dispatch_Async serial queue

Question

I couldn't guess the output of it.

dispatch_async(serial_queue,^{NSlog(@"1");});

NSlog(@"2");

dispatch_async(serial_queue,^{NSlog(@"3");});

NSlog(@"4");

AFAIK

The output is

1

2

3

4

But I am not sure !

Can anybody explain If I am wrong !

the output should be theoretically unpredictable, since there is no guarantee when the async blocks will execute... but i guess maybe those async blocks execute too quickly for the order to ever be different — Fonix
– Fonix, Commented Sep 14, 2015 at 6:52
There should be some response right ! because the question was thrown at me in a iOS written interview test — NaveenKumar
– NaveenKumar, Commented Sep 18, 2015 at 11:10

Abizern · Accepted Answer · 2015-09-24 08:54:41Z

1

Although the interleaving of the operations may not be known, you can see that there are two streams. The first is logging from a serial queue, the other is just plain NSLog.

What you can say about the order is that 1 will precede 3 and 2 will precede 4

answered Sep 24, 2015 at 8:54

Abizern

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