Use rw_trywrlock(3C) to attempt to acquire a write lock on the read-write lock pointed to by rwlp.
#include <synch.h> (or #include <thread.h>) int rw_trywrlock(rwlock_t *rwlp);
When the read-write lock is already locked for reading or writing, rw_trywrlock() returns an error. For POSIX threads, see pthread_rwlock_trywrlock Syntax.
rw_trywrlock() returns zero after completing successfully. Any other return 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.
The read-write lock pointed to by rwlp was already locked.