文件访问策略在多线程环境（Web应用程序） [英] File Access Strategy in a Multi-Threaded Environment (Web App)

问题描述

我有一个文件，它是从一个Web服务，并采取本地缓存Web应用程序中的某些数据的XML重新presentation。这个想法是是，此数据的非常的静态，只是可能的变化。所以我将它设置缓存到一个文件中，并坚持显示器反对，以检查它是否已被删除。一旦删除，该文件将其源刷新和重建。

I have a file which is an XML representation of some data that is taken from a Web service and cached locally within a Web Application. The idea being is that this data is very static, but just might change. So I have set it up to cache to a file, and stuck a monitor against it to check if it has been deleted. Once deleted, the file will be refreshed from its source and rebuilt.

我现在的问题在运行但是，因为很明显的，因为它正试图访问时，它仍然是读取/写入文件中的数据它属于在一个多线程环境。

I am now running in to problems though, because obviously in a multi-threaded environment it falls over as it is trying to access the data when it is still reading/writing the file.

这是混淆了我，因为我添加了一个对象锁定反对，这是读/写过程中始终处于锁定状态。这是我的理解是试图从其它线程访问会被告知要等待直到锁被释放？

This is confusing me, because I added a object to lock against, and this is always locked during read/write. It was my understanding that attempted access from other threads would be told to "wait" until the lock was released?

只是为了让你知道，我是真正的新多线程开发，所以我完全愿意接受，这是一个螺丝钉在我的部分：）

Just to let you know, I am real new to multi-threaded development, so I am totally willing to accept this is a screw up on my part :)

• 我缺少的东西吗


• 什么是在多线程环境最好的文件访问策略？
  

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对不起 - 我应该说这是使用的 ASP.NET 2.0 ：）

Sorry - I should have said this is using ASP.NET 2.0 :)

推荐答案

下面是我用它来确保文件不会被其他进程锁定了code。这不是100％的万无一失，但它能够完成大部分时间工作：

Here is the code that I use to make sure a file is not locked by another process. It's not 100% foolproof, but it gets the job done most of the time:

    /// <summary>
    /// Blocks until the file is not locked any more.
    /// </summary>
    /// <param name="fullPath"></param>
    bool WaitForFile(string fullPath)
    {
        int numTries = 0;
        while (true)
        {
            ++numTries;
            try
            {
                // Attempt to open the file exclusively.
                using (FileStream fs = new FileStream(fullPath,
                    FileMode.Open, FileAccess.ReadWrite, 
                    FileShare.None, 100))
                {
                    fs.ReadByte();

                    // If we got this far the file is ready
                    break;
                }
            }
            catch (Exception ex)
            {
                Log.LogWarning(
                   "WaitForFile {0} failed to get an exclusive lock: {1}", 
                    fullPath, ex.ToString());

                if (numTries > 10)
                {
                    Log.LogWarning(
                        "WaitForFile {0} giving up after 10 tries", 
                        fullPath);
                    return false;
                }

                // Wait for the lock to be released
                System.Threading.Thread.Sleep(500);
            }
        }

        Log.LogTrace("WaitForFile {0} returning true after {1} tries",
            fullPath, numTries);
        return true;
    }

很明显，你可以调整超时和重试次数，以满足您的应用程序。我用这个来处理需要被写入了一阵巨大的FTP文件。

Obviously you can tweak the timeouts and retries to suit your application. I use this to process huge FTP files that take a while to be written.

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