SEM_GETVALUE(3)

NAME
sem_getvalue - get the value of a semaphore

LIBRARY
librt

SYNOPSIS
#include <semaphore.h>
int
sem_getvalue(sem_t * restrict sem, int * restrict sval);

DESCRIPTION
The sem_getvalue() 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() is actually run.

RETURN VALUES

ERRORS
sem_getvalue() will fail if:

[EINVAL]
    sem points to an invalid semaphore.

SEE ALSO
sem_post(3), sem_timedwait(3), sem_trywait(3), sem_wait(3)

STANDARDS
sem_getvalue() conforms to p1003.1-96.

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.