.\" $Darwin$ .\" .\" Copyright (c) 2000-2002 Apple Computer, Inc. All rights reserved. .\" .\" @APPLE_LICENSE_HEADER_START@ .\" .\" The contents of this file constitute Original Code as defined in and .\" are subject to the Apple Public Source License Version 1.1 (the .\" "License"). You may not use this file except in compliance with the .\" License. Please obtain a copy of the License at .\" http://www.apple.com/publicsource and read it before using this file. .\" .\" This Original Code and all software distributed under the License are .\" distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER .\" EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, .\" INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, .\" FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. Please see the .\" License for the specific language governing rights and limitations .\" under the License. .\" .\" @APPLE_LICENSE_HEADER_END@ .\" .Dd June 8, 2000 .Dt SEM_OPEN 2 .Os Darwin .Sh NAME .Nm sem_open .Nd initialize and open a named semaphore .Sh SYNOPSIS .Fd #include <semaphore.h> .Ft sem_t * .Fo sem_open .Fa "const char *name" .Fa "int oflag" .Fa "..." .Fc .Pp The parameters "mode_t mode" and "unsigned int value" are optional. .Sh DESCRIPTION The named semaphore named .Fa name is initialized and opened as specified by the argument .Fa oflag and a semaphore descriptor is returned to the calling process. .Pp The value of .Fa oflag is formed by .Em or Ns 'ing the following values: .Pp .Bd -literal -offset indent -compact O_CREAT create the semaphore if it does not exist O_EXCL error if create and semaphore exists .Ed .Pp If .Dv O_CREAT is specified, .Fn sem_open requires an additional two arguments. .Fa mode specifies the permissions for the semaphore as described in .Xr chmod 2 and modified by the process' umask value (see .Xr umask 2 ) . The semaphore is created with an initial .Fa value , which must be less than or equal to .Dv SEM_VALUE_MAX . .Pp If .Dv O_EXCL is specified and the semaphore exists, .Fn sem_open fails. The check for the existence of the semaphore and the creation of the semaphore are atomic with respect to all processes calling .Fn sem_open with .Dv O_CREAT and .Dv O_EXCL set. .Pp 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. .Pp The returned semaphore descriptor is available to the calling process until it is closed with .Fn sem_close , or until the caller exits or execs. .Pp If a process makes repeated calls to .Fn sem_open , with the same .Fa name argument, the same descriptor is returned for each successful call, unless .Fn sem_unlink has been called on the semaphore in the interim. .Pp If .Fn sem_open fails for any reason, it will return a value of .Dv SEM_FAILED and sets .Va errno . On success, it returns a semaphore descriptor. .Sh ERRORS The named semaphore is opened unless: .Bl -tag -width Er .It Bq Er EACCES The required permissions (for reading and/or writing) are denied for the given flags; or .Dv O_CREAT is specified, the object does not exist, and permission to create the semaphore is denied. .It Bq Er EEXIST .Dv O_CREAT and .Dv O_EXCL were specified and the semaphore exists. .It Bq Er EINTR The .Fn sem_open operation was interrupted by a signal. .It Bq Er EINVAL The .Fn shm_open operation is not supported; or .Dv O_CREAT is specified and .Fa value exceeds .Dv SEM_VALUE_MAX . .It Bq Er EMFILE The process has already reached its limit for semaphores or file descriptors in use. .It Bq Er ENAMETOOLONG .Fa name exceeded .Dv PSEMNAMLEN characters. .It Bq Er ENFILE Too many semaphores or file descriptors are open on the system. .It Bq Er ENOENT .Dv O_CREAT is not set and the named semaphore does not exist. .It Bq Er ENOSPC .Dv O_CREAT is specified, the file does not exist, and there is insufficient space available to create the semaphore. .El .Sh SEE ALSO .Xr sem_close 2 , .Xr sem_post 2 , .Xr sem_trywait 2 , .Xr sem_unlink 2 , .Xr sem_wait 2 , .Xr semctl 2 , .Xr semget 2 , .Xr semop 2 , .Xr umask 2 .Sh HISTORY .Fn sem_open is specified in the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995).