use Fcntl qw/:flock/;
use Data::Dumper;

# Get stored config
my $config = do( '/path/to/my_config.cfg') || {};
# . . .
{   # Serialize current config
    open my $fh, '>', '/path/to/my_config.cfg' or die $!;
    flock $fh, LOCK_EX;
    print $fh Dumper($config);
}