My simulation for concurrent processing didn't work

[Azuki]

I am suppose to write a program to simulate this situation.

A tribe of savages eats communal dinners from a large pot that can hold M servings of stewed missionaries. When a savage wants to eat, he helps himself from the pot, unless it is empty. If the pot is empty, the savage wakes up the cook and then waits until the cook has refilled the pot.

Admin class: This class creates the cook and generates arrival of 10 savages. The class also keeps track of the number of servings in the pot (using an array of size 1) and prints the number of servings left in the pot after all the savages have eaten.

Cook class: This class models the cooking done by the cook.
It should have a method putServingsInPot() that performs the following:

• generate a random number M (between 1 and 5 inclusive)
• show a message the cook has put M missionaries into the pot.
• include a timing delay to represent the cooking relative to M.

This method is invoked only when the pot is empty.

Savage class: This class models the behaviour of the savages.
It should have a suitable method that performs the following:
get a serving from the pot

• include a timing delay to represent the time spent eating
• deduct one serving from the pot
• show messages that the savage starts eating and has finished eating

When getting a serving from the pot, if the pot is empty, the cook’s method putServingsInPot() needs to be invoked.

These are my codes but the output is totally wrong. But I just can't understand where goes wrong Please help!

public class Admin
{
    public static void main (String[] args)
    {
        
        Cook cook = new Cook();
        Savage[] savage = new Savage[10];
        int[] numOfServings = new int[1];
        
        
        for (int i = 0; i<savage.length; i++)
        {
            savage[i] = new Savage(i+1, numOfServings, cook);
            savage[i].start();
   
        }
        
        
        System.out.println("ending...There are " + numOfServings[0] + " missionaries left in the pot");
    }
}

public class Cook extends Thread
{

    
    
    public synchronized void putServingsInPot(int[] numOfServings)
    {
        int m = (int)(Math.random()*5)+1;
        Timer.cook(m);
        numOfServings[0]+=m;
        System.out.println("Cook has put " + m + " missionaries into pot.");
        notifyAll();
    }
}

public class Savage extends Thread
{
    private int id;
    private int[] numOfServings;
    private Cook c;
    
    public Savage(int id, int[] numOfServings, Cook c)
    {
        this.id=id;
        this.numOfServings = numOfServings;
        this.c=c;
    }
    
    public void run()
    {
        for(int i=0; i<2; i++)
        {
            getServingFromPot();
        }
    }
    
    public synchronized void getServingFromPot()
    {
       try
       {
           while(numOfServings[0]==0)
           {
               c.putServingsInPot(numOfServings);
               wait();
           }
           System.out.println("Salvage " + id + " getting a serving to eat");
           Timer.eat(id);
           numOfServings[0]--;
           System.out.println("Salvage " + id + " finished eating");
       }
       catch (Exception e)
       {
           
       }
       
    }
}

public class Timer
{
    public static void eat(int time)
    {
        duration ((time+10)*2);
    }
    
    public static void cook (int share)
    {
        duration (share*100);
    }    
    
    public static void duration(int time)
    {
        int speedFactor = 1000;
        for(int j = 0; j<time; j++)
        {
            for(int k = 0; k<speedFactor; k++)
            {
                double r = (k/2)*2;
            }
        }
    }
}

The output suppose to be like this:

Cook has put 5 missionaries into pot
Savage 0 getting a serving to eat
Savage 3 getting a serving to eat
Savage 5 getting a serving to eat
Savage 1 getting a serving to eat
Savage 9 getting a serving to eat
There are no more missionaries in the pot!
Cook has put 2 missionaries into pot
Savage 5 finished eating
Savage 3 finished eating
Savage 0 finished eating
Savage 1 finished eating
Savage 9 finished eating
Savage 7 getting a serving to eat
Savage 8 getting a serving to eat
There are no more missionaries in the pot!
Cook has put 5 missionaries into pot
Savage 8 finished eating
Savage 7 finished eating
Savage 6 getting a serving to eat
Savage 4 getting a serving to eat
Savage 2 getting a serving to eat
Savage 4 finished eating
Savage 6 finished eating
Savage 2 finished eating
There are 2 missionaries in the pot!

[jim829]

You showed what the output is supposed to be but not what you are producing. Can you include that please?

Regards,
Jim

[jim829]

Well, I got it to compile and it isn't working as expected. However, I did notice that you didn't start your cook thread. In fact, you didn't override the run() method in your thread even though you subclassed Thread. Also, there was at least one try/catch that ignored the exception. At a minimum you should print the stack trace.

Regards,
Jim

[Azuki]

You showed what the output is supposed to be but not what you are producing. Can you include that please?

Regards,
Jim

My output is totally wrong:

Cook has put 2 missionaries into pot.
ending...There are 2 missionaries left in the pot
Salvage 9 getting a serving to eat
Salvage 9 finished eating
Salvage 9 getting a serving to eat
Salvage 9 finished eating
Salvage 8 getting a serving to eat
Cook has put 2 missionaries into pot.
Salvage 8 finished eating
Salvage 8 getting a serving to eat
Cook has put 3 missionaries into pot.
Salvage 8 finished eating
Cook has put 4 missionaries into pot.
Cook has put 5 missionaries into pot.
Cook has put 1 missionaries into pot.
Cook has put 5 missionaries into pot.
Cook has put 3 missionaries into pot.

