0, 10 , CENTER);
  }

  public void setLabel(String label)
  {
    newLabel(label);
    measure();
    repaint();
  }

  public void addNotify()
  {
    super.addNotify();
    measure();
  }

  public Dimension preferredSize()
  {
    return new Dimension(max_width + 2*mw,
                         numlines * lheight + 2 *mh);
  }

  public Dimension minimumSize()
  {
    return new Dimension(max_width,numlines * lheight);
  }

  public void paint(Graphics g)
  {
    int x, y;
    Dimension d= this.size();
    y = lascent + (d.height - numlines * lheight)/2;
    for ( int i =0; i<numlines; i++, y +=lheight)
    {
       switch(alignment)
       {
          case LEFT:
             x = mw;
             break;

          case CENTER:
          default:
             x = (d.width - lwidth[i])/2;
             break;

          case RIGHT:
             x = d.width - mw - lwidth[i];
             break;
       }
       g.drawString(lines[i],x,y);
     }
  }

}



Here are the code changes necessary to fix the problem:



DELTA: src/share/java/java/awt/EventDispatchThread.java (a112 1.2)
*** 1.1 Fri Sep 12 11:11:16 1997
--- 1.2 Fri Sep 12 11:11:17 1997
***************
*** 47,52 ****
--- 47,65 ----
  
      public void stopDispatching() {
          doDispatch = false;
+ // Interrupt the dispatch thread so we won't get stuck here /*ibm.2888*/
+ // if the thread is waiting for an event. /*ibm.2888*/
+ // There is a potential side-effect here of an event handler /*ibm.2888*/
+ // routine being interrupted. /*ibm.2888*/
+ interrupt(); /*ibm.2888*/
+ while (true) { /*ibm.2888*/
+ try { /*ibm.2888*/
+ join(); /*ibm.2888*/
+ break; /*ibm.2888*/
+ } /*ibm.2888*/
+ catch (InterruptedException e) { /*ibm.2888*/
+ } /*ibm.2888*/
+ } /*ibm.2888*/
      }
  
      public void run() {
***************
*** 72,77 ****
--- 85,92 ----
              } catch (ThreadDeath death) {
                  return;
  
+ // Simply loop if we get interrupted /* ibm.2888 */
+ } catch (InterruptedException interr) { /* ibm.2888 */
              } catch (Throwable e) {
                  System.err.println(
                      "Exception occurred during event dispatching:");

======================================================================


Name: mf23781 Date: 09/12/97


Race condition when modal dialog boxes are closed


Platform: All platforms

Version: 1.1.2 - and I believe it is still present in 1.1.4

Abstract: Race condition when modal dialog boxes are closed can
            cause horrible symptoms.


When a modal dialog box is closed, the following symptoms have been
observed on AIX:


1. a 'postEvent' method not found error.


2. a null pointer exception, like this:

Exception occurred during event dispatching:
java.lang.NullPointerException: sun.awt.motif.MFramePeer@300c8d48
        at sun.awt.motif.MComponentPeer.repaint(MComponentPeer.java:134)
        at java.awt.Component.repaint(Component.java:1159)
        at java.awt.Component.repaint(Component.java:1109)
        at java.awt.Window.dispatchEventImpl(Window.java:389)
        at java.awt.Component.dispatchEvent(Component.java:1393)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:63)


3. core dumps have also been reported.


During my investigations, I discovered that there is a race
condition that can occur when a modal dialog box is closed.

In src/share/java/java/awt/Dialog.java, in the show() method,
a new event dispatching thread is created for the modal dialog
box. The peer's show method is called, which blocks until
the dialog box is hidden. At this point, stopDispatching() is
called against the Dialog box's own dispatching thread, and
then control returns to the caller. If the caller of
Dialog.show() had been an event handler, then control goes
straight back to the original dispatching thread. The problem
with this is that the Dialog's thread has actually not
finished yet, so there is a potential race condition here.

