SEM_GETVALUE(3P)                                    POSIX Programmer's Manual                                   SEM_GETVALUE(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_getvalue - get the value of a semaphore (REALTIME)

SYNOPSIS
       #include <semaphore.h>

       int sem_getvalue(sem_t *restrict sem, int *restrict sval);


DESCRIPTION
       The  sem_getvalue() function shall update the location referenced by the sval argument to have the value of the semaphore
       referenced by sem without affecting the state of the semaphore. The updated value represents an  actual  semaphore  value
       that  occurred  at some unspecified time during the call, but it need not be the actual value of the semaphore when it is
       returned to the calling process.

       If sem is locked, then the object to which sval points shall either be set to zero or to a negative number whose absolute
       value represents the number of processes waiting for the semaphore at some unspecified time during the call.

RETURN VALUE
       Upon  successful completion, the sem_getvalue() function shall return a value of zero. Otherwise, it shall return a value
       of -1 and set errno to indicate the error.

ERRORS
       The sem_getvalue() function shall fail if:

       EINVAL The sem argument does not refer to a valid semaphore.


       The following sections are informative.

EXAMPLES
       None.

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

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       semctl(), semget(), semop(), 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_GETVALUE(3P)