Question

I am planning to implement error logging writing something similar to this:

public static void WriteError(string errorMessage)
    {
        try
        {
            string path = "~/Error/" + DateTime.Today.ToString("dd-mm-yy") + ".txt";
            if (!File.Exists(System.Web.HttpContext.Current.Server.MapPath(path)))
            {
                File.Create(System.Web.HttpContext.Current.Server.MapPath(path)).Close();
            }
            using (StreamWriter w = File.AppendText(System.Web.HttpContext.Current.Server.MapPath(path)))
            {
                w.WriteLine("\r\nLog Entry : ");
                w.WriteLine("{0}", DateTime.Now.ToString(CultureInfo.InvariantCulture));
                string err = "Error in: " + System.Web.HttpContext.Current.Request.Url.ToString() +
                              ". Error Message:" + errorMessage;
                w.WriteLine(err);
                w.WriteLine("__________________________");
                w.Flush();
                w.Close();
            }
        }
        catch (Exception ex)
        {
            WriteError(ex.Message);
        }

    }

My question is this: Since it is a website, I will have multiple users simultaneously. In that case, if multiple users encounter exceptions at the same time and try to write to the same file, it will again give me an exception right? In that case, how do I implement error logging correctly for simultaneous users? Or will this work?

Thanks in advance.

Answer 1

Beside using NLog or other log library, the way you lock this cases is with mutex. I suggest mutex, and not lock() because can catch all pools/threads that may throw an error.

On MSDN there are the details about mutex and examples:

http://msdn.microsoft.com/en-us/library/system.threading.mutex.aspx

a simple example

public static void WriteError(string errorMessage)
{
    var mut = new Mutex(true, "LogMutexName");

    try
    {   
        // Wait until it is safe to enter.
        mut.WaitOne();

        // here you open write close your file
    }
    finally
    {
        // Release the Mutex.
        mut.ReleaseMutex();
    }   
}