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 -lrt or -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.

CONFORMING TO
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 3.17 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.