| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | SEE ALSO | COLOPHON | The Linux Programming Interface |
SEM_OPEN(3) Linux Programmer's Manual SEM_OPEN(3)
sem_open - initialize and open a named semaphore
#include <fcntl.h> /* For O_* constants */
#include <sys/stat.h> /* For mode constants */
#include <semaphore.h>
sem_t *sem_open(const char *name, int oflag);
sem_t *sem_open(const char *name, int oflag,
mode_t mode, unsigned int value);
Link with -lrt or -pthread.
sem_open() creates a new POSIX semaphore or opens an existing semaphore. The
semaphore is identified by name. For details of the construction of name, see
sem_overview(7).
The oflag argument specifies flags that control the operation of the call.
(Definitions of the flags values can be obtained by including <fcntl.h>.) If
O_CREAT is specified in oflag, then the semaphore is created if it does not
already exist. The owner (user ID) of the semaphore is set to the effective
user ID of the calling process. The group ownership (group ID) is set to the
effective group ID of the calling process. If both O_CREAT and O_EXCL are
specified in oflag, then an error is returned if a semaphore with the given
name already exists.
If O_CREAT is specified in oflag, then two additional arguments must be
supplied. The mode argument specifies the permissions to be placed on the new
semaphore, as for open(2). (Symbolic definitions for the permissions bits can
be obtained by including <sys/stat.h>.) The permissions settings are masked
against the process umask. Both read and write permission should be granted
to each class of user that will access the semaphore. The value argument
specifies the initial value for the new semaphore. If O_CREAT is specified,
and a semaphore with the given name already exists, then mode and value are
ignored.
On success, sem_open() returns the address of the new semaphore; this address
is used when calling other semaphore-related functions. On error, sem_open()
returns SEM_FAILED, with errno set to indicate the error.
EACCES The semaphore exists, but the caller does not have permission to open
it.
EEXIST Both O_CREAT and O_EXCL were specified in oflag, but a semaphore with
this name already exists.
EINVAL value was greater than SEM_VALUE_MAX.
EINVAL name consists of just "/", followed by no other characters.
EMFILE The process already has the maximum number of files and open.
ENAMETOOLONG
name was too long.
ENFILE The system limit on the total number of open files has been reached.
ENOENT The O_CREAT flag was not specified in oflag and no semaphore with this
name exists; or, O_CREAT was specified, but name wasn't well formed.
ENOMEM Insufficient memory.
POSIX.1-2001.
sem_close(3), sem_getvalue(3), sem_post(3), sem_unlink(3), sem_wait(3),
sem_overview(7)
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at http://www.kernel.org/doc/man-pages/.
Linux 2009-02-20 SEM_OPEN(3)
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