Mulithreading: executing method calls only after finished executing other method

Question

I am trying to process method asynchronously, as per requirements, once the first method has completed, only then the second method should start executing. The Problem is first

Answer 1

Dispatch a Single Queue and call your Methods in order

dispatch_group_async(group, queue, ^{

            [self firstMethod];
            NSLog(@"firstMethod Done");
           [self secondmethod];

        });

Or you might dispatch a group of 3 concurrent queues(This is a Wild guess)