IPC shared memory Proof Of Concept

shm_sysV.c

/*
 *								HOW TO USE ?
 *
 *	1. Compile the program using `gcc shm_sysV.c`
 *  2. Start the master process by typing `./a.out "Any string of your choice"`
 *  3. Finally, you can visualize the shared buffer of memory by starting another process
 * 	   without any arguments: `./a.out`.
 *  4. When you're done you can kill the master process and free the memory (Ctrl+C)
 * 
*/

// General purpose includes
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <signal.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>


// SHM includes
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>

#define PROJ_ID 1
#define KEY_PATH "./key.lock"
#define SIZE 64

static volatile char keep_running = 1;

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

void master(char *str, int shmid) {
    char *buffer;

    signal(SIGINT, keyboard_interrupt);

	if ((buffer = shmat(shmid, NULL, 0)) == -1) {
		printf("Cannot attach memory :%s\n", strerror(errno));
        exit(-1);
	}

	strcpy(buffer, str);

	while (keep_running) {;}

	if (shmdt(buffer) == -1) {
        perror("shmdt");
        exit(1);
    }

	if (shmctl(shmid, IPC_RMID, 0) == -1) {
        perror("shmctl");
        exit(1);
    }

}

void slave(int shmid) {
    char *buffer;

	if ((buffer = shmat(shmid, NULL, SHM_RDONLY)) == -1) {
		printf("Cannot attach memory :%s\n", strerror(errno));
        exit(-1);
	}

	printf("Read: %s\n", buffer);

	if (shmdt(buffer) == -1) {
        perror("shmdt");
        exit(1);
    }
}

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

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

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

	if (argc < 2)
		slave(shmid);
	else
		master(argv[1], shmid);
}