Lock this reader-writer mutex for reading. If there are no active or pending write locks, lock this mutex for reading and return immediately. Otherwise, block until the read lock on this mutex is acquired. Use unlockRead or unlock to release the lock on this mutex. The behavior is undefined if this method is called from a thread that already has a lock on this mutex.
Declared in <bslmt_readerwritermuteximpl.h>
void
lockRead();