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_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(3POSIX)