# Advisory locking
        use Storable qw(lock_store lock_nstore lock_retrieve)
        lock_store \%table, 'file';
        lock_nstore \%table, 'file';
        $hashref = lock_retrieve('file');
[...]
       The "lock_store" and "lock_nstore" routine are equivalent to
       "store" and "nstore", except that they get an exclusive lock on
       the file before writing.  Likewise, "lock_retrieve" does the same
       as "retrieve", but also gets a shared lock on the file before reading.