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

Question

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

User · Answer

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
            }
}

User · Answer

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 lt Process gt  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  amp  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  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    Let s say you don t know the process name that is locking the file  Then  you can do this   List lt Process gt  lstProcs   new List lt Process gt     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                 lt summary gt              Find out what process es  have a lock on the specified file               lt  summary gt               lt param name  path  gt Path of the file  lt  param gt               lt returns gt Processes locking the file lt  returns gt               lt remarks gt 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                            lt  remarks gt          static public List lt Process gt  WhoIsLocking string path                        uint handle              string key   Guid NewGuid   ToString                List lt Process gt  processes   new List lt Process gt                  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 lt Process gt   int pnProcInfo                               Enumerate all of the results and add them to the                             list to be returned                         for  int i   0  i  lt  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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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  lt   NumberOfRetries    i        try              Do stuff with file         break     When done we can break loop           catch  IOException e  when  i  lt   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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

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

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