Manpages - sem_getvalue.3
Table of Contents
![](https://distro.tube/img/logo.png)
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 5.13 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/.