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

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?

This question is related to c# .net language-agnostic ioexception

The answer is


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;
    }
 }

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(); 
}

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! ;
  }

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:

  1. 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.

  2. 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.

  3. 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<Process> lstProcs = ProcessHandler.WhoIsLocking(file);
    

    line in my code below, and could be done in a Windows service, on a loop, if you have a particular file you want to watch and delete regularly when you want to replace it. If you don't always have the same file, a text file or database table could be updated that the service always checks for file names, and then performs that check for processes & subsequently performs the process kills and deletion on it, as I describe in the next option. Note that you'll need an account user name and password that has Admin privileges on the given computer, of course, to perform the deletion and ending of processes.

  4. When you don't know if a file will be in use when you are trying to save it, you can close all processes that could be using it, like Word, if it's a Word document, ahead of the save.

    If it is local, you can do this:

    ProcessHandler.localProcessKill("winword.exe");
    

    If it is remote, you can do this:

    ProcessHandler.remoteProcessKill(computerName, txtUserName, txtPassword, "winword.exe");
    

    where txtUserName is in the form of DOMAIN\user.

  5. Let's say you don't know the process name that is locking the file. Then, you can do this:

    List<Process> lstProcs = new List<Process>();
    lstProcs = ProcessHandler.WhoIsLocking(file);
    
    foreach (Process p in lstProcs)
    {
        if (p.MachineName == ".")
            ProcessHandler.localProcessKill(p.ProcessName);
        else
            ProcessHandler.remoteProcessKill(p.MachineName, txtUserName, txtPassword, p.ProcessName);
    }
    

    Note that file must be the UNC path: \\computer\share\yourdoc.docx in order for the Process to figure out what computer it's on and p.MachineName to be valid.

    Below is the class these functions use, which requires adding a reference to System.Management. The code was originally written by Eric J.:

    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    using System.Threading.Tasks;
    using System.Runtime.InteropServices;
    using System.Diagnostics;
    using System.Management;
    
    namespace MyProject
    {
        public static class ProcessHandler
        {
            [StructLayout(LayoutKind.Sequential)]
            struct RM_UNIQUE_PROCESS
            {
                public int dwProcessId;
                public System.Runtime.InteropServices.ComTypes.FILETIME ProcessStartTime;
            }
    
            const int RmRebootReasonNone = 0;
            const int CCH_RM_MAX_APP_NAME = 255;
            const int CCH_RM_MAX_SVC_NAME = 63;
    
            enum RM_APP_TYPE
            {
                RmUnknownApp = 0,
                RmMainWindow = 1,
                RmOtherWindow = 2,
                RmService = 3,
                RmExplorer = 4,
                RmConsole = 5,
                RmCritical = 1000
            }
    
            [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
            struct RM_PROCESS_INFO
            {
                public RM_UNIQUE_PROCESS Process;
    
                [MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCH_RM_MAX_APP_NAME + 1)]
                public string strAppName;
    
                [MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCH_RM_MAX_SVC_NAME + 1)]
                public string strServiceShortName;
    
                public RM_APP_TYPE ApplicationType;
                public uint AppStatus;
                public uint TSSessionId;
                [MarshalAs(UnmanagedType.Bool)]
                public bool bRestartable;
            }
    
            [DllImport("rstrtmgr.dll", CharSet = CharSet.Unicode)]
            static extern int RmRegisterResources(uint pSessionHandle,
                                                UInt32 nFiles,
                                                string[] rgsFilenames,
                                                UInt32 nApplications,
                                                [In] RM_UNIQUE_PROCESS[] rgApplications,
                                                UInt32 nServices,
                                                string[] rgsServiceNames);
    
            [DllImport("rstrtmgr.dll", CharSet = CharSet.Auto)]
            static extern int RmStartSession(out uint pSessionHandle, int dwSessionFlags, string strSessionKey);
    
            [DllImport("rstrtmgr.dll")]
            static extern int RmEndSession(uint pSessionHandle);
    
            [DllImport("rstrtmgr.dll")]
            static extern int RmGetList(uint dwSessionHandle,
                                        out uint pnProcInfoNeeded,
                                        ref uint pnProcInfo,
                                        [In, Out] RM_PROCESS_INFO[] rgAffectedApps,
                                        ref uint lpdwRebootReasons);
    
