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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | SEE ALSO | COLOPHON |
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 -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 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.
For an explanation of the terms used in this section, see
attributes(7).
┌───────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├───────────┼───────────────┼─────────┤
│sem_open() │ Thread safety │ MT-Safe │
└───────────┴───────────────┴─────────┘
POSIX.1-2001, POSIX.1-2008.
sem_close(3), sem_getvalue(3), sem_post(3), sem_unlink(3),
sem_wait(3), sem_overview(7)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2015-12-28 SEM_OPEN(3)
Pages that refer to this page: umask(2), sem_close(3), sem_unlink(3), sem_overview(7)