Multitasking allows multiple tasks to share system resources like the CPU by rapidly switching between tasks. In iOS, multithreading uses either Cocoa threads via the NSThread class or POSIX threads. Threads offer advantages like lower overhead than processes but also challenges like added complexity. Common threading techniques include atomic operations, locks, conditions, and Grand Central Dispatch which handles scheduling tasks across threads.

12. Thread entry routine § Creating an Autorelease Pool § Setting Up an Exception Handler § Setting Up a Run Loop

13. Runloop

14. Input sources § Port-Based Sources § Custom Input Sources § Cocoa Perform Selector Sources

22. Operation objects § Operation object is a wrapper for a task that would normally be executed on a secondary thread. § This wrapper hides the thread management aspects of performing the task, leaving you free to focus on the task itself.

23. Dispatch queues § With GCD, you define the task you want to perform and add it to a work queue, which handles the scheduling of your task on an appropriate thread. § Work queues take into account the number of available cores and the current load to execute your tasks more efficiently than you could do yourself using threads.