What is the additional gas cost of the OpenZeppelin ReentrancyGuard?

Support Contracts
1

Asked by idevelopthereforeiam on r/ethdev as a comment on a link to Reentrancy After Istanbul

https://www.reddit.com/r/ethdev/comments/dvg8hq/reentrancy_is_becoming_unavoidable_in/f7e9yd4
What is the additional gas cost of the OpenZeppelin ReentrancyGuard?

2

I tried using the nonReentrant modifier on a test contract on Ropsten and got a 7,447 gas overhead.

Calling a function (doStuff)
Gas Used by Transaction: 21,208
https://ropsten.etherscan.io/tx/0x722f698f708fcdd1b435d5b12f845b13cf61794deb2b8c2e7e9aae4ab52e1ba5

Calling a function (doStuffNonReentrant) with the nonReentrant modifier
Gas Used by Transaction: 28,655
https://ropsten.etherscan.io/tx/0x6d8cd74637ae08706691a95c3f359b39353a4421672ac46089ff503861745225

28,655 - 21,208 = 7,447 gas overhead

Test.sol

pragma solidity ^0.5.0;

import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v2.4.0/contracts/utils/ReentrancyGuard.sol";

contract Test is ReentrancyGuard {

    function doStuff() public {
    }

    function doStuffNonReentrant() public nonReentrant {
    }
}
3

@nventuro and @DericEcourcy recently revamped ReentrancyGuard to be cheaper when the upcoming net gas metering lands.

They may have some insights into what the gas costs will be with this change.

4

The overhead should be 4 SLOAD, 5 if the compiler is not smart. SLOADs are being repriced from 200 to 800 however, so I'd expect ~3.5k gas.

5

Hi @nventuro,

Is there a better way to test the overhead, as I got a larger figure than ~3.5k?

6

did you find an alternative here?