dispatch_group_t group = dispatch_group_create();

? ? dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);

dispatch_group_enter(group);

NSLog(@"111");

dispatch_group_leave(group);

dispatch_group_enter(group);

NSLog(@"222");

dispatch_group_leave(group);

dispatch_group_enter(group);

NSLog(@"333");

dispatch_group_leave(group);

dispatch_group_notify(group, queue, ^{

? ? ? ? NSLog(@"全部輸出完成！");

? ? });

NSLog(@"444");

輸出結(jié)果：444 ? 111 ? 222 ?333 ??全部輸出完成！