Ioexception: the Process Cannot Access the File 'File Path' Because It Is Being Used by Another Process

IOException: The process cannot access the file 'file path' because it is being used by another process

What is the cause?

The error message is pretty clear: you're trying to access a file, and it's not accessible because another process (or even the same process) is doing something with it (and it didn't allow any sharing).

Debugging

It may be pretty easy to solve (or pretty hard to understand), depending on your specific scenario. Let's see some.

Your process is the only one to access that file

You're sure the other process is your own process. If you know you open that file in another part of your program, then first of all you have to check that you properly close the file handle after each use. Here is an example of code with this bug:

var stream = new FileStream(path, FileAccess.Read);
var reader = new StreamReader(stream);
// Read data from this file, when I'm done I don't need it any more
File.Delete(path); // IOException: file is in use

Fortunately FileStream implements IDisposable, so it's easy to wrap all your code inside a using statement:

using (var stream = File.Open("myfile.txt", FileMode.Open)) {
    // Use stream
}

// Here stream is not accessible and it has been closed (also if
// an exception is thrown and stack unrolled

This pattern will also ensure that the file won't be left open in case of exceptions (it may be the reason the file is in use: something went wrong, and no one closed it; see this post for an example).

If everything seems fine (you're sure you always close every file you open, even in case of exceptions) and you have multiple working threads, then you have two options: rework your code to serialize file access (not always doable and not always wanted) or apply a retry pattern. It's a pretty common pattern for I/O operations: you try to do something and in case of error you wait and try again (did you ask yourself why, for example, Windows Shell takes some time to inform you that a file is in use and cannot be deleted?). In C# it's pretty easy to implement (see also better examples about disk I/O, networking and database access).

private const int NumberOfRetries = 3;
private const int DelayOnRetry = 1000;

for (int i=1; i <= NumberOfRetries; ++i) {
    try {
        // Do stuff with file
        break; // When done we can break loop
    }
    catch (IOException e) when (i <= NumberOfRetries) {
        // You may check error code to filter some exceptions, not every error
        // can be recovered.
        Thread.Sleep(DelayOnRetry);
    }
}

Please note a common error we see very often on StackOverflow:

var stream = File.Open(path, FileOpen.Read);
var content = File.ReadAllText(path);

In this case ReadAllText() will fail because the file is in use (File.Open() in the line before). To open the file beforehand is not only unnecessary but also wrong. The same applies to all File functions that don't return a handle to the file you're working with: File.ReadAllText(), File.WriteAllText(), File.ReadAllLines(), File.WriteAllLines() and others (like File.AppendAllXyz() functions) will all open and close the file by themselves.

Your process is not the only one to access that file

If your process is not the only one to access that file, then interaction can be harder. A retry pattern will help (if the file shouldn't be open by anyone else but it is, then you need a utility like Process Explorer to check who is doing what).

Ways to avoid

When applicable, always use using statements to open files. As said in previous paragraph, it'll actively help you to avoid many common errors (see this post for an example on how not to use it).

If possible, try to decide who owns access to a specific file and centralize access through a few well-known methods. If, for example, you have a data file where your program reads and writes, then you should box all I/O code inside a single class. It'll make debug easier (because you can always put a breakpoint there and see who is doing what) and also it'll be a synchronization point (if required) for multiple access.

Don't forget I/O operations can always fail, a common example is this:

if (File.Exists(path))
    File.Delete(path);

If someone deletes the file after File.Exists() but before File.Delete(), then it'll throw an IOException in a place where you may wrongly feel safe.

Whenever it's possible, apply a retry pattern, and if you're using FileSystemWatcher, consider postponing action (because you'll get notified, but an application may still be working exclusively with that file).

Advanced scenarios

It's not always so easy, so you may need to share access with someone else. If, for example, you're reading from the beginning and writing to the end, you have at least two options.

1) share the same FileStream with proper synchronization functions (because it is not thread-safe). See this and this posts for an example.

2) use FileShare enumeration to instruct OS to allow other processes (or other parts of your own process) to access same file concurrently.

using (var stream = File.Open(path, FileMode.Open, FileAccess.Write, FileShare.Read))
{
}

In this example I showed how to open a file for writing and share for reading; please note that when reading and writing overlaps, it results in undefined or invalid data. It's a situation that must be handled when reading. Also note that this doesn't make access to the stream thread-safe, so this object can't be shared with multiple threads unless access is synchronized somehow (see previous links). Other sharing options are available, and they open up more complex scenarios. Please refer to MSDN for more details.

