Manpage of SEM_OPEN

SEM_OPEN

Section: Linux Programmer's Manual (3)
Updated: 2015-12-28
Index
 

NAME

sem_open - initialize and open a named semaphore  

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);

Link with -pthread.  

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 oflagargument specifies flags that control the operation of the call. (Definitions of the flags values can be obtained by including <fcntl.h>.) If O_CREATis 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_CREATand O_EXCLare specified in oflag, then an error is returned if a semaphore with the given namealready exists.

If O_CREATis specified in oflag, then two additional arguments must be supplied. The modeargument 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 valueargument specifies the initial value for the new semaphore. If O_CREATis specified, and a semaphore with the given namealready exists, then modeand valueare 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 error, sem_open() returns SEM_FAILED, with errnoset to indicate the error.  

ERRORS

EACCES
The semaphore exists, but the caller does not have permission to open it.
EEXIST
Both O_CREATand O_EXCLwere specified in oflag, but a semaphore with this namealready exists.
EINVAL
valuewas greater than SEM_VALUE_MAX.
EINVAL
nameconsists of just "/", followed by no other characters.
EMFILE
The per-process limit on the number of open file descriptors has been reached.
ENAMETOOLONG
namewas too long.
ENFILE
The system-wide limit on the total number of open files has been reached.
ENOENT
The O_CREATflag was not specified in oflagand no semaphore with this nameexists; or, O_CREATwas specified, but namewasn't well formed.
ENOMEM
Insufficient memory.
 

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).
InterfaceAttributeValue
sem_open() Thread safetyMT-Safe

 

CONFORMING TO

POSIX.1-2001, POSIX.1-2008.  

SEE ALSO

sem_close(3), sem_getvalue(3), sem_post(3), sem_unlink(3), sem_wait(3), sem_overview(7)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 16:30:15 GMT, December 12, 2016 Click Here!