sem_open
NAME
sem_open - initialize and open a named semaphore
SYNOPSIS
#include <semaphore.h> I sem_t *sem_open(const char * name , int oflag ); I sem_t *sem_open(const char * name , int oflag , I mode_t mode , unsigned int value );
DESCRIPTION
R sem_open ()
creates a new POSIX semaphore or opens an existing semaphore.
The semaphore is identified by
R name .
For details of the construction of
R name ,
see
sem_overview(7).
The
oflag
argument specifies flags that control the operation of the call.
If
O_CREAT
is specified in
R 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
R oflag ,
then an error is returned if a semaphore with the given
name
already exists.
If
O_CREAT
is specified in
R 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).
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.
RETURN VALUE
On success,
R sem_open ()
returns the address of the new semaphore;
this address is used when calling other semaphore-related functions.
On error,
R sem_open ()
returns
R SEM_FAILED ,
with
errno
set to indicate the error.
ERRORS
EACCES
The semaphore exists, but the caller does not have permission to
open it.
EEXIST
Both
O_CREAT
and
O_EXCL
were specified in
R oflag ,
but a semaphore with this
name
already exists.
EINVAL
value
was greater than
R SEM_VALUE_MAX .
EMFILE
The process already has the maximum number of files and open.
ENAMETOOLONG
R 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
R oflag ,
and no semaphore with this
name
exists.
ENOMEM
Insufficient memory.
CONFORMING TO
POSIX.1-2001.
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