volatile（C# 参考）

volatile 关键字指示一个字段可以由多个同时执行的线程修改。声明为 volatile 的字段不受编译器优化（假定由单个线程访问）的限制。这样可以确保该字段在任何时间呈现的都是最新的值。

volatile 修饰符通常用于由多个线程访问但不使用 lock 语句对访问进行序列化的字段。

volatile 关键字可应用于以下类型的字段：

引用类型。
指针类型（在不安全的上下文中）。请注意，虽然指针本身可以是可变的，但是它指向的对象不能是可变的。换句话说，您无法声明“指向可变对象的指针”。
类型，如 sbyte、byte、short、ushort、int、uint、char、float 和 bool。
具有以下基类型之一的枚举类型：byte、sbyte、short、ushort、int 或 uint。
已知为引用类型的泛型类型参数。
IntPtr 和 UIntPtr。

可变关键字仅可应用于类或结构字段。不能将局部变量声明为 volatile。

示例

下面的示例说明如何将公共字段变量声明为 volatile。

class VolatileTest

{

public volatile int i;

public void Test(int _i)

{

i = _i;

}

下面的示例演示如何创建辅助线程，并用它与主线程并行执行处理。有关多线程处理的背景信息，请参见托管线程处理和线程处理（C# 和 Visual Basic）。

using System;

using System.Threading;

public class Worker

{

// This method is called when the thread is started.

public void DoWork()

{

while (!_shouldStop)

{

Console.WriteLine("Worker thread: working...");

}

Console.WriteLine("Worker thread: terminating gracefully.");

}

public void RequestStop()

{

_shouldStop = true;

}

// Keyword volatile is used as a hint to the compiler that this data

// member is accessed by multiple threads.

private volatile bool _shouldStop;

}

public class WorkerThreadExample

{

static void Main()

{

// Create the worker thread object. This does not start the thread.

Worker workerObject = new Worker();

Thread workerThread = new Thread(workerObject.DoWork);

// Start the worker thread.

workerThread.Start();

Console.WriteLine("Main thread: starting worker thread...");

// Loop until the worker thread activates.

while (!workerThread.IsAlive) ;

// Put the main thread to sleep for 1 millisecond to

// allow the worker thread to do some work.

Thread.Sleep(1);

// Request that the worker thread stop itself.

workerObject.RequestStop();

// Use the Thread.Join method to block the current thread

// until the object's thread terminates.

workerThread.Join();

Console.WriteLine("Main thread: worker thread has terminated.");

}

// Sample output:

// Main thread: starting worker thread...

// Worker thread: working...

// Worker thread: terminating gracefully.

// Main thread: worker thread has terminated.

}

from:http://msdn.microsoft.com/zh-cn/library/x13ttww7.aspx

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