Can I lock a file?

Question

I am developing an application that checks for changes made to a file in a separate program (not written by me).

If a change is detected, it opens the file, reads the last line and closes the file.

I use the following code to make sure that my program does not try to lock the file, but opens it only in read mode:

FileStream fs =
    new FileStream(
        _scannerFilePath,
        FileMode.Open,
        FileAccess.Read,
        FileShare.ReadWrite);
StreamReader sr = new StreamReader(fs);
var str = sr.ReadToEnd();
sr.Close();
fs.Close();

Unfortunately, despite this, I still get the following error when my program tries to read the file:

System.IO.IOException was unhandled
    Message="The process cannot access the file 'D:\\LSDATA\\IdText.txt' because it is being used by another process."
    Source="mscorlib"
    StackTrace:
        at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
        at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy)
        at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share)
        at LiquorSafe.Verification.Main.CheckLastScannedUser(String changedFileName)
        at LiquorSafe.Verification.Main.OnChanged(Object sender, FileSystemEventArgs e)
        at System.IO.FileSystemWatcher.OnChanged(FileSystemEventArgs e)
        at System.IO.FileSystemWatcher.NotifyFileSystemEventArgs(Int32 action, String name)
        at System.IO.FileSystemWatcher.CompletionStatusChanged(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* overlappedPointer)
        at System.Threading._IOCompletionCallback.PerformIOCompletionCallback(UInt32 errorCode, UInt32 numBytes, NativeOverlapped* pOVERLAP)
    InnerException: 

Is there a possible reason for this?

Could it be that another program is in some way a read-locking file and thus prevents me from even reading it?

Answer 1

, . , , , .

File.Open(). FileShare, None.