code: @Override
      public FileLock lock(long position, long size, boolean shared) throws IOException
      {
          return new FileLockImpl(this, position, size, shared);
      }
docs: Returns always a lock. Locking virtual file makes no sense. Dummy
  implementation is provided so that existing applications don't throw
  exception.
  @param position
  @param size
  @param shared
  @return
  @throws IOException