SEM_GETVALUE(3)            POSIX Programmer's Manual           SEM_GETVALUE(3)



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

NAME
       sem_getvalue -- get the value of a semaphore

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 may fail if:

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

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       semctl(), semget(), semop(), sem__post(), sem__timedwait(), sem__trywait()

       The Base Definitions volume of POSIX.1-2017, <semaphore.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                      SEM_GETVALUE(3)
