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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 (consult 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. Fol-
       lowing 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 per-
       forming sem_wait(), sem_trywait(), sem_post(), and sem_destroy() opera-
       tions.  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 suc-
       cessful 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(3P)