Instantiate a background runloop in iOS
Old post but "background run loop" doesn't equal "background thread" nor does it mean "background queue". Usually there is only one run loop and that is the main thread's run loop. Other threads usually use this run loop but rarely have their own run loop (or their respective run loops are never readily available). To create a run loop for a thread that is not the main thread Apple has a guide and states when this should be done.
Also here is a nice guide I found on run loops in background threads.