File "save and lock" command

Many applications, when they have a file open, lock the file so other applications and computers can't open it. Some applications, however, allow a user to request that a file be opened "read-only", in which case the file on the disk or network will not be locked. If I'm editing a file, it's possible to close and save, and then open read-only to allow others to work with it, then close and open it "normally" when I want to work with it again, but that's rather a pain.

What I would like would be a function which would save the currently-open file (if necessary), release the file, and keep it open locally as read-only. Another key or menu option would allow application to re-lock the file on disk (if available), reload it if and only if necessary (while keeping scroll position etc. the same if practical), and re-enable editing.