Locking a xml file(located in a server) when the same application(from 2 different computers) is trying to write into it

Question

I have a winapp which writes data into a xml(Data.xml). This xml is my data store.

The winapp will be used by atleast 10 ppl. Sometimes 2 users may simaltaneously import some data and store it into Data.xml(import usually takes 60-100secs). During this period which ever process got the first access on Data.xml must hold a lock on it and the other process must be informed that someone else is importing. (i have not used any threading concepts)

I tried the below :-

FileAttributes fileAttributes = File.GetAttributes(m_sDataXMLPath);
if ((fileAttributes & FileAttributes.ReadOnly) != FileAttributes.ReadOnly)
{
    try
    {
        FileStream currentWriteableFile = File.OpenWrite(m_sDataXMLPath);
        currentWriteableFile.Close();
    }
    catch
    {
        throw; // throw the IO exception so that the other process gets the 
               // exception which is ok with my requirement. 
               // the user just needs to know.
    }
}

The above is working if i run 2 instances of the winapp in one computer, but fails when i am running them on 2 seperate machines!

Please give me some suggestions to lock and then let the other user know someone else is writing into it.

Answer 1

Why are you using GetAttributes()? The file could have ReadOnly attribute and still be readable. Just open the file for write and hold it until writing completes.

using (FileStream file = File.Open("c:\\yourpath\\file.xml", FileMode.Create, FileAccess.Write))
{
... // Here the file is locked
}