System_Software_HandsOnList2/031b.c at main · superv13/System_Software_HandsOnList2 · GitHub

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/*
..........................................................................................................................................
Name : 031b.c
Author : SHRUTI VERMA
Description : Write a program to create a semaphore and initialize value to the semaphore.
                a. create a binary semaphore
                b. create a counting semaphore
Date : 16 Sep 2025
..........................................................................................................................................
*/


#include<unistd.h>
#include<stdlib.h>
#include<stdio.h>
#include<sys/types.h>
#include<sys/ipc.h>
#include<sys/sem.h>
#include<semaphore.h>

union semun {
        int val;
        struct semid_ds *buf;
        unsigned short *array;
        struct seminfo *__buf;
    };


int main() {
    int key, semid;
    union semun u;

    struct sembuf lock = {0, -1, SEM_UNDO};
    struct sembuf unlock = {0, 1, SEM_UNDO};

    key = ftok("file.txt",65);
    semid = semget(key, 1, IPC_CREAT | IPC_EXCL | 0666);

    printf("waiting to enter critical section\n");
    if(semid>=0) {
        u.val = 3;
        semctl(semid, 0, SETVAL, u);
    } else semid = semget(key, 1, 0666);

    semop(semid, &lock, 1);
    printf("%d in critical section\n", getpid());
    printf("releasing counting semaphore : press enter\n");
    getchar();
    semop(semid, &unlock, 1);
    printf("counting semaphore released\n");

}

/*------------------------------------OUTPUT----------------------------------------------

terminal 1
vumma@vumma-VivoBook-15-ASUS-Laptop-X507UF:~/Desktop/SS/HOL2$ gcc 031b.c -o 031b.out
vumma@vumma-VivoBook-15-ASUS-Laptop-X507UF:~/Desktop/SS/HOL2$ ./031b.out
waiting to enter critical section
22776 in critical section
releasing counting semaphore : press enter

terminal 2
vumma@vumma-VivoBook-15-ASUS-Laptop-X507UF:~/Desktop/SS/HOL2$ ./031b.out
waiting to enter critical section
22817 in critical section
releasing counting semaphore : press enter

terminal 3
vumma@vumma-VivoBook-15-ASUS-Laptop-X507UF:~/Desktop/SS/HOL2$ ./031b.out
waiting to enter critical section
22808 in critical section
releasing counting semaphore : press enter

terminal 4
vumma@vumma-VivoBook-15-ASUS-Laptop-X507UF:~/Desktop/SS/HOL2$ ./031b.out
waiting to enter critical section


*/