Locks the specified reader-writer lock in the read mode.
#include <synch.h>
int rw_rdlock (
rwlock_t *rwlp );
(IN) Points to the reader-writer lock to be acquired in the read mode.
Returns 0; no error conditions have been defined.
If the lock cannot be acquired immediately, the calling thread waits until the lock can be acquired. No assumptions can be made about the way in which the calling thread might wait for the lock to become free. The reader-writer lock is not guaranteed to be FIFO. On return, the calling thread has acquired the specified lock in the read mode.
UNIX International reader-writer locks are not recursive. Attempting to acquire a recursive read lock causes deadlock.