One situation in which this causes a problem is a test case
in which a modal dialog box is opened from the event handler of
a button in a frame. This event handler calls the dialog's
show method and then disposes the frame. The idea is that when
the dialog box is closed, the frame underneath it is also
closed.

The dialog box is closed by a button method which disposes the
dialog. Now - a dispose starts by issuing a hide, which will
cause the modal dialog peer's show loop to exit - but, the
dispose is still happening. Control is returned to the caller
at this point, and the caller disposes the fame. Now, because
the dialog is a child of the frame, disposing the frame will
also dispose the dialog. Therefore, the dialog is disposed by
two threads at the same time.

The fix I have done here changes the stopDispatching() method
of java.awt.EventDispatchThread to block until the thread has
actually finished doing its job. This means that now no two
events can be processed at the same time. A dialog box's
removeNotify() method (actually in java.awt.Component) checks
the peer before disposing, so, as long as AWT objects are
only disposed by one thread at a time, there is no problem if
you try to dispose an object twice (the second dispose will
have no effect). So, with this fix, the test case will work
reliably.

Here is the test case (wMapAttrs). I'm sure it could be tidied
up a bit!

To use this test case, click on 'Create Mappings', and then
when the dialog box comes up, click on OK. Unfortunately the
problem happens quite rarely!
By mucking about with the AWT code, you can make it happen
more frequently. I would suggest adding a delay after each
pHide method in the C code (on Unix-derived platforms).


------ wMapAttrs.java

import java.awt.*;
import java.util.*;
import java.applet.*;

public
class wMapAttrs extends Frame {

        private static Applet applet;
        Hashtable menuitems = new Hashtable();
        Button pbtnCreateMap, pbtnCancel;
        //wMapAttrsgbxDEDSMap pgbxDEDSMap;

        // Initial size in logical units
        Dimension initialSize = new Dimension(335, 252);
        Point initialLocation;
        // zpb_begin wMapAttrsUserVars
        //RefinedDataSource pRDS;
        //RefinedDataEntity pRDE;
        // zpb_end

public static void main(String argv[])
{
  new wMapAttrs(null, "Hello").setVisible(true);
}

        // zpb_begin wMapAttrsJavadocConstructor
        /**
         * Creates a specialized window with the specified app and title.
         */
         // zpb_end
        wMapAttrs(Applet app, String title) {
                super(title);
                applet = app;

                // zpb_begin wMapAttrsConstructor_1
                // zpb_end

                setBackground(Color.lightGray);
                setFont(new Font("Sansserif", Font.PLAIN, 12));
                setLayout(new FlowLayout());

                //pgbxDEDSMap = new wMapAttrsgbxDEDSMap(applet, (Frame)getParent(), "");
                //add(pgbxDEDSMap);
                //pgbxDEDSMap.setFont(new Font("Sansserif", Font.PLAIN, 12));
                pbtnCreateMap = new Button(" Create Mappings ");
                add(pbtnCreateMap);
                pbtnCancel = new Button(" Cancel ");
                add(pbtnCancel);

                // Add the MenuBar, Menus, and Menuitems
                MenuBar mbMenu1 = new MenuBar();
                MenuItem mi;
                this.setMenuBar(mbMenu1);
                // zpb_begin wMapAttrsConstructor_2

                pbtnCreateMap.setLabel("Create Mappings");
                pbtnCancel.setLabel("Cancel");
                // zpb_end

                pack();

                // zpb_begin wMapAttrsConstructor_3
                // zpb_end
        }

        // zpb_begin wMapAttrsJavadocHandleEvent
        /**
         * Handle events that occur with components in this container.
         *
         * @return Returns a boolean which specifies whether the event
         * handler should stop at this level or continue up the
         * parent hierarchy.
         */
        // zpb_end
        public boolean handleEvent(Event e) {
                if (e.id == Event.WINDOW_DESTROY) {
                        // zpb_begin wMapAttrsDestroy
                        // zpb_end
                        dispose();
                        return true;
                }

