Question

我有以下代码：

private DateTime lastUploadActivityTime = DateTime.Now;
private void HttpSendProgress(object sender, HttpProgressEventArgs e)
{
    // update variable
    lastUploadActivityTime = DateTime.Now;
    ......
    boolThreadAvailableTargetSiteActive = false;
}

// this method is executed in different thread, than method above
private void ThreadCheckAvailableTargetSite()
{
    while (boolThreadAvailableTargetSiteActive)
    {
        if (lastUploadActivityTime.AddSeconds(5) <= DateTime.Now)
        {
            MessageBox.Show("BREAK");
            boolThreadAvailableTargetSiteActive = false;
        }
        Thread.Sleep(500);
    }
}

我需要在第一个方法中阻塞变量lastUploadActivityTime（在lastUploadActivityTime = DateTime.Now;期间），以防止在第二个方法（lastUploadActivityTime.AddSeconds(5) <= DateTime.Now）中读取lastUploadActivityTime。我该怎么做？ Mutex是否帮助我阻止阅读变量？

Answer 1

互斥量会过度，在两种方法中使用锁来同步读取 http://msdn.microsoft.com/en-us/library/c5kehkcz.aspx

Answer 2

lock关键字确保一个线程不进入代码的关键部分，而另一个线程处于临界区。如果另一个线程试图输入锁定的代码，它将等待，阻止，直到该对象被释放。最佳做法是定义要锁定的私有对象，或私有静态对象变量以保护所有实例共有的数据。

private object syncLock = new object();
private DateTime lastUploadActivityTime = DateTime.Now;
private void HttpSendProgress(object sender, HttpProgressEventArgs e)
{
    // update variable
    lock (syncLock)
    {
       lastUploadActivityTime = DateTime.Now;
    }
}

// this method is executed in different thread, than method above
private void ThreadCheckAvailableTargetSite()
{
    while (boolThreadAvailableTargetSiteActive)
    {
        lock (syncLock)
        {
           if (lastUploadActivityTime.AddSeconds(5) <= DateTime.Now)
           {
               MessageBox.Show("BREAK");
               boolThreadAvailableTargetSiteActive = false;
           }
        }
        Thread.Sleep(500);
    }
}

用于读取的块变量

2 个答案: