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Further Threads Programming

Further Threads Programming. Some Terminologies on Multithreading Example 1: Threads Synchronization Example 2: ‘Salaam Shabab’ Animation Example 3: Car Race Animation Example 4: Rocket Launching Animation. Some Terminologies on Multithreading.

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Further Threads Programming

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  1. Further Threads Programming • Some Terminologies on Multithreading • Example 1: Threads Synchronization • Example 2: ‘Salaam Shabab’ Animation • Example 3: Car Race Animation • Example 4: Rocket Launching Animation Unit 16

  2. Some Terminologies on Multithreading • Thread scheduling: arranging the threads to be executed in an order that they may take CPU control • Timeslice: The length of time for which a thread runs and this time may depend on the thread's priority or its use of resources such as memory and I/O • Preemption: to interrupt and suspend (“swap out”) the currently executing thread in order to start or continue running ("swap in") another thread • Synchronization: The process of ensuring that that a shared resource is used by only one of the many contending threads at any moment • Deadlock: A situation where two or more threads are unable to proceed because each is waiting for one of the others to do something • Starvation: indefinite postponement of the execution of lower-priority threads by higher-priority ones Unit 16

  3. Threads Synchronization • When a block of Java code guarded by the synchronized keyword, it can be executed by only one thread at any time • A shared resource (implemented by a given code segment) may be corrupted if it is accessed simultaneously by multiple threads. • E.g., unsynchronized threads accessing the same database • Such blocks of code are usually called critical sections and must be executed in a mutually-exclusive way • You can synchronize an entire method or just a few lines of code by using the synchronized keyword • Note that code that is thread-safe (i.e, guarded by synchronized) is slower than code that is not Unit 16

  4. Example 1: Threads Synchronization 1 class BanckAccount{ 2 private int balance; 3 public BanckAccount(int balance){ 4 this.balance = balance; 5 } 6 void doNothing(){ 7 depositWithdraw(10); 8 depositWithdraw(20); 9 depositWithdraw(30); 10 } 11 void depositWithdraw(int money){ 12 try { 13 balance += money; 14 Thread.sleep((long)(Math.random()*1000)); 15 balance -= money; 16 } catch(Exception e){} 17 } 18 int get(){ 19 return balance; 20 } 21 } Unit 16

  5. Example 1: Threads Synchronization (cont’d) 22 public class UnsafeBankAccount extends Thread{ 23 BanckAccount ba; 24 public static void main( String[] args ){ 25 BanckAccount ba = new 26 BanckAccount(0); 27 for(int i=0; i<9; i++) 28 new UnsafeBankAccount(ba).start(); 29 } 30 public UnsafeBankAccount(BanckAccount ba){ 31 this.ba = ba; 32 } 33 public void run(){ 34 doWork(); 35 } 36 public void doWork(){ 37 System.out.println(getName()+" got balance: "+ba.get()); 38 ba.doNothing(); 39 System.out.println(getName()+" got balance: "+ba.get()); 40 } 41 } • Make depositWithdraw() and get() synchronized to solve this problem Unit 16

  6. Example 2: ‘Salaam Shabab’ Animation 1 import java.awt.*; 2 import java.awt.event.*; 3 import javax.swing.*; 4 class AnimationPanel extends JPanel implements Runnable { 5 private Font myFont; 6 private int increment = 1; 7 public int xSize, ySize, yCoord = 0; 8 int delay; 9 Thread animator; 10 private boolean onOff=true; 11 public AnimationPanel(int delay) { 12 xSize=400; 13 ySize=350; 14 setSize(xSize, ySize); 15 myFont = new Font ("Serif", Font.ITALIC, 30); 16 animator = new Thread(this); 17 animator.start(); 18 } 19 public void setOnOff(boolean onOff) { 20 this.onOff = onOff; 21 } Unit 16

  7. Example 2: ‘Shabab’ Animation (cont’d) 22 public void paintComponent(Graphics g) { 23 super.paintComponent(g); 24 g.setColor(Color.yellow); 25 g.fillRect(0,0,xSize, ySize); 26 g.setColor (Color.red); 27 g.setFont(myFont); 28 if(onOff) { 29 g.drawString ("Salaam ", xSize/2-100, ySize/2 + yCoord); 30 g.drawString ("Shabab!", xSize/2, ySize/2 - yCoord); 31 } 32 } 33 public void run () { 34 while(true){ 35 yCoord = yCoord + increment;//yCoord min is -150 and max 150 36 if((yCoord == (ySize-50)/2 || (yCoord == -(ySize-50)/2))) 37 increment = -increment; // increment by -1 now 38 try{ 39 Thread.sleep(delay); 40 } catch(InterruptedException e){} 41 repaint(); 42 } 43 } 44 } Unit 16

  8. Example 2: ‘Shabab’ Animation (cont’d) 45 public class SalamShababAnimation extends JApplet{ 46 private Button myButton; 47 private boolean onOffButton = true; 48 private AnimationPanel ap; 49 public void init() { //validate parsing the parameter "fps" 50 int delay = Integer.parseInt(getParameter("fps")); 51 delay = (delay<10)? 10 : delay; 52 Container cp = getContentPane(); 53 cp.setLayout(new BorderLayout()); 54 ap = new AnimationPanel(delay); 55 myButton = new Button ("Start/Stop"); 56 myButton.addActionListener(new ActionListener(){ 57 public void actionPerformed(ActionEvent ae){ 58 onOffButton = !onOffButton; 59 ap.setOnOff(onOffButton); 60 }}); 61 cp.add(myButton,BorderLayout.NORTH); 62 cp.add(ap, BorderLayout.CENTER); 63 } 64 } Unit 16

