sem_getvalue - get the value of a semaphore
POSIX threads library (
libpthread,
-lpthread)
#include <semaphore.h>
int sem_getvalue(sem_t *restrict sem, int *restrict sval);
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.
sem_getvalue() returns 0 on success; on error, -1 is returned and
errno is set to indicate the error.
- EINVAL
-
sem is not a valid semaphore. (The glibc
implementation currently does not check whether sem is valid.)
For an explanation of the terms used in this section, see
attributes(7).
Interface |
Attribute |
Value |
sem_getvalue () |
Thread safety |
MT-Safe |
POSIX.1-2001, POSIX.1-2008.
The value of the semaphore may already have changed by the time
sem_getvalue() returns.
sem_post(3),
sem_wait(3),
sem_overview(7)