// playing with synchronized threads...
//
// recommended size: 200h, 200w
// last modified: 3-26-01

import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;

public class TrySync extends Applet implements Runnable, ActionListener
{
        Thread          readIt, catchIt;
        TextField       readField;
        Label           readLabel, catchLabel;
        boolean         startReadIt;

        final Object token = "token";

        public void init()
        {
                setBackground(Color.lightGray);

                Label readFieldInstr = new Label("type stuff here: ");
                add(readFieldInstr);
                readField = new TextField(15);
                readField.setText("");
                readField.addActionListener(this);
                add(readField);
                
                Label readBlurb = new Label("readIt read: ");
                add(readBlurb);
                readLabel = new Label();
                readLabel.setText("                                      ");
                readLabel.setBackground(Color.cyan);
                add(readLabel);

                Label catchBlurb = new Label("catchIt caught: ");
                add(catchBlurb);
                catchLabel = new Label();
                catchLabel.setText("                                     ");
                catchLabel.setBackground(Color.yellow);
                add(catchLabel);

                startReadIt = false;
        }

        public void start()
        {
                if (readIt == null)
                { 
                        readIt = new Thread(this);
                        readIt.start();
                }

                if (catchIt == null)
                { 
                        catchIt = new Thread(this);
                        catchIt.start();
                }
        }

        public void run()
        {
                Thread  execThread;

                execThread = Thread.currentThread();
                
                while (true)
                {
                        // readIt loops with resource1 locked until
                        // text entered into readField causes
                        // startReadIt to be set to true;
                        if (execThread == readIt)
                        {
                                System.out.println("readIt has started");
                                synchronized(token)
                                {
                                        System.out.println("readIt has token");
                                        while (startReadIt == false)
                                        {
                                                try
                                                {
                                                        // sleep for 1 second (1000 msec = 1 sec)
                                                        Thread.sleep(1000);
                                                }
                                                catch(InterruptedException e) 
                                                {
                                                }                                       
                                        }
                                        readLabel.setText(readField.getText());
                                }
                                System.out.println("readIt has released token");
                                startReadIt = false;
                        }
                        
                        else if (execThread == catchIt)
                        {
                                System.out.println("catchIt has started");
                                // pause catchIt just a little, so it
                                // doesn't get resource1 before readIt
                                try
                                {
                                        // sleep for 1 second (1000 msec = 1 sec)
                                        Thread.sleep(1000);
                                }       
                                catch(InterruptedException e) 
                                {
                                }                                       
                                                
                                synchronized(token)
                                {
                                        // when writeIt gets resource1, it
                                        // is safe to grab the text of readLabel
                                        // and display it on writeLabel
                                        System.out.println("catchIt has token");
                                        catchLabel.setText(readLabel.getText());
                                }
                                System.out.println("catchIt has released token");
                        }
                }
        }

        //suspends execution when user leaves page
        public void stop()
        { 
                if (readIt != null)
                {
                        readIt = null;
                }

                if (catchIt != null)
                {
                        catchIt = null;
                }
        }

        // act when text entered into readField
        public void actionPerformed(ActionEvent e)
        {
                // if get here, something was entered into readField;
                // set startReadIt to true so it readIt thread
                // will do something
                startReadIt = true;
                System.out.println("something was entered into readField:");
                System.out.println(readField.getText());
        }
}