How to Create a Synchronous Wrapper Around an Asynchronous Method

Asynchronous methods are the key to keeping your iOS app responsive. Each method running on the main thread has 1/60 of a second to return before it will affect your screen refresh rate. For long-running operations, the typical paradigm is to execute your code on a separate thread (via an abstraction such as dispatch_queue_t or NSOperationQueue), and when it completes, to invoke a completion handler on the main thread. That way the main thread is available to process touch inputs or render UI elements.