SEM_INIT(3P)                                        POSIX Programmer's Manual                                       SEM_INIT(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       sem_init - initialize an unnamed semaphore (REALTIME)

SYNOPSIS
       #include <semaphore.h>

       int sem_init(sem_t *sem, int pshared, unsigned value);


DESCRIPTION
       The sem_init() function shall initialize the unnamed semaphore referred to by sem. The value of the initialized semaphore
       shall be value. Following a successful call to sem_init(), the semaphore may be used in subsequent calls  to  sem_wait(),
       sem_trywait(), sem_post(), and sem_destroy().  This semaphore shall remain usable until the semaphore is destroyed.

       If  the  pshared argument has a non-zero value, then the semaphore is shared between processes; in this case, any process
       that can access the semaphore sem can use sem for performing sem_wait(),  sem_trywait(),  sem_post(),  and  sem_destroy()
       operations.

       Only  sem  itself  may  be  used  for  performing  synchronization.  The result of referring to copies of sem in calls to
       sem_wait(), sem_trywait(), sem_post(), and sem_destroy() is undefined.

       If the pshared argument is zero, then the semaphore is shared between threads of the process; any thread in this  process
       can  use sem for performing sem_wait(), sem_trywait(), sem_post(), and sem_destroy() operations. The use of the semaphore
       by threads other than those created in the same process is undefined.

       Attempting to initialize an already initialized semaphore results in undefined behavior.

RETURN VALUE
       Upon successful completion, the sem_init() function shall initialize the semaphore in sem. Otherwise, it shall return  -1
       and set errno to indicate the error.

ERRORS
       The sem_init() function shall fail if:

       EINVAL The value argument exceeds {SEM_VALUE_MAX}.

       ENOSPC A  resource required to initialize the semaphore has been exhausted, or the limit on semaphores ( {SEM_NSEMS_MAX})
              has been reached.

       EPERM  The process lacks the appropriate privileges to initialize the semaphore.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       The sem_init() function is part of the Semaphores option and need not be available on all implementations.

RATIONALE
       Although this volume of IEEE Std 1003.1-2001 fails to specify a successful return value, it is likely that a  later  ver-
       sion may require the implementation to return a value of zero if the call to sem_init() is successful.

FUTURE DIRECTIONS
       None.

SEE ALSO
       sem_destroy(),    sem_post(),    sem_timedwait(),   sem_trywait(),   sem_wait(),   the   Base   Definitions   volume   of
       IEEE Std 1003.1-2001, <semaphore.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003  Edition,  Standard  for
       Information  Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy  between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group
       Standard  is  the  referee   document.   The   original   Standard   can   be   obtained   online   at   http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                  SEM_INIT(3P)