探秘System.Threading系列第二篇：仍是Thread，Thread.Start 和 Thread.Join

2012-11-03

探秘System.Threading系列第二篇：还是Thread，Thread.Start 和 Thread.Join1.?开始一个Thread开始一个Thre

探秘System.Threading系列第二篇：还是Thread，Thread.Start 和 Thread.Join

1.?开始一个Thread
开始一个Thread很简单，声明一个Thread实例，然后调用Start方法即可

Thread.Start
Thread?threadA?=?new?Thread(new?ThreadStart(WorkMethod));
threadA.Start();

Thread?threadB?=?new?Thread(new?ParameterizedThreadStart(WorkMethodWithParam));
threadB.Start(obj);

2.?Thread.Join阻塞调用线程，直到某个线程终止为止。
我按照msdn上的解释的理解是：
threadA.Join()方法是用来阻塞threadA线程，直到在threadA开始执行之后启动的线程执行完毕（或者Sleep了）之后，才开始执行threadA线程的方法

但是事实并非如我所想，下面是msdn上的例子，先声明了一个thread实例，然后将一个方法放入ThreadPool中执行，并调用thread的Join方法以阻塞thread的执行。显示结果在预料之中

MSDN Thread.Join例子
using?System;
using?System.Threading;

class?IsThreadPool
{
????static?void?Main()
????{
????????AutoResetEvent?autoEvent?=?new?AutoResetEvent(false);

????????Thread?regularThread?=?
????????????new?Thread(new?ThreadStart(ThreadMethod));
????????regularThread.Start();
????????ThreadPool.QueueUserWorkItem(new?WaitCallback(WorkMethod),?
????????????autoEvent);

????????//?Wait?for?foreground?thread?to?end.
????????regularThread.Join();

????????//?Wait?for?background?thread?to?end.
????????autoEvent.WaitOne();
????}

????static?void?ThreadMethod()
????{
????????Console.WriteLine("ThreadOne,?executing?ThreadMethod,?"?+
????????????"is?{0}from?the?thread?pool.",?
????????????Thread.CurrentThread.IsThreadPoolThread???""?:?"not?");
????}

????static?void?WorkMethod(object?stateInfo)
????{
????????Console.WriteLine("ThreadTwo,?executing?WorkMethod,?"?+
????????????"is?{0}from?the?thread?pool.",?
????????????Thread.CurrentThread.IsThreadPoolThread???""?:?"not?");

????????//?Signal?that?this?thread?is?finished.
????????((AutoResetEvent)stateInfo).Set();
????}
}

执行结果是：ThreadTwo,?executing?WorkMethod,?is?from?the?thread?pool.
ThreadOne,?executing?ThreadMethod,?is?not?from?the?thread?pool.

但是当我对这个例子稍作修改之后就出现了不可理解的问题，我在WorkMethod中加上Thread.Sleep让线程池中的线程休眠2秒，这样操作之后执行结果是：

Code
????class?IsThreadPool
????{
????????static?void?Main()
????????{
????????????AutoResetEvent?autoEvent?=?new?AutoResetEvent(false);

????????????Thread?threadA?=
????????????????new?Thread(new?ThreadStart(ThreadMethod));

????????????Thread?threadB?=?new?Thread(new?ParameterizedThreadStart(WorkMethod));

????????????threadA.Start();

????????????//?Wait?for?foreground?thread?to?end.
????????????threadA.Join();
????????????threadB.Start(autoEvent);

????????????//?Wait?for?background?thread?to?end.
????????????autoEvent.WaitOne();

????????????Console.Read();
????????}

????????static?void?ThreadMethod()
????????{
????????????Console.WriteLine("ThreadOne,?executing?ThreadMethod,?"?+
????????????????"is?{0}from?the?thread?pool.",
????????????????Thread.CurrentThread.IsThreadPoolThread???""?:?"not?");
????????}

????????static?void?WorkMethod(object?stateInfo)
????????{
????????????Console.WriteLine("ThreadTwo,?executing?WorkMethod,?"?+
????????????????"is?{0}from?the?thread?pool.",
????????????????Thread.CurrentThread.IsThreadPoolThread???""?:?"not?");
????????????//?Signal?that?this?thread?is?finished.
????????????((AutoResetEvent)stateInfo).Set();
????????}
????}

不知道什么原因，上面的代码中threadA并没有被阻塞，难道是只能阻塞放在ThreadPool中执行的线程？没有道理，我反复做了实验都没有成功，把这个结果贴出来，请大家释疑。

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探秘System.Threading系列 第二篇：仍是Thread，Thread.Start 和 Thread.Join

探秘System.Threading系列第二篇：仍是Thread，Thread.Start 和 Thread.Join