In general N processes can read from same file all together but only one should write, in a controlled scenario you may even enable concurrent writings but this can't be generalized in few text paragraphs inside this answer.

Is it possible to unlock a file used by another process? It's not always safe and not so easy but yes, it's possible.

System.IO.IOException: The process cannot access the file 'C:\Test\test.txt' because it is being used by another process

File.Create(path); opens the file and leaves it opened. When you do TextWriter tw = new StreamWriter(path); you are trying to access the file which is being used by the process which created the file (the code line above).

You should do something like this:

if (!File.Exists(path))
{
    using (var stream = File.Create(path))
    {
        using (TextWriter tw = new StreamWriter(stream))
        {
            tw.WriteLine("abc");
        }
    }
}

System.IO.IOException: The process cannot access the file '.txt' because it is being used by another process

I've added this code to my class:

 public static bool IsFileLocked(FileInfo file)
        {
            FileStream stream = null;

            try
            {
                stream = file.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None);
            }
            catch
            {
                return true;
            }
            finally
            {
                if (stream != null)
                {
                    stream.Close();
                }
            }

            return false;
        }

and now my LogToFile method is like this:

while (IsFileLocked(fi))
            {
            }

            using (StreamWriter myStream = new StreamWriter(sLogFilePath, true))
            {
                if (displayTime == true)
                    myStream.WriteLine(string.Format("{0, -45}{1, -25}{2, -10}{3}", guid, DateTime.Now, StringEnum.GetStringValue(enumMsg), sText));
                else
                    myStream.WriteLine(string.Format("{0, -70}{1, -10}{2} ", guid, StringEnum.GetStringValue(enumMsg), sText));                
            }

I hope this will work.

System.IO.File.Delete throws The process cannot access the file because it is being used by another process

After some testing, I found the problem. turns out I forgot about a function I made that was called every time I saved a media file. the function returned the duration of the file and used NAudio.Wave.WaveFileReader and NAudio.Wave.Mp3FileReader methods which I forgot to close after I called them

I fixed these issues by putting those methods inside of a using statement

Here is the working function:

public static int GetMediaFileDuration(string filePath)
{
    filePath = HostingEnvironment.MapPath("~") + filePath;

    if (Path.GetExtension(filePath) == ".wav")
        using (WaveFileReader reader = new WaveFileReader(filePath))
            return Convert.ToInt32(reader.TotalTime.TotalSeconds);

    else if(Path.GetExtension(filePath) == ".mp3")
        using (Mp3FileReader reader = new Mp3FileReader(filePath))
            return Convert.ToInt32(reader.TotalTime.TotalSeconds);

    return 0;
}

The moral of the story is, to check if you are opening the file anywhere else in your project

System.IO.IOException: 'The process cannot access the file because it is being used by another process

You should dispose myStream variable. That's why you are getting that error.

IOException: The process cannot access the file 'fileName/textFile.txt' because it is being used by another process

You should use the using statement around disposable objects like streams. This will ensure that the objects release every unmanaged resources they hold. And don't open the writer until you need it. Makes no sense to open the writer when first you need to read the records

static void RecordUpdater(string username,int points,string term) 
{
    Player playersRecord = new Player(points, username);
    List<Player> allRecords = new List<Player>();
    int minPoints = 0;
    try
    {
        using(StreamReader reader = new StreamReader($@"Record\{term}"))
        {
            while (!reader.EndOfStream)
            {
                .... load you data line by line
            }
        }        

        ..... process your data .....

        using(StreamWriter streamWriter = new StreamWriter($@"Record\{term}"))
        {
            ... write your data...
        }
    }
    catch(Exception ex)
    {
        ... show a message about the ex.Message or just log everything
            in a file for later analysis
    }
}

Also you should consider that working with files is one of the most probable context in which you could receive an exception due to external events in which your program has no control.

It is better to enclose everything in a try/catch block with proper handling of the exception

How to fix: The process cannot access the file '**' because it is being used by another process when downloading multiple spreadsheet files

As Avi Meltser pointed out in the comments the solution is as follows:

Try changing the file name creation from downloadPath + file.Id to something that's 100% unique like downloadPath + Guid.NewGuid() and see if the problem persists

The problem was solved

---

Related Topics