Question

I have simplified this code for example purposes:

class TextLogger : IDisposable
{
    private FileStream m_FileStream;
    private StreamWriter m_StreamWriter;

    void CreateNewLogFile()
    {
          //Open the File
       m_FileStream = File.Open(
           m_CurrentFileName,
           FileMode.OpenOrCreate,
           FileAccess.Write,
           FileShare.Read );

       m_StreamWriter = new StreamWriter( m_FileStream );
       ....
    }
}

I get an InvalidArgumentException when trying to new up the StreamWriter, because m_FileStream has already been disposed by another thread and is null (m_StreamWriter is also null). How do I put a lock around the member variable?

Answer 1

You should do something like this

class TextLogger : IDisposable
{
    private FileStream m_FileStream;
    private StreamWriter m_StreamWriter;
    private object m_Lock = new object();

    void CreateNewLogFile()
    {
        lock (m_Lock)
        {
            if ( m_FileStream != null )
                m_StreamWriter = new StreamWriter(m_FileStream);
        };
    }

    void CalledFromOtherThread()
    {
        //Do stuff

        lock (m_Lock)
        {
            if (m_FileStream != null)
                m_FileStream.Dispose();
            m_FileStream = null;
        }
    }
}

When CalledFromOtherThread is called from another thread it should acquire the lock and then dispose the m_FileStream. This way in CreateNewLogFile you will never have a disposed FileStream