Wait Until File Is Completely Written

Question

When a file is created  FileSystemWatcher Created  in one directory I copy it to another  But When I create a big   10MB  file it fails to copy the file  because it starts copying already  when the file is not yet finished creating    This causes Cannot copy the file  because it s used by another process to be raised     Any help   class Program       static void Main string   args                string path     D  levan FolderListenerTest ListenedFolder           FileSystemWatcher listener           listener   new FileSystemWatcher path           listener Created    new FileSystemEventHandler listener Created           listener EnableRaisingEvents   true           while  Console ReadLine       exit                public static void listener Created object sender  FileSystemEventArgs e                Console WriteLine                                        File Created  n                        ChangeType      e ChangeType                        nName      e Name                        nFullPath      e FullPath                            File Copy e FullPath    D  levan FolderListenerTest CopiedFilesFolder     e Name           Console Read

User · Answer

I would like to add an answer here  because this worked for me  I used time delays  while loops  everything I could think of   I had the Windows Explorer window of the output folder open  I closed it  and everything worked like a charm   I hope this helps someone

User · Answer

Well you already give the answer yourself  you have to wait for the creation of the file to finish  One way to do this is via checking if the file is still in use  An example of this can be found here  Is there a way to check if a file is in use   Note that you will have to modify this code for it to work in your situation  You might want to have something like  pseudocode    public static void listener Created        while CheckFileInUse         wait 1000 milliseconds     CopyFile       Obviously you should protect yourself from an infinite while just in case the owner application never releases the lock  Also  it might be worth checking out the other events from FileSystemWatcher you can subscribe to  There might be an event which you can use to circumvent this whole problem

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From the documentation for FileSystemWatcher   The OnCreated event is raised as soon as a file is created  If a file is being copied or transferred into a watched directory  the OnCreated event will be raised immediately  followed by one or more OnChanged events   So  if the copy fails   catch the exception   add it to a list of files that still need to be moved  and attempt the copy during the OnChanged event   Eventually  it should work  Something like  incomplete  catch specific exceptions  initialize variables  etc   public static void listener Created object sender  FileSystemEventArgs e        Console WriteLine                                quot File Created  n quot                    quot ChangeType   quot    e ChangeType                   quot  nName   quot    e Name                   quot  nFullPath   quot    e FullPath                    try           File Copy e FullPath    quot D  levani FolderListenerTest CopiedFilesFolder  quot    e Name             catch            waitingForClose Add e FullPath             Console Read       public static void listener Changed object sender  FileSystemEventArgs e         if   waitingForClose Contains e FullPath                    try                 File Copy                      waitingForClose Remove e FullPath                         catch

User · Answer

You re actually in luck - the program writing the file locks it  so you can t open it  If it hadn t locked it  you would have copied a partial file  without having any idea there s a problem   When you can t access a file  you can assume it s still in use  better yet - try to open it in exclusive mode  and see if someone else is currently opening it  instead of guessing from the failure of File Copy   If the file is locked  you ll have to copy it at some other time  If it s not locked  you can copy it  there s slight potential for a race condition here    When is that  other time   I don t rememeber when FileSystemWatcher sends multiple events per file - check it out  it might be enough for you to simply ignore the event and wait for another one  If not  you can always set up a time and recheck the file in 5 seconds

User · Answer

There is only workaround for the issue you are facing   Check whether file id in process before starting the process of copy  You can call the following function until you get the False value   1st Method  copied directly from this answer   private bool IsFileLocked 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                 file is not locked     return false      2nd Method   const int ERROR SHARING VIOLATION   32  const int ERROR LOCK VIOLATION   33  private bool IsFileLocked string file          check that problem is not in destination file     if  File Exists file     true                FileStream stream   null          try                       stream   File Open file  FileMode Open  FileAccess ReadWrite  FileShare None                     catch  Exception ex2                           log WriteLog ex2   Error in checking whether file is locked     file               int errorCode   Marshal GetHRForException ex2   amp    1  lt  lt  16  - 1               if   ex2 is IOException   amp  amp   errorCode    ERROR SHARING VIOLATION    errorCode    ERROR LOCK VIOLATION                                 return true                                  finally                       if  stream    null                  stream Close                        return false

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When the file is writing in binary byte by byte  create FileStream and above solutions Not working because file is ready and wrotted in every bytes so in this Situation you need other workaround like this  Do this when file created or you want to start processing on file  long fileSize   0  currentFile   new FileInfo path    while  fileSize  lt  currentFile Length   check size is stable or increased     fileSize   currentFile Length   get current size   System Threading Thread Sleep 500    wait a moment for processing copy   currentFile Refresh     refresh length value      Now file is ready for any process

