SEM_GETVALUE
Section: Linux Programmer's Manual (3)
Updated: 2021-03-22
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NAME
sem_getvalue - get the value of a semaphore
SYNOPSIS
#include <semaphore.h>
int sem_getvalue(sem_t *restrict sem, int *restrict sval);
Link with -pthread.
DESCRIPTION
sem_getvalue()
places the current value of the semaphore pointed to
sem
into the integer pointed to by
sval.
If one or more processes or threads are blocked
waiting to lock the semaphore with
sem_wait(3),
POSIX.1 permits two possibilities for the value returned in
sval:
either 0 is returned;
or a negative number whose absolute value is the count
of the number of processes and threads currently blocked in
sem_wait(3).
Linux adopts the former behavior.
RETURN VALUE
sem_getvalue()
returns 0 on success;
on error, -1 is returned and
errno
is set to indicate the error.
ERRORS
- EINVAL
-
sem
is not a valid semaphore.
(The glibc implementation currently does not check whether
sem
is valid.)
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
sem_getvalue()
| Thread safety | MT-Safe
|
CONFORMING TO
POSIX.1-2001, POSIX.1-2008.
NOTES
The value of the semaphore may already have changed by the time
sem_getvalue()
returns.
SEE ALSO
sem_post(3),
sem_wait(3),
sem_overview(7)
COLOPHON
This page is part of release 5.11 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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