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main()
{
int shmid;
int semid;
key_t key;
int *child_shm, *parent_shm;
union semun arg;
int i;
struct sembuf operations[1];
int status;
int pid;
/* Create the shared segment.& semaphore. */
if ((shmid = shmget(SHM_KEY, SHMSZ, IPC_CREAT | 0666)) < 0)
{
perror("shmget");
exit(1);
}
if ((semid = semget(SEM_KEY, 1, IPC_CREAT | 0666)) < 0)
{
perror("semget");
exit(1);
}
/*
* Initialize the semaphore to value 1. The idea is multiple processes
* do semop() of -1. So only one is allowed in critical section.
* initialize the shm to 0.
*/
arg.val = 1;
if (semctl(semid, 0, SETVAL, arg) < 0)
{
perror("semctl");
exit(1);
}
NP Lab Manual , RNEC page: 19