What is the difficulty with atomicity using multiple state varibles ?

Example

public class Test {
   private final AtomicReference<BigInteger> values 

        = new AtomicReference<BigInteger>();
   private final AtomicReference<BigInteger[]> factors
        = new AtomicReference<BigInteger[]>();

   public void process(BigInteger in) {

      // ------
   }
}

Problem

Using atomic references, we cannot update both values and factors simultaneously.

Similarly, both values cannot be fetched simultaneously.

Between the time when thread A fetches the two values, thread B could have changed them.

Solution

Update related state variables in single atomic operation instead of 2 different atomic variables.