Function ordered_read_lock 

pub fn ordered_read_lock<'a, R: RwLockLike>(
    r1: &'a R,
    r2: &'a R,
) -> (R::ReadGuard<'a>, R::ReadGuard<'a>)

Lock r1 and r2 in a consistent order (using the memory address of r1 and r2) for reading.