File Access Strategy in a Multi-Threaded Environment (Web App)

Question

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 <

Answer 1

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:

    /// 

    /// Blocks until the file is not locked any more.
    /// 
    /// 
    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;
    }

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.