Banker's Algorithm in Operating System
Last Updated :
05 May, 2023
Prerequisite - Resource Allocation Graph (RAG), Banker’s Algorithm, Program for Banker’s Algorithm
Banker's Algorithm is a resource allocation and deadlock avoidance algorithm. This algorithm test for safety 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.
In simple terms, it checks if allocation of any resource will lead to deadlock or not, OR if is it safe to allocate a resource to a process and if not then resource is not allocated to that process. Determining a safe sequence(even if there is only 1) will assure that system will not go into deadlock.
Banker's algorithm is generally used to find if a safe sequence exist or not. But here we will determine the total number of safe sequences and print all safe sequences.
How does the Banker's Algorithm work?
The Banker's Algorithm works by maintaining a matrix of resources and processes. Each row represents a process, and each column represents a resource. The matrix contains information about the current state of the system, including the maximum number of resources each process needs, the number of resources currently allocated to each process, and the number of resources available in the system.
: What is the purpose of the Banker's Algorithm?
A: The purpose of the Banker's Algorithm is to prevent deadlock, a situation where two or more processes are blocked, waiting for each other to release resources they need in order to proceed. Deadlock can cause a system to become unresponsive and may require a reboot to recover.
The data structure used are:
- Available vector
- Max Matrix
- Allocation Matrix
- Need Matrix
Example:
Input:
Output: Safe sequences are:
P2--> P4--> P1--> P3
P2--> P4--> P3--> P1
P4--> P2--> P1--> P3
P4--> P2--> P3--> P1
There are total 4 safe-sequences
Explanation:
Total resources are R1 = 10, R2 = 5, R3 = 7 and allocated resources are R1 = (0+2+3+2 =) 7, R2 = (1+0+0+1 =) 2, R3 = (0+0+2+1 =) 3. Therefore, remaining resources are R1 = (10 - 7 =) 3, R2 = (5 - 2 =) 3, R3 = (7 - 3 =) 4.
Remaining available = Total resources - allocated resources
and
Remaining need = max - allocated
So, we can start from either P2 or P4. We can not satisfy remaining need from available resources of either P1 or P3 in first or second attempt step of Banker's algorithm. There are only four possible safe sequences.
These are :
P2--> P4--> P1--> P3
P2--> P4--> P3--> P1
P4--> P2--> P1--> P3
P4--> P2--> P3--> P1
Implementation:
C++
// C++ Program to Print all possible safe sequences using banker's algorithm
#include <iostream>
#include <string.h>
#include <vector>
// total number of process
#define P 4
// total number of resources
#define R 3
// total safe-sequences
int total = 0;
using namespace std;
// function to check if process
// can be allocated or not
bool is_available(int process_id, int allocated[][R],
int max[][R], int need[][R], int available[])
{
bool flag = true;
// check if all the available resources
// are less greater than need of process
for (int i = 0; i < R; i++) {
if (need[process_id][i] > available[i])
flag = false;
}
return flag;
}
// Print all the safe-sequences
void safe_sequence(bool marked[], int allocated[][R], int max[][R],
int need[][R], int available[], vector<int> safe)
{
for (int i = 0; i < P; i++) {
// check if it is not marked
// already and can be allocated
if (!marked[i] && is_available(i, allocated, max, need, available)) {
// mark the process
marked[i] = true;
// increase the available
// by deallocating from process i
for (int j = 0; j < R; j++)
available[j] += allocated[i][j];
safe.push_back(i);
// find safe sequence by taking process i
safe_sequence(marked, allocated, max, need, available, safe);
safe.pop_back();
// unmark the process
marked[i] = false;
// decrease the available
