c#中的volatile關鍵字

volatile 關鍵字指示一個欄位可以由多個同時執行的線程修改。聲明為 volatile 的欄位不受編譯器最佳化（假定由單個線程訪問）的限制。這樣可以確保該欄位在任何時間呈現的都是最新的值。

volatile 修飾符通常用於由多個線程訪問但不使用 lock 語句對訪問進行序列化的欄位。

volatile 關鍵字可應用於以下類型的欄位：

• 參考型別。

• 指標類型（在不安全的上下文中）。請注意，雖然指標本身可以是可變的，但是它指向的對象不能是可變的。換句話說，您無法聲明“指向可變對象的指標”。

• 類型，如 sbyte、byte、short、ushort、int、uint、char、float 和 bool。

• 具有以下基底類型之一的枚舉類型：byte、sbyte、short、ushort、int 或 uint。

• 已知為參考型別的泛型型別參數。

• IntPtr 和 UIntPtr。

可變關鍵字僅可應用於類或結構欄位。不能將局部變數聲明為 volatile。

樣本

下面的樣本說明如何將公用欄位變數聲明為 volatile。

C#複製

    class VolatileTest    {        public volatile int i;        public void Test(int _i)        {            i = _i;        }    }

下面的樣本示範如何建立輔助線程，並用它與主線程並存執行處理。有關多執行緒的背景資訊，請參見託管線程處理和線程處理（C# 和 Visual Basic）。

C#複製

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.}