The process cannot access the file <file> because it is being use by another process.


  • I built a small class named "ErrorLog" through which the application creates a text file for each session and writes detailed error messages in it whenever the case. I am aware that this might not be the best approach for a logging class but I find this more comfortable and easier to use, especially for debugging reasons. However, if anyone knows/prefers another approach I'd gladly consider it. 

    So I added a new Class Library Project to my current solution and build my class' functionality as follows:

    My class checks for and creates if needed a directory named 'ErrorLog' in the application startup path, inside which it will create another directory named 'DD-MM-YYYY' (ShortDateString). In this last directory a text file will be created for each application session and its name will be 'HH-MM-SS' (Hours-Minutes-Seconds). 

    I create the file using the File.Create() method, and for the writing I use a StreamWriter object.

    private string NewLogFileSession(string folderName)
            // ...
            string fileName = string.Format(@"{0}\{1:hh-mm-ss}.txt", folderName, DateTime.Now.ToLocalTime());
            return fileName;
    public void WriteLog(string messageText)
            // ...
            using (StreamWriter sw = new StreamWriter(currentLogFileName, true))

    This works smoothly in my solution, but if I try to use the same class, either as .dll file or as new class library project, I get an exception which states that The process cannot access the file <full_fileName> because it is being used by another process, and that 'another' process is my application (or that's what Unlocker is telling me). 

    This is how I use the class:

    ErrorLog eLog = new ErrorLog();
    private void mainForm_Load(object sender, EventArgs e)
         eLog.WriteLog("Hello, World!");

    I can place the WriteLog(message); method anywhere in the app with the same error message, but again, this works fine in the original project. 

    What is that I am missing? 

    Daniel Vlasceanu [Visual Studio 2010 and SQL Server 2005, Professional Editions]

    There is no reasonable excuse for doing anything less than your best.

    Monday, November 28, 2011 11:07 AM


  • File.Create not only creates the file, it also opens the file and returns a FileStream. Since you ignore the result the stream won't be closed until the GC collects it, that can take a while.

    Ideally you should create a StreamWriter on the stream returned by File.Create and use the writer in WriteLog. Note that the writer should probably be stored in a static, otherwise each ErrorLog instance will try to create/open the same file.

    • Proposed as answer by Ragu.R Monday, November 28, 2011 12:22 PM
    • Marked as answer by dan001 Monday, November 28, 2011 12:29 PM
    Monday, November 28, 2011 11:20 AM