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.1-2001 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.
ATTRIBUTES¶
Multithreading (see pthreads(7))¶
The
sem_getvalue() function is thread-safe.
POSIX.1-2001.
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 3.74 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
http://www.kernel.org/doc/man-pages/.
