iOS Run a task in background with a callback

gistfile1.c

    dispatch_queue_t queue = dispatch_queue_create("yourname", NULL);
    
    // execute a task on that queue asynchronously
    dispatch_async(queue, ^{
       
     //Code to execute here 

       dispatch_async(dispatch_get_main_queue(), ^{
      // Callback on the main thread when code above is done            

        });
    });