What's the difference between the “global queue” and the “main queue” in GCD?

Question

Among some other ways, there are these two ways to get queues in GCD:

dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

dispatch_g         


        

Answer 1

The 5 queues (4 background, 1 main) all have different thread priorities (-[NSThread threadPriority]) too:

                            -main- : 0.758065
      DISPATCH_QUEUE_PRIORITY_HIGH : 0.532258
   DISPATCH_QUEUE_PRIORITY_DEFAULT : 0.500000
       DISPATCH_QUEUE_PRIORITY_LOW : 0.467742
DISPATCH_QUEUE_PRIORITY_BACKGROUND : 0.000000

(tested on an iPod 4th gen and the simulator on a MacBook Pro)