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Concurrency is the process by which a computer or individual program can perform multiple tasks simultaneously, including executing tasks or processes in the background. Modern computers have many programs running at the same time. Even “single task” operating systems such as iOS have many unseen programs running in the background, in addition to any user-facing programs that may be open. Each individual programs can run multiple actions at the same time. It is difficult and constraining to design and write iOS and OS X programs without an understanding of the concurrency primitives used by both operating systems.
This chapter introduces you to the foundations for concurrency programming used by OS X and iOS: classes such as NSTimer and NSThread, as well as libraries like Grand Central Dispatch. It also discusses the importance of concurrency, particularly in the use of asynchronous methods, in modern applications. By the end of the chapter, ...