Thread.Join() 在MSDN中的解釋：Blocks the calling thread until the thread represented by this instance terminates.（在此實例表示的線程終止前，阻止調用線程。）

實例應用
Test2 在 thread1.Join() 被調用后被阻塞，直到 Test1 執行完畢才繼續執行。

        static void Main(string[] args)
        {
            Thread thread1 = new Thread(new ThreadStart(Test1));
            thread1.Start();
            thread1.Join();

            Thread thread2 = new Thread(new ThreadStart(Test2));
            thread2.Start();
            thread2.Join();

            Console.WriteLine("finished.");
            Console.Read();
        }

        static void Test1()
        {
            Console.WriteLine("t1 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t1 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t1 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t1 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t1 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t1 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t1 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t1 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t1 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t1 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
        }

        static void Test2()
        {
            Console.WriteLine("t2 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t2 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t2 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t2 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t2 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t2 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t2 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t2 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t2 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
            Console.WriteLine("t2 " + DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff"));
            Thread.Sleep(500);
        }

thread1 啟動后，調用 Join() 方法，直到 thread1 的任務結束，才輪到 thread2 啟動，然后 thread2 也開始任務。實例中，兩個線程就按著嚴格的順序來執行了。如果 thread2 的執行需要依賴于 thread1 中的完整數據的時候，這種方法就可以很好的確保兩個線程的同步性。