The fact that the iPad only lets me see one app at a time often does not help me focus. Instead, it forces me to switch between apps constantly, thus preventing me from focusing on my task. Every time I have to deal with the iPad’s task switching, I’m interrupted.

To see how you can use these, let’s consider how you would write OSAtomicAdd32 using compare and swap. Again, it works using a transaction model. First, fetch the original value. Then add to obtain a new value. Finally, use compare and swap with the original and new values. If it failed, go back and try everything again.