderLayout(10,10) );

reattachButton = new Button( "Reattach Window" );
reattachButton.addActionListener( this );
Label label = new Label("Frame");
label.setAlignment( Label.CENTER );

Panel headerPanel = new Panel();
headerPanel.setLayout( new BorderLayout() );
headerPanel.add( "West", reattachButton );
headerPanel.add( "Center", label );
add( "North", headerPanel );

addWindowListener( new WindowAdapt() );
setBounds( 100 , 100, 300, 200 );
}

class WindowAdapt
extends WindowAdapter
{
public void
windowClosing( WindowEvent event )
{ setVisible( false );
hide();
System.out.println( "WindowAdapt(): Exiting Frame" );
}
}

public void
actionPerformed( ActionEvent event )
{ Object source = event.getSource();
if ( source == reattachButton )
{ parent.createPanel();
setVisible( false );
hide();
System.out.println( "actionPerformed(): Exiting Frame" );
}
}

public synchronized void
finalize()
{
System.out.println("CAlling dispose from finalizer");
dispose();
}

private Button reattachButton;
private CBWindow parent;
}
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>


After further investigating into this issue, I believe that this problem is not with dispose... Actually dispose() in the above code never gets executed. It is also not with the hide() that gets called/executed in the actionPerformed event loop, as shown above in the code snippet.

There is the problem with calling the method remove() within AWT enviornment... the method remove(cbpanel) that gets called in createFrame() of the above code snippet, causes lock/crash.

The symptom of the problem is that AWT causes GPF (General Protection Fault) as page fault, with the alert dialog displayed "The program has performed an illegal operation and will be shut down" (that sometimes requires rebooting of the system, mostly ctrl C will let you exit out of the app).
 
The above code was tested by replacing hide() with dispose() (in the action event loop) and the code still fails at remove(cbpanel). You may put the debug strings before and after calling remove(cbpanel) and witness the problem behaviour.

sandhya.vora@Eng 1997-07-10
sandhya.vora@Eng 1997-07-10