问题描述
我有一个运行在后台有一个WinForm应用程序中的的BackgroundWorker
,有一个无限循环中执行的一些每隔一小时。我的UI 表格
类是这样的:
I have a winform application that runs in background with a BackgroundWorker
that has an infinite loop that execute something every hour. My UI Form
class is something like this:
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();
}
}
和在 frmAutoScript
,我也有一个名为按钮 btnDownload
,单击时,它会下载和变革的挥发性值
varialbe _isDownloading
。按钮的事件是这样的:
And in that frmAutoScript
, I also have a button named btnDownload
that when clicked, it will download and change the value of the volatile
varialbe _isDownloading
. The event of the button is something like this:
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,当我按一下按钮 btnDownload
和 _isDownloading
设置为真
,而当系统时间击中了 16:00
的新下载()下载();
再次执行eventhough该 _isDownloading
设置为true。为什么会这样呢?
But when I click the button btnDownload
and the _isDownloading
is set to true
, and when the system time hit the 4:00 PM
, the new Downloader().Download();
is executed again eventhough the _isDownloading
is set to true. Why was it like this?
我的code是在C#中,框架4,项目是的WinForms,建立在Visual Studio 2010专业版。
My code is in C#, framework 4, project is in winforms, build in Visual Studio 2010 Pro.
推荐答案
您code未测试对挥发性
字段 - 它是对<$ C测试$ C> isDownloading ,其中的看起来的像一个地方,但(因为它被捕获)实际上是一个常规(非 - 挥发性
)领域。所以说:无论是使用某种记忆障碍,或力是挥发性读取。或者更简单地说:摆脱 isDownloading
中的的完全的,然后检查对财产
Your code is not testing against the volatile
field - it is testing against isDownloading
, which looks like a "local", but (because it is captured) is in fact a regular (non-volatile
) field. So: either use some kind of memory barrier, or force that to be a volatile read. Or more simply: get rid of isDownloading
completely, and check against the property.
顺便说一句,的缓存击败性挥发
是不可以的关键字的意图,而在于:结果。它会工作,但的个人的我建议你写code工作按意向而不是结果,也许是使用一个简单的锁定
或类似互锁
。
Incidentally, the cache-defeating properties of volatile
are not the intent of the keyword, but rather: a consequence. It'll work, but personally I'd suggest writing the code to work by intent rather than by consequence, perhaps using either a simple lock
or something like Interlocked
.
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