Why volatile and MemoryBarrier do not prevent operations reordering?

Question

If I understand meaning of volatile and MemoryBarrier correctly than the program below has never to be able to show any result.

It catches reordering of write operations

Answer 1

I don't think this is re-ordering.

This piece of code is simply not thread-safe:

 while (continueChecking)
 {
     int tempA = a;
     int tempB = b;
     ...

I think this scenario is possible:

1. int tempA = a; executes with the values of the last loop (a == 2)
2. There is a context switch to the Write thread
3. b = 10 and the loop stops
4. There is a context switch to the Check thread
5. int tempB = b; executes with b == 10

I notice that the calls to MemoryBarrier() enhance the chances of this scenario. Probably because they cause more context-switching.