get the value of a semaphore
function sets the variable pointed to by sval to the
current value of the semaphore pointed to by sem, as
of the time that the call to
sem_getvalue() function returns the
value 0 if successful; otherwise the value -1 is returned and
the global variable errno is set to indicate the
sem_getvalue() will fail if:
- sem points to an invalid semaphore.
sem_destroy(3), sem_init(3), sem_open(3), sem_post(3), sem_wait(3)
sem_getvalue() conforms to
ISO/IEC 9945-1:1996 (“POSIX.1”).
The value of the semaphore is never negative, even if there are threads blocked on the semaphore. POSIX is somewhat ambiguous in its wording with regard to what the value of the semaphore should be if there are blocked waiting threads, but this behavior is conformant, given the wording of the specification.