I have a suggestion here from your code you either have a race situation or you can speed this up. The race comes from the distance of the actual test of the file exist and the creation of the new file with the new name. If your app is not the only one that may place files in the target dir you may run into a race where you check to see if a filename exists and it does not then someone creates the file and then you try to rename. BAD. Or if your app _IS_ the only one that will be writing to the target directory, why not push all of the files into an hash on startup? you would only need to build the hash once and then you can do _very_ fast lookups and push an entry into the hash when you rename a file.

-Waswas