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 semaphore 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 permissions 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 sem-
     aphore 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 PSEMNAMLEN 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