Why do We Need Concurrency in IOS ?

I know you’re a good developer with experience in iOS. No matter what kinds of apps you’re going to build, however, you will need to know concurrency to make your app more responsive and fast. Here I summarize in points the advantages of learning or using concurrency:

• Utilize iOS devices’ hardware: Now all iOS devices have a multi-core processor that allows developers to execute multiple tasks in parallel. You should utilize this feature and get benefits out of the hardware.Better user experience: You probably have written code to call web services, handle some IO, or perform any heavy tasks. As you know, doing these kind of operations in the UI thread will freeze the app, making it non responsive. Once user faces this situation, the first step that he/she will take is to kill/close your app without a second thought. With concurrency, all these tasks can be done in background without hanging the main thread or disturbing your users. They can still tap on buttons, scroll and navigate through your app, while it handles the heavy loading task in background.
• The APIs like NSOperation and dispatch queues make it easy to use concurrency: Creating and managing threads are not easy tasks. This is why most of developers get scared when they hears the term concurrency and multi-threaded code. In iOS we have great and easy to use concurrency APIs that will make your life easier. You don’t have to care about creating threads or manage any low level stuff. The APIs will do all these tasks for you. Another important advantage about these APIs is that it helps you achieve synchronization easily to avoid race condition. Race condition happens when multiple threads try to access shared resource and that leads to unexpected results. By using synchronization, you protect resources from being shared between threads.

Operation Queues
Operation queues, on the other hand, are high level abstraction of the queue model, and is built on top of GCD. That means you can execute tasks concurrently just like GCD, but in an object-oriented fashion. In short, operation queues just make developers’ life even simpler.
GCD (Grand Central Dispatch)
GCD is the most commonly used API to manage concurrent code and execute operations asynchronously at the Unix level of the system. GCD provides and manages queues of tasks.