rwsem.java

Reader Writer Problem to solve synchronization issues

import java.applet.*;
import java.awt.*;
import java.net.*;

public class RWSem extends Applet {

  private Semaphore[] flags = new Semaphore[5];
  private Semaphore mutx = new Semaphore(1);
  private Semaphore dbs = new Semaphore(1);
  private Data_base database = new Data_base(1);
  private static Boolean[] continuous;
//  private static Integer rrc;
  private static int rrc;
  private Thread[] threads;

  private About frame;

  
  private Button[] step_button;
  private Button[] ctrl_button;
  private Button about;

  private CodeWin reader_win, writer_win;
  private Gui gui_win;
  private Scrollbar sbar;
  private Label	lab;

  private int	scl;

  private Image[] rwimg;
  private Image[] otherimg;
  private Image[] rimg;
  private Image[] wimg;
  
  static final String img_path = 
    "http://www.site.gmu.edu/~apolavar/java_html/kevin/";

  static String[] reader_text = {
    "while (TRUE) {",
    "  down(mutex);",
    "  ++rc;",
    "  if (rc == 1)",
    "    down(db);",
    "  up(mutex);",
    "  read_db();",
    "  down(mutex);",
    "  --rc;",
    "  if (rc == 0);",
    "    up(db);",
    "  up(mutex)};",
    };

  static String[] writer_text = {
    "while (TRUE) {",
    "  create_data();",
    "  down(db);",
    "  write_db();",
    "  up(db);",
    "}"
    };

  public void init() {
    super.init();

    // Use a grid layout for the applet
    setLayout(new GridLayout(2,1));

    Panel pan =new Panel();
    pan.setLayout(new FlowLayout(FlowLayout.CENTER));

    // Create a panel to hold step buttons for the readers,
    // use a grid layout for it
    Panel pr = new Panel();
    pr.setLayout(new GridLayout(3, 1));

    // Create a panel to hold step buttons for the writers,
    // use a grid layout for it
    Panel pw = new Panel();
    pw.setLayout(new GridLayout(2, 1));

    // Create an array of buttons
    step_button = new Button[5];

    // A red reader "Step" button
    step_button[0] = new Button("R1 Step");
    step_button[0].setForeground(Color.white);
    step_button[0].setBackground(Color.red);

    // A green reader "Step" button
    step_button[1] = new Button("R2 Step");
    step_button[1].setForeground(Color.black);
    step_button[1].setBackground(Color.green);

    // A blue reader "Step" button
    step_button[2] = new Button("R3 Step");
    step_button[2].setForeground(Color.white);
    step_button[2].setBackground(Color.blue);

    // A red writer "Step" button
    step_button[3] = new Button("W1 Step");
    step_button[3].setForeground(Color.white);
    step_button[3].setBackground(Color.red);

    // A blue writer "Step" button
    step_button[4] = new Button("W2 Step");
    step_button[4].setForeground(Color.white);
    step_button[4].setBackground(Color.blue);

    // add the buttons to the appropriate panels
    pr.add(step_button[0], 0);
    pr.add(step_button[1], 1);
    pr.add(step_button[2], 2);
    pw.add(step_button[3], 0);
    pw.add(step_button[4], 1);

    // Create the main control panel, and use a grid layout for it
    Panel cp = new Panel();
    cp.setLayout(new FlowLayout(FlowLayout.CENTER));

    // Create an array of buttons for the main control panel
    ctrl_button = new Button[4];
    
    // The "universal" step button
    ctrl_button[0] = new Button("Step All");
    
    // The go button
    ctrl_button[1] = new Button("Continue");

    // The stop button
    ctrl_button[2] = new Button("Stop");

    // The reset button
    ctrl_button[3] = new Button("Reset");

      /*-----------------------------------------------------*/
    // The about button
    about= new Button("About");
          frame = new About();
      /*-----------------------------------------------------*/


   sbar = new Scrollbar(Scrollbar.HORIZONTAL);
   sbar.setValues(10,3,5,15);
   sbar.setPageIncrement(3);

	Panel scrollpanel= new Panel();
	scrollpanel.setLayout(new BorderLayout());

   	lab=(new Label("10"));
   	scrollpanel.add("Center",sbar);

    // Add these buttons to the control panel
    cp.add(ctrl_button[0]);
    cp.add(ctrl_button[1]);
    cp.add(ctrl_button[2]);
    cp.add(ctrl_button[3]);
    cp.add(scrollpanel);
    cp.add(lab);
    cp.add(new Label("Speed"));
    cp.add(about);



    // Load images for the reader and writer markers (in the code window)
    rimg = new Image[3];
    rimg[0] = getImage(getCodeBase(), "rd_ball.gif");
    rimg[1] = getImage(getCodeBase(), "gr_ball.gif");
    rimg[2] = getImage(getCodeBase(), "bl_ball.gif");

    wimg = new Image[2];
    wimg[0] = rimg[0];
    wimg[1] = rimg[2];

