On web server, I have an ASP.NET website with error.txt inside it.
This file always gets written to. And it is in the bin folder.
Should I be concerned if:
I go to web server and open the bin folder
Go to web server and open the error.txt
My C# code always writes to it in a share mode FileShare.ReadWrite
Is copying the file to another folder using command prompt safer to avoid locking?
It depends on the application you are opening it with. For instance, if you open it with Microsoft Word, it will lock the file and other processes will only be able to read it. However, if you open it with Notepad, the file is not locked and another process can read, write, delete, move, or rename it.
You can test simply by opening a file with the application, and then try to delete, rename, write to, or move the file. If you can perform any of those actions then you know that your application did not lock it.
Assuming you are just copying it with Explorer, copying the file will lock it for the time it takes to read the file. If it is a small file, this will just be a very few milliseconds.
To ensure that your application doesn't crash if it tries to write to the file while it is locked, put the write operation(s) in a loop that retry if an exception is returned, with a 100 ms wait between tries.
Related
Searched a lot, but without luck - so here goes
My C# winforms application creates temp files which are opened using the default registered application (let's call them viewer apps). Once the user is done viewing those files, I want to delete them.
Currently, I register for an Application.ApplicationExit event, to delete the file. This approach covers most of the situations but not all. Sometimes the user still has the viewing application open while exiting my app, so the success of my File.Delete depends on whether the viewer has opened the file with FileShare.Delete or not - which is out of my control.
This is what I have found so far, but fall short of what I want
FileOptions.DeleteOnClose does not help, since my app will already be closed in some cases and the temp file will still be needed. Also, when I create the file like this: new FileStream(fn, FileMode.CreateNew, FileAccess.ReadWrite, FileShare.ReadWrite | FileShare.Delete, 4096, FileOptions.DeleteOnClose), the viewer apps like say adobe reader & notepad, still complain about file in use by my application The process cannot access the file because it is being used by another process
MoveFileEx with MOVEFILE_DELAY_UNTIL_REBOOT dwFlags works, but it would wait till a reboot to delete it - I would rather have it deleted once the use is done, since reboots can be few and far between and forcing reboots IMO is not the most user friendly approach. On a side note, does windows automatically clear the %temp% folder on restart? Or is there any temp folder that windows automatically clears on restart?
I can write another background process which constantly tries to delete the temp files till it succeeds, but I would like to avoid deploying one more piece of software to accomplish this. It can be done using a windows service or scheduled task or adding command line switches to my existing app and making it run in "delete mode" in background or through task scheduler. All of it decrease my ease of deployment and use along with increasing my footprint on client's computer
In a nutshell, I am wondering if there is any Win32 API or .NET Framework API that will delete a file as soon as there are no processes with open handle to that file?
EDIT:
The information in the temp files are reasonably private (think your downloaded bank account statements) and hence the need for immediate deletion after viewing as opposed to waiting for a reboot or app restart
Summary of all Answers and Comments
After doing some more experiments with inputs from Scott Chamberlain's answer, and other comments on this question, the best path seems to be to force the end users to close the viewer app before closing my application, if the viewer app disallows deletion (FileShare.Delete) of the temp file. The below factors played a role in the decision
The best option is FileOptions.DeleteOnClose, but this only works if all files open before or after this call use FileShare.Delete option to open the file.
Viewer apps can frequently open files without FileShare.Delete option.
Some viewers close the handle immediately after reading/displaying the file contents (like notepad), whereas some other apps (like Adobe Reader) retain such handle till the file is closed in the viewer
Keeping sensitive files on disk for any longer than required is definitely not a good way to proceed. So waiting till reboot should only be used as a fail-safe and not as the main strategy.
The costs of maintaining another process to do the temp file cleanup, far exceeds the slight user inconvenience when they are forced to "close" the viewer before proceeding further.
This answer is based on my comments in the question.
Try write the file without the delete, close the file, let the editor open the file, then open a new filestream as a read with DeleteOnClose with an empty body in the using section.
