int create_sema(int key, int val) {
int semid;
struct sembuf sem_tmp;
semid = semget(key, 1, 0777|IPC_CREAT|IPC_EXCL);
if(semid == -1) {
perror("create_sema: ");
if (errno == EEXIST) {
semid = semget(key, 1, 0777);
if (semctl(semid, 0, IPC_RMID) >= 0) {
semid = semget(key, 1, 0777|IPC_CREAT|IPC_EXCL);
if (semid == -1) {
perror("create_sema: semget: ");
return FALSE;
}
} else {
perror("create_sema: semaphore exists and can't be removed: ");
return FALSE;
}
} else {
perror("create_sema: ");
return FALSE;
}
}
set_sembuf_struct(&sem_tmp, 0, val, 0);
semop(semid, &sem_tmp, 1);
return TRUE;
}
int main(int argc, char *argv[])
{
pid_t pid, ppid, childpid, w; // For process ID, parent process ID, child process, and wait
pid_t leader = getpid(); // Used to make sure the child process finishes before the parent is killed
int semid, semop_ret, sem_value, i, j, opt; // Semaphore ID, Semaphore value, i and j for for statement, and Semaphore option
int N, status, k; // Number of processes, the status for wait, and the delay paramater
char buf_num[MAX_CANON], *c_ptr; // Character buffer and pointer to navigate it
key_t ipc_key; // Key for Semaphore
struct semid_ds sem_buf; // Allows access for Semaphore set and reference to the array of type sem
/* Check input arguments are 4 */
if (argc != 4)
{
printf("Invalid input. The number of arguments must be 4.\n");
exit(1);
}
/* Make sure number of precesses is more than 0 */
if(atoi(argv[1]) > 0)
{
N = atoi(argv[1]);
}
else
{
printf("Invalid input. %d(N) must be greater then 0.\n", atoi(argv[1]));
exit(1);
}
/* Declare the operation for semaphore protection */
if (strcmp(argv[2], "n") == 0) /* No semaphore protection */
{
opt = 0;
}
else if (strcmp(argv[2], "s") == 0) /* Semaphore protection */
{
opt = 1;
}
else
{
printf("Invalid input for the second argument. %s should be 'n' or 's'.\n", argv[1]);
exit(1);
}
/* Initialize the delay parameter, 'k', if it is greater than 0 */
if(atoi(argv[3]) > 0)
k = atoi(argv[3]);
else
{
printf("Invalid input. %d(k) must be greater then 0.\n", atoi(argv[3]));
exit(1);
}
/* Decalre semaphore wait and increment */
struct sembuf semwait[1];
struct sembuf semsignal[1];
/* Initialize semaphore element to 1 */
set_sembuf_struct(semwait, 0, -1, 0);
set_sembuf_struct(semsignal, 0, 1, 0);
ipc_key = ftok(".", 'S'); // Generate a key from a pathname
/* Create semaphore */
/* A semaphore is always created reguardless of semaphore procetion. It is only used if k = s */
if ((semid = semget(ipc_key, 1, IPC_CREAT | IPC_EXCL | 0666)) == -1)
{
perror ("semget: IPC | 0666");
exit(1);
}
/* Attempt to increment the semaphore */
if(semop(semid, semsignal, 1) == -1)
{
printf("%ld: semaphore increment failed - %s\n", (long)getpid(), strerror(errno));
/* Remove the semaphore if unable to increment */
if (semctl(semid, 0, IPC_RMID) == -1)
printf ("%ld: could not delete semaphore - %s\n", (long)getpid(), strerror(errno));
exit(1);
}
/* Create the processes based on the value of 'N' */
childpid = 0;
for(i = 1; i < N; i++)
{
if(childpid = fork()) break;
}
/* If semaphore protection is used, decrement the semaphore and enter it */
if(opt)
{
while (( (semop_ret = semop(semid, semwait, 1) ) == -1) && (errno ==EINTR));
if (semop_ret == -1)
printf ("%ld: semaphore decrement failed - %s\n", (long)getpid(), strerror(errno));
}
/* Create the output message and put in into a character buffer */
sprintf(buf_num,"i: %d: process ID: %6ld parent ID: %6ld child ID: %6ld\n",i,(long)getpid(), (long)getppid(), (long)childpid);
/* Direct the pointer to the char buffer */
c_ptr = buf_num;
/* Specifies the buffer to be used by the stream for I/O operations, which becomes a */
/* fully buffered stream. Or, alternatively, if buffer is a null pointer, buffering is */
/* disabled for the stream, which becomes an unbuffered stream. */
setbuf(stdout, NULL);
/* Cycle through the char buffer using the pointer until it points to NULL */
while (*c_ptr != '\0')
{
fputc(*c_ptr, stderr);
/* Sleep in usec microsecond using the delay adjustment parameter */
usleep(k);
c_ptr++;
}
/* If semaphor protection is enabled, increment the semaphore */
if(opt)
{
while ( ( (semop_ret = semop(semid, semsignal, 1) ) == -1) && (errno == EINTR) );
if (semop_ret == -1)
printf ("%ld: semaphore increment failed - %s\n", (long)getpid(), strerror(errno));
}
/* Wait for the child process to complete before the parent is killed */
waitpid(childpid, &status, 0);
/* Once the process has completed, remove the semaphore */
if(leader == getpid())
{
if(semctl(semid, 0, IPC_RMID) == -1)
{
printf("%ld: couldn't delete semaphore - %s\n", (long)getpid(), strerror(errno));
exit(1);
}
}
exit(0);
}
