Banker's Algorithm Implementation in C

This program demonstrates the Banker's Algorithm, a classic deadlock avoidance strategy used in operating systems to manage resource allocation safely.

C Source Code

#include <stdio.h>

int n, m;
int alloc[10][10], max[10][10], need[10][10];
int avail[10], work[10], finish[10];

// Safety Algorithm
int checkSafety() {
    int seq[10], count = 0;

    for (int i = 0; i < n; i++) finish[i] = 0;
    for (int i = 0; i < m; i++) work[i] = avail[i];

    while (count < n) {
        int found = 0;
        for (int i = 0; i < n; i++) {
            if (!finish[i]) {
                int j;
                for (j = 0; j < m; j++) {
                    if (need[i][j] > work[j]) break;
                }
                if (j == m) {
                    for (int k = 0; k < m; k++) work[k] += alloc[i][k];
                    seq[count++] = i;
                    finish[i] = 1;
                    found = 1;
                }
            }
        }
        if (!found) break;
    }

    if (count == n) {
        printf("\nSystem is SAFE\nSafe Sequence: ");
        for (int i = 0; i < n; i++) printf("P%d ", seq[i]);
        printf("\n");
        return 1;
    } else {
        printf("\nSystem is UNSAFE\n");
        return 0;
    }
}

int main() {
    int p, req[10];
    printf("Enter number of processes and resources: ");
    scanf("%d %d", &n, &m);

    printf("\nEnter Allocation Matrix:\n");
    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++) scanf("%d", &alloc[i][j]);

    printf("\nEnter Max Matrix:\n");
    for (int i = 0; i < n; i++)
        for (int j = 0; j < m; j++) {
            scanf("%d", &max[i][j]);
            need[i][j] = max[i][j] - alloc[i][j];
        }

    printf("\nEnter Available Resources:\n");
    for (int i = 0; i < m; i++) scanf("%d", &avail[i]);

    // Initial Safety Check
    checkSafety();

    // Request Section
    printf("\nEnter process number (0 to %d): ", n - 1);
    scanf("%d", &p);
    printf("Enter request for that process:\n");
    for (int i = 0; i < m; i++) scanf("%d", &req[i]);

    // Check request <= need
    for (int i = 0; i < m; i++) {
        if (req[i] > need[p][i]) {
            printf("\nRequest exceeds need → DENIED\n");
            return 0;
        }
    }

    // Check request <= available
    for (int i = 0; i < m; i++) {
        if (req[i] > avail[i]) {
            printf("\nResources not available → WAIT\n");
            return 0;
        }
    }

    // Pretend allocation
    for (int i = 0; i < m; i++) {
        avail[i] -= req[i];
        alloc[p][i] += req[i];
        need[p][i] -= req[i];
    }

    printf("\nChecking system after allocation...\n");

    // Final safety check
    if (checkSafety()) {
        printf("Request GRANTED\n");
    } else {
        printf("Request leads to UNSAFE state → ROLLING BACK\n");
        // Rollback
        for (int i = 0; i < m; i++) {
            avail[i] += req[i];
            alloc[p][i] -= req[i];
            need[p][i] += req[i];
        }
    }
    return 0;
}

How the Algorithm Works

• Safety Check: Determines if the system can satisfy all requests without entering a deadlock.
• Resource Request: Validates if the requested resources are within the process's declared maximum needs.
• Rollback Mechanism: If a request leads to an unsafe state, the system reverts the allocation to maintain stability.