// File: Race10.java (Module 12)
//
// Author: Rahul Simha
// Created: Nov 17, 1998
//
// Waiting and notification without deadlock: a cleaner version.

import java.awt.*;
import java.awt.event.*;

class NewFrame extends Frame {

  Canvas c;

  public NewFrame ()
  {
    // Frame properties.
    this.setTitle ("Dog Race");
    this.setBackground (Color.cyan);
    this.setResizable (true);
    this.setSize (600,200);

    // Quit button.
    Panel p = new Panel ();
    Button quitb = new Button ("QUIT");
    quitb.addActionListener (
      new ActionListener () {
        public void actionPerformed (ActionEvent a)
        {
	  System.exit (0);
	}
      }
    );
    p.add (quitb);

    // Pressing "start" calls race()
    Button startb = new Button ("START");
    startb.addActionListener (
      new ActionListener () {
        public void actionPerformed (ActionEvent a)
        {
	  race ();
	}
      }
    );
    p.add (startb);

    this.add (p, BorderLayout.SOUTH);

    // A canvas to draw the results.
    c = new Canvas();
    c.setBackground (Color.white);
    this.add (c, BorderLayout.CENTER);

    this.setVisible (true);
  }


  void race ()
  {
    Dimension D = c.getSize ();

    // Finish-line is at the right end of the canvas.
    int finish_line = D.width;

    // Create the dog monitor.
    DogMonitor monitor = new DogMonitor (2);

    // Create two dog instances with different ID's.
    Dog d1 = new Dog (1, c, monitor, 2);
    Dog d2 = new Dog (2, c, monitor, 1);

    // Create a Thread instance for each dog.
    // Note: the class Dog must implement the
    // Runnable interface.
    Thread d1_thread = new Thread (d1);
    Thread d2_thread = new Thread (d2);

    // Start running the threads.
    // ("start" is a method in Thread).
    d1_thread.start();
    d2_thread.start();
  }


}


class DogMonitor {

  int[] position;
  boolean[] is_waiting;
  int num_dogs;

  public DogMonitor (int num_dogs)
  {
    this.num_dogs = num_dogs;
    position = new int [num_dogs+1];
    for (int i=1; i<=num_dogs; i++)
      position[i] = 20;
    is_waiting = new boolean [num_dogs+1];
    for (int i=1; i<=num_dogs; i++)
      is_waiting [i] = false;
  }

  // Set the new position of Dog# ID.
  public synchronized void set_position (int ID, int new_position)
  {
    position[ID] = new_position;
  }

  // Get the current position of Dog# ID.
  public synchronized int get_position (int ID)
  {
    return position[ID];
  }

  // Before waiting, make sure no-one else waits.
  public synchronized void synch_wait (int ID)
  {
    boolean someone_waiting = false;
    for (int i=1; i<=num_dogs; i++)
      if (is_waiting[i]) {
	System.out.println ("synch_wait: i=" + i + " is waiting");
	someone_waiting= true;
      }
    if (someone_waiting) {
      notifyAll();
      for (int i=1; i<=num_dogs; i++)
        is_waiting[i] = false;
    }

    try {
      is_waiting[ID] = true;
      System.out.println ("ID=" + ID + " waiting");
      wait ();
    }
    catch (InterruptedException e)
    {
      System.out.println (e);
    }
  }

  public synchronized void synch_notify (int ID)
  {
    System.out.println ("ID=" + ID + " notifying");
    notify ();
  }

}


class Dog implements Runnable {

  int ID;                    // An ID.
  Canvas c;                  // The canvas on which to draw.

  DogMonitor monitor;        // Store a reference to the monitor.
  int OtherID;               // ID of the other dog.

  public Dog (int ID, Canvas c, DogMonitor monitor, int OtherID)
  {
    this.ID = ID;
    this.c = c;
    this.monitor = monitor;
    this.OtherID = OtherID;

    // Draw ID on canvas.
    Graphics g = c.getGraphics ();
    g.drawString (""+ID, 5, 20*ID+8);
  }

  public void move ()
  {
    // Move a random amount.
    int position = monitor.get_position (ID);
    int new_position = position + (int) UniformRandom.uniform (1,50);
    monitor.set_position (ID, new_position);

    // Draw new position.
    Graphics g = c.getGraphics ();
    int size = new_position - position;
    g.fillRect (position, 20*ID, size, 10);
  }

  public void run ()
  {
    // Compute the finish line distance.
    int finish_line = c.getSize().width;

    // While not complete...
    while (monitor.get_position (ID) < finish_line) {
      try {
	Thread.sleep ((int)UniformRandom.uniform (300,600));
      }
      catch (InterruptedException e) {
	System.out.println (e);
      }
      
      move ();
      
      // Check if you need to wait.
      if (monitor.get_position (ID) 
	  - monitor.get_position (OtherID) > 20) {
	monitor.synch_wait (ID);
      }
      
      // See if the other guy is waiting for me.
      if (monitor.get_position (OtherID) 
	  - monitor.get_position (ID) <= 20) {
	monitor.synch_notify(ID);
      }
    } // endwhile

  }

}


public class Race11 {
  public static void main (String[] argv)
  {
    NewFrame nf = new NewFrame ();
  }
}