4-part series from Mike Ash:
- http://www.mikeash.com/pyblog/friday-qa-2009-08-28-intro-to-grand-central-dispatch-part-i-basics-and-dispatch-queues.html
- http://www.mikeash.com/pyblog/friday-qa-2009-09-04-intro-to-grand-central-dispatch-part-ii-multi-core-performance.html
- http://www.mikeash.com/pyblog/friday-qa-2009-09-11-intro-to-grand-central-dispatch-part-iii-dispatch-sources.html
The official reference document from apple:
