	CS 580 Client-Server Programming Fall Semester, 2002 Threads & GUI
	Previous Lecture Notes Index Next © 2002, All Rights Reserved, SDSU & Roger Whitney San Diego State University -- This page last updated 24-Sep-02

Contents of Doc 9, Threads & GUI

References
http://java.sun.com/j2se/1.4.1/docs/api/javax/swing/SwingUtilities.html#invokeLater(java.lang.Runnable) for Swing

ForkedUI & ForkedUIExamples parcels, in other/parc directory in the VW7 installation, See ForkedUI parcel comment

Lecture Source Code Java

Class cvs repository module guiThread

Smalltalk

Class store repository package guiThread


Doc 9, Threads & GUI Slide # 2

Threads & GUIs

Swing & VisualWorks GUIs maintain an event queues

Only the GUI thread should add events to the queue

Odd things may happen if

A non-GUI thread adds an event to the event queue
And the GUI thread is using the event queue

In simple examples it is hard to cause the problem
In complex examples is it really hard to debug the problem


Doc 9, Threads & GUI Slide # 3

Swing Solution
Use SwingUtilities.invokeLater to run a thread to change a GUI element

For more information see:

javax.swing.SwingUtilities doc on method invokeLater

VisualWorks Solution
File in the ForkedUi parcel

In the others/parc directory of the VW 7 installation

Use Processor performUIBlock: to run a thread to change a GUI element

See ForkedUIExamples parcel for examples of use


Doc 9, Threads & GUI Slide # 4

Example

A window with:

A button
A label with the number of button clicks
A thread that increases the number of button clicks

Swing Window

VisualWorks Example

Doc 9, Threads & GUI Slide # 5

Swing Example

Swing code adapted from Sun on-line Swing Tutorial

import javax.swing.*;          
import java.awt.*;
import java.awt.event.*;
public class SwingApplication {
    private static String labelPrefix = "Number of button clicks: ";
    private int numClicks = 0;
    private UnSafeGUIAccess clock;
    private JLabel label;
    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel(
                UIManager.getCrossPlatformLookAndFeelClassName());
        } catch (Exception e) { }
        //Create the top-level container and add contents to it.
        JFrame frame = new JFrame("SwingApplication");
        SwingApplication app = new SwingApplication();
        Component contents = app.createComponents();
        frame.getContentPane().add(contents, BorderLayout.CENTER);
        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        frame.pack();
        frame.setVisible(true);
    }
  
Doc 9, Threads & GUI Slide # 6
  public Component createComponents() {
        label = new JLabel(labelPrefix + "0    ");
        JButton button = new JButton("I'm a Swing button!");
        button.setMnemonic(KeyEvent.VK_I);
        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                addClicks( 1);
            }
        });
        label.setLabelFor(button);
        clock = new UnSafeGUIAccess( this );
        clock.start();
        clock.secondsToSleep( 2);
        JPanel pane = new JPanel();
        pane.setBorder(BorderFactory.createEmptyBorder(
                                        30, //top
                                        30, //left
                                        10, //bottom
                                        30) //right
                                        );
        pane.setLayout(new GridLayout(0, 1));
        pane.add(button);
        pane.add(label);
        return pane;
    }
   public  synchronized void addClicks(int clicksToAdd) {
      numClicks = numClicks + clicksToAdd;
      label.setText(labelPrefix + numClicks);
   }
}
Doc 9, Threads & GUI Slide # 7

Unsafe Thread
This thread directly modifies a GUI element

See gui.addClicks( 1);

public class UnSafeGUIAccess extends Thread {
   private SwingApplication gui;
   int sleepMillseconds;
   public UnSafeGUIAccess(SwingApplication owner) {
      gui = owner;
      secondsToSleep( 1);
   }
   
   public void run() {
      try {
         while (true) {
         sleep( sleepMillseconds);
         gui.addClicks( 1);
         }
      } catch (InterruptedException interrupt) {
         //On interrupt end thread
      }
   }
   
   public void secondsToSleep(int seconds ) {
      sleepMillseconds = seconds * 1000;
   }
}


Doc 9, Threads & GUI Slide # 8

Safe Thread

import javax.swing.SwingUtilities;
public class SafeGUIAccess extends Thread {
   private SwingApplication gui;
   int sleepMillseconds;
   public SafeGUIAccess(SwingApplication owner) {
      gui = owner;
      secondsToSleep( 1);
   }
   
   public void run() {
      try {
         while (true) {
         sleep( sleepMillseconds);
         Runnable click = new Runnable() {
               public void run() {
                  gui.addClicks( 1);
               }
            };
         SwingUtilities.invokeLater(click);
         }
      } catch (InterruptedException interrupt) {
         //On interrupt end thread
      }
   }
   
   public void secondsToSleep(int seconds ) {
      sleepMillseconds = seconds * 1000;
   }
}
Doc 9, Threads & GUI Slide # 9

VisualWorks Unsafe Example

Smalltalk defineClass: #VisualWorksApplication
   superclass: #{UI.ApplicationModel}
   indexedType: #none
   private: false
   instanceVariableNames: 'clicks sleepSeconds '
   classInstanceVariableNames: ''
   imports: ''
   category: 'Examples-cs580'!
   
!VisualWorksApplication class methodsFor: 'interface specs'!
   
windowSpec
   "UIPainter new openOnClass: self andSelector: #windowSpec"
   <resource: #canvas>
   ^#(#{UI.FullSpec} 
      #window: 
      #(#{UI.WindowSpec} 
         #label: 'VW Application' 
         #bounds: #(#{Graphics.Rectangle} 682 378 956 576 ) ) 
      #component: 
      #(#{UI.SpecCollection} 
         #collection: #(
            #(#{UI.ActionButtonSpec} 
               #layout: #(#{Graphics.Rectangle} 57 22 138 45 ) 
               #name: #ActionButton1 
               #model: #buttonPressed 
               #label: 'Smalltalk button' 
               #defaultable: true ) 
            #(#{UI.LabelSpec} 
               #layout: #(#{Core.Point} 12 63 ) 
               #name: #Label1 
               #label: 'Number of button clicks:' ) 
            #(#{UI.InputFieldSpec} 
               #layout: #(#{Graphics.Rectangle} 136 63 214 87 ) 
               #name: #InputField1 
               #model: #clicks 
               #isReadOnly: true 
               #type: #number ) ) ) )


Doc 9, Threads & GUI Slide # 10

Unsafe Example Instance methods

buttonPressed
   ^self addClicks: 1
clicks
   ^clicks
   
initialize
   super initialize.
   clicks := 0 asValue.
   sleepSeconds :=2.
   self startClock
   
addClicks: anInteger
   clicks value: (clicks value + anInteger)
   
processPriority
   ^60
   
startClock
   clock := 
         [
         [(Delay forSeconds: sleepSeconds) wait.
         self addClicks: 1] repeat] 
               forkAt: self processPriority


Doc 9, Threads & GUI Slide # 11

VisualWorks Safe Example

Change the previous startClock method to the following:

startClock
   clock := 
         [
         [(Delay forSeconds: sleepSeconds) wait.
         Processor performUIBlock: [self addClicks: 1]] 
               repeat] 
               forkAt: self processPriority

Previous visitors since 24-Sep-02 Next