for (int j = 0; j < R; j++)
available[j] -= allocated[i][j];
}
}
// if a safe-sequence is found, display it
if (safe.size() == P) {
total++;
for (int i = 0; i < P; i++) {
cout << "P" << safe[i] + 1;
if (i != (P - 1))
cout << "--> ";
}
cout << endl;
}
}
// Driver Code
int main()
{
// allocated matrix of size P*R
int allocated[P][R] = { { 0, 1, 0 },
{ 2, 0, 0 },
{ 3, 0, 2 },
{ 2, 1, 1 } };
// max matrix of size P*R
int max[P][R] = { { 7, 5, 3 },
{ 3, 2, 2 },
{ 9, 0, 2 },
{ 2, 2, 2 } };
// Initial total resources
int resources[R] = { 10, 5, 7 };
// available vector of size R
int available[R];
for (int i = 0; i < R; i++) {
int sum = 0;
for (int j = 0; j < P; j++)
sum += allocated[j][i];
available[i] = resources[i] - sum;
}
// safe vector for displaying a safe-sequence
vector<int> safe;
// marked of size P for marking allocated process
bool marked[P];
memset(marked, false, sizeof(marked));
// need matrix of size P*R
int need[P][R];
for (int i = 0; i < P; i++)
for (int j = 0; j < R; j++)
need[i][j] = max[i][j] - allocated[i][j];
cout << "Safe sequences are:" << endl;
safe_sequence(marked, allocated, max, need, available, safe);
cout << "\nThere are total " << total << " safe-sequences" << endl;
return 0;
}
// Java Program to Print all possible safe
// sequences using banker's algorithm
import java.util.*;
public class GFG
{
// total number of process
static int P = 4;
// total number of resources
static int R = 3;
// total safe-sequences
static int total = 0;
// function to check if process
// can be allocated or not
static boolean is_available(int process_id, int allocated[][],
int max[][], int need[][], int available[])
{
boolean flag = true;
// check if all the available resources
// are less greater than need of process
for (int i = 0; i < R; i++)
{
if (need[process_id][i] > available[i])
{
flag = false;
}
}
return flag;
}
// Print all the safe-sequences
static void safe_sequence(boolean marked[], int allocated[][], int max[][],
int need[][], int available[], Vector<Integer> safe)
{
for (int i = 0; i < P; i++)
{
// check if it is not marked
// already and can be allocated
if (!marked[i] && is_available(i, allocated, max, need, available))
{
// mark the process
marked[i] = true;
// increase the available
// by deallocating from process i
for (int j = 0; j < R; j++)
{
available[j] += allocated[i][j];
}
safe.add(i);
// find safe sequence by taking process i
safe_sequence(marked, allocated, max, need, available, safe);
safe.removeElementAt(safe.size() - 1);
// unmark the process
marked[i] = false;
// decrease the available
for (int j = 0; j < R; j++)
{
available[j] -= allocated[i][j];
}
}
}
// if a safe-sequence is found, display it
if (safe.size() == P)
{
total++;
for (int i = 0; i < P; i++)
{
System.out.print("P" + (safe.get(i) + 1));
if (i != (P - 1))
{
System.out.print("--> ");
}
}
System.out.println("");;
}
}
// Driver Code
public static void main(String[] args)
{
// allocated matrix of size P*R
int allocated[][] = {{0, 1, 0},
{2, 0, 0},
{3, 0, 2},
{2, 1, 1}};
// max matrix of size P*R
int max[][] = {{7, 5, 3},
{3, 2, 2},
{9, 0, 2},
{2, 2, 2}};
// Initial total resources
int resources[] = {10, 5, 7};
// available vector of size R
int[] available = new int[R];
for (int i = 0; i < R; i++)
{
int sum = 0;
for (int j = 0; j < P; j++)
{
sum += allocated[j][i];
}
available[i] = resources[i] - sum;
}
// safe vector for displaying a safe-sequence
Vector<Integer> safe = new Vector<Integer>();
// marked of size P for marking allocated process
boolean[] marked = new boolean[P];
// need matrix of size P*R
int[][] need = new int[P][R];
for (int i = 0; i < P; i++)
{
for (int j = 0; j < R; j++)
{
need[i][j] = max[i][j] - allocated[i][j];
}
}
System.out.println("Safe sequences are:");
safe_sequence(marked, allocated, max, need, available, safe);
