Makes a single attempt to acquire the specified reader-writer lock in the write mode.
#include <synch.h> int rw_trywrlock ( rwlock_t *rwlp );
(IN) Points to the reader-writer lock to acquire in the write mode.
If successful, returns 0; otherwise, returns a nonzero error code.
If the lock being acquired is not immediately available, rw_trywrlock returns.