面试题考察输出结果

- (void)testAsync3{
  //注意这个地方是全局队列，dispatch_get_global_queue
  dispatch_queue_t queue = dispatch_get_global_queue(0, 0);
  
  for (int i = 0; i<100; i++) {
      dispatch_async(queue, ^{
          NSLog(@"%@",@(i));
      });
  }
  dispatch_barrier_async(queue, ^{
      NSLog(@"a");
  });
  NSLog(@"b");
  
  for (int i = 0; i< 100; i++) {
      dispatch_async(queue, ^{
          NSLog(@"%@",@(i));
      });
  }
}
- (void)testAsync2{
  dispatch_queue_t queue = dispatch_queue_create("queue", DISPATCH_QUEUE_CONCURRENT);
  NSMutableArray *a = [NSMutableArray array];
  for (int i = 0; i< 100; i++) {
      dispatch_async(queue, ^{
          [a addObject:@(i)];
      });
  }
  NSLog(@"%@",a);
}