以下代码输出顺序是?( )
dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(queue, ^{
NSLog(@"1");
});
dispatch_sync(queue, ^{
sleep(1);
NSLog(@"2");
});
dispatch_async(queue, ^{
NSLog(@"3");
});