SEM_GETVALUE(3) Linux Programmer's Manual SEM_GETVALUE(3)
NAME
sem_getvalue - get the value of a semaphore
SYNOPSIS
#include <semaphore.h>
int sem_getvalue(sem_t *sem, int *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 be-
havior.
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 cur-
rently does not check whether sem is valid.)
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(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 5.07 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/.
Linux 2020-06-09 SEM_GETVALUE(3)