    // create a reader and writer code window
    reader_win = new CodeWin(3, reader_text, rimg);
    writer_win = new CodeWin(2, writer_text, wimg);


   pan.add(pr);
   pan.add(reader_win);
   pan.add(writer_win);
   pan.add(pw);
   pan.add(cp);

    rwimg = new Image[5];
    rwimg[0] = getImage(getCodeBase(), "bookred.gif");
    rwimg[1] = getImage(getCodeBase(), "bookgreen.gif");
    rwimg[2] = getImage(getCodeBase(), "bookblue.gif");
    rwimg[3] = getImage(getCodeBase(), "pencil_red.gif");
    rwimg[4] = getImage(getCodeBase(), "pencil_blue.gif");
	
    otherimg = new Image[5];
    otherimg[0] = getImage(getCodeBase(),"mutexunlock.gif"); 
    otherimg[1] = getImage(getCodeBase(),"mutexlock.gif"); 
    otherimg[2] = getImage(getCodeBase(),"dbunlock.gif"); 
    otherimg[3] = getImage(getCodeBase(),"dblock.gif"); 
    otherimg[4] = getImage(getCodeBase(),"textbox.gif"); 


    gui_win = new Gui(rwimg,otherimg);

   add(gui_win);
   add(pan);

    // Create and initialize the global rc
//    rrc = new Integer(0);
    rrc = 0; 

    // create and initialize the continuous flag
    continuous = new Boolean[1];
    continuous[0] = Boolean.FALSE;

    // Create an array of control flags
    for (int i = 0; i < 5; ++i)
      flags[i] = new Semaphore(0);
    
    // Create the reader and writer threads
    threads = new Thread[5];
    threads[0] = new ReaderThread(0, flags, continuous, rrc,mutx,dbs,database, reader_win,gui_win);
    threads[1] = new ReaderThread(1, flags, continuous, rrc,mutx,dbs,database, reader_win,gui_win);
    threads[2] = new ReaderThread(2, flags, continuous, rrc,mutx,dbs,database, reader_win,gui_win);
    threads[3] = new WriterThread(3, flags, continuous, dbs,database, writer_win,gui_win);
    threads[4] = new WriterThread(4, flags, continuous, dbs,database, writer_win,gui_win);

    threads[0].start();
    threads[1].start();
    threads[2].start();
    threads[3].start();
    threads[4].start();
  }

  public boolean handleEvent(Event evt){
 
    if(evt.id==Event.SCROLL_ABSOLUTE
	|| evt.id == Event.SCROLL_LINE_DOWN
	|| evt.id == Event.SCROLL_LINE_UP
	|| evt.id == Event.SCROLL_PAGE_DOWN
	|| evt.id == Event.SCROLL_PAGE_UP)
     {
 
    scl = ((Scrollbar)evt.target).getValue();
    lab.setText(String.valueOf(scl));
	gui_win.updatescale(scl);
    }
 
    return super.handleEvent(evt);
   }

  public boolean action(Event e, Object arg) 
  {
        if (e.target == about)
        {
        if(!frame.isShowing())
         {
          frame.resize(300,300);
          frame.show();
         }
        }

    for (int i = 0; i < 5; ++i) 
      {
      	if (e.target == step_button[i] &&
	  continuous[0].booleanValue() == false) 
	{
		if(i<3) gui_win.rc_reset();
		flags[i].up();
		return true;
        }
      }

    if (e.target == ctrl_button[0] &&
	continuous[0].booleanValue() == false) 
      {
      	for (int i = 0; i < 5; ++i) 
	{
		flags[i].up();
		if(i<3) gui_win.rc_reset();
        }
      	return true;
      }

    if (e.target == ctrl_button[1] &&
	continuous[0].booleanValue() == false) 
    {
      	continuous[0] = Boolean.TRUE;
      	for (int i = 0; i < 5; ++i) 
	{
		flags[i].up();
        }
      	return true;
    }

    if (e.target == ctrl_button[2] &&
	continuous[0].booleanValue() == true) {
      continuous[0] = Boolean.FALSE;
      return true;
    }

    if (e.target == ctrl_button[3]) {
      // add code to handle the reset button here

	for (int i = 0; i < 5; ++i) threads[i].stop();


	rrc=0;

  // create and initialize the continuous flag
    continuous = new Boolean[1];
    continuous[0] = Boolean.FALSE;

 	// Create an array of control flags
	for (int i = 0; i < 5; ++i)
     		flags[i]=new Semaphore(0);

	dbs= new Semaphore(1);
	mutx= new Semaphore(1);
	database.reset();

	sbar.setValues(10,3,5,15);
	sbar.setPageIncrement(3);
 
    	lab.setText("10");


// Create the reader and writer threads
//    threads = new Thread[5];
    threads[0] = new ReaderThread(0, flags, continuous, rrc,mutx,dbs,database, reader_win,gui_win);
    threads[1] = new ReaderThread(1, flags, continuous, rrc,mutx,dbs,database, reader_win,gui_win);
    threads[2] = new ReaderThread(2, flags, continuous, rrc,mutx,dbs,database, reader_win,gui_win);
    threads[3] = new WriterThread(3, flags, continuous, dbs,database, writer_win,gui_win);
    threads[4] = new WriterThread(4, flags, continuous, dbs,database, writer_win,gui_win);
 
    threads[0].start();
    threads[1].start();
    threads[2].start();
    threads[3].start();
    threads[4].start();

	gui_win.reset();
	reader_win.reset();
	writer_win.reset();	

      return true;
    }
    
    return false;
  }
  
}