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sem_open(2) [osx man page]

SEM_OPEN(2)						      BSD System Calls Manual						       SEM_OPEN(2)

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 SEM_NAME_LEN 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

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SEM_OPEN(3)						   BSD Library Functions Manual 					       SEM_OPEN(3)

sem_open, sem_close, sem_unlink -- named semaphore operations LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <semaphore.h> sem_t * sem_open(const char *name, int oflag, ...); int sem_close(sem_t *sem); int sem_unlink(const char *name); DESCRIPTION
The sem_open() function creates or opens the named semaphore specified by name. The returned semaphore may be used in subsequent calls to sem_getvalue(3), sem_wait(3), sem_trywait(3), sem_post(3), and sem_close(). This implementation places strict requirements on the value of name: it must begin with a slash ('/') and contain no other slash characters. The following bits may be set in the oflag argument: O_CREAT Create the semaphore if it does not already exist. The third argument to the call to sem_open() must be of type mode_t and specifies the mode for the semaphore. Only the S_IWUSR, S_IWGRP, and S_IWOTH bits are examined; it is not possible to grant only ``read'' permission on a semaphore. The mode is modified according to the process's file creation mask; see umask(2). The fourth argument must be an unsigned int and specifies the initial value for the semaphore, and must be no greater than SEM_VALUE_MAX. O_EXCL Create the semaphore if it does not exist. If the semaphore already exists, sem_open() will fail. This flag is ignored unless O_CREAT is also specified. The sem_close() function closes a named semaphore that was opened by a call to sem_open(). The sem_unlink() function removes the semaphore named name. Resources allocated to the semaphore are only deallocated when all processes that have the semaphore open close it. RETURN VALUES
If successful, the sem_open() function returns the address of the opened semaphore. If the same name argument is given to multiple calls to sem_open() by the same process without an intervening call to sem_close(), the same address is returned each time. If the semaphore cannot be opened, sem_open() returns SEM_FAILED and the global variable errno is set to indicate the error. The sem_close() and sem_unlink() functions return the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ERRORS
The sem_open() function will fail if: [EACCES] The semaphore exists and the permissions specified by oflag at the time it was created deny access to this process. [EACCES] The semaphore does not exist, but permission to create it is denied. [EEXIST] O_CREAT and O_EXCL are set but the semaphore already exists. [EINTR] The call was interrupted by a signal. [EINVAL] The sem_open() operation is not supported for the given name. [EINVAL] The value argument is greater than SEM_VALUE_MAX. [ENAMETOOLONG] The name argument is too long. [ENFILE] The system limit on semaphores has been reached. [ENOENT] O_CREAT is not set but the named semaphore does not exist. [ENOSPC] There is not enough space to create the semaphore. The sem_close() function will fail if: [EINVAL] The sem argument is not a valid semaphore. The sem_unlink() function will fail if: [EACCES] Permission is denied to unlink the semaphore. [ENAMETOOLONG] The specified name is too long. [ENOENT] The named semaphore does not exist. SEE ALSO
close(2), open(2), umask(2), unlink(2), sem_getvalue(3), sem_post(3), sem_trywait(3), sem_wait(3) STANDARDS
The sem_open(), sem_close(), and sem_unlink() functions conform to ISO/IEC 9945-1:1996 (``POSIX.1''). HISTORY
Support for named semaphores first appeared in FreeBSD 5.0. BSD
January 9, 2010 BSD
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