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It s an old thread  but I ll add some info for other people   I experienced a similar issue with a program that writes PDF files  sometimes they take 30 seconds to render   which is the same period that my watcher FileCreated class waits before copying the file   The files were not locked   In this case I checked the size of the PDF and then waited 2 seconds before comparing the new size  if they were unequal the thread would sleep for 30 seconds and try again

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So  having glanced quickly through some of these and other similar questions I went on a merry goose chase this afternoon trying to solve a problem with two separate programs using a file as a synchronization  and also file save  method  A bit of an unusual situation  but it definitely highlighted for me the problems with the  check if the file is locked  then open it if it s not  approach   The problem is this  the file can become locked between the time that you check it and the time you actually open the file  Its really hard to track down the sporadic Cannot copy the file  because it s used by another process error if you aren t looking for it too   The basic resolution is to just try to open the file inside a catch block so that if its locked  you can try again  That way there is no elapsed time between the check and the opening  the OS does them at the same time    The code here uses File Copy  but it works just as well with any of the static methods of the File class  File Open  File ReadAllText  File WriteAllText  etc        lt param name  timeout  gt how long to keep trying in milliseconds lt  param gt  static void safeCopy string src  string dst  int timeout        while  timeout  gt  0                try                       File Copy src  dst                  don t forget to either return from the function or break out fo the while loop             break                    catch  IOException                          you could do the sleep in here  but its probably a good idea to exit the error handler as soon as possible                   Thread Sleep 100              if its a very long wait this will acumulate very small errors             For most things it s probably fine  but if you need precision over a long time span  consider              using some sort of timer or DateTime Now as a better alternative         timeout -  100            Another small note on parellelism  This is a synchronous method  which will block its thread both while waiting and while working on the thread  This is the simplest approach  but if the file remains locked for a long time your program may become unresponsive  Parellelism is too big a topic to go into in depth here   and the number of ways you could set up asynchronous read write is kind of preposterous  but here is one way it could be parellelized   public class FileEx       public static async void CopyWaitAsync string src  string dst  int timeout  Action doWhenDone                while  timeout  gt  0                        try                               File Copy src  dst                   doWhenDone                    break                            catch  IOException                   await Task Delay 100               timeout -  100                       public static async Task lt string gt  ReadAllTextWaitAsync string filePath  int timeout                while  timeout  gt  0                        try                   return File ReadAllText filePath                             catch  IOException                   await Task Delay 100               timeout -  100                    return                public static async void WriteAllTextWaitAsync string filePath  string contents  int timeout                while  timeout  gt  0                        try                               File WriteAllText filePath  contents                   return                            catch  IOException                   await Task Delay 100               timeout -  100                      And here is how it could be used   public static void Main         test FileEx        Console WriteLine  Me First            public static async void test FileEx         await Task Delay 1          you can do this  but it gives a compiler warning because it can potentially return immediately without finishing the copy       As a side note  if the file is not locked this will not return until the copy operation completes  Async functions run synchronously       until the first  await   See the documentation for async  https   msdn microsoft com en-us library hh156513 aspx     CopyWaitAsync  file1 txt    file1 bat   1000          this is the normal way of using this kind of async function  Execution of the following lines will always occur AFTER the copy finishes     await CopyWaitAsync  file1 txt    file1 readme   1000       Console WriteLine  file1 txt copied to file1 readme           The following line doesn t cause a compiler error  but it doesn t make any sense either      ReadAllTextWaitAsync  file1 readme   1000          To get the return value of the function  you have to use this function with the await keyword     string text   await ReadAllTextWaitAsync  file1 readme   1000       Console WriteLine  file1 readme says      text        Output    Me First    file1 txt copied to file1 readme   file1 readme says  Text to be duplicated

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You can use the following code to check if the file can be opened with exclusive access  that is  it is not opened by another application   If the file isn t closed  you could wait a few moments and check again until the file is closed and you can safely copy it   You should still check if File Copy fails  because another application may open the file between the moment you check the file and the moment you copy it   public static bool IsFileClosed string filename        try               using  var inputStream   File Open filename  FileMode Open  FileAccess Read  FileShare None                         return true                      catch  IOException                return false

[c#] Wait Until File Is Completely Written

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