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# 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](https://msdn.microsoft.com/zh-CN/library/c5kehkcz.aspx) 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](https://msdn.microsoft.com/zh-CN/library/system.intptr.aspx) 和 [UIntPtr](https://msdn.microsoft.com/zh-CN/library/system.uintptr.aspx)。 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**。 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[Managed Threading](https://msdn.microsoft.com/zh-CN/library/3e8s7xdd.aspx)和[线程处理(C# 和 Visual Basic)](https://msdn.microsoft.com/zh-CN/library/ms173178.aspx)。 ``` 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: working... // Worker thread: working... // Worker thread: working... // Worker thread: working... // Worker thread: working... // Worker thread: terminating gracefully. // Main thread: worker thread has terminated. } ``` ## C# 语言规范 有关详细信息,请参阅 [C# 语言规范](https://msdn.microsoft.com/zh-CN/library/ms228593.aspx)。该语言规范是 C# 语法和用法的权威资料。 ## 请参阅 [C# 参考](https://msdn.microsoft.com/zh-CN/library/618ayhy6.aspx) [C# 编程指南](https://msdn.microsoft.com/zh-CN/library/67ef8sbd.aspx) [C# 关键字](https://msdn.microsoft.com/zh-CN/library/x53a06bb.aspx) [修饰符(C# 参考)](https://msdn.microsoft.com/zh-CN/library/6tcf2h8w.aspx)