                // zpb_begin wMapAttrsHandleEvent
                // zpb_end

                return super.handleEvent(e);
        }

        // zpb_begin wMapAttrsJavadocAction
        /**
         * Action handling routine.
         *
         * @return Returns a boolean specifying whether the event should be handled
         * furthur up the parent hierarchy.
         */
        // zpb_end
        public boolean action(Event evt, Object obj) {
                if (evt.target instanceof MenuItem) {

                        return false;
                }


                if (evt.target == pbtnCreateMap) {
                        // zpb_begin wMapAttrsbtnCreateMapClicked
                             boolean rc;
                   BDS_Context.showError(this);

                   dispose();

                 return true;
                        // zpb_end
                }
                else if (evt.target == pbtnCancel) {
                        // zpb_begin wMapAttrsbtnCancelClicked
                        dispose();
                        return false;
                        // zpb_end
                }

                // zpb_begin wMapAttrsAction
                // zpb_end

                return false;
        }


        // zpb_begin wMapAttrsUserMethods

}


------ BDS_Context.java

import java.awt.*;

public class BDS_Context
{

  public static void showError(Frame frame)
  {
    // TEMPORARY FIX: DON"T SHOW ANY MORE ERRORS IF COMMS FAILURE !!

    String newtitle="Hello, there!";
    String newmessage="And this is the message to be displayed.";
   
    //********************************************************
    // Make AIX error messages modal and Windows error messages
    // non-modal due to bugs in both JDK's
    //*********************************************************
    boolean modality ;
    String osName = System.getProperty("os.name");

    modality = true ;

    dlgError pdlgError = new dlgError(null,
                                      frame,
                                      newtitle,
                                      modality);

    pdlgError.setErrorMsg(newmessage);
    pdlgError.show();
  }
}


------ dlgError.java

import java.awt.*;
import java.util.*;
import java.applet.*;
//import com.roguewave.widgets.*;
// zpb_begin UserImports
//import ilsTextTable;
// zpb_end

/**
 * Class dlgError.
 *
 *
 * @author BDS Development Team
 * @version 1.0 12/05/96 10:46:02am
 * @copyright IBM
 */
public
class dlgError extends Dialog {

        private static Applet applet;
        Button pButton1;

        // Initial size in logical units
        Dimension initialSize = new Dimension(200, 200);
        Point initialLocation;
        // zpb_begin dlgErrorUserVars
        GridBagLayout gridbag;
        GridBagConstraints gbc;
        TextBox ptxtErr;
        // zpb_end

        // zpb_begin dlgErrorJavadocConstructor
        /**
         * Creates a specialized dialog with the specified app, parent, title and
         * modality.
         */
         // zpb_end
        dlgError(Applet app, Frame parent, String title, boolean modal) {
                super(parent, title, modal);
                applet = app;

                // zpb_begin dlgErrorConstructor_1
                 setResizable(true);
/***********
                // zpb_end

                // zpb_begin dlgErrorConstructor_2
***********/
                gridbag = new GridBagLayout();
                gbc = new GridBagConstraints();
                setFont(new Font("Sansserif", Font.PLAIN, 12));
                setLayout(gridbag);
/***********
                // zpb_end
                // Size and Position in logical units
                // zpb_begin dlgErrorConstructor_3
************/
                pack();
                // zpb_end
        }

        // zpb_begin dlgErrorJavadocMinimumSize
        /**
         * @return Returns a Dimension with the minimum width and height
         * of this container.
         */
         // zpb_end


        public Dimension minimumSize() {

        return gridbag.minimumLayoutSize(this);
    }

    public Dimension preferredSize() {

         return gridbag.preferredLayoutSize(this);
    }
        // zpb_begin dlgErrorJavadocHandleEvent
        /**
         * Handle events that occur with components in this container.
         *
         * @return Returns a boolean which specifies whether the event
         * handler should stop at this level or continue up the
         * parent hierarchy.
         */
        // zpb_end
        public boolean handleEvent(Event e) {
                if (e.id == Event.WINDOW_DESTROY) {
                        // zpb_begin dlgErrorDestroy
                        // zpb_end
                        dispose();
                        return true;
                }

