volatile (C# 參考)
volatile 關鍵字表示同時執行的多執行緒可能修改了欄位。 宣告為 volatile 的欄位不遵從假設單一執行緒存取的編譯器最佳化。 這確保最新的值會一直出現在欄位中。
由多個執行緒在未以 lock 陳述式 (Statement) 將存取動作序列化的情況下所存取的欄位上，經常會使用 volatile 修飾詞 (Modifier)。
volatile 關鍵字可套用至以下型別的欄位：
參考型別。
指標型別 (在 unsafe 內容中)。 請注意，即使指標本身可以為 Volatile，但所指向的物件不可為 Volatile。 換句話說，您不能宣告 Volatile 的指標。
sbyte、byte、short、ushort、int、uint、char、float 和 bool 之類的型別。
具有下列一種基底型別的列舉型別：byte、sbyte、short、ushort、int 或 uint。
已知為參考型別的泛用型別參數。
Volatile 關鍵字只能套用至類別或結構 (Struct) 的欄位。 區域變數無法宣告為 volatile。
範例
下列範例將示範如何將公用欄位變數宣告為 volatile。
class VolatileTest
{
public volatile int i;
public void Test(int _i)
{
i = _i;
}
}
下列範例會示範如何建立輔助執行緒或背景工作執行緒，以及使用它們和主要執行緒執行平行的處理過程。 如需多執行緒處理的背景資訊，請參閱 Managed 執行緒處理和執行緒 (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: working...
// Worker thread: working...
// Worker thread: working...
// Worker thread: working...
// Worker thread: working...
// Worker thread: terminating gracefully.
// Main thread: worker thread has terminated.
}
C# 語言規格
如需詳細資訊，請參閱 C# 語言規格。 語言規格是 C# 語法和用法的決定性來源。