All following notes related to concurrency are written for swift language. but all the concepts are mostly universal among the other languages.

What is concurrency ?

  • concurrency is the execution of multiple instructions sequences at the same time .

What is parallelism ?

  • parallelism is using multiple resource to execute the multiple instruction sequences at the same time.
  • for an example: there is two queues for the single hot dog stand. in parallelism we can use another new resource of hot dog stand to feed the second queue.

Concurrency vs parallelism


  • in concurrency multiple tasks are appeared to be happen at the same time. but at the core only single instance working at a one time.
  • in parallelism truly tasks are happens in the same time. so they need to multiple resources to do it. as show in the above image.

How to achieve concurrency

Achieving Multi Threading in iOS