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 construction 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 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_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  per-
       missions  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 value argument specifies the ini-
       tial 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)