How to deal with File Exception: cannot access the file because it is being used by another process

Question

How to deal with the this Exception. I have a text file. And this code rewrites the file every 3 sec. At the same time another MS Excel file reads the data from the file. And sometimes I get this exception.

Is there a way for StreamWriter to wait until MS Excel finishes reading the file and start rewriting the file right after that?

string path = @"C:\My Path\my_file.txt";

 using (StreamWriter fs = new StreamWriter(File.OpenWrite(path)))
  {
    fs.Write(text);
    fs.Close();
  }

This is the exact reason why you should always handle an IO exception — Steve, Oct 27 '16 at 19:17
No, excel just reads the data from the text file every 3 seconds. It works fine mostly, but now and then it throws this exception.. — Totallama, Oct 27 '16 at 19:18
Possible duplicate of [Is there a way to check if a file is in use?](http://stackoverflow.com/questions/876473/is-there-a-way-to-check-if-a-file-is-in-use) — Sebi, Oct 27 '16 at 19:18
@usmanlqbal The process that reads the file would need to use that same lock in order for synchronization to work.. — Matias Cicero, Oct 27 '16 at 19:18
@Totallama check the duplicate link. This exactly describes your needs i think. — Sebi, Oct 27 '16 at 19:19
Matias Cicero: How can I do that? I have VBA script (macro) in Excel that refreshes the cell, that is set to get data from the text file.. — Totallama, Oct 27 '16 at 19:20
Lock just helps on multithreading. But if another file outside your code access the same file, this will not work i think. — Sebi, Oct 27 '16 at 19:21
1. Check the duplicate link. 2. Catch the exception and wait the next 3sek. — Sebi, Oct 27 '16 at 19:22
@Totallama You can't do it. `lock` was designed for multithreading synchronization. We're talking about different processes here. — Matias Cicero, Oct 27 '16 at 19:23

score -1 · Answer 1 · answered Oct 27 '16 at 19:27

This is one way:

string path = @"C:\My Path\my_file.txt";
string text = "Declare text variable so this code compiles";
FileStream fileS = null;
bool done = false;
while (!done)
{
    done = true;

    try
    {
        fileS = File.OpenWrite(path);
    }
    catch (IOException ex)
    {
        done = false;
    }
}

using (StreamWriter fs = new StreamWriter(fileS))
{
    fs.Write(text);
    fs.Close();
};

I would also add in a StopWatch call to have the above while loop timeout after so long, and possibly a small Thread.Sleep() so you don't spin at full speed while essentially trying to obtain the FileStream lock.

How to deal with File Exception: cannot access the file because it is being used by another process

1 Answers1