php recursive iterator fails on file rename

Question

I am having issue with RecursiveIteratorIterator moving to next item. I have a directory which has multiple files, and I am trying to go to each file, rename it, and do some other stuff on it. The RecursiveIteratorIterator picks the first file from the directory and renames it successfully. When I do $it->next(), it stays on same file, and tries to look for the file which was already renamed to something else. Below is my code sample. File permission are set to 777. Any ideas would be appreciated.

This only happens if I rename the file. If I remove renaming functionality, its moves to next item as expected.

   //initialize iterator object
  $it = new RecursiveIteratorIterator(new RecursiveDirectoryIterator($directory, 0));

 /*  loop directly over the object */

while ($it->valid()) {
// check if value is a directory 

if (!$it->isDot()) {
    if (!is_writable($directory . '/' . $it->getSubPathName())) {

        //direcotry not writable, throw error

    } else {

        // get current file info
        $fileinfo = pathinfo($it->getSubPathName());

        //get file extension
        $ext = $fileinfo['extension'];

        //if its a '.', move to next item
        if (in_array($fileinfo['filename'], array(".", ".."))) {
            $it->next();
        }

        // the current file name with complete path
        $old_file = $directory . '/' . $it->getSubPathName();
        throw new Exception('source file doesnot exist ' . $old_file, error::DOESNOTEXIST);
        }

        //generate new file name with path
        $new_file = $directory . '/' . $it->getSubPath() . '/' . $filename . '.' . $ext;

        //rename the file
        rename($old_file, $new_file);

    }

}
/*             * * move to the next iteration ** */
$it->next();

}