Understanding dispatch_sync routine

Question

Im learning GCD. Please consider following code:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    dispatch_sync(dispatch_get_main_queue(), ^{
        NSLog(@"Hello world");
    });

   /* Another implementation */
   return YES;
}

I know, that there will be a deadlock. But can somebody explain why? What exactly steps application will do, before it (app) will "freeze"?

Why do you assert there will be a deadlock? – trojanfoe May 13 '16 at 11:00 — trojanfoe, May 13 '16 at 11:00
@trojanfoe because app will freeze. Please try it. – Evgeniy Kleban May 13 '16 at 11:02 — Evgeniy Kleban, May 13 '16 at 11:02
@DhawalSodhaParmar its not swift – Evgeniy Kleban May 13 '16 at 11:02 — Evgeniy Kleban, May 13 '16 at 11:02
Won't it depend what queue that code is called from? – trojanfoe May 13 '16 at 11:03 — trojanfoe, May 13 '16 at 11:03
@trojanfoe ok, my bad, i will edit question body. – Evgeniy Kleban May 13 '16 at 11:04 — Evgeniy Kleban, May 13 '16 at 11:04
This question has already been answered here – Reinhard Männer May 13 '16 at 11:09 — Reinhard Männer, May 13 '16 at 11:09

score 1 · Answer 1 · answered May 13 '16 at 11:38

1

because the code runs in main queue and you tell it to wait for the block to execute in main queue

answered May 13 '16 at 11:38

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Understanding dispatch_sync routine

1 Answers1