function releaseOnce() public {
        uint64 head = roots[msg.sender];
        require(head != 0);
        require(uint64(block.timestamp) > head);
        bytes32 currentKey = toKey(msg.sender, head);

        uint64 next = chains[currentKey];

        address currentAddress = address(keccak256(currentKey));
        uint amount = balances[currentAddress];
        delete balances[currentAddress];

        balances[msg.sender] += amount;

        if (next == 0) {
            delete roots[msg.sender];
        }
        else {
            roots[msg.sender] = next;
        }
        Released(msg.sender, amount);
    }