Check if a file is open

Question

Is there a way to find if a file is already open or not?

Please offer more specifics. Already open by your process, or another process? Opened period, or just opened with write access? What about sharing? etc. This question is too vague. — hemp, Jun 07 '10 at 07:11

Pranay Rana · Accepted Answer · 2010-06-10T20:04:57.937

32

protected virtual bool IsFileinUse(FileInfo file)
{
     FileStream stream = null;

     try
     {
         stream = file.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None);
     }
     catch (IOException)
     {
         //the file is unavailable because it is:
         //still being written to
         //or being processed by another thread
         //or does not exist (has already been processed)
         return true;
     }
     finally
     {
         if (stream != null)
         stream.Close();
     }
     return false; 
}

edited Jun 10 '10 at 20:04

answered Jun 07 '10 at 06:53

Pranay Rana

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3

If the process doesn't have write access to the file this will produce a misleading result (the open will fail, but not necessarily because a handle exists.) Opening for Read access would be less error-prone. – hemp Jun 07 '10 at 07:08
4

Amazing that most languages don't have a method to test file is open. We used to use the same type of method under C++ in OS/2. i.e. try to open the file exclusive. It works well enough, but I've never thought it elegant. – hookenz Jun 07 '10 at 07:34
2

It's not a language feature, it's an OS feature. There just doesn't exist a simple API (in Windows) to query for that information. It is possible to get, but it's low-level and there are a lot of parameters that would have to be specified to know what was meant by "open". – hemp Jun 07 '10 at 08:07
3

This answer is identical to this answer on another question: (http://stackoverflow.com/a/937558/38657)... that said, it's a good answer. – Nate Sauber Sep 19 '12 at 13:02
I just tested this and an exception is not thrown when the text file is open in Notepad. – James Oct 18 '16 at 21:44
-1 because maybe after closing the file in you method (_IsFileinUse_) maybe another thread/process lock the file before your thread – Mehdi Dehghani Mar 16 '17 at 09:35

score 9 · Answer 2 · edited Feb 09 '12 at 15:15

9

As @pranay rana, but we need to make sure we close our file handle:

public bool IsFileInUse(string path)
{
  if (string.IsNullOrEmpty(path))
    throw new ArgumentException("'path' cannot be null or empty.", "path");

  try {
    using (var stream = new FileStream(path, FileMode.Open, FileAccess.Read)) { }
  } catch (IOException) {
    return true;
  }

  return false;
}

edited Feb 09 '12 at 15:15

Pranay Rana

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answered Jun 07 '10 at 06:59

Matthew Abbott

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Same as @pranay rana, I tested this method, but it does not detect when the file is open in Notepad. – James Oct 19 '16 at 12:42

score 1 · Answer 3 · answered Jun 07 '10 at 07:05

If you mean that you want to check if a file is open before you try to open it, then no. (At least not without going low level and examine every file handle that is open in the system.)

Besides, the information would be old when you get it. Even if the test would return that the file is not open, it could have been opened before you have a chance to use the return value.

So, the proper way to handle the situation is to try to open the file, and handle any error than may occur.

score 0 · Answer 4 · answered Jun 07 '10 at 07:43

Agreed. I would create a designated class which wraps the open file logic or at least the test (IsFileAvailable). This will allow you to place the exception management with a class specifically responsible and make it reusable. You may even apply further logic, such as testing the file size to see if the file is being written to etc, to give a more detailed response. It will also make your consuming code much cleaner.

Check if a file is open

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