sem_open(3) Library Functions Manual sem_open(3)
NAME
sem_open - initialize and open a named semaphore
LIBRARY
POSIX threads library (libpthread, -lpthread)
SYNOPSIS
#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);
DESCRIPTION
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 sema-
phore 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 er-
ror 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 per-
missions bits can be obtained by including <sys/stat.h>.) The permis-
sions settings are masked against the process umask. Both read and
write permission should be granted to each class of user that will ac-
cess 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, sem_open() returns the address of the new semaphore; this
address is used when calling other semaphore-related functions. On er-
ror, sem_open() returns SEM_FAILED, with errno set to indicate the er-
ror.
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 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 per-process limit on the number of open file descriptors has
been reached.
ENAMETOOLONG
name was too long.
ENFILE The system-wide 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.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│ sem_open() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
POSIX.1-2008.
HISTORY
POSIX.1-2001.
SEE ALSO
sem_close(3), sem_getvalue(3), sem_post(3), sem_unlink(3), sem_wait(3),
sem_overview(7)
Linux man-pages 6.9.1 2024-05-02 sem_open(3)
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