NAME

sem_getvalue - get the value of a semaphore (REALTIME)

 SYNOPSIS

#include <semaphore.h>

int sem_getvalue(sem_t *sem, int *sval);

 DESCRIPTION

The sem_getvalue() function updates the location referenced by the sval argument to have the value of the semaphore referenced by sem without affecting the state of the semaphore. The updated value represents an actual semaphore value that occurred at some unspecified time during the call, but it need not be the actual value of the semaphore when it is returned to the calling process.

If sem is locked, then the value returned by sem_getvalue() is either zero or a negative number whose absolute value represents the number of processes waiting for the semaphore at some unspecified time during the call.

 RETURN VALUE

Upon successful completion, the function returns a value of zero. Otherwise, the function returns a value of -1 and sets errno to indicate the error.

 ERRORS

The sem_getvalue() function will fail if:

[EINVAL]

The sem argument does not refer to a valid semaphore.

[ENOSYS]

The function sem_getvalue() is not supported by this implementation.

 EXAMPLES

None.

 APPLICATION USAGE

None.

 FUTURE DIRECTIONS

None.

 SEE ALSO

semctl(), semget(), semop(), sem_post(), sem_trywait(), sem_wait(), <semaphore.h>.

DERIVATION

Derived from the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995)