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 version 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, Copyright (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.opengroup.org/unix/online.html .

IEEE/The Open Group                                   2003                                           SEM_INIT(P)