System.out.println("\nThere are total " + total + " safe-sequences");
}
}
/* This code contributed by PrinciRaj1992 */
# Python3 program to print all
# possible safe sequences
# using banker's algorithm
# Total number of process
P = 4
# Total number of resources
R = 3
# Total safe-sequences
total = 0
# Function to check if process
# can be allocated or not
def is_available(process_id, allocated,
max, need, available):
flag = True
# Check if all the available resources
# are less greater than need of process
for i in range(R):
if (need[process_id][i] > available[i]):
flag = False
return flag
# Print all the safe-sequences
def safe_sequence(marked, allocated,
max, need, available, safe):
global total, P, R
for i in range(P):
# Check if it is not marked
# already and can be allocated
if (not marked[i] and
is_available(i, allocated, max,
need, available)):
# mark the process
marked[i] = True
# Increase the available
# by deallocating from process i
for j in range(R):
available[j] += allocated[i][j]
safe.append(i)
# Find safe sequence by taking process i
safe_sequence(marked, allocated, max,
need, available, safe)
safe.pop()
# unmark the process
marked[i] = False
# Decrease the available
for j in range(R):
available[j] -= allocated[i][j]
# If a safe-sequence is found, display it
if (len(safe) == P):
total += 1
for i in range(P):
print("P" + str(safe[i] + 1), end = '')
if (i != (P - 1)):
print("--> ", end = '')
print()
# Driver code
if __name__=="__main__":
# Allocated matrix of size P*R
allocated = [ [ 0, 1, 0 ],
[ 2, 0, 0 ],
[ 3, 0, 2 ],
[ 2, 1, 1 ]]
# max matrix of size P*R
max = [ [ 7, 5, 3 ],
[ 3, 2, 2 ],
[ 9, 0, 2 ],
[ 2, 2, 2 ] ]
# Initial total resources
resources = [ 10, 5, 7 ]
# Available vector of size R
available = [0 for i in range(R)]
for i in range(R):
sum = 0
for j in range(P):
sum += allocated[j][i]
available[i] = resources[i] - sum
# Safe vector for displaying a
# safe-sequence
safe = []
# Marked of size P for marking
# allocated process
marked = [False for i in range(P)]
# Need matrix of size P*R
need = [[0 for j in range(R)]
for i in range(P)]
for i in range(P):
for j in range(R):
need[i][j] = (max[i][j] -
allocated[i][j])
print("Safe sequences are:")
safe_sequence(marked, allocated, max,
need, available, safe)
print("\nThere are total " + str(total) +
" safe-sequences")
# This code is contributed by rutvik_56
// C# Program to Print all possible safe
// sequences using banker's algorithm
using System;
using System.Collections.Generic;
class GFG
{
// total number of process
static int P = 4;
// total number of resources
static int R = 3;
// total safe-sequences
static int total = 0;
// function to check if process
// can be allocated or not
static Boolean is_available(int process_id,
int [,]allocated,
int [,]max, int [,]need,
int []available)
{
Boolean flag = true;
// check if all the available resources
// are less greater than need of process
for (int i = 0; i < R; i++)
{
if (need[process_id, i] > available[i])
{
flag = false;
}
}
return flag;
}
// Print all the safe-sequences
static void safe_sequence(Boolean []marked,
int [,]allocated,
int [,]max, int [,]need,
int []available,
List<int> safe)
{
for (int i = 0; i < P; i++)
{
// check if it is not marked
// already and can be allocated
if (!marked[i] &&
is_available(i, allocated, max,
need, available))
{
// mark the process
marked[i] = true;
// increase the available
// by deallocating from process i
for (int j = 0; j < R; j++)
{
available[j] += allocated[i, j];
}
safe.Add(i);
// find safe sequence by taking process i
safe_sequence(marked, allocated, max,
need, available, safe);
safe.RemoveAt(safe.Count - 1);
// unmark the process
marked[i] = false;
// decrease the available
for (int j = 0; j < R; j++)
{
available[j] -= allocated[i, j];
}
}
}
// if a safe-sequence is found,
