SEM_OPEN(2) BSD System Calls Manual SEM_OPEN(2)
NAME
sem_open -- initialize and open a named semaphore
SYNOPSIS
#include <semaphore.h>
sem_t *
sem_open(const char *name, int oflag, ...);
The parameters "mode_t mode" and "unsigned int value" are optional.
DESCRIPTION
The named semaphore named name is initialized and opened as specified by the argument oflag and a sema-phore semaphore
phore descriptor is returned to the calling process.
The value of oflag is formed by or'ing the following values:
O_CREAT create the semaphore if it does not exist
O_EXCL error if create and semaphore exists
If O_CREAT is specified, sem_open() requires an additional two arguments. mode specifies the permis-sions permissions
sions for the semaphore as described in chmod(2) and modified by the process' umask value (see
umask(2)). The semaphore is created with an initial value, which must be less than or equal to
SEM_VALUE_MAX.
If O_EXCL is specified and the semaphore exists, sem_open() fails. The check for the existence of the
semaphore and the creation of the semaphore are atomic with respect to all processes calling sem_open()
with O_CREAT and O_EXCL set.
When a new semaphore is created, it is given the user ID and group ID which correspond to the effective
user and group IDs of the calling process. There is no visible entry in the file system for the created
object in this implementation.
The returned semaphore descriptor is available to the calling process until it is closed with
sem_close(), or until the caller exits or execs.
If a process makes repeated calls to sem_open(), with the same name argument, the same descriptor is
returned for each successful call, unless sem_unlink() has been called on the semaphore in the interim.
If sem_open() fails for any reason, it will return a value of SEM_FAILED and sets errno. On success,
it returns a semaphore descriptor.
ERRORS
The named semaphore is opened unless:
[EACCES] The required permissions (for reading and/or writing) are denied for the given
flags; or O_CREAT is specified, the object does not exist, and permission to create
the semaphore is denied.
[EEXIST] O_CREAT and O_EXCL were specified and the semaphore exists.
[EINTR] The sem_open() operation was interrupted by a signal.
[EINVAL] The shm_open() operation is not supported; or O_CREAT is specified and value exceeds
SEM_VALUE_MAX.
[EMFILE] The process has already reached its limit for semaphores or file descriptors in use.
[ENAMETOOLONG] name exceeded SEM_NAME_LEN characters.
[ENFILE] Too many semaphores or file descriptors are open on the system.
[ENOENT] O_CREAT is not set and the named semaphore does not exist.
[ENOSPC] O_CREAT is specified, the file does not exist, and there is insufficient space
available to create the semaphore.
SEE ALSO
sem_close(2), sem_post(2), sem_trywait(2), sem_unlink(2), sem_wait(2), semctl(2), semget(2), semop(2),
umask(2)
HISTORY
sem_open() is specified in the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995).
Darwin June 8, 2000 Darwin
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