I have some code and when it executes, it throws a IOException
, saying that
The process cannot access the file 'filename' because it is being used by another process
What does this mean, and what can I do about it?
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.
Using FileShare fixed my issue of opening file even if it is opened by another process.
using (var stream = File.Open(path, FileMode.Open, FileAccess.Write, FileShare.ReadWrite))
{
}
Had an issue while uploading an image and couldn't delete it and found a solution. gl hf
//C# .NET
var image = Image.FromFile(filePath);
image.Dispose(); // this removes all resources
//later...
File.Delete(filePath); //now works
Problem
one is tying to open file System.IO.File.Open(path, FileMode)
with this method and want a shared access on file but
if u read documentation of System.IO.File.Open(path, FileMode) it is explicitly saying its does not allow sharing
https://i.stack.imgur.com/f5prn.png
Solution
https://i.stack.imgur.com/dRRj6.png
using FileStream fs = System.IO.File.Open(filePath, FileMode.Open, FileAccess.Read, FileShare.Read);
with FileShare.Read
As other answers in this thread have pointed out, to resolve this error you need to carefully inspect the code, to understand where the file is getting locked.
In my case, I was sending out the file as an email attachment before performing the move operation.
So the file got locked for couple of seconds until SMTP client finished sending the email.
The solution I adopted was to move the file first, and then send the email. This solved the problem for me.
Another possible solution, as pointed out earlier by Hudson, would've been to dispose the object after use.
public static SendEmail()
{
MailMessage mMailMessage = new MailMessage();
//setup other email stuff
if (File.Exists(attachmentPath))
{
Attachment attachment = new Attachment(attachmentPath);
mMailMessage.Attachments.Add(attachment);
attachment.Dispose(); //disposing the Attachment object
}
}
File.Move()
won't work & gives the same error. If just adding a file to an e-mail I don't think it errors when in use during the Attachments.Add()
operation because this is just a copy operation. If it did for some reason you could copy it to a Temp directory, attach the copy, & delete the copied file afterwards. But I don't think, if the OP wants to modify a file & use that, that this kind of solution (which you didn't show the code of, only the attaching portion) would work. .Dispose()
is always a good idea, but not relevant here unless file is opened in a prior op.
I got this error because I was doing File.Move to a file path without a file name, need to specify the full path in the destination.
The error indicates another process is trying to access the file. Maybe you or someone else has it open while you are attempting to write to it. "Read" or "Copy" usually doesn't cause this, but writing to it or calling delete on it would.
There are some basic things to avoid this, as other answers have mentioned:
In FileStream operations, place it in a using block with a FileShare.ReadWrite mode of access. For example: using (FileStream stream = File.Open(path, FileMode.Open, FileAccess.Write, FileShare.ReadWrite))
{
}
Note that FileAccess.ReadWrite is not possible if you use FileMode.Append. I ran across this issue when I was using an input stream to do a File.SaveAs when the file was in use. In my case I found, I didn't actually need to save it back to the file system at all, so I ended up just removing that, but I probably could've tried creating a FileStream in a using statement with FileAccess.ReadWrite, much like the code above. Saving your data as a different file and going back to delete the old one when it is found to be no longer in use, then renaming the one that saved successfully to the name of the original one is an option. How you test for the file being in use is accomplished through the List
I had this problem and it was solved by following the code below
var _path=MyFile.FileName;
using (var stream = new FileStream
(_path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
{
// Your Code! ;
}
I had a very specific situation where I was getting an "IOException: The process cannot access the file 'file path'" on the line
File.Delete(fileName);
Inside an NUnit test that looked like:
Assert.Throws<IOException>(() =>
{
using (var sr = File.OpenText(fileName) {
var line = sr.ReadLine();
}
});
File.Delete(fileName);
It turns out NUnit 3 uses something they call "isolated context" for exception assertions. This probably runs on a separate thread.
My fix was to put the File.Delete
in the same context.
Assert.Throws<IOException>(() =>
{
try
{
using (var sr = File.OpenText(fileName) {
var line = sr.ReadLine();
}
}
catch
{
File.Delete(fileName);
throw;
}
});
I had the following scenario that was causing the same error:
Upload files to the server
Then get rid of the old files after they have been uploaded
Most files were small in size, however, a few were large, and so attempting to delete those resulted in the cannot access file error.
It was not easy to find, however, the solution was as simple as Waiting "for the task to complete execution":
using (var wc = new WebClient())
{
var tskResult = wc.UploadFileTaskAsync(_address, _fileName);
tskResult.Wait();
}
In my case this problem was solved by Opening the file for Shared writing/reading. Following are the sample codes for shared reading and writing:- Stream Writer
using(FileStream fs = new FileStream("D:\\test.txt",
FileMode.Append, FileAccess.Write, FileShare.ReadWrite))
using (StreamWriter sw = new StreamWriter(fs))
{
sw.WriteLine("any thing which you want to write");
}
Stream Reader
using (FileStream fs = new FileStream("D:\\test.txt", FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
using (StreamReader rr=new StreamReader(fs))
{
rr.ReadLine())
}
My below code solve this issue, but i suggest First of all you need to understand what causing this issue and try the solution which you can find by changing code
I can give another way to solve this issue but better solution is to check your coding structure and try to analyse what makes this happen,if you do not find any solution then you can go with this code below
try{
Start:
///Put your file access code here
}catch (Exception ex)
{
//by anyway you need to handle this error with below code
if (ex.Message.StartsWith("The process cannot access the file"))
{
//Wait for 5 seconds to free that file and then start execution again
Thread.Sleep(5000);
goto Start;
}
}
GC.*()
then you probably have other issues with your code. 2) Message is localized and fragile, use the HRESULT instead. 3) You may want to sleep with Task.Delay()
(and ten seconds is somehow excessive in manyt cases). 4) You do not have an exit condition: this code could hang forver. 5) You definitely do not need goto
here. 6) To catch Exception
is usually a bad idea, in this case also because... 6) If anything else happen then you're swallowing the error.
GC.Collect()
has been when dealing with some COM objects.
StackOverflowException
or OutOfMemoryException
in this way (swalling and repeating)? After those errors are you sure that your program data is still correct? No, it's VERY hard to write code that can handle and resume an out of memory condition. VERY hard, and definitely not swallowing and ignoring the error.
while (true)
loop using goto
, catching all exceptions and then discriminate using the error message. Nothing to understand better, just suboptimal (IMHO) even for a throw-away script.
Success story sharing
File.Create(path)
, you should add.Close()
on the end of that before you write to it. There are pitfalls like that, in addition tousing
statements for writing the files, then deleting after them. You should post the code in your question for how you are creating & deleting your file. But probably falls in line with something mentioned above.Directory.SetCreationTimeUTC()
but it fails when File Explorer is open, claiming the directory is being accessed by another process. How should I handle this situation?