// display it
if (safe.Count == P)
{
total++;
for (int i = 0; i < P; i++)
{
Console.Write("P" + (safe[i] + 1));
if (i != (P - 1))
{
Console.Write("--> ");
}
}
Console.WriteLine("");;
}
}
// Driver Code
public static void Main(String[] args)
{
// allocated matrix of size P*R
int [,]allocated = {{0, 1, 0},
{2, 0, 0},
{3, 0, 2},
{2, 1, 1}};
// max matrix of size P*R
int [,]max = {{7, 5, 3},
{3, 2, 2},
{9, 0, 2},
{2, 2, 2}};
// Initial total resources
int []resources = {10, 5, 7};
// available vector of size R
int[] available = new int[R];
for (int i = 0; i < R; i++)
{
int sum = 0;
for (int j = 0; j < P; j++)
{
sum += allocated[j,i];
}
available[i] = resources[i] - sum;
}
// safe vector for displaying a safe-sequence
List<int> safe = new List<int>();
// marked of size P for marking
// allocated process
Boolean[] marked = new Boolean[P];
// need matrix of size P*R
int[,] need = new int[P, R];
for (int i = 0; i < P; i++)
{
for (int j = 0; j < R; j++)
{
need[i, j] = max[i, j] - allocated[i, j];
}
}
Console.WriteLine("Safe sequences are:");
safe_sequence(marked, allocated, max,
need, available, safe);
Console.WriteLine("\nThere are total " +
total + " safe-sequences");
}
}
// This code is contributed by Rajput-Ji
// total number of process
const P = 4;
// total number of resources
const R = 3;
// total safe-sequences
let total = 0;
// function to check if process
// can be allocated or not
function is_available(process_id, allocated, max, need, available) {
let flag = true;
// check if all the available resources
// are less greater than need of process
for (let i = 0; i < R; i++) {
if (need[process_id][i] > available[i]) {
flag = false;
break;
}
}
return flag;
}
// Print all the safe-sequences
function safe_sequence(marked, allocated, max, need, available, safe) {
for (let i = 0; i < P; i++) {
// check if it is not marked
// already and can be allocated
if (!marked[i] && is_available(i, allocated, max, need, available)) {
// mark the process
marked[i] = true;
// increase the available
// by deallocating from process i
for (let j = 0; j < R; j++)
available[j] += allocated[i][j];
safe.push(i);
// find safe sequence by taking process i
safe_sequence(marked, allocated, max, need, available, safe);
safe.pop();
// unmark the process
marked[i] = false;
// decrease the available
for (let j = 0; j < R; j++)
available[j] -= allocated[i][j];
}
}
// if a safe-sequence is found, display it
if (safe.length === P) {
total++;
let result = "";
for (let i = 0; i < P; i++) {
result += "P" + (safe[i] + 1);
if (i !== P - 1) {
result += "--> ";
}
}
console.log(result);
}
}
// allocated matrix of size P*R
const allocated = [
[0, 1, 0],
[2, 0, 0],
[3, 0, 2],
[2, 1, 1]
];
// max matrix of size P*R
const max = [
[7, 5, 3],
[3, 2, 2],
[9, 0, 2],
[2, 2, 2]
];
// Initial total resources
const resources = [10, 5, 7];
// available vector of size R
const available = [];
for (let i = 0; i < R; i++) {
let sum = 0;
for (let j = 0; j < P; j++) {
sum += allocated[j][i];
}
available.push(resources[i] - sum);
}
// safe vector for displaying a safe-sequence
const safe = [];
// marked of size P for marking allocated process
let marked = new Array(P).fill(false);
// need matrix of size P*R
let need = new Array(P);
for (let i = 0; i < P; i++) {
need[i] = new Array(R);
for (let j = 0; j < R; j++) {
need[i][j] = max[i][j] - allocated[i][j];
}
}
console.log("Safe sequences are:");
safe_sequence(marked, allocated, max, need, available, []);
console.log(`\nThere are total ${total} safe-sequences`);
// This code is contributed by Prince Kumar
OutputSafe sequences are:
P2--> P4--> P1--> P3
P2--> P4--> P3--> P1
P4--> P2--> P1--> P3
P4--> P2--> P3--> P1
There are total 4 safe-sequences
Time complexity: O(P*R)
Auxiliary Space: O(P*R)
FAQ:
Q1: What are the advantages of using the Banker's Algorithm?
