Initializes a read/write mutex reader proxy object.
Acquires a read lock on the enclosing mutex.
Attempts to acquire a read lock on the enclosing mutex. If one can be obtained without blocking, the lock is acquired and true is returned. If not, the lock is not acquired and false is returned.
Releases a read lock on the enclosing mutex.
This class can be considered a mutex in its own right, and is used to negotiate a read lock for the enclosing mutex.