C#中的volatile关键字
2021-02-17 23:18
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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：
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引用类型。
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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，不能声明“指向可变对象的指针”。
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类型，如 sbyte、byte、short、ushort、int、uint、char、float 和 bool。
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具有以下基类型之一的枚举类型：byte、sbyte、short、ushort、int 或 uint。
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已知为引用类型的泛型类型参数。
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IntPtr 和 UIntPtr。
可变关键字仅可应用于类或结构的字段。 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; } }
示例
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，请参阅 线程和线程。
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. }
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