Employing the Banker's Algorithm has various benefits such as averting a state of deadlock and enabling every process to finish its execution seamlessly. This could aid in boosting the overall stability and dependability of the system.
Q2: What are the limitations of the Banker's Algorithm?
The Banker's Algorithm has certain limitations as it assumes resources to be fixed in number that may not be feasible in several circumstances. Additionally, the algorithm supposes that a process's maximum resource requirements are known beforehand, which may not hold true every time.
Q3: What are some real-world examples of where the Banker's Algorithm is used?
The Banker's Algorithm finds widespread usage across operating systems, resource allocation systems, manufacturing control systems, and airline reservation systems.
Similar Reads
Deadlock Detection Algorithm in Operating System
In operating systems, managing resources like memory, files, and processors is very important. Sometimes, processes (or programs) get stuck waiting for each other to release resources, leading to a situation called a deadlock. To handle deadlocks, operating systems use special methods called deadloc
7 min read
Sequence Step Algorithm in Operating System
A Discrete Event Simulation models operation of a system as a series of events in time. Each event occurs at a particular instant in time and between these instances the system is assumed to be unchanged. The Sequence Step Algorithm is implemented in a discrete event simulation system to maximize re
2 min read
Page Replacement Algorithms in Operating Systems
In an operating system that uses paging for memory management, a page replacement algorithm is needed to decide which page needs to be replaced when a new page comes in. Page replacement becomes necessary when a page fault occurs and no free page frames are in memory. in this article, we will discus
7 min read
Critical Regions in Operating System
In an operating system, a critical region refers to a section of code or a data structure that must be accessed exclusively by one method or thread at a time. Critical regions are utilized to prevent concurrent entry to shared sources, along with variables, information structures, or devices, that a
3 min read
Architecture of linux operating system
Linux is an open-source UNIX-based operating system. The main component of the Linux operating system is Linux kernel. It is developed to provide low-cost or free operating system service to personal system users, which includes an X-window system, Emacs editor, IP/TCP GUI, etc.Linux distributionA L
7 min read
Kernel I/O Subsystem in Operating System
The kernel provides many services related to I/O. Several services such as scheduling, caching, spooling, device reservation, and error handling - are provided by the kernel's I/O subsystem built on the hardware and device-driver infrastructure. The I/O subsystem is also responsible for protecting i
7 min read
Interactive Operating System
Interactive operating systems are computers that accept human inputs. Users give commands or some data to the computers by typing or by gestures. Some examples of interactive systems include MS Word and Spreadsheets, etc. They facilitate interactive behavior. Mac and Windows OS are some examples of
5 min read
Most Frequently Used (MFU) Algorithm in Operating System
MFU Algorithm is a Page Replacement Algorithm in the Operating System that replaces the page accessed a maximum number of times in the past. If more than one page is accessed the same number of times, then the page which occupied the frame first will be replaced. Page ReplacementIt is a technique of
5 min read
Last Minute Notes – Operating Systems
An Operating System (OS) is a system software that manages computer hardware, software resources, and provides common services for computer programs. It acts as an interface between the user and the computer hardware.Table of Content Types of Operating System (OS): ThreadsProcessCPU Scheduling Algor
15+ min read
Components of Operating System
An Operating system is an interface between users and the hardware of a computer system. It is a system software that is viewed as an organized collection of software consisting of procedures and functions, providing an environment for the execution of programs. The operating system manages system s
7 min read