Objective-C Language Grand Central Dispatch


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!

What is Grand central dispatch.

What is Concurrency?

  • Doing multiple things at the same time.
  • Taking advantage of number of cores available in multicore CPUs.
  • Running multiple programs in parallel.

Objectives of Concurrency

  • Running program in background without hogging CPU.
  • Define Tasks, Define Rules and let the system take the responsibility of performing them.
  • Improve responsiveness by ensuring that the main thread is free to respond to user events.


Grand central dispatch – dispatch queues allows us to execute arbitrary blocks of code either asynchronously or synchronously All Dispatch Queues are first in – first out All the tasks added to dispatch queue are started in the order they were added to the dispatch queue.