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 -pthread.

DESCRIPTION
       sem_open()  creates  a  new  POSIX semaphore or opens an existing sema-
       phore.  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 sema-
       phore  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 per-
       missions bits can be obtained by including <sys/stat.h>.)  The  permis-
       sions  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 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.

ATTRIBUTES
       For  an	explanation  of	 the  terms  used   in	 this	section,   see
       attributes(7).

       +-----------+---------------+---------+
       |Interface  | Attribute	   | Value   |
       +-----------+---------------+---------+
       |sem_open() | Thread safety | MT-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)

COLOPHON
       This page is part of release 4.10 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)