Banker’s algorithm

Multiple instances.

Each process must a priori claim maximum use.

When a process requests a resource it may have to wait.

When a process gets all its resources it must return them in a finite amount of time.

import java.util.Scanner;

public class Banker {

int available[] = new int[]{3,3,2};

int max[][] = new int[][]{{7,5,3},{3,2,2},{9,0,2},{2,2,2},{4,3,3}};

int allocation[][] = new int[][]{{0,1,0},{2,0,0},{3,0,2},{2,1,1},{0,0,2}};

int need[][] = new int[][]{{7,4,3},{1,2,2},{6,0,0},{0,1,1},{4,3,1}};

void showData() {

System.out.println("Process number  Max     All     Need   ");

System.out.println("     A  B  C  A  B  C  A  B  C");

for(int i = 0;i<5;i++){

System.out.print(i+"    ");

for(int m = 0;m<3;m++) System.out.print(max[i][m]+"  ");

for(int m = 0;m<3;m++) System.out.print(allocation[i][m]+"  ");

for(int m = 0;m<3;m++) System.out.print(need[i][m]+"  ");

System.out.println();

}

}

 

boolean change(int inRequestNum,int inRequest[])

{

int requestNum = inRequestNum;

int request[] = inRequest;

// for(int i=0;i<3;i++)System.out.println("Before modification available"+available[i]);

if(!(request[0]<=need[requestNum][0]&&request[1]<=need[requestNum][1]&&request[2]<=need[requestNum][2]))

{

//request[0]<=need[requestNum][0]

//request[1]<=need[requestNum][1]

//request[2]<=need[requestNum][2]

System.out.println("The number of resources requested exceeds the maximum required, allocation error");

return false;

}

if((request[0]<=available[0]&&request[1]<=available[1]&&request[2]<=available[2])==false)

{

System.out.println("Not enough resources have been allocated and must wait");

return false;

}

 

for(int i = 0;i<3;i++)

{

available[i] = available[i]-request[i];

allocation[requestNum][i] = allocation[requestNum][i] + request[i];

need[requestNum][i] = need[requestNum][i] - request[i];

}

// for(int i=0;i<3;i++)System.out.println("After modificationavailable"+available[i]);

boolean flag = checkSafe(available[0],available[1],available[2]);

// System.out.println("After safety check"+flag);

if(flag==true)

{

System.out.println("Able to safely distribute");

return true;

}

else

{

System.out.println("Cannot be safely assigned");

for(int i = 0;i<3;i++)

{

available[i] = available[i]+request[i];

allocation[requestNum][i] = allocation[requestNum][i] - request[i];

need[requestNum][i] = need[requestNum][i] + request[i];

}

return false;

}

}

boolean checkSafe(int a,int b,int c)

{

int work[] = new int[3];

work[0] = a;

work[1] = b;

work[2] = c;

int i=0;

boolean finish[] = new boolean[5];

while(i<5)

{

if(finish[i]==false&&need[i][0]<=work[0]&&need[i][1]<=work[1]&&need[i][2]<=work[2])

{

System.out.println("The key to successful allocation is"+i);

for(int m = 0;m<3;m++)

work[m] =work[m] + allocation[i][m];

finish[i] = true;

i=0;

}

else

i++;

}

for(i=0;i<5;i++)

{

if(finish[i]==false)

return false;

}

return true;

}

public static void main(String[] args)

{

Banker bank = new Banker();

bank.showData();

int request[] =new int[3];

int requestNum;

String source[] = new String[]{"A","B","C"};

Scanner s = new Scanner(System.in);

String choice = new String();

while(true)

{

System.out.println("Please enter the process number to request (0 -- 4):");

requestNum = s.nextInt();

System.out.print("Please enter the number of resources requested");

for(int i = 0;i<3;i++)

{

System.out.println(source[i]+"Number of resources：");

request[i] = s.nextInt();

}

bank.change(requestNum, request);

System.out.println("Re request allocation (Y / N)");

choice = s.next();

if(choice.equals("n"))

break;

}

}

}