Program for Banker’s Algorithm | Set 1 (Safety Algorithm)

Prerequisite: Banker’s Algorithm

The banker’s algorithm is a resource allocation and deadlock avoidance algorithm that tests for safety by simulating the allocation for predetermined maximum possible amounts of all resources, then makes an “s-state” check to test for possible activities, before deciding whether allocation should be allowed to continue.

Following Data structures are used to implement the Banker’s Algorithm:

Let ‘n’ be the number of processes in the system and ‘m’ be the number of resources types.

Available :

  • It is a 1-d array of size ‘m’ indicating the number of available resources of each type.
  • Available[ j ] = k means there are ‘k’ instances of resource type Rj

Max :

  • It is a 2-d array of size ‘n*m’ that defines the maximum demand of each process in a system.
  • Max[ i, j ] = k means process Pi may request at most ‘k’ instances of resource type Rj.

Allocation :

  • It is a 2-d array of size ‘n*m’ that defines the number of resources of each type currently allocated to each process.
  • Allocation[ i, j ] = k means process Pi is currently allocated ‘k’ instances of resource type Rj

Need :

  • It is a 2-d array of size ‘n*m’ that indicates the remaining resource need of each process.
  • Need [ i, j ] = k means process Pi currently allocated ‘k’ instances of resource type Rj
  • Need [ i, j ] = Max [ i, j ] – Allocation [ i, j ]

Allocationi specifies the resources currently allocated to process Pi and Needi specifies the additional resources that process Pi may still request to complete its task.

Banker’s algorithm consist of Safety algorithm and Resource request algorithm

Safety Algorithm

The algorithm for finding out whether or not a system is in a safe state can be described as follows:

  1. Let Work and Finish be vectors of length ‘m’ and ‘n’ respectively.
    Initialize: Work= Available
    Finish [i]=false; for i=1,2,……,n

  2. Find an i such that both
    a) Finish [i]=false
    b) Need_i<=work

    if no such i exists goto step (4)

  3. Work=Work + Allocation_i
    Finish[i]= true
    goto step(2)

  4. If Finish[i]=true for all i,
    then the system is in safe state.

Safe sequence is the sequence in which the processes can be safely executed.

In this post, implementation of Safety algorithm of Banker’s Algorithm is done.

C++

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// C++ program to illustrate Banker's Algorithm
#include<iostream>
using namespace std;
  
// Number of processes
const int P = 5;
  
// Number of resources
const int R = 3;
  
// Function to find the need of each process
void calculateNeed(int need[P][R], int maxm[P][R],
                   int allot[P][R])
{
    // Calculating Need of each P
    for (int i = 0 ; i < P ; i++)
        for (int j = 0 ; j < R ; j++)
  
            // Need of instance = maxm instance -
            //                    allocated instance
            need[i][j] = maxm[i][j] - allot[i][j];
}
  
// Function to find the system is in safe state or not
bool isSafe(int processes[], int avail[], int maxm[][R],
            int allot[][R])
{
    int need[P][R];
  
    // Function to calculate need matrix
    calculateNeed(need, maxm, allot);
  
    // Mark all processes as infinish
    bool finish[P] = {0};
  
    // To store safe sequence
    int safeSeq[P];
  
    // Make a copy of available resources
    int work[R];
    for (int i = 0; i < R ; i++)
        work[i] = avail[i];
  
    // While all processes are not finished
    // or system is not in safe state.
    int count = 0;
    while (count < P)
    {
        // Find a process which is not finish and
        // whose needs can be satisfied with current
        // work[] resources.
        bool found = false;
        for (int p = 0; p < P; p++)
        {
            // First check if a process is finished,
            // if no, go for next condition
            if (finish[p] == 0)
            {
                // Check if for all resources of
                // current P need is less
                // than work
                int j;
                for (j = 0; j < R; j++)
                    if (need[p][j] > work[j])
                        break;
  
