      glockfile (filename) (type) (duration)

      lock the given file, using the Elixir locking functions, for the
      specified number of seconds.  The lock type may be SOFT, XCLD, or
      HARD.  These have the following meanings:

      SOFT : read-only lock; will not block a SOFT lock.  will only last
             for the duration of the program.

      XCLD : write lock; blocks, and is blocked by, all lock types.  will
             only last for the duration of the program.

      HARD : write lock; blocks, and is blocked by, all lock types.  If
      the program is interrupted, the lock will remain until cleared by
      hand (by deleting the file with the name .filename.lck, where
      'filename' is replaced the the name of the locked file.