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)

Answer 2

You can use a completion block. You just need to modify firstMethod this way:

- (void)firstMethodWithOnComplete:(void (^)(void))onComplete {
      dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
          //processing here.....
          onComplete();
       });
}    

And then use it this way:

[self firstMethodWithOnComplete:^{
    [self secondMethod];
}];