Watch folder for files being Read

I am trying to watch files in a directory to determine when files are opened/accessed. I thought FileSystemWatcher would do the trick using the event Changed.

Problem is that some applications do not create a lock on the file they open/access or change either the date modified or date accessed (even after fsutil behavior set disablelastaccess 0). Notepad for example. Apparently is makes a copy of the file in memory and plays with it there until you save it. Nor does it update the Date Accessed.

How can I monit开发者_开发知识库or a directory of files and be notified when a file is simply opened/accessed by any program (e.g. Notepad)? Files may be opened from another computer, not necessarily on the computer running the "watcher".

I found lots of similar questions but did not see one focusing on file "access".

This is quite normal. Updating an existing file is quite dangerous since it can cause irretrievable data loss. A disk error (like disk full) while writing is very bad news. The common algorithm used:

• rename the original file
• write a new file using the original name
• no error: delete the renamed file
• error: delete the new file, rename original file back

Clearly this doesn't cause a Changed event to be raised, no file was changed.

Sorry, I didn't read the question well enough. There is no notification whatsoever for an app just opening a file for reading. FSW can only detect changes to the file system. There is no ready alternative either, this requires a custom file system filter driver that snoops on driver requests. Like the kind that SysInternals' ProcMon utility uses. I'm not aware of such a driver ready for use in a C# program, you can't write them in C# either. This just isn't a common requirement.