You can actually do a double flashloan, but the success will depend on the total amount of gas consumed in the transaction.
In fact, you don't need to have two contracts and you can request the two loans from the same contract.
Below is a simple example on how this could be done:
// SPDX-License-Identifier: MIT
pragma solidity ^0.7.3;
import {IERC20} from "../aave-flashloan/interfaces/IERC20.sol";
import {FlashloanProvider2} from "./FlashloanProvider.sol";
import {IFlashloanUser2} from "./IFlashloanUser.sol";
contract FlashloanUser2 is IFlashloanUser2 {
string public output1;
string public output2;
/**
* @notice Start the flashloan (triggered by user)
* @param flashloan The flashloan contract address
* @param amount The amount to be borrowed
* @param token The token to be borrowed
*/
function startFlashloan(
address flashloan,
uint256 amount,
address token
) external {
// Flashloan call #1
FlashloanProvider2(flashloan).executeFlashloan(
address(this),
amount,
token,
'flash1',
1
);
// Flashloan call #2
FlashloanProvider2(flashloan).executeFlashloan(
address(this),
amount,
token,
'flash2',
2
);
}
/**
* @notice Callback function to do arbitrage (or whatever) after
* receiving the borrowed amount and before returning it
* @param amount The amount to be returned
* @param token The token to be returned
* @param data Arbitrary data
*/
function flashloanCallback(
uint256 amount,
address token,
string memory data,
uint256 flashNumber
) external override {
// do some arbitrage, liquidation, etc.
if (flashNumber == 1) {
output1 = data;
} else {
output2 = data;
}
// Reimburse borrowed tokens to Flashloan contract
IERC20(token).transfer(msg.sender, amount);
}
}
In function startFlashloan(), there are two calls to the same flashloan provider, but it could be different contracts (e.g.: Uniswap, Kyber).
In this simple example, the same amount is borrowed in the two loans, and the callback function is updating variables output1 and output2 with values 'flash1' and 'flash2' respectively.
It is just a basic demo to show that technically speaking and for a simple case, it is possible. For a real case using Production exchanges, I am not fully sure you could make it without running out of gas.