                // If all needs of p were satisfied.
                if (j == R)
                {
                    // Add the allocated resources of
                    // current P to the available/work
                    // resources i.e.free the resources
                    for (int k = 0 ; k < R ; k++)
                        work[k] += allot[p][k];
  
                    // Add this process to safe sequence.
                    safeSeq[count++] = p;
  
                    // Mark this p as finished
                    finish[p] = 1;
  
                    found = true;
                }
            }
        }
  
        // If we could not find a next process in safe
        // sequence.
        if (found == false)
        {
            cout << "System is not in safe state";
            return false;
        }
    }
  
    // If system is in safe state then
    // safe sequence will be as below
    cout << "System is in safe state.\nSafe"
         " sequence is: ";
    for (int i = 0; i < P ; i++)
        cout << safeSeq[i] << " ";
  
    return true;
}
  
// Driver code
int main()
{
    int processes[] = {0, 1, 2, 3, 4};
  
    // Available instances of resources
    int avail[] = {3, 3, 2};
  
    // Maximum R that can be allocated
    // to processes
    int maxm[][R] = {{7, 5, 3},
                     {3, 2, 2},
                     {9, 0, 2},
                     {2, 2, 2},
                     {4, 3, 3}};
  
    // Resources allocated to processes
    int allot[][R] = {{0, 1, 0},
                      {2, 0, 0},
                      {3, 0, 2},
                      {2, 1, 1},
                      {0, 0, 2}};
  
    // Check system is in safe state or not
    isSafe(processes, avail, maxm, allot);
  
    return 0;
}

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Java

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// Java program to illustrate Banker's Algorithm
import java.util.*;
  
class GFG
{
  
// Number of processes
static int P = 5;
  
// Number of resources
static int R = 3;
  
// Function to find the need of each process
static void calculateNeed(int need[][], int maxm[][],
                int allot[][])
{
    // Calculating Need of each P
    for (int i = 0 ; i < P ; i++)
        for (int j = 0 ; j < R ; j++)
  
            // Need of instance = maxm instance -
            //                 allocated instance
            need[i][j] = maxm[i][j] - allot[i][j];
}
  
// Function to find the system is in safe state or not
static boolean isSafe(int processes[], int avail[], int maxm[][],
            int allot[][])
{
    int [][]need = new int[P][R];
  
    // Function to calculate need matrix
    calculateNeed(need, maxm, allot);
  
    // Mark all processes as infinish
    boolean []finish = new boolean[P];
  
    // To store safe sequence
    int []safeSeq = new int[P];
  
    // Make a copy of available resources
    int []work = new int[R];
    for (int i = 0; i < R ; i++)
        work[i] = avail[i];
  
    // While all processes are not finished
    // or system is not in safe state.
    int count = 0;
    while (count < P)
    {
        // Find a process which is not finish and
        // whose needs can be satisfied with current
        // work[] resources.
        boolean found = false;
        for (int p = 0; p < P; p++)
        {
            // First check if a process is finished,
            // if no, go for next condition
            if (finish[p] == false)
            {
                // Check if for all resources of
                // current P need is less
                // than work
                int j;
                for (j = 0; j < R; j++)
                    if (need[p][j] > work[j])
                        break;
  
                // If all needs of p were satisfied.
                if (j == R)
                {
                    // Add the allocated resources of
                    // current P to the available/work
                    // resources i.e.free the resources
                    for (int k = 0 ; k < R ; k++)
                        work[k] += allot[p][k];
  
                    // Add this process to safe sequence.
                    safeSeq[count++] = p;
  
                    // Mark this p as finished
                    finish[p] = true;
  
                    found = true;
                }
            }
        }
  
        // If we could not find a next process in safe
        // sequence.
        if (found == false)
        {
            System.out.print("System is not in safe state");
            return false;
        }
    }
  
