c# - Multi processes read&write one file

Question

I have a txt file ABC.txt which will be read and wrote by multi processes. So when one process is reading from or writing to file ABC.txt, file ABC.txt must be locked so that any other processes can not reading from or writing to it. I know the enum System.IO.FileShare may be the right way to handle this problem. But I used another way which I'm not sure if it is right. The following is my solution.

I added another file Lock.txt to the folder. Before I can read from or write to file ABC.txt, I must have the capability to read from file Lock.txt. And after I have read from or written to file ABC.txt, I have to release that capability. The following is the code.

        #region Enter the lock
        FileStream lockFileStream = null;
        bool lockEntered = false;
        while (lockEntered == false)
        {
            try
            {
                lockFileStream = File.Open("Lock.txt", FileMode.Open, FileAccess.Read, FileShare.None);
                lockEntered = true;
            }
            catch (Exception)
            {
                Thread.Sleep(500);
            }
        }
        #endregion

        #region Do the work
        // Read from or write to File ABC.txt
        // Read from or write to other files
        #endregion

        #region Release the lock
        try
        {
            if (lockFileStream != null)
            {
                lockFileStream.Dispose();
            }
        }
        catch
        {
        }
        #endregion

On my computer, it seems that this solution works well, but I still can not make sure if it is appropriate..

Edit: Multi processes, not multi threads in the same process.

Answer 1

C#'s named EventWaitHandle is the way to go here. Create an instance of wait handle in every process which wants to use that file and give it a name which is shared by all such processes.

EventWaitHandle waitHandle = new EventWaitHandle(true, EventResetMode.AutoReset, "SHARED_BY_ALL_PROCESSES");

Then when accessing the file wait on waitHandle and when finished processing file, set it so the next process in the queue may access it.

waitHandle.WaitOne();
/* process file*/
waitHandle.Set();

When you name an event wait handle then that name is shared across all processes in the operating system. Therefore in order to avoid possibility of collisions, use a guid for name ("SHARED_BY_ALL_PROCESSES" above).