Benchmark.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

contract Benchmark {
    mapping (uint => uint) onchainStorage;
    mapping (uint => uint) params;
    address bridge;

    constructor(){
        bridge = msg.sender;
    }

    function storeOnchain(uint key, uint val) public {
        onchainStorage[key] = val;
    }

    function checkOnchainStorage(uint key) public view returns(bool) {
        return onchainStorage[key] == 0;
    }


    event CheckOffChainStorage(uint id, uint key);
    event DummyAction(bool);

    function foo(uint param) public {
        uint key = 1;
        uint id = uint(keccak256(abi.encodePacked(block.timestamp, msg.sender)));
        params[id] = param;
        emit CheckOffChainStorage(id, key);
    }

    // ... wait for callback before continuing

    function foo_callback(bool ret_val, uint id) public {
        require(msg.sender == bridge, "Only bridge can call this function");
        uint param = params[id];
        delete params[id];
        emit DummyAction(ret_val);
    }

}