NAME
sem_open,
sem_close, sem_unlink
— open and close named
semaphores
SYNOPSIS
#include
<semaphore.h>
sem_t *
sem_open(const
char *name, int
oflag, ...);
int
sem_close(sem_t
*sem);
int
sem_unlink(const
char *name);
DESCRIPTION
The
sem_open()
function opens and returns a named semaphore. The
sem_close()
function closes a previously opened named semaphore without removing it. The
sem_unlink()
function removes the named semaphore from the system without closing it.
RETURN VALUES
On success, sem_open() returns a pointer
to a semaphore. sem_close() and
sem_unlink() return 0 on success.
sem_open() returns SEM_FAILED and sets
errno to indicate an error.
sem_close() and sem_unlink()
return -1 and set errno to indicate an error.
ERRORS
It is an error to call sem_close() with an
unnamed semaphore or to call
sem_destroy(3) with a named semaphore.
sem_open() may fail if:
- [
ENOSPC] - Insufficient memory is available.
- [
EPERM] - An attempt was made to open a shared semaphore owned by another user.
sem_unlink() may fail for any of the
reasons listed in unlink(2).
SEE ALSO
sem_destroy(3), sem_getvalue(3), sem_init(3), sem_post(3), sem_wait(3)
STANDARDS
sem_open(),
sem_close(), and
sem_unlink() appear in ISO/IEC
9945-1:1996 (“POSIX.1”). This implementation deviates
from the standard by permitting less sharing.