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在 C# 中，Thread.Join 是一个非常有用的方法，它可以让主线程（调用线程）等待子线程（被调用线程）执行完毕后再继续执行。

1、经典示例1

using System;
using System.Threading;public class Example
{static Thread thread1, thread2;public static void Main(){thread1 = new Thread(ThreadProc);thread1.Name = "Thread1";thread1.Start();thread2 = new Thread(ThreadProc);thread2.Name = "Thread2";thread2.Start();Console.ReadKey();}private static void ThreadProc(){Console.WriteLine("\nCurrent thread: {0}", Thread.CurrentThread.Name);if (Thread.CurrentThread.Name == "Thread1" &&thread2.ThreadState != ThreadState.Unstarted){Console.WriteLine("thread2.Join");thread2.Join(); }Thread.Sleep(1000);Console.WriteLine("\nCurrent thread: {0}", Thread.CurrentThread.Name);Console.WriteLine("Thread1: {0}", thread1.ThreadState);Console.WriteLine("Thread2: {0}\n", thread2.ThreadState);}
}

运行结果

Current thread: Thread1
thread2.JoinCurrent thread: Thread2Current thread: Thread2
Thread1: WaitSleepJoin
Thread2: RunningCurrent thread: Thread1
Thread1: Running
Thread2: Stopped

这个例子演示了“Thread.Join 会阻塞调用线程，直到被调用线程完成执行”

2、经典示例2

using System.Threading;
using System;class TestThread
{private static void ThreadTst(){Console.WriteLine("  " + Thread.CurrentThread.Name + "   开始执行");for (int i = 0; i < 10; i++){Console.WriteLine("     " + Thread.CurrentThread.Name + "   i =  " + i);Thread.Sleep(10);}Console.WriteLine("  " + Thread.CurrentThread.Name + "   执行完毕");}static void Main(string[] args){//程序调用了Main()函数时,就起动了一个进程,同时也启动了一个线程[这个线程就是主线程].Thread.CurrentThread.Name = "MainThread";//创建第一个线程Thread tA = new Thread(new ThreadStart(TestThread.ThreadTst));tA.Name = "线程A";Thread tB = new Thread(new ThreadStart(TestThread.ThreadTst));tB.Name = "线程B";Thread tC = new Thread(new ThreadStart(TestThread.ThreadTst));tC.Name = "线程C";Thread tD = new Thread(new ThreadStart(TestThread.ThreadTst));tD.Name = "线程D";for (int z = 0; z < 20; z++){if (z == 3){Console.WriteLine("tA.Start");tA.Start();Console.WriteLine("tB.Start");tB.Start();}else if (z == 6){Console.WriteLine("tA.Join");tA.Join();Console.WriteLine("tB.Join");tB.Join();}else if (z == 9){Console.WriteLine("tC.Start");tC.Start();Console.WriteLine("tD.Start");tD.Start();}else{Console.WriteLine(Thread.CurrentThread.Name + "   z =  " + z);}}Console.Read();}
}

运行结果

MainThread   z =  0
MainThread   z =  1
MainThread   z =  2
tA.Start
tB.Start
MainThread   z =  4
MainThread   z =  5
tA.Join线程A   开始执行线程A   i =  0线程B   开始执行   ->注意这里并没有返回调用线程，这里是线程B线程B   i =  0线程A   i =  1线程B   i =  1线程A   i =  2线程B   i =  2线程A   i =  3线程B   i =  3线程A   i =  4线程B   i =  4线程A   i =  5线程B   i =  5线程A   i =  6线程B   i =  6线程A   i =  7线程B   i =  7线程A   i =  8线程B   i =  8线程B   i =  9线程A   i =  9线程A   执行完毕线程B   执行完毕
tB.Join              ->注意线程B已经执行完毕了
MainThread   z =  7
MainThread   z =  8
tC.Start
tD.Start
MainThread   z =  10
MainThread   z =  11
MainThread   z =  12
MainThread   z =  13
MainThread   z =  14
MainThread   z =  15
MainThread   z =  16
MainThread   z =  17
MainThread   z =  18
MainThread   z =  19线程C   开始执行    ->线程C是等主线程结束后才开始执行的线程C   i =  0线程D   开始执行线程D   i =  0线程C   i =  1线程D   i =  1线程C   i =  2线程D   i =  2线程C   i =  3线程D   i =  3线程C   i =  4线程D   i =  4线程C   i =  5线程D   i =  5线程C   i =  6线程D   i =  6线程C   i =  7线程D   i =  7线程C   i =  8线程D   i =  8线程C   i =  9线程D   i =  9线程C   执行完毕线程D   执行完毕

这个例子主要目的是对比使用join（线程A、）和未使用join（线程C）的区别