SEM_GETVALUE(3) Linux Programmer's Manual SEM_GETVALUE(3)NAMEsem_getvalue - get the value of a semaphore
SYNOPSIS
#include <semaphore.h>
int sem_getvalue(sem_t *sem, int *sval);
DESCRIPTIONsem_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 be‐
haviour.
RETURN VALUEsem_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.
NOTES
The value of the semaphore may already have changed by the time
sem_getvalue() returns.
CONFORMING TO
POSIX.1-2001.
SEE ALSOsem_post(3), sem_wait(3), sem_overview(7)Linux 2.6.16 2006-03-25 SEM_GETVALUE(3)