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&＃xff08;假定由单个线程访问&＃xff09;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&＃xff1a;
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引用类型。
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指针类型&＃xff08;在不安全的上下文中&＃xff09;。 请注意&＃xff0c;虽然指针本身可以是可变的&＃xff0c;但是它指向的对象不能是可变的。 换句话说&＃xff0c;不能声明“指向可变对象的指针”。
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类型&＃xff0c;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&＃xff1a;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 &＃61; _i;}
}
示例
下面的示例演示如何创建辅助线程&＃xff0c;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&＃xff0c;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 &＃61; 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 &＃61; new Worker();Thread workerThread &＃61; 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&＃39;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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