#include <synch.h> (or #include <thread.h>) int rw_trywrlock(rwlock_t *rwlp);
Use rw_trywrlock(3THR) to attempt to acquire a write lock on the read-write lock pointed to by rwlp. When the read-write lock is already locked for reading or writing, it returns an error. (For POSIX threads, see "pthread_rwlock_trywrlock(3THR)".)
rw_trywrlock() 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.