UserA                    UserB                    Orig File
Open $orig                                        Original Content
                                                          |
Reads $orig              Opens $orig                      |
                                                          |
Modify $orig in Memory   Reads $orig                      |
                                                          |
Write $orig to FS        Modify $orig in Memory     UserA Content
                                                          |
                         Write $orig to FS          UserB Content