SEM_GETVALUE
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
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 .