ThreadPool.SetMaxThreads(8, 8);
ManualResetEvent mre = new ManualResetEvent(false);
for (int i = 0; i < 10; i++)
{
    int k = i;
    ThreadPool.QueueUserWorkItem(t =>
    {
        Console.WriteLine($"{Thread.CurrentThread.ManagedThreadId.ToString("00")} show {k}");
        if (k == 9)
        {
            mre.Set();
        }
        else
        {
            mre.WaitOne();
        }
    });
}
if (mre.WaitOne())
{
    Console.WriteLine("任务全部执行成功！");
}