c# - 为什么值变量不改变？

Question

我的winForms中有一个Timer，当TimeSpan是0时，我将done设置为true，然后尝试检查该值是否是一个线程。

我的代码:

初始变量:

private DateTime endTime = DateTime.UtcNow.AddMinutes(1);
private bool done;
private bool running = true;
private int count = 0;
private delegate void setLabelMethod(string msg);
private void setLabelValue(string msg) { label2.Text = msg; }

计时器处理:

private void timer1_Tick_1(object sender, EventArgs e)
        {
            TimeSpan remainingTime = endTime - DateTime.UtcNow;

            if (remainingTime <= TimeSpan.Zero)
            {
                label1.Text = "Done!";
                timer1.Enabled = false;
                done = true;
                running = false;
            }
            else
            {
               //...
            }

        }

线程回调函数:

private void test()
        {
            do
            {
                if (done)
                {
                    Invoke(new setLabelMethod(setLabelValue), "yeah");
                    done = false;
                }

                Thread.Sleep(500); 

            } while (running);
        }

开始 timer1_Tick和 Thread执行。

 private void button2_Click(object sender, EventArgs e)
        {
            Thread th = new Thread(new ThreadStart(test));
            th.Start();
            timer1.Enabled = true;
        }

问题是 .test()方法中的以下语句永远都不是 true，为什么？

语句

 if (done)
 {
    Invoke(new setLabelMethod(setLabelValue), "yeah");
    done = false;
 }

有人可以指出我的错误吗？提前致谢。

Answer 1

正如Martin James所提到的，您应该使用而不是轮询标志
线程同步机制。

这个简单的示例说明了如何使用Monitor.Wait，Monitor.Pulse和lock进行此操作。

此代码与您的代码之间的重要区别在于，这将阻止线程运行直到满足条件，从而改善了的性能的代码。

class Program
{
 static void Main(string[] args)
 {
 ThreadExample example = new ThreadExample();
 Thread thread = new Thread(example.Run);

 Console.WriteLine("Main: Starting thread...");
 thread.Start();

 Console.WriteLine("Press a key to send a pulse");
 Console.ReadKey();

 lock (example) //locks the object we are using for synchronization
 {
 Console.WriteLine("Sending pulse...");
 Monitor.Pulse(example); //Sends a pulse to the thread
 Console.WriteLine("Pulse sent.");
 }
 thread.Join();

 Console.ReadKey();
 }
}

class ThreadExample
{
 public void Run()
 {
 Console.WriteLine("Thread: Thread has started");
 lock (this) //locks the object we are using for synchronization
 {
 Monitor.Wait(this); //Waits for one pulse - thread stops running until a pulse has been sent
 Console.WriteLine("Thread: Condition has been met");
 }
 }
}

要修改代码以使用此机制，您需要维护对用于启动线程的对象的引用(在本示例中，我将其称为threadObject)

private void timer1_Tick_1(object sender, EventArgs e)
    {
        TimeSpan remainingTime = endTime - DateTime.UtcNow;

        if (remainingTime <= TimeSpan.Zero)
        {
            label1.Text = "Done!";
            timer1.Enabled = false;
            lock(threadObject){
                Monitor.Pulse(threadObject); //You signal the thread, indicating that the condition has been met
            }
        }
        else
        {
           //...
        }
    }

然后，在test()方法中，您只需要这样做:

private void test()
    {
        lock(this)
        {
            Monitor.Wait(this); //Will stop the thread until a pulse has been recieved.
            Invoke(new setLabelMethod(setLabelValue), "yeah");
        }
    }