If you're on Windows, the operating system won't let you do this. On other operating systems you'll have to do something like create a temporary ".lock" file and not process the XML file if a ".lock" file exists. You must be careful because there is a race condition creating the .lock file so you must be able to tell which process created it first. I usually write the process number to the file then read back the first line of the file to make sure it is my process. Otherwise some other process created the .lock file so the current process must wait until it is deleted by the owning process.