sem_t *
sem_open(const char *name, int oflag, ...)
int
sem_close(sem_t *sem)
int
sem_unlink(const char *name)
)
function creates or opens the named semaphore specified by
name.
The returned semaphore may be used in subsequent calls to
sem_getvalue(3),
sem_wait(3),
sem_trywait(3),
sem_post(3),
and
sem_close().
The following bits may be set in the
oflag
argument:
O_CREAT
The third argument to the call to
sem_open()
must be of type
and specifies the mode for the semaphore.
Only the
S_IWUSR, S_IWGRP,
and
S_IWOTH
bits are examined;
it is not possible to grant only
``read''
permission on a semaphore.
The mode is modified according to the process's file creation
mask; see
umask(2).
The fourth argument must be an
and specifies the initial value for the semaphore,
and must be no greater than
SEM_VALUE_MAX.
O_EXCL)
will fail.
This flag is ignored unless
O_CREAT
is also specified.
The
sem_close()
function closes a named semaphore that was opened by a call to
sem_open().
The
sem_unlink()
function removes the semaphore named
name.
Resources allocated to the semaphore are only deallocated when all
processes that have the semaphore open close it.
)
function returns the address of the opened semaphore.
If the same
name
argument is given to multiple calls to
sem_open()
by the same process without an intervening call to
sem_close(),
the same address is returned each time.
If the semaphore cannot be opened,
sem_open()
returns
SEM_FAILED
and the global variable
errno
is set to indicate the error.
)
function will fail if:
EACCES]oflag
at the time it was created deny access to this process.
EACCES]EEXIST]O_CREAT
and
O_EXCL
are set but the semaphore already exists.
EINTR]EINVAL])
operation is not supported for the given
name.
EINVAL]value
argument is greater than
SEM_VALUE_MAX.
ENAMETOOLONG]name
argument is too long.
ENFILE]ENOENT]O_CREAT
is not set and the named semaphore does not exist.
ENOSPC]
The
sem_close()
function will fail if:
EINVAL]sem
argument is not a valid semaphore.
The
sem_unlink()
function will fail if:
EACCES]ENAMETOOLONG]name
is too long.
ENOENT]),
sem_close(),
and
sem_unlink()
functions conform to
ISO/IEC 9945-1:1996 (``POSIX.1'') .
name:
it must begin with a slash
(`/'),
contain no other slash characters,
and be less than 14 characters in length
not including the terminating null character.