grand central dispatch - iOS - GCD groups and significant UI delay on finish -

i using gcd run code in background. operation finished in few seconds , in end "done" printed expected. have wait ~5 seconds (simulator) ~1 minute (device) hud hide. might reason such long delay? know processing finished because can see result every element.

mbprogresshud *hud = [mbprogresshud showhudaddedto:self.view animated:yes]; hud.mode = mbprogresshudmodeannulardeterminate; dispatch_group_t group = dispatch_group_create(); dispatch_queue_t queue = dispatch_get_global_queue(dispatch_queue_priority_high,0);  nsarray *keys = [nsarray arraywitharray: [codepositions allkeys]]; (id key in keys) {     if (key == nil)         continue;     dispatch_group_async(group, queue, ^{         ... // processing         nslog(@"element %d result: %@", element.id, element.result);         hud.progress += 1.0/96.0;     }); } dispatch_group_notify(group, queue, ^{     nslog(@"done");     [hud hide:yes]; }); 

thanks time.

you need perform ui updates on main thread. update code follows:

for (id key in keys) {     if (key == nil)         continue;     dispatch_group_async(group, queue, ^{         ... // processing         nslog(@"element %d result: %@", element.id, element.result);         dispatch_async(dispatch_get_main_queue(), ^{             hud.progress += 1.0/96.0;         });     }); } dispatch_group_notify(group, queue, ^{     nslog(@"done");     dispatch_async(dispatch_get_main_queue(), ^{         [hud hide:yes];     }); });