Question

My program is logging data to a file, at the same time a user interface displays the incoming data live. I want the logged data to be on disk within a second or two if computer/program/os/whatever shuts down. Data is coming in at least 100 times/sec.

I want the user to be able to give the log-file a new name, while logging is active. The problem is that i can’t change the name of the file while it is open, even if it is by the same process.

Test case:

string fileName1 = "test.txt";
string fileName2 = "test2.txt";

using (StreamWriter sw = new StreamWriter(new FileStream(fileName1, FileMode.Create)))
{
     sw.WriteLine("before");
     File.Move(fileName1, fileName2);  //<<-- IOException - The process cannot access the file because it is being used by another process.
     w.WriteLine("after");
 }

So, How do i rename a file from a process while the same process is having a stream to the file open?

Answer 1

You should close the first stream, rename the file, then reopen the stream:

using (StreamWriter sw = new StreamWriter(new FileStream(fileName1, FileMode.Create)))
{
  sw.WriteLine("before");
  sw.Close();
}

File.Move(fileName1, fileName2);

using (StreamWriter sw = new StreamWriter(new FileStream(fileName2, FileMode.Append)))
{
  sw.WriteLine("after");
}