"Dave'd and Confused" <Dave'd and Confused@discussions.microsoft.com> wrote
in message news:BD8B9E43-6A9D-4EDA-9E0D-4DA3823D4D01@microsoft.com...
> Hi All!
>
> I'm developing in C# using .NET 2003 Enterprise Developer (.NET Framework
> 1.1.4322 SP1) running on Windows 2000.
>
> I'm attempting to "lock" a file that's used by two processes by adding a
> ".LOK" extension to the end of the filename. When I rename the file in a
> local directory using the System.IO.File.Move method, there seems to be a
> slight delay between the time the file is renamed and the time that other
> processes recognize that the change occurred. For example, I have two
> instances of the same application running on the same machine (Process A
> and
> Process B). Both processes are working with the same local file
> (c:\temp\TestLockFile\TestFile.txt). Process A checks to see whether
> TestFile.txt exists (in other words has not been renamed by Process B)
> using
> the File.Exists method. If the file exists (has not been renamed by
> Process
> B), Process A attempts to rename TestFile.txt to TestFile.txt.LOK using
> the
> File.Move method.
>
> Meanwhile, Process B is performing the same logic described above for
> Process A. Inevitably, this leads to situations where Process A and
> Process
> B check to see whether TestFile.txt exists using the File.Exists method at
> almost the same instant. As expected, since neither process has renamed
> the
> file yet, each process sees that TestFile.txt exists (has not been renamed
> by
> the other process). However, the issue that I'm running into is that
> neither
> process is throwing an error in these situations. Instead, each process
> proceeds as if it was the one that renamed TestFile.txt. It seems to me,
> for
> example, that if Process A executes the File.Move method even a
> millisecond
> before Process B does, the File.Move method should throw a
> FileNotFoundException in Process B (since Process A already renamed
> TestFile.txt to TestFile.txt.LOK). Am I missing something? Is there a
> way
> to ensure that both processes can't rename TestFile.txt at the same time?
> Or
> is there perhaps a different proven approach to "locking" a file that's
> used
> by multiple processes?
>
> I'm able to reproduce the scenario above (most of the time) by forcing
> both
> processes to rename TestFile.txt at almost the same instant using the
> following code. Notice that the logic makes each process wait until the
> system clock reaches the next minute.
>
> private void LockFile(string strOriginalPath)
> {
> try
> {
> string strNewPath = strOriginalPath + ".LOK";
> string strMessage = "";
>
> //see if the original file exists
> if(File.Exists(strOriginalPath))
> {
> //get the datetime object for the next minute and wait for it
> to
> elapse
> System.DateTime dtNow = System.DateTime.Now;
> int iYear = dtNow.Year;
> int iMonth = dtNow.Month;
> int iDay = dtNow.Day;
> int iHour = dtNow.Hour;
> int iMinute = dtNow.Minute + 1;
> System.DateTime dtNextMinute = new System.DateTime(iYear,
> iMonth, iDay, iHour, iMinute, 0);
> while(dtNextMinute.CompareTo(System.DateTime.Now) > 0)
> {
> //wait until calculated time (ie. next even minute on
> system
> clock)...
> }
>
> //attempt to rename the file
> File.Move(strOriginalPath, strNewPath);
>
> //verify it was renamed
> if(!File.Exists(strNewPath))
> {
> strMessage += "Unable to lock file " + strOriginalPath +
> ".";
> throw new ApplicationException(strMessage);
> }
> }
> else
> {
> //see if the file was already renamed
> if(File.Exists(strNewPath))
> strMessage += strOriginalPath + " already locked.";
> else
> strMessage += strOriginalPath + " does not exist.";
>
> throw new ApplicationException(strMessage);
> }
> }
> catch
> {
> throw;
> }
> }
>
>
> Thanks in advance for your advice, Dave
>

"Trevor Braun" wrote:

> Could this be an issue with write caching?
>
> As an answer to your second part, to lock a file, use:
> File.Open(path2File, FileMode.Open, FileAccess.Read, FileShare.None);
>
> This will ensure that no other process can touch the file until you're done
> with it.
