C# file is being used by another process

Question

I am not sure how can I solve my problem. From time to time I get the error: "The process cannot access the file 'xxxx' because it is being used by another proces".

Here is my method where the error happens:

private static void write_history(int index, int time_in_sec, int[] sent_resources)
        {
            string filepath = "Config\\xxx.txt";
            int writing_index = 0;

            if (File.Exists(filepath))
            {
                System.Threading.Thread.Sleep(5000);
                StreamReader reader = new StreamReader(new FileStream(filepath, FileMode.Open, FileAccess.Read, FileShare.Read));
                string temp = reader.ReadToEnd();
                reader.Close();

                for (int i = 0; i < 20; i++)
                {
                    if (temp.IndexOf("<hst_" + i.ToString() + ">") == -1)
                    {
                        writing_index = i;
                        break;
                    }
                }
            }

            System.Threading.Thread.Sleep(5000);
            // write to the file
            StreamWriter writer = new StreamWriter(filepath, true);
            writer.WriteLine("<hst_" + writing_index.ToString() + ">" + DateTime.Now.AddSeconds(time_in_sec).ToString() + "|" + sent_resources[0] + "|" + sent_resources[1] + "|" + sent_resources[2] + "|" + sent_resources[3] + "</hst_" + writing_index.ToString() + ">");
            writer.Close();
        }

And the error I get:

************** Exception Text **************
System.IO.IOException: The process cannot access the file 'Config\\xxx.txt' because it is being used by another process.
   at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath)

Answer 1

If you have made sure that you are genuinely opening and closing the file correctly, the most likely culprit is your virus detector. Virus detectors are notorious for observing that a log file has changed, opening it up to search it for a virus, and then while it is being read by the virus checker, an attempt to write to the file fails.

If that's the case, then I would ask the vendor of your virus checker what their recommended workaround is.