int sem_getvalue (
The sem_getvalue function updates a location referenced by the sval argument with the value of semaphore sem. The updated value represents an actual semaphore value that occurred during the call, but may not be the actual value of the semaphore at the time that the value is returned to the calling process.
If the semaphore is locked, the value returned will either be zero or a negative number indicating the number of processes waiting for the semaphore at some time during the call.
On a successful call, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate that an error occurred.
The sem_getvalue function fails under the following condition:
Functions: sem_post(3), sem_trywait(3), sem_wait(3) delim off