My code is the following:
# include <stdio.h>
# include <sys/types.h>
# include <sys/ipc.h>
# include <sys/sem.h>
# include <unistd.h>
# include <stdlib.h>
# include <time.h>
# define NS 3
union semun {
int val; struct semid_ds *buf; ushort *array;
};
int main(void)
{
int sem_id, sem_value, i; key_t ipc_key; struct semid_ds sem_buf;
static ushort sem_array[NS] = {3, 1, 4}; union semun arg;
ipc_key = ftok(".", 'S');
/* Create semaphore */
if ((sem_id = semget(ipc_key, NS, IPC_EXCL | IPC_CREAT | 0666)) == -1) {
perror ("semget: IPC | 0666");
exit(1);
}
printf ("Semaphore identifier %d\n", sem_id);
/* Set arg (the union) to the address of the storage location for */
/* returned semid_ds value */
arg.buf = &sem_buf;
if (semctl(sem_id, 0, IPC_STAT, arg) == -1) {
perror ("semctl: IPC_STAT");
exit(2);
}
printf ("Create %s", ctime(&sem_buf.sem_ctime));
/* Set arg (the union) to the address of the initializing vector */
arg.array = sem_array;
if (semctl(sem_id, 0, SETALL, arg) == -1) {
perror("semctl: SETALL");
exit(3);
}
for (i=0; i<NS; ++i) {
if ((sem_value = semctl(sem_id, i, GETVAL, 0)) == -1) {
perror("semctl : GETVAL");
exit(4);
}
printf ("Semaphore %d has value of %d\n",i, sem_value);
}
}It worked a few times, but now it just gives the following error from the CREAT | EXCL line:
semget: IPC | 0666: File exists
and when I run ipcs at the command line, I get:
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
------ Semaphore Arrays --------
key semid owner perms nsems
------ Message Queues --------
key msqid owner perms used-bytes messages
which indicates that there are no semaphores, right? So, I'm not sure how to get rid of something that "isn't there."
Any ideas?