  9. Example 3: Car Race Animation 1 import java.awt.*; 2 import java.awt.event.*; 3 import javax.swing.*; 4 import java.util.*; 5 class DrivingPanel extends JPanel implements Runnable { 6 private int delay; 7 private Thread animator; 8 private Image car; 9 static final int WIDTH = 600; 10 static final int HEIGHT = 200; 11 private int xPosition, speed; 12 private Random random; 13 public DrivingPanel(Image car, int delay) { 14 this.car = car; 15 this.delay = delay; 16 setSize(WIDTH,HEIGHT); 17 xPosition = getWidth(); 18 random = new Random(); 19 speed = random.nextInt(5);//+1; 20 animator = new Thread(this); 21 animator.start(); 22 } Unit 16

  10. Example 3: Car Race Animation (cont’d) 23 public void run() { 24 while (true) { 25 repaint(); 26 speed = random.nextInt(5)+1; 27 xPosition -= speed; 28 if (xPosition < -car.getWidth(this)) 29 xPosition = getWidth(); 30 try { 31 Thread.sleep(delay); 32 } catch (InterruptedException e) { 33 break; 34 } 35 } 36 } 37 public void paintComponent(Graphics g) { 38 super.paintComponent(g); 39 g.setColor(Color.white); 40 g.fillRect(0, 0, getWidth(), getHeight()); 41 g.drawImage(car, xPosition, getHeight()/2, this); 42 } 43 } Unit 16

  11. Example 3: Car Race Animation (cont’d) 44 public class CarRaceAnimation extends JApplet { 45 public void init() { // You should validate parsing the parameter! 46 int delay = Integer.parseInt(getParameter("fps")); 47 delay = (delay<10)? 10: delay; 48 Image car = getImage(getCodeBase(),"car.gif"); 49 DrivingPanel lane1 = new DrivingPanel(car, delay); 50 DrivingPanel lane2 = new DrivingPanel(car, delay); 51 Container cp = getContentPane(); 52 cp.setLayout(new GridLayout(2,1)); 53 cp.add(lane1); 54 cp.add(lane2); 55 } 56 } • Download the car image used in the example from here. • You can also obtain the rocket image for the next example. Unit 16

  12. Example 4: Rocket Launcher 1 import java.applet.*; 2 import java.awt.*; 3 import java.awt.event.*; 4 import javax.swing.*; 5 public class RocketLauncher extends JApplet implements Runnable, ActionListener { 6 private Image rocket; 7 private int x, y, sec=10; 8 private Thread myThread; 9 private Timer timer = new Timer(1000,this); 10 JTextField tf = new JTextField(5); 11 JButton b = new JButton("Start Count Down"); 12 public void init() { 13 rocket = Toolkit.getDefaultToolkit().getImage("rocket.jpg"); 14 x = 50; 15 y = getSize().height-rocket.getHeight(this)-380; 16 myThread = new Thread(this); 17 tf.setText(" "+sec+" "); 18 b.addActionListener(this); 19 } Unit 16

  13. Example 4: Rocket Launcher (cont’d) 20 public void actionPerformed( ActionEvent ae) { 21 if(ae.getSource() == b) 22 timer.start(); 23 if(ae.getSource() == timer) 24 if(--sec>0) 25 tf.setText(" "+sec+" "); 26 else{ 27 timer.stop(); 28 myThread.start(); 29 } 30 } 31 public void run() { 32 while (y-- != -rocket.getHeight(this)) { 33 try { 34 myThread.sleep(10); 35 } catch (InterruptedException e) {} 36 repaint(); 37 } 38 } 39 public void update(Graphics g){ 40 paint(g); 41 } Unit 16

  14. Example 4: Rocket Launcher (cont’d) 42 public void paint(Graphics g) { 43 g.drawImage(rocket,x,y,null); 44 } 45 public static void main(String [] args){ 46 JFrame frame = new JFrame("My Rocket Launch Pad"); 47 frame.setSize(400,750); 48 Container cp = frame.getContentPane(); 49 cp.setLayout(new GridLayout(1,2)); 50 JPanel p = new JPanel(); 51 JPanel p1 = new JPanel(); 52 p.setLayout(new BoxLayout(p,BoxLayout.Y_AXIS)); 53 RocketLauncher applet = new RocketLauncher(); 54 p.add(applet.b); 55 p1.add(applet.tf); 56 p.add(p1); 57 cp.add(p); 58 applet.setBackground(Color.white); 59 cp.add(applet); 60 frame.setVisible(true); 61 applet.init(); 62 } 63 } Unit 16

  15. Exercises • Modify Example 2 so that when the animation is stopped, the strings Salaam and Shabab remain displayed on the animation screen. • Improve the car race animation by • Adding a button to control when to start the next race • Incorporating up to four cars in the race • Displaying the winning car after every race • Incorporating different car models • Modify each of the preceding examples so that each of them can work as an applet as well as a standalone application. Unit 16

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