ios - Mulithreading: executing method calls only after finished executing other method -

i trying process method asynchronously, per requirements, once first method has completed, second method should start executing. problem first method has code runs on background thread.

i tried dispatch_semaphore_wait, didnt work either.

dispatch_queue_t queue = dispatch_get_global_queue(dispatch_queue_priority_high, 0);          dispatch_group_t group = dispatch_group_create();           dispatch_group_async(group, queue, ^{              [self firstmethod];             nslog(@"firstmethod done");          });         dispatch_group_notify(group, queue, ^ {              nslog(@"1st method completed");             nslog(@"2nd method starting");              [self secondmethod];          }); 

firstmethod runs on worker thread this

-(void)firstmethod {     dispatch_async(dispatch_get_global_queue(dispatch_queue_priority_high, 0), ^{    //processing here.....          }]; 

what best way achieve it, cannot change definition of firstmethod provided 3rd party , changing means changing lots of existing code method being called

you can use completion block. need modify firstmethod way:

- (void)firstmethodwithoncomplete:(void (^)(void))oncomplete {       dispatch_async(dispatch_get_global_queue(dispatch_queue_priority_high, 0), ^{           //processing here.....           oncomplete();        }); }     

and use way:

[self firstmethodwithoncomplete:^{     [self secondmethod]; }];