If that 2nd opening does not fail it will behave exactly like you wanted, it will delete the file as soon as there are no processes with open handle to that file. If the 2nd opening for the delete does fail you can use MoveFileEx as a fallback failsafe.
How do I copy any file that is being used to another process to a specified folder, without affecting / corrupting what that process is doing?
Context: I'm making a program that will copy a project folder each X minutes to 2 cloud servers and 1 hard-drive, while that project is still open.
As mentioned in the post below:
The important part is the FileShare.ReadWrite when opening the
FileStream
.
How to copy a file while it is being used by another process
In short, make sure that you specify the correct access parameters while opening the file.
Step 1- I am copying a file manually by reading from source then writing to target files in chunk. I keep the file handle open until all copy is not over. The handle is safely closed as copy is over.
Step 2- After copy is over, I set the time stamp, attributes, ACL and may more things.
Sometime in step 2, I get the issue that file is being used by some other process. This issue raise mostly for exe files. I got the answer which process was using that file from File locked by other process. A sper answer, OS locks the file to set the icon or some other information on file for a very minor time.
But if I go to perform step 2 without any delay after finishing step 1 then I get access error. How I can ensure that OS will not lock the file?
Looping to check for file access is not an solution as per because the locking may be happen at any point of time in step 2. Step 2 is not atomic, there I need to open/close same file multiple times.
I want to provide my users with the ability to post a log file onto my server rather than requiring them to find it and email it to me.
I am using this library http://ftplib.codeplex.com/ to open an ftp session on the server and send the file. There is a bit of renaming involved but that is it.
Unfortunately the log file to be sent is actually open so I got a 'file is being used by another process' exception. This makes sense when I think about it in so far as the log is open while my app is running. I closed it but, of course, uploading is a long process. I put the upload code into a background thread so that the user may continue. However the log cannot be re-opened until the upload is complete. In the meantime there could be some event that should be written to the log.
So I am looking for a way to copy the log and then upload it. What would be the best way to do that? The log is a binary file BTW.
If you don't own the code that has the log file open (ie, it's another app or a closed source dll), you can try doing a File.Copy(<log>, <tempdest>) and send that file, deleting it when you're done. This only sometimes works when you don't have read access to the file.
If you do own the code that is accessing the file in the first place, you want to open it with an explicit ShareMode ie
File.Open(path, FileMode.Open, FileAccess.ReadWrite, FileShare.Read)
This is what I'm trying to do :
Download a file (txt, doc, xls, whatever) from a server
Open the file with the appropriate application using System.Diagnostics.Process.Start(path to file)
Monitor for file changes using a FileSystemWatcher.
Each time the file is changed, upload the file back to the server
Continue monitoring until the user has finished editing the file
Delete the local copy of the file
Exit the application
I'm stuck at step 5. How can I know whether a user has finished working on a file ?
I cannot rely on the file being locked (notepad doesn't lock txt files for example).
I cannot rely on a process having exited or not (an example is Notepad++ for txt files : the file could be open in a tab. When you close the tab, you've finished editing the file, but the process is still running)
Any idea/points on how to do that in C# ?
You've excluded the two ways you could go about detecting the file being in use: file locking, and the process you start exiting.
The only alternative I an think of is to display a dialog to ask the user when they've finished editing.
Edit: For what it's worth - FileZilla has this type of behaviour. You can choose to edit a file on the remote server, it downloads the file, launches the default editor, and (in the background) shows a "If you've finished editing - Click OK" button.
This gives me the opportunity to cancel an edit, if I've mucked up the file and saved it.
This is really hard to do - we've tried various things but never found anything that was foolproof. If you know the program you have launched then, in theory, you can find the file handles it uses and see when it stops using the one you're interested in.....but if you rely on Windows to resolve the default application to launch even this becomes tricky.
We copy editable files into a temp folder named with the date and rely on users uploading them back when they have finished their edit session. We then clean up previous days folders on application startup.
You could check the date of last change of the file. This date gets set when you save changes to the file. Mind though that this field is not very reliable since one can set it to any value (with appropriate tools).