sem_open(3) [suse man page]
SEM_OPEN(3) Linux Programmer's Manual SEM_OPEN(3) 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 -lrt or -pthread. DESCRIPTION
sem_open() creates a new POSIX semaphore or opens an existing semaphore. The semaphore is identified by name. For details of the con- struction 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 sem- aphore 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 per- missions 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, 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. 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 process already has the maximum number of files and open. ENAMETOOLONG 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 oflag and no semaphore with this name exists; or, O_CREAT was specified, but name wasn't well formed. ENOMEM Insufficient memory. CONFORMING TO
POSIX.1-2001. SEE ALSO
sem_close(3), sem_getvalue(3), sem_post(3), sem_unlink(3), sem_wait(3), sem_overview(7) COLOPHON
This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. Linux 2009-02-20 SEM_OPEN(3)
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SEM_OPEN(2) BSD System Calls Manual SEM_OPEN(2) NAME
sem_open -- initialize and open a named semaphore SYNOPSIS
#include <semaphore.h> sem_t * sem_open(const char *name, int oflag, ...); The parameters "mode_t mode" and "unsigned int value" are optional. DESCRIPTION
The named semaphore named name is initialized and opened as specified by the argument oflag and a semaphore descriptor is returned to the calling process. The value of oflag is formed by or'ing the following values: O_CREAT create the semaphore if it does not exist O_EXCL error if create and semaphore exists If O_CREAT is specified, sem_open() requires an additional two arguments. mode specifies the permissions for the semaphore as described in chmod(2) and modified by the process' umask value (see umask(2)). The semaphore is created with an initial value, which must be less than or equal to SEM_VALUE_MAX. If O_EXCL is specified and the semaphore exists, sem_open() fails. The check for the existence of the semaphore and the creation of the sem- aphore are atomic with respect to all processes calling sem_open() with O_CREAT and O_EXCL set. When a new semaphore is created, it is given the user ID and group ID which correspond to the effective user and group IDs of the calling process. There is no visible entry in the file system for the created object in this implementation. The returned semaphore descriptor is available to the calling process until it is closed with sem_close(), or until the caller exits or execs. If a process makes repeated calls to sem_open(), with the same name argument, the same descriptor is returned for each successful call, unless sem_unlink() has been called on the semaphore in the interim. If sem_open() fails for any reason, it will return a value of SEM_FAILED and sets errno. On success, it returns a semaphore descriptor. ERRORS
The named semaphore is opened unless: [EACCES] The required permissions (for reading and/or writing) are denied for the given flags; or O_CREAT is specified, the object does not exist, and permission to create the semaphore is denied. [EEXIST] O_CREAT and O_EXCL were specified and the semaphore exists. [EINTR] The sem_open() operation was interrupted by a signal. [EINVAL] The shm_open() operation is not supported; or O_CREAT is specified and value exceeds SEM_VALUE_MAX. [EMFILE] The process has already reached its limit for semaphores or file descriptors in use. [ENAMETOOLONG] name exceeded PSEMNAMLEN characters. [ENFILE] Too many semaphores or file descriptors are open on the system. [ENOENT] O_CREAT is not set and the named semaphore does not exist. [ENOSPC] O_CREAT is specified, the file does not exist, and there is insufficient space available to create the semaphore. SEE ALSO
sem_close(2), sem_post(2), sem_trywait(2), sem_unlink(2), sem_wait(2), semctl(2), semget(2), semop(2), umask(2) HISTORY
sem_open() is specified in the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995). Darwin June 8, 2000 Darwin