>
> Trevor Braun
>
>
> "Dave'd and Confused" <Dave'd and Confused@discussions.microsoft.com> wrote
> in message news:BD8B9E43-6A9D-4EDA-9E0D-4DA3823D4D01@microsoft.com...
> > Hi All!
> >
> > I'm developing in C# using .NET 2003 Enterprise Developer (.NET Framework
> > 1.1.4322 SP1) running on Windows 2000.
> >
> > I'm attempting to "lock" a file that's used by two processes by adding a
> > ".LOK" extension to the end of the filename. When I rename the file in a
> > local directory using the System.IO.File.Move method, there seems to be a
> > slight delay between the time the file is renamed and the time that other
> > processes recognize that the change occurred. For example, I have two
> > instances of the same application running on the same machine (Process A
> > and
> > Process B). Both processes are working with the same local file
> > (c:\temp\TestLockFile\TestFile.txt). Process A checks to see whether
> > TestFile.txt exists (in other words has not been renamed by Process B)
> > using
> > the File.Exists method. If the file exists (has not been renamed by
> > Process
> > B), Process A attempts to rename TestFile.txt to TestFile.txt.LOK using
> > the
> > File.Move method.
> >
> > Meanwhile, Process B is performing the same logic described above for
> > Process A. Inevitably, this leads to situations where Process A and
> > Process
> > B check to see whether TestFile.txt exists using the File.Exists method at
> > almost the same instant. As expected, since neither process has renamed
> > the
> > file yet, each process sees that TestFile.txt exists (has not been renamed
> > by
> > the other process). However, the issue that I'm running into is that
> > neither
> > process is throwing an error in these situations. Instead, each process
> > proceeds as if it was the one that renamed TestFile.txt. It seems to me,
> > for
> > example, that if Process A executes the File.Move method even a
> > millisecond
> > before Process B does, the File.Move method should throw a
> > FileNotFoundException in Process B (since Process A already renamed
> > TestFile.txt to TestFile.txt.LOK). Am I missing something? Is there a
> > way
> > to ensure that both processes can't rename TestFile.txt at the same time?
> > Or
> > is there perhaps a different proven approach to "locking" a file that's
> > used
> > by multiple processes?
> >
> > I'm able to reproduce the scenario above (most of the time) by forcing
> > both
> > processes to rename TestFile.txt at almost the same instant using the
> > following code. Notice that the logic makes each process wait until the
> > system clock reaches the next minute.
> >
> > private void LockFile(string strOriginalPath)
> > {
> > try
> > {
> > string strNewPath = strOriginalPath + ".LOK";
> > string strMessage = "";
> >
> > //see if the original file exists
> > if(File.Exists(strOriginalPath))
> > {
> > //get the datetime object for the next minute and wait for it
> > to
> > elapse
> > System.DateTime dtNow = System.DateTime.Now;
> > int iYear = dtNow.Year;
> > int iMonth = dtNow.Month;
> > int iDay = dtNow.Day;
> > int iHour = dtNow.Hour;
> > int iMinute = dtNow.Minute + 1;
> > System.DateTime dtNextMinute = new System.DateTime(iYear,
> > iMonth, iDay, iHour, iMinute, 0);
> > while(dtNextMinute.CompareTo(System.DateTime.Now) > 0)
> > {
> > //wait until calculated time (ie. next even minute on
> > system
> > clock)...
> > }
> >
> > //attempt to rename the file
> > File.Move(strOriginalPath, strNewPath);
> >
> > //verify it was renamed
> > if(!File.Exists(strNewPath))
> > {
> > strMessage += "Unable to lock file " + strOriginalPath +
> > ".";
> > throw new ApplicationException(strMessage);
> > }
> > }
> > else
> > {
> > //see if the file was already renamed
> > if(File.Exists(strNewPath))
> > strMessage += strOriginalPath + " already locked.";
> > else
> > strMessage += strOriginalPath + " does not exist.";
> >
> > throw new ApplicationException(strMessage);
> > }
> > }
> > catch
> > {
> > throw;
> > }
> > }
> >
> >
> > Thanks in advance for your advice, Dave
> >
>
>