Reader Paul Kim pointed out an entry on Michael Tsai's blog about making dispatch_once fast. While the comment in the dispatch_once source code is fascinating and informative, it doesn't quite delve into the detail that some would like to see. Since this is one of my favorite hacks, for today's article I'm going to discuss exactly what's going on there and how it all works.

It's time for another crazy edition of Friday Q&A. Today, Paul Kim has suggested that I give a tour of OSAtomic, OS X's built-in low-level functions for lockless thread-safe operations. Given the announcement Wednesday of the dual-core iPad 2, this was a particularly prescient suggestion on his part.

Readers of this blog may be interested in my recent appearance on Late Night Cocoa. I discussed the fundamental principles and basic concepts behind lockless thread-safe data structures. You can access the episode here.