sem_open - initialize and open a named semaphore
#include <fcntl.h> /* For O_* constants */
#include <sys/stat.h> /* For mode constants */
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 -pthread
() creates a new POSIX semaphore or opens an existing semaphore.
The semaphore is identified by name
. For details of the construction of
, see sem_overview(7)
argument specifies flags that control the operation of the
call. (Definitions of the flags values can be obtained by including
.) If O_CREAT
is specified in oflag
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
are specified in
, then an error is returned if a semaphore with the given
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
already exists, then mode
On success, sem_open
() returns the address of the new semaphore; this
address is used when calling other semaphore-related functions. On error,
() returns SEM_FAILED
, with errno
set to indicate
- The semaphore exists, but the caller does not have permission to open
- Both O_CREAT and O_EXCL were specified in oflag, but
a semaphore with this name already exists.
- value was greater than SEM_VALUE_MAX.
- name consists of just "/", followed by no other
- The process already has the maximum number of files and open.
- name was too long.
- The system limit on the total number of open files has been reached.
- 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.
- Insufficient memory.
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