sem_getvalue(3p)
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, 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 .