Grand Central Dispatch (GCD) is Apple's answer to multithreading. It is a lightweight framework for performing tasks synchronously or asynchronously in queues and handles CPU threads for you behind the scenes.
Grand Central Dispatch (GCD) In iOS, Apple provides two ways to do multitasking: The Grand Central Dispatch (GCD) and NSOperationQueue frameworks.We will discuss here about GCD. GCD is a lightweight way to represent units of work that are going to be executed concurrently You don’t schedule these units of work; the system takes care of scheduling for you. Adding dependency among blocks can be a headache. Canceling or suspending a block creates extra work for you as a developer!