Use rw_tryrdlock(3C) to attempt to acquire a read lock on the read-write lock pointed to by rwlp.
#include <synch.h> (or #include <thread.h>) int rw_tryrdlock(rwlock_t *rwlp);
When the read-write lock is already locked for writing, rw_tryrdlock() returns an error. Otherwise, the read lock is acquired. For POSIX threads, see pthread_rwlock_tryrdlock Syntax.
rw_tryrdlock() 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.