我有一个在后台运行的 winform 应用程序,它有一个 BackgroundWorker
,它有一个每小时执行一些东西的无限循环。我的 UI Form
类是这样的:
public partial class frmAutoScript : Form
{
private volatile bool _isDownloading = false;
private bool IsDownloading { get { return this._isDownloading; } set { this._isDownloading = value; } }
public frmAutoScript()
{
InitializeComponent();
this.RunAutoSynchronization();
}
private void RunAutoSynchronization()
{
bool isDownloading = this.IsDownloading;
BackgroundWorker bgwDownloader = new BackgroundWorker();
bgwDownloader.WorkerReportsProgress = true;
bgwDownloader.ProgressChanged += (sndr, evnt) =>
{
if (evnt.ProgressPercentage == 2)
isDownloading = this.IsDownloading;
else
{
this.IsDownloading = evnt.ProgressPercentage == 1;
isDownloading = this.IsDownloading;
}
};
bgwDownloader.DoWork += (sndr, evnt) =>
{
while (true)
{
if (DateTime.Now.Hour == 16 &&
DateTime.Now.Minute == 0)
{
try
{
bgwDownloader.ReportProgress(2);
if (!isDownloading)
{
bgwDownloader.ReportProgress(1);
new Downloader().Download();
}
bgwDownloader.ReportProgress(0);
}
catch { }
}
System.Threading.Thread.Sleep(60000);
}
};
bgwDownloader.RunWorkerAsync();
}
}
在 frmAutoScript
中,我还有一个名为 btnDownload
的按钮,单击该按钮时,它将下载并更改 volatile
的值变量 _isDownloading
。按钮的事件是这样的:
private void btnDownload_Click(object sender, EventArgs e)
{
if (IsDownloading)
MessageBox.Show("A download is currently ongoing. Please wait for the download to finish.",
"Force Download", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
else
{
this.IsDownloading = true;
BackgroundWorker bgwDownloader = new BackgroundWorker();
bgwDownloader.DoWork += (sndr, evnt) =>
{
try
{
new Downloader().Download();
}
catch(Exception ex)
{
MessageBox.Show("An error occur during download. Please contact your system administrator.\n Exception: " +
ex.GetType().ToString() + "\nError Message:\n" + ex.Message + " Stack Trace:\n" + ex.StackTrace, "Download Error!", MessageBoxButtons.OK, MessageBoxIcon.Error);
}
};
bgwDownloader.RunWorkerCompleted += (sndr, evnt) =>
{
this.IsDownloading = false;
};
bgwDownloader.RunWorkerAsync();
}
}
但是当我单击按钮 btnDownload
并且 _isDownloading
设置为 true
时,当系统时间达到 4 :00 PM
,尽管 _isDownloading
设置为 true,但 new Downloader().Download();
再次执行。为什么会这样?
我的代码在 C# 中,框架 4,项目在 winforms 中,在 Visual Studio 2010 Pro 中构建。
最佳答案
您的代码不是针对 volatile
字段进行测试 - 它是针对 isDownloading
进行测试,它看起来像“本地”,但是 (因为它被捕获)实际上是一个常规(非volatile
)字段。所以:要么使用某种内存屏障,要么强制其成为 volatile 读取。或者更简单:完全摆脱isDownloading
,并检查该属性。
顺便说一句,volatile
的缓存失效属性不是关键字的意图,而是一个结果。它会工作,但个人我建议编写代码以按意图而不是结果,也许使用简单的锁
或类似 Interlocked
的内容。
关于c# - volatile 变量的值在多线程中不改变,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/10781772/