[Azuki]

The cook thread should start only when the pot is empty. I rewrite my classes here, but still it doesn't work.

public class Cook extends Thread
{
	private int[] numOfServings;

	public Cook(int[] numOfServings)
	{
		this.numOfServings = numOfServings;
	}

	public void run()
	{
			putServingsInPot(numOfServings);
	}

    private synchronized void putServingsInPot(int[] numOfServings)
    {
        int m = (int)(Math.random()*5)+1;
        Timer.cook(m);
        numOfServings[0]+=m;
        System.out.println("Cook has put " + m + " missionaries into pot.");
        notifyAll();
    }
}

public class Savage extends Thread
{
    private int id;
    private int[] numOfServings;
    private Cook c;

    public Savage(int id, int[] numOfServings, Cook c)
    {
        this.id=id;
        this.numOfServings = numOfServings;
        this.c=c;
    }

    public void run()
    {
        for(int i=0; i<2; i++)
        {

		    getServingFromPot();

        }
    }

    private synchronized void getServingFromPot()
    {

        while(numOfServings[0]==0)
   		{
       		c.start();

	           try{
	           	wait();
	           } catch (Exception e){}
	    }

		//out of while means cook has put missionaries into pot
       System.out.println("Salvage " + id + " getting a serving to eat");
       Timer.eat(id);
       numOfServings[0]--;
       System.out.println("Salvage " + id + " finished eating");

    }
}

public class Admin
{
    public static void main (String[] args)
    {
		int[] numOfServings = new int[1];
        Cook cook = new Cook(numOfServings);
        Savage[] savage = new Savage[10];



        for (int i = 0; i<savage.length; i++)
        {
            savage[i] = new Savage(i+1, numOfServings, cook);
            savage[i].start();

        }


        System.out.println("ending...There are " + numOfServings[0] + " missionaries left in the pot");
    }
}

Well, I got it to compile and it isn't working as expected. However, I did notice that you didn't start your cook thread. In fact, you didn't override the run() method in your thread even though you subclassed Thread. Also, there was at least one try/catch that ignored the exception. At a minimum you should print the stack trace.

Regards,
Jim

[jim829]

The cook method should be started at the beginning. In the run method, you need a synchronized block with a wait statement. Something like this (but additional code will probably be necessary. Like letting the Savages know the pot has been updated).

synchronized(lock) {
      while (potContents > 0) {// non-empty pot
            lock.wait();
            updatePot();  // must update potContents or loop will exit
      }
}

If you are unfamiliar with threads, please check The Java™ Tutorial.


Regards,
Jim

[Azuki]

I modified my codes as below and start my Cook thread in Admin. But still the result is not what I expect

public class Cook extends Thread
{
    private int[] numOfServings;
    
    public Cook (int[] numOfServings)
    {
        this.numOfServings = numOfServings;
    }
    
    public void run()
    {
        putServingsInPot(numOfServings);
    }

    public synchronized void putServingsInPot (int[] numOfServings)
    {
        int m = (int)(Math.random()*5)+1;
        Timer.cook(m);
        numOfServings[0]+=m;
        System.out.println("Cook has put " + m + " missionaries into pot.");
        notifyAll();
        
    }
    
}

public class Savage extends Thread
{
    private int[] numOfServings;
    private int id;
    private Cook c;

    public Savage(int[] numOfServings, int id, Cook c)
    {
        this.numOfServings=numOfServings;
        this.id=id;
        this.c=c;
    }

    public void run()
    {
        for(int i = 0; i<2; i++)
        {
            getServingsFromPot(id, numOfServings);
        }
    }

    public synchronized void getServingsFromPot(int id, int[] numOfServings)
    {
        try{
            while(numOfServings[0]==0)
            {
                System.out.println("There's no more missionary in the pot!");
                c.putServingsInPot(numOfServings);
                wait();
            }
        } catch(Exception e){}

        System.out.println("Savage " + id + " getting a serving to eat");
        Timer.eat(id);
        numOfServings[0]--;
        System.out.println("Savage " + id + " finished eating");
    }
}

public class Admin
{
    public static void main (String[] args)
    {
        
        int[] numOfServings = new int[1];
        Cook cook = new Cook(numOfServings);
        Savage[] savage = new Savage[10];
        
        
        cook.start();        
        for(int i = 0; i<savage.length; i++)
        {
            savage[i] = new Savage(numOfServings, i+1, cook);
            savage[i].start();
        }
        
        
        
        System.out.println("Ending...There are " + numOfServings[0] + " missionarie left in the pot");
    }
}

There's no more missionary in the pot!
There's no more missionary in the pot!
There's no more missionary in the pot!
There's no more missionary in the pot!
There's no more missionary in the pot!
There's no more missionary in the pot!
There's no more missionary in the pot!
There's no more missionary in the pot!
There's no more missionary in the pot!
There's no more missionary in the pot!
Cook has put 3 missionaries into pot.
Cook has put 1 missionaries into pot.
Cook has put 5 missionaries into pot.
Cook has put 3 missionaries into pot.
Cook has put 5 missionaries into pot.
Cook has put 3 missionaries into pot.
Cook has put 4 missionaries into pot.
Cook has put 2 missionaries into pot.
Cook has put 3 missionaries into pot.
Cook has put 2 missionaries into pot.
Cook has put 1 missionaries into pot.

[jim829]

Did you read thru the tutorials and try out some examples.? Take some small steps first to see how threads behave. Concurrent programming ins one of the more complex (and difficult to debug) aspects of programming.

Also, please don't change the title when posting replies.

Regards,
Jim