为什么Dispatch\u group\u notify在不同的环境中工作不同?

第一种情况是,我创建了一个命令行工具应用程序,并运行此代码。

    NSLog(@"Main:%@", [NSThread currentThread]);

    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
    dispatch_group_t group = dispatch_group_create();

    dispatch_group_async(group, queue, ^{
        NSLog(@"Task1:%@", [NSThread currentThread]);
    });

    dispatch_group_async(group, queue, ^{
        NSLog(@"Task2:%@", [NSThread currentThread]);
    });

    dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"Finish:%@", [NSThread currentThread]);
    });

登录终端为

    Main:<NSThread: 0x1028033b0>{number = 1, name = main}
    Task2:<NSThread: 0x10040f0f0>{number = 2, name = (null)}
    Task1:<NSThread: 0x1006008d0>{number = 3, name = (null)}

如果我想显示上次登录 queue 并更换 main queue

     dispatch_group_notify(group, dispatch_get_main_queue(), ^{
        NSLog(@"Finish:%@", [NSThread currentThread]);
    });

具有 队列

     dispatch_group_notify(group, queue, ^{
        NSLog(@"Finish:%@", [NSThread currentThread]);
    });

终端打印最后一个日志。但为什么它不能在主队列中撤销?

当我将此代码复制到简单的iOS应用程序时。所有工作正常:

Main:<NSThread: 0x600000070ac0>{number = 1, name = main}
Task2:<NSThread: 0x6000002633c0>{number = 3, name = (null)}
Task1:<NSThread: 0x600000263480>{number = 4, name = (null)}
MainFinish:<NSThread: 0x600000070ac0>{number = 1, name = main}

我尝试添加 sleep(1) 在“命令工具行”中的Task1上,但它似乎阻止了队列并仅打印日志:Task2。。。。但这一切在简单的iOS应用程序中都能很好地工作。

为什么会导致这些不同?