            /// <summary>
            /// Find out what process(es) have a lock on the specified file.
            /// </summary>
            /// <param name="path">Path of the file.</param>
            /// <returns>Processes locking the file</returns>
            /// <remarks>See also:
            /// http://msdn.microsoft.com/en-us/library/windows/desktop/aa373661(v=vs.85).aspx
            /// http://wyupdate.googlecode.com/svn-history/r401/trunk/frmFilesInUse.cs (no copyright in code at time of viewing)
            /// 
            /// </remarks>
            static public List<Process> WhoIsLocking(string path)
            {
                uint handle;
                string key = Guid.NewGuid().ToString();
                List<Process> processes = new List<Process>();
    
                int res = RmStartSession(out handle, 0, key);
                if (res != 0) throw new Exception("Could not begin restart session.  Unable to determine file locker.");
    
                try
                {
                    const int ERROR_MORE_DATA = 234;
                    uint pnProcInfoNeeded = 0,
                        pnProcInfo = 0,
                        lpdwRebootReasons = RmRebootReasonNone;
    
                    string[] resources = new string[] { path }; // Just checking on one resource.
    
                    res = RmRegisterResources(handle, (uint)resources.Length, resources, 0, null, 0, null);
    
                    if (res != 0) throw new Exception("Could not register resource.");
    
                    //Note: there's a race condition here -- the first call to RmGetList() returns
                    //      the total number of process. However, when we call RmGetList() again to get
                    //      the actual processes this number may have increased.
                    res = RmGetList(handle, out pnProcInfoNeeded, ref pnProcInfo, null, ref lpdwRebootReasons);
    
                    if (res == ERROR_MORE_DATA)
                    {
                        // Create an array to store the process results
                        RM_PROCESS_INFO[] processInfo = new RM_PROCESS_INFO[pnProcInfoNeeded];
                        pnProcInfo = pnProcInfoNeeded;
    
                        // Get the list
                        res = RmGetList(handle, out pnProcInfoNeeded, ref pnProcInfo, processInfo, ref lpdwRebootReasons);
                        if (res == 0)
                        {
                            processes = new List<Process>((int)pnProcInfo);
    
                            // Enumerate all of the results and add them to the 
                            // list to be returned
                            for (int i = 0; i < pnProcInfo; i++)
                            {
                                try
                                {
                                    processes.Add(Process.GetProcessById(processInfo[i].Process.dwProcessId));
                                }
                                // catch the error -- in case the process is no longer running
                                catch (ArgumentException) { }
                            }
                        }
                        else throw new Exception("Could not list processes locking resource.");
                    }
                    else if (res != 0) throw new Exception("Could not list processes locking resource. Failed to get size of result.");
                }
                finally
                {
                    RmEndSession(handle);
                }
    
                return processes;
            }
    
            public static void remoteProcessKill(string computerName, string userName, string pword, string processName)
            {
                var connectoptions = new ConnectionOptions();
                connectoptions.Username = userName;
                connectoptions.Password = pword;
    
                ManagementScope scope = new ManagementScope(@"\\" + computerName + @"\root\cimv2", connectoptions);
    
                // WMI query
                var query = new SelectQuery("select * from Win32_process where name = '" + processName + "'");
    
                using (var searcher = new ManagementObjectSearcher(scope, query))
                {
                    foreach (ManagementObject process in searcher.Get()) 
                    {
                        process.InvokeMethod("Terminate", null);
                        process.Dispose();
                    }
                }            
            }
    
            public static void localProcessKill(string processName)
            {
                foreach (Process p in Process.GetProcessesByName(processName))
                {
                    p.Kill();
                }
            }
    
            [DllImport("kernel32.dll")]
            public static extern bool MoveFileEx(string lpExistingFileName, string lpNewFileName, int dwFlags);
    
            public const int MOVEFILE_DELAY_UNTIL_REBOOT = 0x4;
    
        }
    }
    

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.


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))
{
}

I'm using FileStream and having same issue.. When ever Two request try to read same file it throw this exception.

solution use FileShare

using FileStream fs = System.IO.File.Open(filePath, FileMode.Open, FileAccess.Read, FileShare.Read);

I'm Just Reading a file concurrently FileShare.Read solve my issue.


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
            }
} 

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

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