    // If system is in safe state then
    // safe sequence will be as below
    System.out.print("System is in safe state.\nSafe"
        +" sequence is: ");
    for (int i = 0; i < P ; i++)
        System.out.print(safeSeq[i] + " ");
  
    return true;
}
  
// Driver code
public static void main(String[] args) 
{
    int processes[] = {0, 1, 2, 3, 4};
  
    // Available instances of resources
    int avail[] = {3, 3, 2};
  
    // Maximum R that can be allocated
    // to processes
    int maxm[][] = {{7, 5, 3},
                    {3, 2, 2},
                    {9, 0, 2},
                    {2, 2, 2},
                    {4, 3, 3}};
  
    // Resources allocated to processes
    int allot[][] = {{0, 1, 0},
                    {2, 0, 0},
                    {3, 0, 2},
                    {2, 1, 1},
                    {0, 0, 2}};
  
    // Check system is in safe state or not
    isSafe(processes, avail, maxm, allot);
}
}
  
// This code has been contributed by 29AjayKumar

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Python3

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# Python3 program to illustrate 
# Banker's Algorithm
  
# Number of processes 
P = 5
  
# Number of resources 
R = 3
  
# Function to find the need of each process 
def calculateNeed(need, maxm, allot):
  
    # Calculating Need of each P 
    for i in range(P):
        for j in range(R):
              
            # Need of instance = maxm instance - 
            # allocated instance
            need[i][j] = maxm[i][j] - allot[i][j] 
  
# Function to find the system is in
# safe state or not
def isSafe(processes, avail, maxm, allot):
    need = []
    for i in range(P):
        l = []
        for j in range(R):
            l.append(0)
        need.append(l)
          
    # Function to calculate need matrix 
    calculateNeed(need, maxm, allot)
  
    # Mark all processes as infinish 
    finish = [0] * P
      
    # To store safe sequence 
    safeSeq = [0] *
  
    # Make a copy of available resources 
    work = [0] *
    for i in range(R):
        work[i] = avail[i] 
  
    # While all processes are not finished 
    # or system is not in safe state. 
    count = 0
    while (count < P):
          
        # Find a process which is not finish 
        # and whose needs can be satisfied 
        # with current work[] resources. 
        found = False
        for p in range(P): 
          
            # First check if a process is finished, 
            # if no, go for next condition 
            if (finish[p] == 0): 
              
                # Check if for all resources 
                # of current P need is less 
                # than work
                for j in range(R):
                    if (need[p][j] > work[j]):
                        break
                      
                # If all needs of p were satisfied. 
                if (j == R - 1): 
                  
                    # Add the allocated resources of 
                    # current P to the available/work 
                    # resources i.e.free the resources 
                    for k in range(R): 
                        work[k] += allot[p][k] 
  
                    # Add this process to safe sequence. 
                    safeSeq[count] = p
                    count += 1
  
                    # Mark this p as finished 
                    finish[p] = 1
  
                    found = True
                  
        # If we could not find a next process 
        # in safe sequence. 
        if (found == False):
            print("System is not in safe state")
            return False
          
    # If system is in safe state then 
    # safe sequence will be as below 
    print("System is in safe state.",
              "\nSafe sequence is: ", end = " ")
    print(*safeSeq) 
  
    return True
  
# Driver code 
if __name__ =="__main__":
      
    processes = [0, 1, 2, 3, 4]
  
    # Available instances of resources 
    avail = [3, 3, 2
  
    # Maximum R that can be allocated 
    # to processes 
    maxm = [[7, 5, 3], [3, 2, 2],
            [9, 0, 2], [2, 2, 2],
            [4, 3, 3]]
  
    # Resources allocated to processes 
    allot = [[0, 1, 0], [2, 0, 0],
             [3, 0, 2], [2, 1, 1],
             [0, 0, 2]] 
  
    # Check system is in safe state or not 
    isSafe(processes, avail, maxm, allot) 
  
# This code is contributed by
# Shubham Singh(SHUBHAMSINGH10)

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C#

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// C# program to illustrate Banker's Algorithm
using System;
  
class GFG
{
      
// Number of processes
static int P = 5;
  
