Name
sem_getvalue — get the value of a semaphore
Synopsis
#include <semaphore.h>
int
sem_getvalue( |
sem_t * |
sem, |
|
int * |
sval) ; |
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 behaviour.
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.
NOTES
The value of the semaphore may already have changed by the
time sem_getvalue
()
returns.
CONFORMING TO
POSIX.1-2001.
SEE ALSO
sem_post(3), sem_wait(3), sem_overview(7)
t
Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
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