int sem_getvalue(sem_t *restrict sem, int *restrict
The sem_getvalue() function shall update 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 object to which sval points shall either be set to zero or to a negative number whose absolute value represents the number of processes waiting for the semaphore at some unspecified time during the call.
Upon successful completion, the sem_getvalue() function shall return a value of zero. Otherwise, it shall return a value of -1 and set errno to indicate the error.
The sem_getvalue() function shall fail if:
The following sections are informative.
The sem_getvalue() function is part of the Semaphores option and need not be available on all implementations.
semctl() , semget() , semop() , sem_post() , sem_timedwait() , sem_trywait() , sem_wait() , the Base Definitions volume of IEEE Std 1003.1-2001, <semaphore.h>