Understanding dispatch_sync

Question

Please consider following code:

- (void)viewDidLoad {
    [super viewDidLoad];

    dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{


        for (int i; i < 100 ; i++) {

            NSLog(@"%i", i);

        }

    });

    NSLog(@"Main thread code");

}

Why its only output is - 2016-01-26 16:15:28.842 Test[1051:35933] Main thread code ?

I mean, code in global queue is never executed, why? I only want it to execute synchronously. Of course i could easy write dispatch_async, but im just curious why code above not work, does not output anything execept 2016-01-26 16:15:28.842 Test[1051:35933] Main thread code?

@originaluser2 i paste that code in empty project, i created for testing purpose. — Evgeniy Kleban
– Evgeniy Kleban, Commented Jan 26, 2016 at 13:27
I also pasted the code into an empty project, and it worked! Although it's also worth mentioning that this code makes no sense. This will block the main thread until something on a background thread has completed... why not just run it on the main thread in that case? You should be using dispatch_async for this. — Hamish
– Hamish, Commented Jan 26, 2016 at 13:28
no, I mean it blocks the main thread while it is running. Once it's finished running, the main thread will continue. Also, try using %d as your string formatting option. Not sure what %i is. — Hamish
– Hamish, Commented Jan 26, 2016 at 13:30
problem is in for (int i; i < 100 ; i++) u r not initialise value of i , for (int i = 0 ; i < 100 ; i++) — Bhargav B. Bajani
– Bhargav B. Bajani, Commented Jan 26, 2016 at 13:42

Bhargav B. Bajani · Accepted Answer · 2016-01-26 13:52:17Z

1

problem is in

for (int i; i < 100 ; i++)

for above code value of i = 72339625 so condition not satisfied and not goes into loop

solution : initialise value of i ,

for (int i = 0 ; i < 100 ; i++)

answered Jan 26, 2016 at 13:52

Bhargav B. Bajani

9279 silver badges22 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Understanding dispatch_sync

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related