Question

Here is my custom “logger” class, which helps me create logs file in my project.

namespace MyProject
{
class Logger
{
    private FileInfo fFile;
    private DirectoryInfo dDir;

    /// <summary>Add a new entry to the log file.</summary>
    /// <param name="sData">The line to add.</param>
    public void Add(string sData)
    {
        DateTime CurrTime = DateTime.Now;

        if (fFile.Length > 1048576)
        {
            fFile.MoveTo(Path.Combine(dDir.FullName, CurrTime.ToShortDateString() + fFile.Name));
            fFile = new FileInfo(Path.Combine(dDir.FullName,fFile.Name));
            using (StreamWriter sw = fFile.CreateText())
            {
                sw.WriteLine("{0:u}|{1}", CurrTime, sData);
            }
        }
        else
        {
            using (StreamWriter sw = fFile.AppendText())
            {
                sw.WriteLine("{0:u}|{1}", CurrTime, sData);
            }
        }
    }

    /// <summary>Logger instance</summary>
    /// <param name="sFile">Full name of the file to use as logs. Ex : "MyLogs.txt"</param>
    public Logger(string sFile)
    {
        dDir = new DirectoryInfo(Path.Combine(MyProject.AppPath, "logs"));
        if (!dDir.Exists)
        {
            dDir.Create();
        }

        fFile = new FileInfo(Path.Combine(dDir.FullName,sFile));

        if (!fFile.Exists)
        {
            using (StreamWriter sw = fFile.CreateText())
            {
                sw.WriteLine("{0:u}|Logger Started", DateTime.Now);
            }
        }
        else
        {
            Add("Logger Started");
        }           
    }
}
}

The problem I have with this code is, apparently, sometimes, Logger.Add is called before the new instance of that logger had time to create the file. So my program crashes saying “file not found”, although, the file ends up being created in the end, and if I restart my program using the same filename for the logs, everything works fine (because the file exists now …)

Instead of just making sure logger.add is not called before the file is created, is there a way to “lock” the class ?

I’ve tried the lock method but it didn’t work … Lock(this) didn’t do anything, and I can’t use it on the method itself.

Answer 1

The exception is actually caused not because the file doesn’t exist, but because the FileInfo instance is stale! You created the FileInfo when the file didn’t exist, and it takes a snapshot of the state of the file at this time. When I test it the exception is getting thrown when you invoke fFile.Length in the Add method. If I add in a call to fFile.Refresh() I find it works:

...
DateTime currTime = DateTime.Now;
fFile.Refresh();
if (fFile.Length > 1048576)
...

See here:

http://msdn.microsoft.com/en-us/library/system.io.filesysteminfo.refresh.aspx

“Calls must be made to Refresh before attempting to get the attribute information, or the information will be outdated.”