If an error condition occurs, this routine returns an integer
    value indicating the type of error. Possible return values are as
    follows:

    Return      Description

    0           Successful completion, the read-write lock object was
                acquired for write access.
    [EBUSY]     The read-write lock could not be acquired for write
                access because it was already locked for write access
                or for read access.
    [EDEADLCK]  The current thread already owns the read-write lock
                for write or read access.
    [EINVAL]    The value specified by rwlock does not refer to an
                initialized read-write lock object.