title: UIAlertController dismiss is slow
body: <p>After iOS 8, changing my implementation to UIAlertController instead of UIAlertView is giving me some headaches.</p>
  
  <p>The dismissal takes around a full second before the UI becomes responsive after clicking a button. It means users think there's something wrong.</p>
  
  <p>Am I the only one suffering from this? It's across several apps, and true for an implementation as simple as this. I tried this in a new blank project.</p>
  
  <pre><code>- (IBAction)showAlertView {
  
      [[[UIAlertView alloc] initWithTitle:@"test" message:@"test" delegate:self cancelButtonTitle:@"OK" otherButtonTitles: nil] show];
  }
  
  -(void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex {
  
      NSLog(@"this is fast");
  }
  
  -(IBAction)showAlert {
  
      UIAlertController *controller = [UIAlertController alertControllerWithTitle:@"test" message:@"test" preferredStyle:UIAlertControllerStyleAlert];
  
      [controller addAction:[UIAlertAction actionWithTitle:@"OK" style:UIAlertActionStyleDefault handler:^(UIAlertAction * _Nonnull action) {
  
          NSLog(@"this is slow");
  
      }]];
  
      [self presentViewController:controller animated:NO completion:nil];
  
  }
  </code></pre>
  
  <p>Clicking the button gives around a 1-second delay before anything is printed to the console. Presentation of the alert is not delayed at all.</p>
  
  <p>Edit: By closer timing it's probably more like 700ms, so not a full second, but still way too long for something that should be instantaneous.</p>