多线程共享对象之volatile关键字

在一般的多线程访问共享对象的程序中，一般是通过加锁来保证读/写访问的是正确的值：

Lock(object)
{
        //范围并处理共享数据
}

但这样的做法在每次访问共享对象的时候都有可能造成了线程的上下文切换，影响了程序的效率。

对于简单的多线程访问，可以使用volatile关键字确保该共享对象volatile are not subject to compiler optimizations that assume access by a single thread." data-guid="2ab5b8fdd040c8f707f3d233fceeec38">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

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.
}