GCD, NSThread, and performSelector:onThread: issues

Question

I\'m attempting to debug some iOS crash logs that contain the following error message:

*** Terminating app due to uncaught exception \'NSDestinationInvali

Answer 1

There is no mapping at all between queues and threads, with the sole exception of the main queue which always runs on the main thread. Any queue which targets the main queue will, of course, also run on the main thread. Any background queue can run on any thread, and can change thread from one block execution to the next. This is equally true for serial queues and for concurrent queues.

GCD maintains a thread pool which gets used for executing blocks according to the policies determined by the queue to which the block belongs. You are not supposed to know anything about those particular threads.