#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <pthread.h>
#include <string.h>
#include <stdlib.h>

// gcc -pthread concat.c -o concat


// set pshared for interprocess operation
pthread_mutexattr_t attr;



int shmid_mutex,shmid_str;
key_t key;

// shared memory segment for the mutex
pthread_mutex_t *shm_mutex;

// shared memory for the string
char* shm_str;

int main(){

	pthread_mutexattr_setpshared(&attr,PTHREAD_PROCESS_SHARED);
	key = 1234;

	// create shm for mutex
	if ((shmid_mutex = shmget(key,sizeof(pthread_mutex_t),IPC_CREAT | 0666)) < 0){
		perror("Could not create shm for mutex");
		exit(1);
	}

	if ((shm_mutex = shmat(shmid_mutex,NULL,0)) < 0){
		perror("Could not attach shm for mutex");
		exit(1);
	}

	// initialize the mutex lock to the shared memory segment
	pthread_mutex_init(shm_mutex,&attr);

	key = 4567;


	// create shared memory segment for storing the string
	if ((shmid_str = shmget(key,sizeof(char)*100,IPC_CREAT | 0666)) < 0){
		perror("Could not create shm for string");
		exit(1);
	}

	if ((shm_str = shmat(shmid_str,NULL,0)) < 0){
		perror("Could not attach shm for string");
		exit(1);
	}

	// initialize the string in shared memory segment
	strcpy(shm_str,"Model Engineering College");


	while(1){
		// lock before modifying the string
		pthread_mutex_lock(shm_mutex);
		printf("%s\n",shm_str);
		strcpy(shm_str,"Model Engineering College");
		// release the lock after modification
		pthread_mutex_unlock(shm_mutex);

		// sleep for 5 secs
		sleep(5);
	}

	return 0;
}