Program to work on Semapores.

/* Program to work on Semapores */

# include < unistd.h>
# include < stdlib.h>
# include < stdio.h>
# include < sys/types.h>
# include < sys/ipc.h>
# include < sys/sem.h>
#ifndef _SEMUN_H
#define _SEMUN_H
union semun{
int val;
struct semid_ds * buf;
unsigned short int * array;
struct seminfo *__buf;
};
# endif

static int set_semvalue(void);
static void del_semvalue(void);
static int semaphore_p(void);
static int semaphore_v(void);
static int sem_id;

int main(int argc, char *argv[])
{ int i;
int pause_time;
char  op_char = 'O';
srand((unsigned int) getpid());
sem_id = semget((key_t)1234,1,0666| IPC_CREAT);
    if ( argc > 1 )
    {
        if (!set_semvalue())
        {
            fprintf(stderr, "Failed to initialize semapore
");
            exit(EXIT_FAILURE);
        }
    op_char = 'X';
    sleep(2);
    }

for ( i=0; i<10;i++)
    {
    if (!semaphore_p()) exit(EXIT_FAILURE);
    printf("%c", op_char);fflush(stdout);
    pause_time = rand() % 3;
    sleep(pause_time);
    printf("%c", op_char);fflush(stdout);
    if (!semaphore_p()) exit(EXIT_FAILURE);
    pause_time = rand()  % 2;
    sleep(pause_time);
    }
printf("
 %d - finished 
", getpid());
if (argc >1 )
    {
    sleep(10);
    del_semvalue();
    }
exit(EXIT_SUCCESS);
}

static int set_semvalue(void)
{
    union semun sem_union;
    sem_union.val = 1;
    if (semctl(sem_id,0,SETVAL, sem_union) == -1) return(0);
    return(1);
}

static void del_semvalue(void)
{
    union semun sem_union;
    if (semctl(sem_id,0, IPC_RMID, sem_union) == -1)
    fprintf(stderr, "Failed to delete semaphore
");
}

static int semaphore_p(void)
{
    struct sembuf sem_b;
    sem_b.sem_num = 0;
    sem_b.sem_op = -1;
    sem_b.sem_flg = SEM_UNDO;
    if (semop(sem_id, &sem_b,1) == -1)
    {
        fprintf(stderr, "semaphore_p failed
 ");
        return(0);
    }
    return(1);
}