使用一个任务开启线程，这个任务中再开启一个子任务，然而理论上父任务会在子任务结束之后，状态才会变为
RunToCompletion，子任务结束之前因该为WaitingForChildrenToComplete，然而我写出的代码运行后没有等待子任务的状
态，直接父任务结束之后父任务状态就变为RunToCompletion，没有父子任务关联了。难道现在C#去掉父子任务了嘛


源码：
private static void Example10()
{
    _parentTaskCheck = true;
    var parent = new Task(Example10_ParentTask);
    parent.Start();
    while (_parentTaskCheck)
    {
        
        Console.WriteLine("parent task status: " + parent.Status);
        Thread.Sleep(500);
    }

    Console.WriteLine(parent.Status==TaskStatus.WaitingForChildrenToComplete);
}

private static void Example10_ParentTask()
{
    Console.WriteLine("parent task is running.");
    var child = new Task(Example10_ChildTask);
    child.Start();
    Thread.Sleep(1000);
    Console.WriteLine("parent task is over.");
}

private static bool _parentTaskCheck;
private static void Example10_ChildTask()
{
    Console.WriteLine("child task is running.");
    Thread.Sleep(5000);
    Console.WriteLine("child task is over.");
    _parentTaskCheck = false;
}
输出结果：

parent task is running.
parent task status: WaitingToRun
child task is running.
parent task status: Running
parent task is over.
parent task status: Running
parent task status: RanToCompletion
parent task status: RanToCompletion
parent task status: RanToCompletion
parent task status: RanToCompletion
parent task status: RanToCompletion
parent task status: RanToCompletion
parent task status: RanToCompletion
child task is over.
RanToCompletion