// Number of resources
static int R = 3;
  
// Function to find the need of each process
static void calculateNeed(int [,]need, int [,]maxm,
                int [,]allot)
{
    // Calculating Need of each P
    for (int i = 0 ; i < P ; i++)
        for (int j = 0 ; j < R ; j++)
  
            // Need of instance = maxm instance -
            //           allocated instance
            need[i,j] = maxm[i,j] - allot[i,j];
}
  
// Function to find the system is in safe state or not
static bool isSafe(int []processes, int []avail, int [,]maxm,
            int [,]allot)
{
    int [,]need = new int[P,R];
  
    // Function to calculate need matrix
    calculateNeed(need, maxm, allot);
  
    // Mark all processes as infinish
    bool []finish = new bool[P];
  
    // To store safe sequence
    int []safeSeq = new int[P];
  
    // Make a copy of available resources
    int []work = new int[R];
    for (int i = 0; i < R ; i++)
        work[i] = avail[i];
  
    // While all processes are not finished
    // or system is not in safe state.
    int count = 0;
    while (count < P)
    {
        // Find a process which is not finish and
        // whose needs can be satisfied with current
        // work[] resources.
        bool found = false;
        for (int p = 0; p < P; p++)
        {
            // First check if a process is finished,
            // if no, go for next condition
            if (finish[p] == false)
            {
                // Check if for all resources of
                // current P need is less
                // than work
                int j;
                for (j = 0; j < R; j++)
                    if (need[p,j] > work[j])
                        break;
  
                // If all needs of p were satisfied.
                if (j == R)
                {
                    // Add the allocated resources of
                    // current P to the available/work
                    // resources i.e.free the resources
                    for (int k = 0 ; k < R ; k++)
                        work[k] += allot[p,k];
  
                    // Add this process to safe sequence.
                    safeSeq[count++] = p;
  
                    // Mark this p as finished
                    finish[p] = true;
  
                    found = true;
                }
            }
        }
  
        // If we could not find a next process in safe
        // sequence.
        if (found == false)
        {
            Console.Write("System is not in safe state");
            return false;
        }
    }
  
    // If system is in safe state then
    // safe sequence will be as below
        Console.Write("System is in safe state.\nSafe"
        +" sequence is: ");
    for (int i = 0; i < P ; i++)
            Console.Write(safeSeq[i] + " ");
  
    return true;
}
  
// Driver code
static public void Main ()
{
    int []processes = {0, 1, 2, 3, 4};
  
    // Available instances of resources
    int []avail = {3, 3, 2};
  
    // Maximum R that can be allocated
    // to processes
    int [,]maxm = {{7, 5, 3},
                    {3, 2, 2},
                    {9, 0, 2},
                    {2, 2, 2},
                    {4, 3, 3}};
  
    // Resources allocated to processes
    int [,]allot = {{0, 1, 0},
                    {2, 0, 0},
                    {3, 0, 2},
                    {2, 1, 1},
                    {0, 0, 2}};
  
    // Check system is in safe state or not
    isSafe(processes, avail, maxm, allot);
  
    }
}
  
// This code has been contributed by ajit.

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Output:

System is in safe state.
Safe sequence is: 1 3 4 0 2

Illustration :
Considering a system with five processes P0 through P4 and three resources types A, B, C. Resource type A has 10 instances, B has 5 instances and type C has 7 instances. Suppose at time t0 following snapshot of the system has been taken:

We must determine whether the new system state is safe. To do so, we need to execute Safety algorithm on the above given allocation chart.
banker's algorithm

Following is the resource allocation graph:
Bankers
Executing safety algorithm shows that sequence < P1, P3, P4, P0, P2 > satisfies safety requirement.

This article is contributed by Sahil Chhabra (akku). If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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