#include <synch.h> (or #include <thread.h>) int rw_unlock(rwlock_t *rwlp);
Use rw_unlock(3THR) to unlock a read-write lock pointed to by rwlp. The read-write lock must be locked and the calling thread must hold the lock either for reading or writing. When any other threads are waiting for the read-write lock to become available, one of them is unblocked. (For POSIX threads, see "pthread_rwlock_unlock(3THR)".)
rw_unlock() returns zero after completing successfully. Any other returned value indicates that an error occurred. When any of the following conditions occurs, the function fails and returns the corresponding value.
rwlp points to an illegal address.