function unlock (uint256 _id) public {
        TokenTimeLockInfo memory lockInfo = locks [_id];
        delete locks [_id];

        require (lockInfo.amount > 0);
        require (lockInfo.unlockTime <= block.timestamp);
        require (msg.sender == owner);

        emit Unlock (_id);

        require (
            lockInfo.token.transfer (
                lockInfo.beneficiary, lockInfo.amount));
    }