                // zpb_begin dlgErrorHandleEvent
                // zpb_end

                return super.handleEvent(e);
        }

        // zpb_begin dlgErrorJavadocAction
        /**
         * Action handling routine.
         *
         * @return Returns a boolean specifying whether the event should be handled
         * furthur up the parent hierarchy.
         */
        // zpb_end
        public boolean action(Event evt, Object obj) {

                if (evt.target == pButton1) {
                        // zpb_begin dlgErrorButton1Clicked
                        // zpb_end
                        dispose();
                        return false;
                }

                // zpb_begin dlgErrorAction
                // zpb_end

                return false;
        }


        // zpb_begin dlgErrorUserMethods


        void setErrorMsg(String msg)
        {
        gbc.anchor = GridBagConstraints.CENTER;
        gbc.fill = GridBagConstraints.HORIZONTAL;
        gbc.ipadx = 50;
        gbc.ipady = 50;

        ptxtErr = new TextBox(msg);
        constrain(ptxtErr,
                  GridBagConstraints.REMAINDER,
                  1.0,1.0,
                  1,1,0,1);


        pButton1 = new Button("OK");
        Panel p = new Panel();
        p.setLayout(new FlowLayout(FlowLayout.CENTER,10,10));
        p.add(pButton1);
        pButton1.setLabel("OK");
        constrain(p,
                  GridBagConstraints.REMAINDER,
                  0.0,0.0,
                  0,0,0,0);
        initialLocation = gridbag.location(15,28);
                pack();
                move(initialLocation.x, initialLocation.y);
        }


        void constrain(Component comp,
                       int w,
                       double wx, double wy,
                       int top, int left, int bottom, int right)
        {
           gbc.gridwidth = w;

           // wx and wy are use to determine how much will a
           // component grow if the window is resized

           gbc.weightx = wx; gbc.weighty = wy;

           if (top+bottom+left+right > 0)
              gbc.insets = new Insets(top,left,bottom,right);

           gridbag.setConstraints(comp, gbc);
           add(comp);
       }
        // zpb_end
}


------ TextBox.java

import java.awt.*;
import java.util.*;

public class TextBox extends Canvas {
   public static final int LEFT = 0;
   public static final int CENTER = 1;
   public static final int RIGHT = 2;
   protected int alignment = CENTER;
   protected String[] lines;
   protected int numlines;
   protected int mw, mh; // margins
   protected int lheight, lascent;
   protected int[] lwidth;
   protected int max_width;



  // newLabel: breaks a label into an array of lines
  //
  protected void newLabel(String label) {
    StringTokenizer t =new StringTokenizer(label, "\n");
    numlines = t.countTokens();
    lines = new String[numlines];
    lwidth = new int[numlines];
    for(int i=0; i< numlines; i++)
       lines[i] = t.nextToken();
  }


  // measure : figures out how large the font is and how
  // wide each line of the label is.

  protected void measure() {
    FontMetrics fm= getFontMetrics(getFont());
    if (fm != null)
    {
       lheight = fm.getHeight();
       lascent = fm.getAscent();
       max_width = 0;
       for (int i=0; i< numlines; i++) {
          lwidth[i] = fm.stringWidth(lines[i]);
          if (lwidth[i] >max_width)
             max_width = lwidth[i];
       }
    }
  }


  // TextBox : Break up label into separate lines
  //
  public TextBox(String label, int w, int h , int alignment)
  {
     newLabel(label);
     mw = w;
     mh = h;
     this.alignment = alignment;
  }


  public TextBox(String label, int w, int h)
  {
    this(label, w, h , CENTER);
  }

  public TextBox(String label, int alignment)
  {
    this(label, 10, 10 , alignment);
  }

  public TextBox(String label)
  {
    this(label, 1