Task是基于线程池调度的，不过微软说不要把Task理解为线程之上的抽象，要把它理解为异步工作的抽象

List<int> tid = new List<int>();
for (int i = 0; i < 100; i++)
{
	ThreadPool.QueueUserWorkItem((state) =>
	{
	    int id = Thread.CurrentThread.ManagedThreadId;
	    if (tid.Contains(id))
	    {
		Console.WriteLine($"{id} reuse " + tid.Count());
	    }
	    else
	    {
		tid.Add(id);
		Console.WriteLine($"{id} new " + tid.Count());
	    }
	});
	Thread t = new Thread(() =>
	{
	    int id = Thread.CurrentThread.ManagedThreadId;
	    if (tid.Contains(id))
	    {
		Console.WriteLine($"{id} reuse " + tid.Count());
	    }
	    else
	    {
		tid.Add(id);
		Console.WriteLine($"{id} new " + tid.Count());
	    }
	});
	t.Start();
	Task<int> t = new Task<int>(() =>
	{
	    int id = Thread.CurrentThread.ManagedThreadId;
	    if (tid.Contains(id))
	    {
		Console.WriteLine($"{id} reuse " + tid.Count());
	    }
	    else
	    {
		tid.Add(id);
		Console.WriteLine($"{id} new " + tid.Count());
	    }
	    return 10;
	});
	t.Start();
	Task<int>.Factory.StartNew(() =>
	{
	    int id = Thread.CurrentThread.ManagedThreadId;
	    if (tid.Contains(id))
	    {
		Console.WriteLine($"{id} reuse " + tid.Count());
	    }
	    else
	    {
		tid.Add(id);
		Console.WriteLine($"{id} new " + tid.Count());
	    }
	    //Thread.Sleep(0);
	    return 10;
	});
}