multithreaded Java program to compute the generalized Fibonacci number specified by the parameters

[Alex Kozitski]

A monitor class containing the F array. The monitor class must have the following public methods, and no other public methods.
Constructor (int n). This constructor initializes the monitor to calculate the generalized Fibonacci number for argument n.
void putValue (int i, BigInteger value). This method puts the given value into array element i. It is an error if a value has already been put into array element i.
BigInteger getValue (int i). This method returns the value stored in array element i. This method does not return until array element i has been put.
A thread that prints the output.
A thread that computes one and only one array element and stores it in the monitor. There is a separate instance of this thread for each array element, including array elements 0 and 1.
A main program. The main program must create the above objects. The main program must start the threads in this order: first the output printing thread, then the thread that computes the last array element, then the thread that computes the next-to-last array element, and so on backwards through the array elements. The main program must not wait for the threads to terminat

import java.math.*;
import java.io.*;


class Print extends Fib implements Runnable{
	int n;
	Print(int n){
		super(n);
		this.n = n;
		System.out.print("\nSpawning Print Thread\n");
	}
	@Override
	public void run(){
		System.out.print("Inside Print Run method\n");
		try{
			System.out.printf("Printing element %s ",super.getValue(n-1));
		}catch(InterruptedException ie){
			ie.printStackTrace();
		}
	}
}



class Compute extends Fib implements Runnable{
	BigInteger a;
	BigInteger b;
	int n;
	Compute (Integer a, Integer b,int n){
		super(n);
		this.b = BigInteger.valueOf(b);
		this.a = BigInteger.valueOf(a);
	
		this.n =  n;
		System.out.printf("\nSpawning Compute Thread with %d\n",this.n);			
	}

	@Override
	public void run(){
		try{
			super.putValue(0,this.a);
			super.putValue(1,this.b);
		}catch (InterruptedException ie){
			ie.printStackTrace();
		}
		if(this.a.compareTo(this.b)==1){
			System.err.print("Second argument must be greater than first\n");
			System.exit(0);
		}
		try{
		                //this part never executes
				BigInteger next = super.getValue(this.n-2).add(super.getValue(this.n-1));
				System.out.print("Inside run method\n");
				super.putValue(n,next);
			
		}catch (InterruptedException ie){
			ie.printStackTrace();
		}	
	}
}



public class Fib{
	
	protected BigInteger F[];
	protected int n;
	Fib(int n){
		if(n<0){
			System.err.print("N must be >= 0\n");
			System.exit(0);
		}else{
			F = new BigInteger[n+1];
			this.n = n;	
		}
		
	
	}
	//I am stuck in this part
	public synchronized void putValue(int i, BigInteger element)throws InterruptedException{
		if (F[i] == null){
			System.out.printf("Calling putValue with %s\n",element.toString());
			F[i] = element;
			notifyAll();
		}
		else{
			
			System.err.printf("Element at position %d exists in the list\n",i);
			System.exit(0);
		}
	}
	public synchronized BigInteger getValue(int i) throws InterruptedException{
		while(F[i]==null){
			System.out.printf("Still stuck on %d-> element \n",i);
			for(int x=0;x<F.length;x++){
				System.out.print(i+") ");
				System.out.print(F[x]);
				System.out.print(" ");
			}
			System.out.println();
			wait();
		}
		
		return F[i];
	}
	//end of the stuck part
	public static void main(String[] args) {
		if (args.length<3){
			System.err.print("Invalid number of argumnets\n");
			System.exit(0);
		}
		Integer n = 0;
		Integer a = 0;
		Integer b = 0;
		try{
			n = Integer.parseInt(args[2]);
			a = Integer.parseInt(args[0]);
			b = Integer.parseInt(args[1]);
		}catch(Exception ex){
			System.err.print("Invalid type of command line argumnents \n");
			System.exit(0);
		}
		Fib fib  = new Fib(n);
		
		new Thread(new Print(n)).start();
		for(int i=n;i>=0;i--){
			Thread comp = new Thread (new Compute(a,b,n));
			comp.start();
		}
	}	
}

[Paul Clapham]

Hi Alex, welcome to the Ranch!

Ummm... did you have a question about that code?

[Alex Kozitski]

yes, I do not understand why new element is never calculated

[praveen kumaar]

Hello alex,a warm welcome to Ranch!

i have noticed some things in your code -


1. you have synchronized the putValue and getValue of supercalss and implement this method in the different sublasses which are runnable also.but in actual         whenever the 2 methods are implemented in subclass each time they create a new superclass instance and use them as lock.i.e.,you are not using the same lock
for doing your stuff each time you are calling the two methods they are using the lock associated with new super instance.

2. you have used wait,notifyAll in your class actually whenever you use the 2 methods make it sure that condition queue related with them is a same object along  with the lock,they are using for checking condition predicate and for blocking wait and notify,should be the same.in your case the condition queue you are using for the wait and notify are different objects along with different lock being used their for the 3 things just mentioned.

try to nest the classes as static private member inside the "Fib" which you have extended prior and their inside instantiate the one variable of enclosing class(Fib) and use that instead of the super keyword.

if still you don't understand any part hit the reply button.
hope it will help!

kind regards,
praveen.

[Norm Radder]

Topic added to the Threads section

[praveen kumaar]

One more thing Alex if you will use the same key for

[praveen kumaar]

praveen kumaar wrote:One more thing Alex if you will use the same key for

sorry for the above post actually i am cancelling it but by mistake hits the submit button.