如何关闭子线程？征集析构函数与多线程的讨论！

下面的代码是可以执行，大家都来说说为什么这个程序不会自动退出？
也就是说mian函数执行完毕后，为什么.net不会释放ThreadEx对象？

using  System;
using  System.Threading;

public   class  ThreadEx : IDisposable {    
    private Thread thread;
    private volatile bool bExit;
    public ThreadEx(){
        Console.WriteLine("ThreadEx output");
        bExit = false;
        thread = new Thread(OnThread);
        thread.Start();
    }

    ~ThreadEx(){
        Console.WriteLine("~ThreadEx output");
        bExit = true;
    }

    private void OnThread(){
        while(true){
            if(bExit){
                break;
            }
            Console.WriteLine("Thread output");
            Thread.Sleep(1000);
        }
        Console.WriteLine("Thread exit");
    }

    private void Close(){
        bExit = true;
    }

    public void Dispose() {
        // TODO:  添加 ThreadEx.Dispose 实现
        Console.WriteLine("~Dispose output");
        bExit = true;
    }

    static void Main(){
        ThreadEx threadEx = new ThreadEx();
    }
}