[Proof Of Concept] IPCc in C

sem_sysV.c

/*
 *								HOW TO USE ?
 *
 *	1. Compile the program using `gcc sem_sysV.c`
 *  2. Start the processes one by one
 *  3. You'll see that only one process will enter the "main loop"
 *  4. if you want another process to enter the loop, you must kill the process that is running the loop.
 * 
*/

// general purpose includes
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <signal.h>

//perms
#include <sys/stat.h>

// IPCs related includes
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>

#define PROJ_ID 1
#define KEY_PATH "./key.lock"
#define NSEMS 1
#define P 1
#define V -1
#define T 0

static volatile char keep_running = 1;


void test(int semid)
{
    int toto;
    struct sembuf buf[2];

    buf[0].sem_num = 0;
    buf[0].sem_op = T;
    buf[0].sem_flg = 0;
	buf[1].sem_num = 0;
    buf[1].sem_op = P;
    buf[1].sem_flg = 0;
    if ((toto = semop(semid, buf, 2)) == -1)
    {
        printf("Error during test: %s\n", strerror(errno));
        exit(-1);
    }
}

void increment(int semid)
{
    struct sembuf buf;

    buf.sem_num = 0;
    buf.sem_op = P;
    buf.sem_flg = 0;
    if ((semop(semid, &buf, 1)) == -1)
    {
        printf("Error during increment: %s\n", strerror(errno));
        exit(-1);
    }
}

void decrement(int semid)
{
    struct sembuf buf;

    buf.sem_num = 0;
    buf.sem_op = V;
    buf.sem_flg = 0;
    if ((semop(semid, &buf, 1)) == -1)
    {
        printf("Error during decrement: %s\n", strerror(errno));
        exit(-1);
    }
}

void keyboard_interrupt(int dummy)
{
    keep_running = 0;
}

int main(int argc, char **argv)
{
    int semid;
    key_t ipc_key;

    signal(SIGINT, keyboard_interrupt);

    if ((ipc_key = ftok(KEY_PATH, PROJ_ID)) == -1)
    {
        printf("cannot acquire key :%s\n", strerror(errno));
        exit(-1);
    }

    if ((semid = semget(ipc_key, NSEMS, IPC_CREAT | S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP )) == -1)
    {
        printf("Cannot create/get Semaphore: %s\n", strerror(errno));
        exit(-1);
    }
    printf("Get sem, id: %d\n", semid);

	if (argc > 1 && !strcmp(argv[1], "destroy"))
	{
		// Destroying semaphore
		semctl(semid, 0, IPC_RMID, 0);
		return(0);
	}

    printf("testing...\n");
    test(semid);

    while (keep_running) {
        printf("execution...\n");
    }
    printf("decrementing...\n");
    decrement(semid);

    return (0);
}