Overridden for testing asynchronous behavior with GCD queues
[x]dispatch_queue_t [x]dispatch_queue_create [x]dispatch_sync [x]dispatch_async [/]dispatch_once_t [/]dispatch_once [x]dispatch_group_t [x]dispatch_group_create [ ]dispatch_group_enter [ ]dispatch_group_leave [ ]dispatch_group_async [ ]dispatch_group_notify [ ]dispatch_group_wait [ ]dispatch_suspend [ ]dispatch_resume [x]dispatch_get_main_queue [x]dispatch_get_global_queue [ ]dispatch_semaphore_t [ ]dispatch_semaphore_create [ ]dispatch_semaphore_signal [ ]dispatch_semaphore_wait [?]dispatch_set_context [?]dispatch_get_context [?]dispatch_set_finalizer_f [?]dispatch_apply [?]dispatch_apply_f
Additional methods: [x]dispatch_queues [x]dispatch_groups [x]dispatch_queue_tasks
[x]dispatch_execute_next_task // SERIAL [x]dispatch_execute_task_at_index // CONCURRENT [x]dispatch_execute_all_tasks // SERIAL or CONCURRENT